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Classifications

Harrison's Chapter

C

Comorbidities

Inclusion Body Myositis <-> T Cell Large Granular Lymphocytic Leukemia

◈

Mechanistic Hypotheses

3

IBM is primarily a T cell-mediated autoimmune disease; protein aggregation is a downstream or secondary marker

autoimmune_primary CANONICAL

Evidence balance 1 support

The dominant contemporary model holds that clonally expanded, highly differentiated cytotoxic CD8+ T cells are the primary pathogenic effectors, and that the degenerative pathology (rimmed vacuoles, aggregates) is downstream of, or secondary to, chronic immune injury. Supporting arguments are the HLA association, the circulating anti-cN1A autoantibody, the marked cytotoxic T cell transcriptomic signature, the clonality and persistence of the effector population, and the observation that invasion of non-necrotic fibres is far more frequent than amyloid-containing fibres. The treatment refractoriness is explained on this model by the effector cells being terminally differentiated and resistant to conventional immunotherapy rather than by the disease being non-immune.

Pathograph links

Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells -> Cytotoxic T Cell Invasion of Non-Necrotic Myofibres DIRECT The expanded cytotoxic clone invades and attacks myofibres via perforin/granzyme-mediated cytotoxicity.

Myofibre MHC Class I Overexpression -> Cytotoxic T Cell Invasion of Non-Necrotic Myofibres DIRECT MHC class I presentation on non-necrotic fibres is the substrate for CD8+ T cell recognition and attack.

Cytotoxic T Cell Invasion of Non-Necrotic Myofibres -> Progressive Myofibre Degeneration and Selective Muscle Loss DIRECT Repeated cytotoxic attack over years destroys myofibres and drives the progressive loss of muscle mass and strength.

Cytotoxic T Cell Invasion of Non-Necrotic Myofibres -> Myofibre MHC Class I Overexpression INDIRECT KNOWN INTERMEDIATES Feed-forward loop: interferon-gamma released by the infiltrating T cells drives further MHC class I upregulation on myofibres, amplifying antigen presentation and sustaining the cytotoxic attack. This edge closes the cycle with the MHC class I node's own upstream edge into invasion, and is the reason MHC class I upregulation is experimentally T cell-dependent.

Show evidence (1 reference)

PMID:30837708 SUPPORT Human Clinical

"Findings from the past decade that implicate autoimmunity in IBM include the identification of a circulating autoantibody (anti-cN1A); the absence of any statistically significant genetic risk factor other than the common autoimmune disease 8.1 MHC haplotype in whole-genome sequencing studies;..."

Enumerates the principal lines of evidence marshalled in support of the autoimmune-primary model.

IBM is primarily a cell-autonomous degenerative myopathy with secondary or non-essential inflammation

degeneration_primary ALTERNATIVE

Evidence balance 1 support

A competing model holds that cell-autonomous myofibre degeneration (proteostasis failure, TDP-43 loss of function, mitochondrial damage) drives the disease and that the inflammatory infiltrate, while conspicuous, is not the essential driver. The strongest direct evidence is the IBM muscle xenograft experiment in which depleting human T cells suppressed myofibre MHC class I upregulation but left rimmed vacuoles and TDP-43 loss of function intact. The consistent failure of immunosuppression to alter functional decline is the main clinical argument. Note that this model is not mutually exclusive with the autoimmune-primary model; both arms are likely to operate, and the disputed question is which is upstream.

Pathograph links

TDP-43 Nuclear Clearance and Loss of Splicing Repression -> Autophagy-Lysosome Failure and Rimmed Vacuole Formation INDIRECT UNKNOWN INTERMEDIATES TDP-43 mislocalization co-occurs with, and is thought to contribute to, the aggregate and rimmed-vacuole pathology; the two persist together after T cell depletion.

Autophagy-Lysosome Failure and Rimmed Vacuole Formation -> Progressive Myofibre Degeneration and Selective Muscle Loss INDIRECT UNKNOWN INTERMEDIATES On the degeneration-primary model, proteostasis failure drives cell-autonomous myofibre degeneration independently of immune attack.

Mitochondrial Dysfunction and Somatic mtDNA Deletion -> Progressive Myofibre Degeneration and Selective Muscle Loss INDIRECT UNKNOWN INTERMEDIATES Bioenergetic failure and oxidative stress in COX-deficient fibre segments contribute to myofibre degeneration.

Fibro-Adipogenic Progenitor Senescence -> Progressive Myofibre Degeneration and Selective Muscle Loss INDIRECT KNOWN INTERMEDIATES Loss of collagen type XV from senescent FAPs removes structural and neuromuscular-junction support required by myofibres.

Show evidence (1 reference)

PMID:35044790 SUPPORT Model Organism

"Reduction of human T cells within IBM xenografts by treating mice intraperitoneally with anti-CD3 (OKT3) suppressed MHC-I up-regulation. However, rimmed vacuoles and loss of TDP-43 function persisted. These data suggest that T cell depletion does not alter muscle degenerative pathology in IBM."

Direct experimental dissociation of the degenerative arm from T cell activity in a human-muscle xenograft, the key evidence for the degeneration-primary model.

Amyloid-beta and its precursor APP are abnormally and specifically over-produced in IBM myofibres and are the upstream proteotoxic driver of the disease

amyloid_beta_proteotoxicity ⚠ DEPRECATED

⚠ Overturned model — shown for reference, not as current mechanism

DisMech records superseded hypotheses explicitly rather than deleting them, so that claims still circulating in reviews, textbooks and older diagnostic criteria can be checked against an assessment. This model is not part of the disease mechanism DisMech asserts.

Citation volume does not decide standing here. A hypothesis may retain more supporting than refuting citations simply because the supporting literature accumulated for decades before the refutation landed; where the two conflict, DisMech follows the more recent and more direct evidence. Supporting citations below are retained for the historical record.

Evidence balance 3 support 5 partial 6 refute

Proposed by Askanas and Engel from the early 1990s, this model cast sporadic IBM as a muscle analogue of Alzheimer disease: increased APP transcription in vacuolated fibres leads to intracellular accumulation of APP and its proteolytic fragment amyloid-beta, preferentially the more aggregation-prone Abeta42, whose soluble oligomers are cytotoxic and sit upstream of tau phosphorylation, oxidative stress, proteasome inhibition, ER stress and vacuolar degeneration. It was the dominant degenerative account of IBM for roughly two decades and supplied the rationale for the Congo red / amyloid criterion in older diagnostic schemes. It is recorded here as DEPRECATED, and the two claims embedded in the label fail for different reasons. The claim of SPECIFICITY fails outright: beta-amyloid-immunoreactive, Congo-red-positive rimmed vacuoles with tubulofilaments occur in long-standing denervation (postpoliomyelitis muscular atrophy) and in congenital myopathies of childhood, so the finding tracks chronicity of fibre injury rather than IBM itself. (Oculopharyngeal muscular dystrophy is deliberately excluded from this list: it shares the ubiquitinated filamentous inclusions, but the one study here that stained it for beta-amyloid found labelling in IBM and not in OPMD.) Comparative quantification puts the point sharply: in the same biopsies in which sarcoplasmic TDP-43 marked 23% of myofibres, focal beta-amyloid immunoreactivity (R1282) was found in 0.00% and fluorescent Congo red material in 0.57%. TDP-43 mislocalization, not amyloid, is now the sensitive and specific molecular marker of IBM. The claim of ABNORMAL PRESENCE is weaker than the literature suggests rather than plainly false. Positive immunoblot and ADDL data exist, but almost entirely from the originating laboratory; unbiased laser-capture mass spectrometry of rimmed vacuoles recovered 213 enriched proteins dominated by protein-folding and autophagy machinery without reporting amyloid-beta or APP enrichment; cultured IBM myotubes from the same laboratory do not accumulate betaAPP, so any accumulation is not cell-autonomous; the companion phospho-tau claim was shown to rest on antibodies that stain normal myonuclei and recognize proteins other than tau, which impugns the reagent class the histological arm depended on; and a formal citation-network analysis of the entire literature on this belief found its authority inflated by citation bias, amplification and invention rather than by accumulated data. What survives is modest and is retained in the entry: protein aggregates of several kinds, amyloid-beta among them, are demonstrable in a small minority of IBM myofibres and are best read as a marker of overwhelmed proteostasis (see the `Autophagy-Lysosome Failure and Rimmed Vacuole Formation` node) rather than as a specific or upstream cause. Neither of the two live models for IBM requires amyloid-beta, and no anti-amyloid therapeutic strategy has been taken into IBM trials.

Retained rather than deleted because the hypothesis remains widely cited in reviews, textbooks and older diagnostic criteria, and curators encountering amyloid claims in the IBM literature need the assessment recorded rather than silently absent.

Pathograph links

Amyloid-beta and APP Accumulation in Myofibres -> Autophagy-Lysosome Failure and Rimmed Vacuole Formation INDIRECT UNKNOWN INTERMEDIATES On the amyloid model, misfolded APP and Abeta oligomers overwhelm and inhibit the proteasome and autophagy-lysosome systems, generating the vacuolar and aggregate pathology. The direction of this edge is contested: an influential review argues the reverse order, with inflammation and overloaded degradation systems coming first and amyloid deposits appearing afterwards as a consequence.

Amyloid-beta and APP Accumulation in Myofibres -> Progressive Myofibre Degeneration and Selective Muscle Loss INDIRECT UNKNOWN INTERMEDIATES The proposed proteotoxic endpoint of the amyloid model, in which Abeta42 oligomer cytotoxicity drives vacuolar degeneration and atrophy of muscle fibres.

Deep research

OpenScientist citations 27 citations 2026-08-02T19:47:47.016429

Show evidence (14 references)

PMID:8394158 SUPPORT Human Clinical

"Vacuolated muscle fibers in muscle biopsies of 8 out of 8 inclusion body myositis (IBM) patients, including 2 hereditary patients, manifested increased mRNA for the beta-amyloid precursor protein (beta APP) that contains Kunitz-type protease inhibitor motif."

The founding observation of the hypothesis: increased APP transcript in vacuolated IBM fibres, offered as evidence that APP accumulation is generated locally rather than deposited.

PMID:16432144 SUPPORT Human Clinical

"In s-IBM, abnormal accumulation of the amyloid-beta (Abeta) precursor protein and its proteolytic fragment, Abeta, associated with the aging intracellular milieu of the muscle fiber, appear to be key upstream pathogenic events."

The canonical statement of the hypothesis by its originators, asserting APP/Abeta accumulation as the key upstream pathogenic event.

PMID:20711838 SUPPORT Human Clinical

"We now report for the first time that in s-IBM muscle biopsies Aβ-dimer, -trimer, and -tetramer are identifiable by immunoblots. While all the s-IBM samples we studied had Aβ-oligomers, their molecular weights and intensity varied between the patient samples. None of the control muscle biopsies..."

The strongest biochemical evidence offered for the hypothesis, and the closest thing to a direct test of abnormal presence; it reports oligomers in every IBM sample and none in controls, but comes from the originating laboratory and has not been widely replicated independently.

+ 11 more references

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Discussions and Knowledge Gaps

4

Is sporadic inclusion body myositis primarily a T cell-mediated autoimmune disease with secondary degeneration, or primarily a cell-autonomous degenerative myopathy with secondary inflammation?

CONTROVERSY OPEN ibm_autoimmune_vs_degenerative_primacy

Attached to

pathophysiology#Cytotoxic T Cell Invasion of Non-Necrotic Myofibres pathophysiology#Autophagy-Lysosome Failure and Rimmed Vacuole Formation

This is the central unresolved question in IBM and it determines therapeutic strategy. The autoimmune-primary case rests on the HLA association, the anti-cN1A autoantibody, the clonal cytotoxic T cell signature, and the observation that invasion of non-necrotic fibres is far more common than aggregate-bearing fibres (fewer than 1% of myofibres). The degeneration-primary case rests on the consistent failure of immunosuppression and on the xenograft experiment showing rimmed vacuoles and TDP-43 loss of function persist after T cell depletion. The two models are not mutually exclusive; the disputed point is which arm is upstream and therefore which is the therapeutic target. The single most informative test has now reported: the registrational anti-KLRG1 (ulviprubart) MUSCLE trial depleted precisely the effector population the autoimmune model implicates, sparing broader immunity in a way conventional immunosuppression does not, and per sponsor topline announcements it missed its primary and key secondary endpoints in the overall population. If that result holds on peer-reviewed publication it is substantial negative evidence for the autoimmune-primary model as a complete account, and shifts weight toward the degeneration-primary arm or toward a model in which immune injury initiates but does not sustain the disease. The `autoimmune_primary` hypothesis is retained as CANONICAL for now because it remains the dominant published interpretation and the trial result is not yet peer-reviewed; that status should be revisited when it is.

Proposed experiments

Peer-reviewed publication of the anti-KLRG1 MUSCLE trial with target engagement

ibm_klrg1_trial_peer_reviewed_publication

Publish the full MUSCLE (ulviprubart, NCT05721573) dataset in the peer-reviewed literature, reporting functional outcomes alongside confirmed pharmacodynamic depletion of KLRG1+ T cells in blood and muscle. The topline result is already announced as negative in the overall population, so the decisive remaining question is whether the effector population was actually cleared from muscle.

Would support

A null functional result together with documented near-complete depletion of muscle-invading KLRG1+ T cells would be strong evidence against the autoimmune-primary model, since the mechanism was engaged and the disease progressed anyway.

Would refute

A null functional result with poor muscle-compartment depletion would leave the autoimmune-primary model intact and reframe the trial as a pharmacokinetic rather than a mechanistic failure.

Longitudinal paired-biopsy ordering of the two arms

ibm_paired_biopsy_temporal_ordering

Serial paired muscle biopsies measuring TDP-43 cryptic exon burden alongside quantified cytotoxic T cell infiltration in the same patients over time.

Decision criterion

Whichever readout rises first, and predicts subsequent change in the other, identifies the upstream arm.

Show evidence (1 reference)

PMID:35044790 SUPPORT Model Organism

"Sporadic inclusion body myositis (IBM) is the most common acquired muscle disease in adults over age 50, yet it remains unclear whether the disease is primarily driven by T cell-mediated autoimmunity."

Explicitly states the controversy as an open question in the primary literature.

Are amyloid-beta and its precursor APP abnormally and specifically present in inclusion body myositis muscle, and if some amyloid-beta is genuinely present, is it a cause of myofibre injury or a downstream marker?

CONTROVERSY OPEN ibm_amyloid_beta_specificity

Attached to

pathophysiology#Amyloid-beta and APP Accumulation in Myofibres pathophysiology#Autophagy-Lysosome Failure and Rimmed Vacuole Formation

The two halves of the claim have different answers and should not be resolved together. SPECIFICITY is settled in the negative. Amyloid-positive, ubiquitinated filamentous rimmed vacuoles indistinguishable from those of IBM occur in long-standing denervation after poliomyelitis and in congenital myopathies of children, so the finding indexes chronic myofibre injury rather than IBM. Oculopharyngeal muscular dystrophy is not part of this argument: it shares the ubiquitinated filamentous inclusions, but the single study here that applied a beta-amyloid antibody to it found labelling in IBM and not in OPMD, so it is used below only as an experimental control arm. Quantitatively the marker performs poorly: in the series that compared markers head to head, sarcoplasmic TDP-43 was present in 23% of IBM myofibres while focal beta-amyloid immunoreactivity was present in 0.00% and Congo-red material in 0.57%. TDP-43 mislocalization has displaced amyloid as the specific molecular signature of IBM. ABNORMAL PRESENCE remains genuinely open, and is the reason this discussion is filed as a CONTROVERSY rather than closed. Immunoblot and ADDL data reporting Abeta oligomers in every IBM sample and no control exist and have not been formally retracted or directly rebutted, but they issue almost entirely from the laboratory that proposed the hypothesis; the corresponding negative is largely an absence — unbiased laser-capture proteomics of rimmed vacuoles does not report amyloid-beta or APP among 213 enriched proteins — and absence of detection in a spectral-count experiment is weak evidence of absence for a small, aggregation-prone, poorly soluble peptide. What makes the open question tractable is that nobody has run the decisive experiment: a blinded, multi-centre, targeted mass-spectrometric quantification of amyloid-beta peptides in IBM versus disease-control muscle. Two further considerations bear on how much weight the existing literature can carry. The companion phospho-tau claim was shown to rest on antibodies that stain normal myonuclei and bind proteins other than tau, which impugns the reagent class the histological arm depended on; and a citation-network analysis taking this precise belief as its subject found its authority built by citation bias, amplification and invention rather than by data. Both argue for resolving the question with orthogonal, antibody-independent methods rather than with more immunohistochemistry.

Proposed experiments

Blinded targeted mass-spectrometric quantification of amyloid-beta in IBM versus disease-control muscle

ibm_targeted_ms_amyloid_quantification

Parallel reaction monitoring or immunoprecipitation-mass spectrometry with stable-isotope-labelled Abeta40/Abeta42 internal standards, applied to whole muscle lysates and to laser-captured rimmed vacuoles, from IBM, polymyositis, dermatomyositis, chronically denervated, oculopharyngeal muscular dystrophy and age-matched normal muscle, with samples blinded and analysed in more than one laboratory. This is antibody-independent and so is not vulnerable to the cross-reactivity that undermined the immunohistochemical literature.

Would support

Quantifiable Abeta42 above disease controls, in IBM muscle, reproduced across laboratories, would establish abnormal presence and reopen the question of whether it is specific and upstream.

Would refute

Abeta peptides at or below disease-control levels, with adequate sensitivity demonstrated on spiked standards, would close the abnormal presence claim and retire the hypothesis outright.

Targeted re-interrogation of existing rimmed-vacuole LCM-MS peptide libraries for APP and amyloid-beta

ibm_lcm_ms_peptide_library_reinterrogation

Re-query the already-acquired laser-capture mass-spectrometry peptide libraries from the rimmed-vacuole proteomics study for APP and amyloid-beta peptides specifically, reporting detection limits and spiked-standard sensitivity. The published analysis reports 213 enriched proteins but does not state whether these peptides were sought, so "not reported" cannot currently be read as "absent".

Would support

Detection of APP or amyloid-beta peptides enriched in rimmed vacuoles would restore a constituent role for amyloid in the defining lesion.

Would refute

Confirmed non-detection at a demonstrated spiked-standard sensitivity would convert the present silence in the published analysis into a real negative. This is far cheaper than a new prospective study and should precede one.

Independent replication of the Abeta oligomer immunoblot result

ibm_independent_abeta_oligomer_replication

Replication of the Abeta-dimer/trimer/tetramer and ADDL immunoblot findings in an independent laboratory with pre-registered antibodies, peptide-competition controls, and disease controls that include chronically denervated and oculopharyngeal muscular dystrophy muscle rather than normal muscle alone.

Would support

Reproduction of the oligomer signal in IBM but not in chronic-denervation or OPMD controls would restore the hypothesis to ALTERNATIVE status.

Would refute

Failure to reproduce the signal, or an equal signal in the chronic-injury controls, would confirm the DEPRECATED assessment.

Amyloid burden against clinical progression

ibm_amyloid_burden_versus_progression

Test whether quantified muscle amyloid-beta burden at biopsy predicts subsequent rate of functional decline, independently of T cell infiltrate density and TDP-43 cryptic exon burden, in a prospectively followed cohort.

Would support

An association between amyloid burden and subsequent decline that survives adjustment for T cell infiltrate density and TDP-43 cryptic exon burden would support a causal role even at low fibre frequency.

Would refute

No independent association would confirm amyloid as a bystander marker of chronic fibre injury.

Show evidence (3 references)

PMID:19533646 REFUTE Human Clinical

"The presence of as little as >1% of myofibers with nonnuclear sarcoplasmic TDP-43 was highly sensitive (91%) and specific (100%) to IBM among 50 inflammatory myopathy patient samples"

Establishes the marker that displaced amyloid-beta: TDP-43 mislocalization, not amyloid, carries the diagnostic specificity that the amyloid hypothesis claimed.

PMID:9781653 REFUTE Human Clinical

"The chronicity of the underlying disease, rather than the cause, may lead to vacuolar formation, amyloid deposition, and accumulation of ubiquitinated filaments."

States the alternative reading directly: amyloid deposition indexes chronicity of muscle injury and is therefore not specific to IBM.

PMID:20711838 SUPPORT Human Clinical

"Dot-immunoblots using highly specific anti-ADDL monoclonal antibodies also showed highly increased ADDLs in all s-IBM biopsies studied, while controls were negative."

The unrebutted positive result that keeps the abnormal-presence half of this controversy open; note the controls are normal and disease controls generally rather than the chronic-injury controls the specificity literature identifies as the relevant comparison.

Why are the quadriceps and the deep finger flexors selectively vulnerable in inclusion body myositis?

KNOWLEDGE GAP OPEN ibm_muscle_selectivity_unexplained

Attached to

pathophysiology#Progressive Myofibre Degeneration and Selective Muscle Loss

The weakness distribution is the single most reliable diagnostic feature of IBM and is unique among muscle diseases, yet no proposed mechanism explains it. Neither the HLA-restricted autoimmune arm nor the proteostasis and mitochondrial arms predict selective involvement of these particular muscles. Selective type 2 myofibre vulnerability and a functional denervation program have been demonstrated at the transcriptomic level, but these are fibre-type rather than muscle-group explanations and do not account for the specific anatomical pattern.

Proposed experiments

Affected-versus-spared muscle transcriptomic comparison

ibm_affected_vs_spared_transcriptomics

Comparative single-nucleus and spatial transcriptomics of affected (quadriceps, flexor digitorum profundus) versus clinically spared muscles sampled from the same patients.

Decision criterion

Identification of muscle-group-intrinsic transcriptional programs that segregate with clinical involvement independently of fibre type would supply the missing determinant of selectivity.

Regional molecular lesion burden mapping

ibm_regional_lesion_burden_mapping

Quantify somatic mtDNA deletion burden and TDP-43 cryptic exon load across affected versus spared muscle groups in the same individuals.

Decision criterion

A gradient of lesion burden tracking clinical involvement would place the selectivity determinant within the degenerative arm rather than the immune arm.

Show evidence (1 reference)

PMID:38834884 PARTIAL Human Clinical

"Moreover, causal factors and molecular drivers of IBM progression are largely unknown."

Confirms that the molecular drivers underlying IBM progression, including the selective pattern of muscle involvement, remain unexplained.

Can any available experimental model reproduce sporadic IBM faithfully enough to establish drug efficacy, given that no animal model recapitulates the combination of HLA-restricted clonal autoimmunity, aging stroma, selective muscle distribution and decade-long progression?

HUMAN MODEL MISMATCH OPEN ibm_no_faithful_animal_model

Attached to

pathophysiology#Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells

VCP-mutant mice model hereditary VCP multisystem proteinopathy, not sporadic IBM, and were nonetheless part of the preclinical rationale for arimoclomol, which subsequently failed in humans. The human muscle xenograft model is the closest available system and reproduces both inflammatory and degenerative features, but it is short-term and cannot capture years-long progression. Cultured myoblasts cannot recreate chronic HLA-restricted immunity or aging stroma. This model gap is a plausible contributor to the repeated translational failures in IBM and should temper confidence in any mechanism supported only by model-system evidence.

Proposed experiments

Autologous T cell reconstitution of the IBM muscle xenograft

ibm_xenograft_autologous_t_cell_reconstitution

Extend the human IBM muscle xenograft model with autologous reconstitution of the patient's clonal KLRG1+ T cell population.

Would support

De novo emergence of degenerative pathology in previously unaffected grafted muscle would establish that the immune arm is sufficient to initiate degeneration.

Would refute

Absence of new degenerative pathology despite robust T cell engraftment would indicate the immune arm is not sufficient.

Prospective xenograft benchmarking of candidate therapies

ibm_xenograft_prospective_benchmarking

Test candidate therapies against the human muscle xenograft model before committing to phase 3 trials, using TDP-43 cryptic exon burden as a molecular endpoint.

Decision criterion

Concordance between xenograft molecular response and subsequent human trial outcomes would qualify the model as a translational filter; repeated discordance would confirm the model gap.

Show evidence (2 references)

PMID:35044790 SUPPORT Model Organism

"To determine the role of T cells in pathogenesis, we generated a xenograft model by transplanting human IBM muscle into the hindlimb of immunodeficient mice."

Describes the human-muscle xenograft as the model developed precisely because no conventional animal model of sporadic IBM exists.

PMID:37739573 SUPPORT Human Clinical

"Arimoclomol is an oral co-inducer of the cellular heat shock response that was safe and well-tolerated in a pilot study of inclusion body myositis, reduced key pathological markers of inclusion body myositis in two in-vitro models representing degenerative and inflammatory components of this..."

Documents a case where in-vitro and VCP-mutant-mouse efficacy did not translate to human benefit, illustrating the model-fidelity problem.

⚙

Pathophysiology

11

HLA-Associated Autoimmune Susceptibility

The HLA/MHC region carries by far the strongest genetic risk for sporadic IBM, with HLA-DRB1*03:01 (part of the 8.1 ancestral haplotype) the leading association. Fine-mapping attributes the risk to specific amino acid residues within the peptide-binding groove of the DR-beta 1 chain, implicating altered peptide presentation as the susceptibility mechanism. No non-HLA locus has reached genome-wide significance, and there is no Mendelian causal gene.

antigen processing and presentation via MHC class II GO:0002504 ⚠ ABNORMAL

Downstream

Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells HLA-restricted presentation of an as-yet-unidentified antigen is presumed to prime and sustain the pathogenic cytotoxic T cell population, but the inciting antigen is unknown.

Show evidence (2 references)

PMID:28086002 SUPPORT Human Clinical

"The HLA region was confirmed as the most strongly associated region in IBM"

The largest immune-array genetic association study of IBM confirms the HLA region as the dominant risk locus.

PMID:29611059 SUPPORT Human Clinical

"In a study of 252 IBM patients, the class II MHC allele HLA-DRB1*03:01 showed the most significant association with IBM, and that risk could be largely attributed to amino acids within the peptide-binding pocket."

Localizes the HLA risk to peptide-binding-groove residues, supporting altered antigen presentation as the susceptibility mechanism.

Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells

Large clonal populations of terminally differentiated, KLRG1-positive effector-memory and TEMRA CD8+ T cells accumulate in blood and muscle. These cells are minimally proliferative, persist over years, and in a majority of patients meet standard diagnostic criteria for T cell large granular lymphocytic leukaemia. Their terminally differentiated, apoptosis-resistant phenotype is the leading explanation for why IBM resists conventional immunosuppression, and it is the rationale for KLRG1-directed depleting therapy.

IBM is primarily a T cell-mediated autoimmune disease; protein aggregation is a downstream or secondary marker

KLRG1+ terminally differentiated cytotoxic CD8+ T cell CL:0000794

T cell mediated cytotoxicity GO:0001913 ↑ INCREASED

Downstream

Cytotoxic T Cell Invasion of Non-Necrotic Myofibres The expanded cytotoxic clone invades and attacks myofibres via perforin/granzyme-mediated cytotoxicity.

Refractoriness to Conventional Immunosuppression Terminally differentiated, minimally proliferative effector cells are intrinsically resistant to immunosuppressants that act on proliferating lymphocytes.

Show evidence (4 references)

PMID:31326977 SUPPORT Human Clinical

"we identified a signature of T-cell cytotoxicity in inclusion body myositis muscle coupled with a signature of highly differentiated CD8 T-cell effector memory and terminally differentiated effector cells"

Establishes the highly differentiated cytotoxic CD8+ T cell signature as a defining feature of IBM muscle.

PMID:31326977 SUPPORT Human Clinical

"identified the presence of KLRG1 on pathogenic inclusion body myositis muscle invading T cells and an increase in KLRG1 expressing T cells in inclusion body myositis blood"

Identifies KLRG1 as a surface marker of the pathogenic population in both muscle and blood, the basis for KLRG1-targeted therapy.

PMID:35131904 SUPPORT Human Clinical

"We found that a population of KLRG1+ Tem and TemRA were expanded in both the CD4+ and CD8+ T-cell subpopulations in patients with IBM."

Independent flow-cytometric confirmation in 51 IBM patients that the KLRG1+ expansion is confined to highly differentiated memory compartments.

+ 1 more reference

Myofibre MHC Class I Overexpression

Non-necrotic myofibres aberrantly and widely overexpress MHC class I on the sarcolemma and in the sarcoplasm, driven largely by interferon-gamma from the infiltrating T cells. This makes the fibre a target for CD8+ T cell recognition and is also a cell-intrinsic endoplasmic reticulum stressor. MHC class I upregulation is one of the few pathological features shown experimentally to be T cell-dependent.

IBM is primarily a T cell-mediated autoimmune disease; protein aggregation is a downstream or secondary marker

Skeletal muscle fibre CL:0008002

antigen processing and presentation via MHC class I GO:0002474 ↑ INCREASED response to endoplasmic reticulum stress GO:0034976 ↑ INCREASED

Downstream

Cytotoxic T Cell Invasion of Non-Necrotic Myofibres MHC class I presentation on non-necrotic fibres is the substrate for CD8+ T cell recognition and attack.

Show evidence (2 references)

PMID:29611059 SUPPORT Human Clinical

"Histological features of IBM include rimmed vacuoles, protein aggregates, cytochrome oxidase (COX)-deficient fibers, MHC-I upregulation, and an endomysial inflammatory infiltrate containing autoaggressive CD8+ T cells"

Establishes MHC class I upregulation as a canonical histological feature of IBM alongside the degenerative markers.

PMID:35044790 SUPPORT Model Organism

"Myofibers in IBM xenografts showed invasion by human, oligoclonal CD8+ T cells and exhibited MHC-I up-regulation, rimmed vacuoles, mitochondrial pathology, p62-positive inclusions, and nuclear clearance and cytoplasmic aggregation of TDP-43, associated with cryptic exon inclusion."

The xenograft model recapitulates MHC-I upregulation together with the full degenerative phenotype, and the same study shows this feature is T cell-dependent.

Cytotoxic T Cell Invasion of Non-Necrotic Myofibres

The pathognomonic IBM lesion: partial invasion of morphologically intact, non-necrotic muscle fibres by CD8+ T cells within an endomysial inflammatory infiltrate, with perforin/granzyme-mediated cytotoxic injury. Invasion of non-necrotic fibres is markedly more common than amyloid-containing fibres, an observation used to argue that immune injury precedes visible aggregation.

IBM is primarily a T cell-mediated autoimmune disease; protein aggregation is a downstream or secondary marker

CD8-positive, alpha-beta cytotoxic T cell CL:0000794

T cell mediated cytotoxicity GO:0001913 ↑ INCREASED

Skeletal muscle tissue UBERON:0001134

Downstream

Progressive Myofibre Degeneration and Selective Muscle Loss Repeated cytotoxic attack over years destroys myofibres and drives the progressive loss of muscle mass and strength.

Myofibre MHC Class I Overexpression Feed-forward loop: interferon-gamma released by the infiltrating T cells drives further MHC class I upregulation on myofibres, amplifying antigen presentation and sustaining the cytotoxic attack. This edge closes the cycle with the MHC class I node's own upstream edge into invasion, and is the reason MHC class I upregulation is experimentally T cell-dependent.

Show evidence (2 references)

PMID:30837708 SUPPORT Human Clinical

"Its clinical features (finger flexor and quadriceps weakness) and pathological features (invasion of myofibres by cytotoxic T cells) are unique among muscle diseases."

Identifies cytotoxic T cell invasion of myofibres as the pathological hallmark that distinguishes IBM from all other muscle diseases.

PMID:36237625 SUPPORT Human Clinical

"On muscle biopsy, IBM is characterized by a peculiar combination of endomysial inflammation, rimmed vacuoles, and protein aggregation."

Confirms endomysial inflammation as one of the three canonical biopsy features of IBM.

TDP-43 Nuclear Clearance and Loss of Splicing Repression

TDP-43 is cleared from myonuclei and aggregates in the cytoplasm, producing a loss of its normal splicing-repressor function and consequent inclusion of cryptic exons in target transcripts. This is a molecular convergence with ALS and frontotemporal dementia, is the most disease-specific molecular lesion described in IBM, and forms the basis of a highly specific diagnostic assay. Critically, this arm persists after T cell depletion in a human muscle xenograft, indicating it is at least partly T cell-independent.

IBM is primarily a cell-autonomous degenerative myopathy with secondary or non-essential inflammation

Skeletal muscle fibre CL:0008002

regulation of mRNA splicing, via spliceosome GO:0048024 ⚠ ABNORMAL

Downstream

Autophagy-Lysosome Failure and Rimmed Vacuole Formation TDP-43 mislocalization co-occurs with, and is thought to contribute to, the aggregate and rimmed-vacuole pathology; the two persist together after T cell depletion.

Mitochondrial Dysfunction and Somatic mtDNA Deletion TDP-43 and phospho-TDP-43 co-localize with mitochondrial oxidative phosphorylation complexes in the same fibres, and this association is proposed to contribute to mitochondrial dysfunction.

Show evidence (2 references)

PMID:35044790 SUPPORT Human Clinical

"Here, we show that loss of TDP-43-mediated splicing repression, as determined by inclusion of cryptic exons, occurs in skeletal muscle of subjects with IBM."

Establishes loss of TDP-43 splicing repression as a molecular lesion in IBM muscle.

PMID:30742062 SUPPORT Human Clinical

"Inclusion body myositis (IBM) is the most common cause of primary myopathy in individuals aged 50 years and over, and is pathologically characterized by protein aggregates of p62 and mislocalized cytoplasmic TDP-43, as well as mitochondrial abnormalities in affected muscle fibers."

Confirms cytoplasmic TDP-43 mislocalization as a defining pathological feature of IBM muscle.

Autophagy-Lysosome Failure and Rimmed Vacuole Formation

Sarcoplasmic aggregates accumulate p62/SQSTM1, ubiquitin, LC3, amyloid-beta and phosphorylated tau, alongside rimmed vacuoles (autophagic vacuoles rimmed with basophilic granular material). The aggregate composition and the vacuolar morphology together implicate failure of the autophagy-lysosome and ubiquitin-proteasome clearance pathways, though the evidence cited here documents the aggregates rather than directly measuring autophagic flux. Aggregates are present in fewer than 1% of myofibres, a quantitative observation used to argue that they are a marker rather than the principal driver of injury.

IBM is primarily a cell-autonomous degenerative myopathy with secondary or non-essential inflammation

Skeletal muscle fibre CL:0008002

aggrephagy GO:0035973 ↓ DECREASED autophagy GO:0006914 ⚠ ABNORMAL

Downstream

Progressive Myofibre Degeneration and Selective Muscle Loss On the degeneration-primary model, proteostasis failure drives cell-autonomous myofibre degeneration independently of immune attack.

Show evidence (2 references)

PMID:30837708 SUPPORT Human Clinical

"enormous attention has been focused for decades on several biomarkers of myofibre protein aggregates, which are present in <1% of myofibres in patients with IBM"

Quantifies the rarity of aggregate-bearing fibres, the key argument that aggregation is a marker rather than the dominant injury mechanism.

PMID:30742062 SUPPORT Human Clinical

"is pathologically characterized by protein aggregates of p62 and mislocalized cytoplasmic TDP-43"

Identifies the specific aggregate constituents (p62 and cytoplasmic TDP-43) that define this node, replacing a previous snippet that spoke only of mechanistic complexity in general terms.

Amyloid-beta and APP Accumulation in Myofibres

Disputed node, curated to make the historical amyloid model of IBM explicit and assessable rather than absent. On the `amyloid_beta_proteotoxicity` model, IBM myofibres transcribe APP at increased levels, accumulate APP and its cleavage product amyloid-beta intracellularly (preferentially Abeta42), and are injured by soluble Abeta oligomers upstream of proteostasis failure and vacuolar degeneration. The node is marked HYPOTHETICAL because the evidence does not support it as curated fact. Amyloid-beta immunoreactivity is detectable in only a very small minority of IBM myofibres and in one quantitative series in none at all, it is not specific to IBM (the same amyloid-positive filamentous vacuoles occur in chronic denervation and in congenital childhood myopathies), unbiased proteomics of rimmed vacuoles does not report it as an enriched constituent, and cultured IBM myofibres do not accumulate APP. Any real amyloid-beta present is best read as one constituent of the aggregate pathology captured by the `Autophagy-Lysosome Failure and Rimmed Vacuole Formation` node rather than as a specific or upstream driver. No IBM therapeutic has targeted it.

⚠ Amyloid-beta and its precursor APP are abnormally and specifically over-produced in IBM myofibres and are the upstream proteotoxic driver of the disease

Skeletal muscle fibre CL:0008002

APP hgnc:620

amyloid precursor protein metabolic process GO:0042982 ⚠ ABNORMAL amyloid-beta formation GO:0034205 ↑ INCREASED

Downstream

Autophagy-Lysosome Failure and Rimmed Vacuole Formation On the amyloid model, misfolded APP and Abeta oligomers overwhelm and inhibit the proteasome and autophagy-lysosome systems, generating the vacuolar and aggregate pathology. The direction of this edge is contested: an influential review argues the reverse order, with inflammation and overloaded degradation systems coming first and amyloid deposits appearing afterwards as a consequence.

Progressive Myofibre Degeneration and Selective Muscle Loss The proposed proteotoxic endpoint of the amyloid model, in which Abeta42 oligomer cytotoxicity drives vacuolar degeneration and atrophy of muscle fibres.

Show evidence (3 references)

PMID:8394158 SUPPORT Human Clinical

"In affected fibers, increased beta APP-mRNA correspond to abnormally accumulated beta APP immunoreactivity (including beta-amyloid protein epitope)."

The primary observation this node represents: coincident APP transcript and APP/beta-amyloid immunoreactivity in vacuolated IBM fibres.

PMID:19533646 REFUTE Human Clinical

"focal R1282 beta-amyloid immunoreactivity in 0.00% of myofibers"

Quantitative refutation of the node as a general feature of IBM muscle: no myofibre in the series carried focal beta-amyloid immunoreactivity, in biopsies where sarcoplasmic TDP-43 marked 23%.

PMID:10599804 REFUTE In Vitro

"Thus, factors responsible for betaAPP accumulation and denervation-like changes in s-IBM muscle biopsies are not operative in the relatively short-term, non-aged, cultured s-IBM muscle fibers."

Shows APP accumulation is not intrinsic to the IBM myofibre, undermining the node as a cell-autonomous primary lesion.

Mitochondrial Dysfunction and Somatic mtDNA Deletion

IBM muscle accumulates clonally expanded large-scale somatic mitochondrial DNA deletions, producing cytochrome c oxidase-negative and ragged-red fibre segments, impaired oxidative phosphorylation and oxidative stress. Mitochondrial abnormalities are more prominent in IBM than in the other idiopathic inflammatory myopathies, and mitochondrial damage can itself release danger signals that perpetuate injury and inflammation.

IBM is primarily a cell-autonomous degenerative myopathy with secondary or non-essential inflammation

Skeletal muscle fibre CL:0008002

mitochondrion organization GO:0007005 ⚠ ABNORMAL

Downstream

Progressive Myofibre Degeneration and Selective Muscle Loss Bioenergetic failure and oxidative stress in COX-deficient fibre segments contribute to myofibre degeneration.

Show evidence (3 references)

PMID:38808223 SUPPORT Human Clinical

"Notably, abnormal mitochondrial structure and activities are more prominent in the muscle of sIBM than in other types of IIM, suggesting the presence of defective mitochondria might represent an overlooked contributor to the disease onset."

Establishes that mitochondrial pathology is disproportionately prominent in IBM relative to other inflammatory myopathies.

PMID:38808223 SUPPORT Human Clinical

"The large-scale mitochondrial DNA deletion, aberrant protein aggregation, and slowed organelle turnover have provided mechanistic insights into the genesis of impaired mitochondria in sIBM."

Identifies large-scale mtDNA deletion and impaired organelle turnover as the mechanisms generating defective mitochondria in IBM.

PMID:30742062 SUPPORT Human Clinical

"Further immunoblot analysis showed increased levels of TDP-43, truncated TDP-43, phosphorylated TDP-43, and p62, but decreased levels of key subunits of mitochondrial oxidative phosphorylation complexes I and III in IBM patients compared to aged matched control subjects."

Quantifies loss of respiratory chain complex subunits in IBM muscle relative to age-matched controls.

Fibro-Adipogenic Progenitor Senescence

Cellular senescence in IBM muscle is concentrated not in myofibres but in tissue-resident fibro-adipogenic progenitors (FAPs), which express p21, show increased senescence-associated beta-galactosidase activity and adopt a pro-inflammatory secretory phenotype. Senescent FAPs lose collagen type XV expression, which is required to support myofibre structural integrity and neuromuscular junction formation. This provides a stromal, lymphocyte-independent route to myofibre damage. Note it is muscle-intrinsic but NOT cell-autonomous with respect to the myofibre: the senescent cell and the damaged cell are different cells, and the damage is paracrine.

IBM is primarily a cell-autonomous degenerative myopathy with secondary or non-essential inflammation

Fibro-adipogenic progenitor CL:0000057

cellular senescence GO:0090398 ↑ INCREASED

Downstream

Progressive Myofibre Degeneration and Selective Muscle Loss Loss of collagen type XV from senescent FAPs removes structural and neuromuscular-junction support required by myofibres.

Show evidence (2 references)

PMID:37773216 SUPPORT Human Clinical

"Histopathological analysis suggested that cellular senescence is a prominent feature of IBM, primarily affecting non-myogenic cells."

Establishes senescence as a prominent IBM feature and localizes it to non-myogenic (stromal) cells rather than myofibres.

PMID:37773216 SUPPORT Human Clinical

"Among these, we identified a specific cluster of fibro-adipogenic progenitors (FAPs) that demonstrated key hallmarks of senescence, including a pro-inflammatory secretome, expression of p21, increased β-galactosidase activity, and engagement of senescence pathways."

Identifies the senescent population as FAPs and documents the canonical senescence markers (p21, SA-beta-gal, SASP) that anchor conformance to the cellular_senescence module.

Progressive Myofibre Degeneration and Selective Muscle Loss

Cumulative myofibre injury from the immune and degenerative arms produces fibre atrophy and loss, endomysial fibrosis, fatty replacement, and failed regeneration. Loss is selective: type 2 myonuclei are preferentially depleted and acetylcholine receptor expressing fibres are rarefied, indicating a functional denervation program. Clinically this manifests as the characteristic quadriceps and deep finger flexor weakness. Why these particular muscles are selectively vulnerable is unexplained.

Skeletal muscle fibre CL:0008002 Skeletal muscle satellite cell CL:0000594

skeletal muscle tissue regeneration GO:0043403 ↓ DECREASED

Skeletal muscle tissue UBERON:0001134

Show evidence (2 references)

PMID:38834884 SUPPORT Human Clinical

"In IBM muscles, we observed a selective loss of type 2 myonuclei"

Single-nucleus RNA sequencing of patient biopsies demonstrates selective type 2 myofibre vulnerability in IBM.

PMID:37773216 SUPPORT Human Clinical

"the transcriptomic landscape of IBM was also characterized by changes to the myogenic compartment demonstrating a pronounced loss of type 2A myofibers and a rarefication of acetylcholine receptor expressing myofibers"

Independently confirms selective type 2A myofibre loss and documents the neuromuscular-junction rarefaction consistent with functional denervation.

Refractoriness to Conventional Immunosuppression

Unlike dermatomyositis, polymyositis and immune-mediated necrotizing myopathy, IBM does not respond to glucocorticoids, methotrexate, azathioprine or most tested biologics. This is a defining clinical property of the disease and a diagnostic clue: steroid-refractory "polymyositis", particularly with finger-flexor or quadriceps selectivity, should prompt reassessment for IBM. The proposed mechanism is that the effector clone has acquired a neoplastic or neoplastic-like character, making it a self-sustaining population rather than an antigen-driven response that immunosuppression can switch off.

Show evidence (3 references)

PMID:26920676 SUPPORT Human Clinical

"In many patients with inclusion body myositis, the autoimmune T cell expansion has evolved into a neoplastic-like or overtly neoplastic disorder, perhaps contributing to its relative refractoriness to immune-directed therapies previously reported."

Supplies the mechanistic account for this node: refractoriness is attributed to neoplastic evolution of the effector clone. Note the authors hedge with "perhaps contributing", so this is the proposed explanation rather than a demonstrated one.

PMID:38273639 SUPPORT Human Clinical

"Classical immunosuppressants are ineffective in treating inclusion body myositis, and to date there are no recommendations for pharmacological approaches to treatment."

States the treatment refractoriness that defines IBM against the other inflammatory myopathies.

PMID:36237625 SUPPORT Human Clinical

"No pharmacological treatment is yet available for IBM."

Confirms the absence of any established disease-modifying pharmacotherapy.

✶

Histopathology

4

Endomysial Inflammatory Infiltrate with Invasion of Non-Necrotic Fibres

Endomysial mononuclear infiltrate containing autoaggressive CD8+ T cells partially invading morphologically intact, non-necrotic muscle fibres. This combination is the pathological hallmark of IBM.

Show evidence (1 reference)

PMID:29611059 SUPPORT Human Clinical

"Histological features of IBM include rimmed vacuoles, protein aggregates, cytochrome oxidase (COX)-deficient fibers, MHC-I upregulation, and an endomysial inflammatory infiltrate containing autoaggressive CD8+ T cells"

Enumerates the canonical IBM biopsy features including the endomysial autoaggressive CD8+ infiltrate.

Rimmed Vacuoles

Sarcoplasmic vacuoles rimmed with basophilic granular material on modified Gomori trichrome staining, representing autophagic vacuoles. A cardinal but not universally present feature; absence in an early or poorly targeted biopsy does not exclude IBM.

Show evidence (1 reference)

PMID:36237625 SUPPORT Human Clinical

"On muscle biopsy, IBM is characterized by a peculiar combination of endomysial inflammation, rimmed vacuoles, and protein aggregation."

Establishes rimmed vacuoles as one of the three defining biopsy features.

Cytochrome c Oxidase-Negative Muscle Fibres

Fibre segments lacking cytochrome c oxidase activity, reflecting clonally expanded somatic mitochondrial DNA deletions. Present in far greater abundance than in age-matched normal muscle.

Show evidence (1 reference)

PMID:29611059 SUPPORT Human Clinical

"Histological features of IBM include rimmed vacuoles, protein aggregates, cytochrome oxidase (COX)-deficient fibers, MHC-I upregulation, and an endomysial inflammatory infiltrate containing autoaggressive CD8+ T cells"

Lists COX-deficient fibres among the canonical histological features of IBM.

p62 and TDP-43 Positive Sarcoplasmic Inclusions

Immunohistochemically detectable sarcoplasmic aggregates of p62/SQSTM1 and mislocalized cytoplasmic TDP-43, with corresponding nuclear clearance of TDP-43. p62 staining has largely superseded amyloid stains in routine practice.

Show evidence (1 reference)

PMID:30742062 SUPPORT Human Clinical

"We found that IBM pathological markers TDP-43, phosphorylated TDP-43, and p62 all coexisted with intensively stained key subunits of mitochondrial oxidative phosphorylation complexes I-V in the same skeletal muscle fibers of patients with IBM."

Documents co-occurrence of p62 and TDP-43 inclusions within IBM myofibres.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

10

Immune 1

Aspiration Pneumonia Aspiration pneumonia HP:0011951

Show evidence (1 reference)

PMID:36237625 SUPPORT Human Clinical

"Furthermore, IBM mildly affects longevity with aspiration pneumonia and respiratory complications being the most common cause of death."

Identifies aspiration pneumonia as the leading disease-related cause of death in IBM.

Metabolism 1

Elevated Serum Creatine Kinase Elevated circulating creatine kinase concentration HP:0003236

Show evidence (1 reference)

PMID:36237625 SUPPORT Human Clinical

"Less common presentations include isolated dysphagia, asymptomatic hyper-CKemia, and axial or limb weakness beyond the typical pattern."

Documents hyper-CKemia as a recognized, sometimes presenting, laboratory abnormality in IBM.

Musculoskeletal 1

Falls Frequent falls HP:0002359

Show evidence (1 reference)

PMID:31397289 SUPPORT Human Clinical

"Falls were the most frequent adverse event"

In the 251-participant RESILIENT trial falls were the most frequent adverse event across all groups including placebo, reflecting the high background fall burden of the IBM population.

Other 7

Deep Finger Flexor Weakness VERY_FREQUENT Finger flexor weakness HP:0031177

Course: PROGRESSIVE

Show evidence (2 references)

PMID:36237625 SUPPORT Human Clinical

"The typical clinical phenotype is characterized by prominent involvement of deep finger flexors and quadriceps muscles."

Establishes deep finger flexor involvement as part of the typical, i.e. very frequent, clinical phenotype of IBM.

PMID:30837708 SUPPORT Human Clinical

"Its clinical features (finger flexor and quadriceps weakness) and pathological features (invasion of myofibres by cytotoxic T cells) are unique among muscle diseases."

Confirms finger flexor weakness as a defining and disease-specific clinical feature.

Quadriceps Weakness VERY_FREQUENT Quadriceps muscle weakness HP:0003731

Course: PROGRESSIVE

Show evidence (2 references)

PMID:36399165 SUPPORT Human Clinical

"Inclusion body myositis (IBM) belongs to the group of idiopathic inflammatory myopathies and is characterized by a slowly progressive disease course with asymmetric muscle weakness of predominantly the finger flexors and knee extensors."

Establishes knee extensor weakness as a predominant, characteristic and progressive feature.

PMID:36237625 SUPPORT Human Clinical

"The typical clinical phenotype is characterized by prominent involvement of deep finger flexors and quadriceps muscles."

Confirms quadriceps involvement as part of the typical clinical phenotype.

Dysphagia FREQUENT Oral-pharyngeal dysphagia HP:0200136

Course: PROGRESSIVE

Show evidence (3 references)

PMID:33879596 SUPPORT Human Clinical

"Two-thirds of patients developed dysphagia, and half required a feeding tube."

Population-based cohort quantifies dysphagia in about two-thirds of patients, supporting the FREQUENT (30-79%) frequency band.

PMID:37678324 SUPPORT Human Clinical

"Dysphagia is a common symptom of sporadic inclusion body myositis (IBM), affecting disease trajectory and patient quality-of-life."

Confirms dysphagia is common and materially affects disease trajectory and quality of life.

PMID:36237625 SUPPORT Human Clinical

"Less common presentations include isolated dysphagia, asymptomatic hyper-CKemia, and axial or limb weakness beyond the typical pattern."

Documents that dysphagia can be the isolated presenting manifestation.

Loss of Ambulation Loss of ambulation HP:0002505

Course: PROGRESSIVE

Show evidence (2 references)

PMID:29611059 SUPPORT Human Clinical

"Sporadic Inclusion Body myositis (IBM) is the most common myopathy in individuals over the age of 50, and patients typically lose the ability to ambulate 10 to 15 years after diagnosis"

Quantifies the typical interval from diagnosis to loss of ambulation.

PMID:36237625 SUPPORT Human Clinical

"IBM is associated with marked morbidity as majority of patients eventually become wheelchair dependent with limited use of their hands and marked dysphagia."

Confirms that the majority of patients ultimately become wheelchair dependent.

Foot Drop Foot dorsiflexor weakness HP:0009027

`frequency` deliberately omitted: the cited snippet places foot extensors in the characteristic weakness distribution but supports no quantitative band, and published estimates vary widely. Per the repository frequency-evidence guidelines, omit rather than guess.

Show evidence (1 reference)

PMID:38473988 SUPPORT Human Clinical

"slowly progressive asymmetrical muscle weakness, predominantly affecting the quadriceps, deep finger flexors, and foot extensors"

Includes foot extensor (dorsiflexor) involvement in the characteristic IBM weakness distribution.

Rimmed Vacuoles Rimmed vacuoles HP:0003805

Show evidence (1 reference)

PMID:36237625 SUPPORT Human Clinical

"On muscle biopsy, IBM is characterized by a peculiar combination of endomysial inflammation, rimmed vacuoles, and protein aggregation."

Establishes rimmed vacuoles as one of the three defining biopsy features.

Cytochrome c Oxidase-Negative Muscle Fibres Cytochrome C oxidase-negative muscle fibers HP:0003688

Show evidence (1 reference)

PMID:29611059 SUPPORT Human Clinical

"Histological features of IBM include rimmed vacuoles, protein aggregates, cytochrome oxidase (COX)-deficient fibers, MHC-I upregulation, and an endomysial inflammatory infiltrate containing autoaggressive CD8+ T cells"

Lists COX-deficient fibres among the canonical histological features of IBM.

🧬

Genetic Associations

3

HLA-DRB1

Gene: HLA-DRB1 hgnc:4948 relationship_type: SUSCEPTIBILITY

Show evidence (5 references)

PMID:29611059 SUPPORT Human Clinical

"In a study of 252 IBM patients, the class II MHC allele HLA-DRB1*03:01 showed the most significant association with IBM, and that risk could be largely attributed to amino acids within the peptide-binding pocket."

Establishes HLA-DRB1*03:01 as the leading susceptibility allele and localizes the effect to the peptide-binding pocket.

PMID:38043487 SUPPORT Human Clinical

"Human Leukocyte Antigens (HLA) is the highest genetic risk factor for developing IBM."

Confirms HLA as the dominant genetic risk factor; the same study refines the association to DRB1*03:01:01 and arginine-74 of the DR-beta 1 chain.

PMID:28086002 SUPPORT Human Clinical

"No association with anti-cytosolic 5'-nucleotidase 1A-positive status was found independent of HLA-DRB1*03:01."

Shows the HLA signal does not stratify by anti-cN1A serostatus, relevant to whether seropositive IBM is a genetically distinct subgroup.

+ 2 more references

NT5C1A

Gene: NT5C1A hgnc:17819 relationship_type: BIOMARKER

Show evidence (1 reference)

PMID:23596012 SUPPORT Human Clinical

"Autoantibodies against cN1A are common in and highly specific to IBM among muscle diseases, and may provide a link between IBM's dual processes of autoimmunity and myodegeneration."

Identifies cN1A (NT5C1A) as the IBM autoantigen and frames it as a candidate bridge between the autoimmune and degenerative arms.

VCP and SQSTM1 (rare proteostasis variants)

relationship_type: DISPUTED

Show evidence (2 references)

PMID:29611059 PARTIAL Human Clinical

"Candidate gene sequencing identified rare missense variants in proteins regulating protein homeostasis including VCP and SQSTM1."

Reports the rare proteostasis-gene variants; the same review notes only the HLA association has reached genome-wide significance, so these remain unvalidated.

PMID:29611059 SUPPORT Human Clinical

"Many variants have been reported at an increased frequency in IBM in small studies; however, only HLA association has shown genome-wide significance."

Explicitly limits the confidence that can be placed in non-HLA candidate variants in IBM.

💊

Medical Actions

11

Resistance and Aerobic Exercise Therapy

Action: physical therapy Ontology label: Physical Therapy NCIT:C15302

Individualized supervised resistance and aerobic exercise, with contracture prevention, energy conservation, orthoses, mobility aids and fall prevention. Exercise appears safe and may improve strength or conditioning, but consistent mobility benefit has not been demonstrated. Together with swallowing and respiratory surveillance this constitutes the mainstay of management.

Show evidence (1 reference)

PMID:36237625 SUPPORT Human Clinical

"Monitoring for swallowing and respiratory complications, exercise, and addressing mobility issues are the mainstay of management."

Establishes exercise and supportive monitoring as the standard of care in the absence of pharmacotherapy.

Dysphagia Management

Action: speech therapy Ontology label: Speech Language Therapy NCIT:C159273

Multidisciplinary swallowing care: periodic symptom screening, speech-language assessment, videofluoroscopy or endoscopy when indicated, texture and volume adaptation, nutrition support and aspiration precautions, with rehabilitative swallowing exercise protocols. Cricopharyngeal dilation, botulinum toxin injection or myotomy may help selected obstructive cases; myotomy is irreversible.

Target Phenotypes: Dysphagia HP:0002015

Show evidence (2 references)

PMID:37678324 SUPPORT Human Clinical

"Small scale research and clinical anecdotal data support a multidisciplinary and multipronged patient-centered approach, including rehabilitative exercise protocols, for dysphagia management in IBM."

Supports the multidisciplinary rehabilitative approach while indicating the evidence base is small-scale.

PMID:37678324 PARTIAL Human Clinical

"A paucity exists in the literature to effectively guide clinical decision-making for patients with IBM and dysphagia."

Documents the weak evidence base underlying dysphagia management recommendations in IBM.

Occupational Therapy and Assistive Devices

Action: occupational therapy Ontology label: Occupational Therapy NCIT:C121351

Occupational therapy for the hand disability that follows deep finger flexor weakness: adaptive grip aids, built-up utensils, home modification and energy conservation. Ankle-foot orthoses for foot drop, and canes, walkers, wheelchairs and transfer devices as ambulation declines. Because there is no disease-modifying therapy, maintaining function and independence with assistive technology is a substantial part of actual care rather than an adjunct.

Show evidence (2 references)

PMID:36237625 SUPPORT Human Clinical

"Monitoring for swallowing and respiratory complications, exercise, and addressing mobility issues are the mainstay of management."

Establishes addressing mobility issues, which is what assistive devices and occupational therapy deliver, as a mainstay of IBM management.

PMID:36237625 SUPPORT Human Clinical

"IBM is associated with marked morbidity as majority of patients eventually become wheelchair dependent with limited use of their hands and marked dysphagia."

Documents the hand-function and mobility disability that occupational therapy and assistive devices are directed at.

Falls Prevention

Action: physical therapy Ontology label: Physical Therapy NCIT:C15302

Structured fall-risk assessment, home safety modification, gait aids and balance work. Falls are a leading cause of injury in IBM and were the single most frequent adverse event across all arms of the RESILIENT trial, including placebo, which indicates the background rate in this population rather than a drug effect.

Target Phenotypes: Frequent falls HP:0002359

Show evidence (1 reference)

PMID:31397289 SUPPORT Human Clinical

"Falls were the most frequent adverse event"

Quantifies falls as the dominant adverse event in a large IBM trial population, establishing the clinical need for fall prevention.

Intravenous Immunoglobulin (IVIG)

Action: immunoglobulin infusion therapy Ontology label: Immunoglobulin Therapy NCIT:C62710

IVIG has been tested in randomised controlled trials in IBM without demonstrating a sustained strength benefit; the Cochrane review could not pool the trials or draw conclusions from them. It retains a limited, non-consensus role in selected patients with refractory dysphagia, where transient swallowing improvement has been reported, but it does not alter the overall course of the disease.

Target Phenotypes: Oral-pharyngeal dysphagia HP:0200136

Show evidence (2 references)

PMID:35658164 PARTIAL Human Clinical

"Three trials (n = 78) compared intravenous immunoglobulin (combined in one trial with prednisone) to a placebo, but we were unable to perform meta-analysis because of variations in study analysis and presentation of trial data, with no access to the primary data for re-analysis."

Documents that IVIG has been trialled in IBM but that the evidence base is too weak and heterogeneous to support pooling, so no efficacy claim is made.

PMID:35658164 PARTIAL Human Clinical

"We were unable to draw conclusions from trials of IVIg, oxandrolone, and AZA plus MTX versus MTX."

The Cochrane authors explicitly decline to draw any conclusion on IVIG, which is why this treatment is curated as PARTIAL rather than SUPPORT or REFUTE.

Interventional Dysphagia Procedures

Action: surgical procedure Ontology label: Surgical Procedure NCIT:C15329

When conservative swallowing management fails, interventional options are used for the obstructive cricopharyngeal component: balloon dilation, botulinum toxin injection of the cricopharyngeus, and cricopharyngeal myotomy. Myotomy is irreversible. Gastrostomy (PEG) placement is used for nutritional support once oral intake becomes unsafe; roughly half of patients in a population-based cohort eventually required a feeding tube. Evidence is limited to small series and clinical experience rather than randomised trials.

Target Phenotypes: Oral-pharyngeal dysphagia HP:0200136

Show evidence (2 references)

PMID:41161903 SUPPORT Human Clinical

"Dysphagia, a major contributor to morbidity, is receiving increased attention through both conservative and interventional approaches."

Confirms that interventional (procedural) approaches to dysphagia sit alongside conservative management in contemporary IBM practice.

PMID:33879596 SUPPORT Human Clinical

"Two-thirds of patients developed dysphagia, and half required a feeding tube."

Quantifies the proportion progressing to gastrostomy-level nutritional support, establishing the clinical need for this treatment category.

Conventional Immunosuppression (corticosteroids, methotrexate, azathioprine)

Action: Pharmacotherapy NCIT:C15986

Agent: prednisone CHEBI:8382 methotrexate CHEBI:44185 azathioprine CHEBI:2948

Glucocorticoids and conventional immunosuppressants are NOT effective in IBM and are not recommended. They add toxicity without durable functional benefit. This entry is retained deliberately to record a negative treatment result: failure to respond to corticosteroids is itself a diagnostic clue that should prompt reassessment of a "polymyositis" label.

Show evidence (1 reference)

PMID:38273639 REFUTE Human Clinical

"Classical immunosuppressants are ineffective in treating inclusion body myositis, and to date there are no recommendations for pharmacological approaches to treatment."

Directly refutes any therapeutic claim for conventional immunosuppression in IBM.

Sirolimus (rapamycin)

Action: Pharmacotherapy NCIT:C15986

Agent: sirolimus CHEBI:9168

An mTOR inhibitor that blocks effector T cell proliferation while relatively sparing regulatory T cells and inducing autophagy, targeting both the immune and degenerative arms of IBM. A 44-patient phase 2b trial missed its primary endpoint of knee extension strength but showed significant differences favouring sirolimus on several secondary outcomes. Sirolimus is investigational, not established therapy.

Mechanism Target:

INHIBITS Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells — mTOR inhibition blocks effector T cell proliferation while relatively sparing regulatory T cells.

Show evidence (3 references)

PMID:38273639 PARTIAL Human Clinical

"We observed no difference in the primary outcome of relative percentage change from baseline to month 12 of the maximal voluntary isometric knee extension strength (median difference 3·78, 95% CI -10·61 to 17·31; p=0·85)."

The primary endpoint was negative, so any therapeutic claim must be qualified as at best partially supported.

PMID:38273639 PARTIAL Human Clinical

"However, we observed significant differences in favour of sirolimus between the study groups for HAQ-DI, forced vital capacity, thigh fat fraction, and 6-min walking distance."

Secondary-endpoint signals that motivated further trials, but which do not establish efficacy given the negative primary endpoint.

PMID:38273639 SUPPORT Human Clinical

"When used after organ transplantation, sirolimus can block the proliferation of effector T cells, while preserving T regulatory cells, and induce autophagy, all of which are processes that are impaired in inclusion body myositis."

States the mechanistic rationale linking sirolimus to the effector T cell and autophagy nodes of the IBM pathograph.

Arimoclomol

Action: Pharmacotherapy NCIT:C15986

Agent: arimoclomol CHEBI:747211

An oral co-inducer of the cellular heat shock response intended to enhance proteostasis. Despite encouraging preclinical and pilot data it failed to improve the IBM Functional Rating Scale in a 150-participant, 20-month randomised placebo-controlled trial and is not standard care. Recorded here as a negative result relevant to the degeneration-primary hypothesis.

Show evidence (1 reference)

PMID:37739573 REFUTE Human Clinical

"Arimoclomol did not improve efficacy outcomes, relative to placebo, but had an acceptable safety profile in individuals with inclusion body myositis."

Refutes efficacy of heat-shock-response co-induction as a treatment strategy in IBM.

Bimagrumab

Action: Pharmacotherapy NCIT:C15986

Agent: monoclonal antibody NCIT:C20401

A fully human anti-activin type II receptor monoclonal antibody intended to increase muscle mass by blocking myostatin signalling. It targeted the atrophy arm rather than disease causation, increased lean mass, but failed its primary 6-minute walking distance endpoint in the 251-participant RESILIENT phase 2b trial.

Show evidence (1 reference)

PMID:31397289 REFUTE Human Clinical

"At week 52, 6MWD change from baseline did not differ between any bimagrumab dose and placebo"

Refutes functional efficacy of bimagrumab at any tested dose in IBM.

Ulviprubart (ABC008, anti-KLRG1)

Action: Pharmacotherapy NCIT:C15986

Agent: monoclonal antibody NCIT:C20401

A monoclonal antibody designed to deplete highly differentiated KLRG1+ cytotoxic T cells while sparing naive and regulatory compartments, directly targeting the effector population identified as pathogenic in IBM. The registrational phase 2/3 MUSCLE trial (NCT05721573, 272 participants, primary endpoint IBMFRS change at week 76) completed in November 2025. Sponsor topline announcements report that the trial did NOT meet its primary endpoint or key secondary endpoints in the overall population, with favourable trends limited to a mild-to-moderate disease subgroup. This is the most direct test of the autoimmune-primary hypothesis conducted to date and its failure is meaningful negative evidence for that model. See notes for the important provenance caveat.

Mechanism Target:

INHIBITS Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells — Anti-KLRG1 antibody depletes the highly differentiated KLRG1-positive cytotoxic T cell population while sparing naive and regulatory compartments.

Show evidence (2 references)

PMID:31326977 SUPPORT Human Clinical

"Targeting highly differentiated cytotoxic T cells could be a favourable approach to treatment of inclusion body myositis."

States the therapeutic rationale for KLRG1-directed depletion that ulviprubart implements.

clinicaltrials:NCT05721573 PARTIAL Human Clinical

"A Phase II/III Randomized, Double-blind, Placebo-controlled, Multicenter Study to Determine the Efficacy and Safety of ABC008 in the Treatment of Subjects with Inclusion Body Myositis"

Documents the existence and design of the pivotal trial; results are not yet published, so no efficacy claim is made.

🔬

Biochemical Markers

2

Anti-cN1A (NT5C1A) Autoantibody (PRESENT)

Show evidence (3 references)

PMID:23460448 SUPPORT Human Clinical

"By immunoprecipitation of recombinant cN1A, high concentrations of anti-Mup44 autoantibodies were detected in 33% of sIBM patient sera, whereas their prevalence in dermatomyositis, polymyositis, and other neuromuscular disorders appeared to be rare (4.2%, 4.5%, and 3.2%, respectively)."

Original identification of the cN1A autoantigen, quantifying frequency in IBM against comparator neuromuscular diseases.

PMID:23596012 SUPPORT Human Clinical

"Moderate reactivity of anti-cN1A autoantibodies was 70% sensitive and 92% specific, and high reactivity was 34% sensitive and 98% specific for the diagnosis of IBM."

Provides the threshold-dependent sensitivity and specificity figures for anti-cN1A as a diagnostic test.

PMID:23596012 SUPPORT Human Clinical

"cN1A reactivity by immunohistochemistry accumulated in perinuclear regions and rimmed vacuoles in IBM muscle, localizing to areas of myonuclear degeneration."

Localizes the autoantigen to the degenerative lesions themselves, supporting a link between the autoimmune and myodegenerative arms.

TDP-43 Cryptic Exon Inclusion in Muscle (PRESENT)

Show evidence (1 reference)

PMID:35044790 SUPPORT Human Clinical

"Of 119 muscle biopsies tested, RT-PCR-mediated detection of cryptic exon inclusion was able to diagnose IBM with 84% sensitivity and 99% specificity."

Quantifies the diagnostic performance of cryptic exon detection in a large biopsy series.

🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Inclusion Body Myositis:

Polymyositis MONDO:0019127

Overlapping Features Historically the most common misdiagnosis. Contemporary opinion holds that many cases labelled polymyositis are better classified as IBM, immune-mediated necrotizing myopathy or antisynthetase syndrome. Steroid-refractory "polymyositis", especially with finger-flexor or quadriceps selectivity, should prompt reassessment for IBM.

Distinguishing Features

Selective deep finger flexor and quadriceps weakness in IBM
Rimmed vacuoles and p62/TDP-43 aggregates on biopsy in IBM, absent in polymyositis
Refractoriness to corticosteroids in IBM
Invasion of muscle by large granular lymphocytes in IBM but rarely in polymyositis

Show evidence (1 reference)

PMID:26920676 SUPPORT Human Clinical

"Muscle immunohistochemistry demonstrated invasion of large granular lymphocytes into muscle in 15/15 inclusion body myositis patients but in only 1/28 patients with dermatomyositis or polymyositis."

Provides a discriminating pathological feature between IBM and polymyositis/dermatomyositis.

GNE Myopathy (hereditary inclusion body myopathy)

Overlapping Features An autosomal recessive hereditary myopathy that shares rimmed vacuoles and protein inclusions on biopsy but is a mechanistically distinct disease. It is the most important hereditary mimic of IBM and a recurring source of entity confusion.

Distinguishing Features

Onset typically before age 40
Characteristic sparing of the quadriceps
Absence of endomysial inflammatory infiltrate and MHC class I upregulation
Autosomal recessive GNE variants identifiable

Show evidence (1 reference)

PMID:29611059 SUPPORT Human Clinical

"For example, hIBM2 caused by autosomal recessive inheritance of mutations in the GNE gene typically spares the quadriceps, and biopsy shows rimmed vacuoles and protein inclusions but lacks inflammation."

States the specific features distinguishing GNE myopathy from sporadic IBM.

VCP-Associated Multisystem Proteinopathy

Overlapping Features Autosomal dominant VCP-related inclusion body myopathy with Paget disease of bone and frontotemporal dementia. Shares the rimmed vacuole and TDP-43 pathology of IBM but is monogenic and multisystem.

Distinguishing Features

Earlier onset and positive family history
Extramuscular features (Paget disease of bone, frontotemporal dementia, motor neuron disease)
Identifiable pathogenic VCP variant

Show evidence (1 reference)

PMID:29611059 PARTIAL Human Clinical

"Thus, mutations in known hIBM genes cause syndromes that share degenerative features on biopsy but otherwise are clinically distinct from IBM."

Supports the general boundary between hereditary inclusion body myopathy genes (including VCP) and sporadic IBM; the snippet covers the class rather than VCP specifically.

T Cell Large Granular Lymphocytic Leukaemia

Overlapping Features Not merely a mimic but a genuine overlap: the majority of IBM patients meet standard diagnostic criteria for T-LGL leukaemia on blood flow cytometry. This is better understood as a shared clonal cytotoxic T cell process than as a differential to exclude, and it can prompt inappropriate haematological workup if not recognized. Retained here because it is a real bedside diagnostic consideration, but the association itself is modelled properly in kb/comorbidities/com_Inclusion_Body_Myositis__T_Cell_Large_Granular_Lymphocytic_Leukemia.yaml, which is the authoritative record for it.

Distinguishing Features

Large granular lymphocyte expansion is present in the majority of IBM patients and does not by itself indicate a separate haematological disease

Show evidence (1 reference)

PMID:26920676 SUPPORT Human Clinical

"Most (22/38; 58%) patients with inclusion body myositis had aberrant populations of large granular lymphocytes in their blood meeting standard diagnostic criteria for T cell large granular lymphocytic leukaemia."

Quantifies the overlap between IBM and formal T-LGL leukaemia criteria.

🔬

Clinical Trials

5

NCT02753530 PHASE_II COMPLETED

Multicentre randomised double-blind placebo-controlled trial of arimoclomol, an oral heat shock response co-inducer, in sporadic IBM. Enrollment 152. Reported in Lancet Neurology 2023 (PMID:37739573); did not improve the IBMFRS relative to placebo.

Show evidence (1 reference)

clinicaltrials:NCT02753530 SUPPORT Human Clinical

"The purpose of this study is to evaluate the safety and efficacy of the study drug, arimoclomol in IBM patients."

Confirms the trial intervention and indication.

NCT01925209 PHASE_III COMPLETED

RESILIENT: randomised double-blind placebo-controlled dose-finding phase 2b/3 trial of intravenous bimagrumab (BYM338) in sporadic IBM, enrollment 251, primary endpoint 6-minute walking distance at 52 weeks. Reported in Lancet Neurology 2019 (PMID:31397289); primary endpoint not met at any dose. Recorded as PHASE_III because the schema enum has no combined phase 2b/3 value.

Show evidence (1 reference)

clinicaltrials:NCT01925209 SUPPORT Human Clinical

"This study evaluated the efficacy, safety and tolerability of multiple doses of bimagrumab/BYM338 vs placebo, when administered intravenously (i.v.), on physical function, muscle strength, and mobility in patients with sporadic inclusion body myositis (sIBM)."

Confirms the RESILIENT design, intervention, outcomes and indication.

NCT02573467 PHASE_III COMPLETED

Long-term extension of the RESILIENT bimagrumab study, enrollment 211, intended to evaluate efficacy, safety and tolerability up to 2 years. Reported in Neurology 2021 (PMID:33597289); extended treatment did not produce clinical benefit in mobility. The extension was terminated per protocol once the core study missed its primary endpoint, so no participants entered the planned open-label period. Registry status is COMPLETED.

Show evidence (1 reference)

clinicaltrials:NCT02573467 SUPPORT Human Clinical

"the core study did not meet the primary end point (no bimagrumab dose was identified based on the core study efficacy results) the extension study was terminated as per protocol/sponsor's decision"

The registry record itself documents that the core RESILIENT study missed its primary endpoint and that this triggered termination of the extension, independently corroborating the published negative result.

NCT04789070 PHASE_III ACTIVE_NOT_RECRUITING

"Optimism in IBM": confirmatory double-blind randomised controlled phase III trial of sirolimus, enrollment 140, primary endpoint IBM Functional Rating Scale. Follows the phase 2b proof-of-concept trial (PMID:38273639) that missed its primary endpoint but showed secondary-endpoint signals. Results not yet available.

Show evidence (1 reference)

clinicaltrials:NCT04789070 SUPPORT Human Clinical

"The hypothesis is that Sirolimus, (Rapamycin (R)) which is currently used in organ transplantation and works by blocking the activity of T effector cells but preserving T regulatory cells, as well as by inducing autophagy (protein degradation), will be effective in IBM to slow or stabilize..."

Confirms the confirmatory sirolimus trial and states its dual mechanistic rationale, matching the target_mechanisms link on the sirolimus treatment.

NCT05721573 PHASE_III COMPLETED

Randomized, double-blind, placebo-controlled multicenter phase II/III trial of ABC008 (ulviprubart), an anti-KLRG1 monoclonal antibody depleting highly differentiated cytotoxic T cells, in inclusion body myositis. Actual enrollment 272 participants. Recorded as PHASE_III because the schema enum has no combined phase II/III value.

Show evidence (1 reference)

clinicaltrials:NCT05721573 SUPPORT Human Clinical

"A Phase II/III Randomized, Double-blind, Placebo-controlled, Multicenter Study to Determine the Efficacy and Safety of ABC008 in the Treatment of Subjects with Inclusion Body Myositis"

Confirms the trial design, intervention and indication.

{ }

Source YAML

click to show

name: Inclusion Body Myositis
creation_date: '2026-07-30T00:00:00Z'
category: Autoimmune
parents:
- Inflammatory Myopathy
- Autoimmune Disease
disease_term:
  preferred_term: Sporadic Inclusion Body Myositis
  term:
    id: MONDO:0007827
    label: inclusion body myositis
synonyms:
- sporadic inclusion body myositis
- sIBM
- IBM
description: >-
  Sporadic inclusion body myositis (sIBM) is the most common acquired myopathy
  after age 50. It is characterized by slowly progressive, frequently asymmetric
  weakness with a distinctive predilection for the knee extensors (quadriceps)
  and the deep finger flexors, together with frequent oropharyngeal dysphagia.
  Muscle biopsy shows a unique combination of an inflammatory component
  (clonally expanded, highly differentiated cytotoxic CD8+ T cells invading
  non-necrotic fibres that overexpress MHC class I) and a degenerative component
  (rimmed vacuoles, p62/TDP-43 protein aggregates, COX-negative fibres). Unlike
  the other idiopathic inflammatory myopathies it is refractory to
  corticosteroids and conventional immunosuppression, and no disease-modifying
  drug therapy is established. Sporadic IBM must be distinguished from the
  hereditary inclusion body myopathies (GNE myopathy, VCP multisystem
  proteinopathy), which share degenerative biopsy features but lack the
  characteristic inflammation and weakness distribution.
classifications:
  harrisons_chapter:
  - classification_value: IMMUNE_RHEUMATOLOGIC
mechanistic_hypotheses:
- hypothesis_group_id: autoimmune_primary
  hypothesis_label: >-
    IBM is primarily a T cell-mediated autoimmune disease; protein aggregation
    is a downstream or secondary marker
  status: CANONICAL
  description: >-
    The dominant contemporary model holds that clonally expanded, highly
    differentiated cytotoxic CD8+ T cells are the primary pathogenic effectors,
    and that the degenerative pathology (rimmed vacuoles, aggregates) is
    downstream of, or secondary to, chronic immune injury. Supporting arguments
    are the HLA association, the circulating anti-cN1A autoantibody, the marked
    cytotoxic T cell transcriptomic signature, the clonality and persistence of
    the effector population, and the observation that invasion of non-necrotic
    fibres is far more frequent than amyloid-containing fibres. The treatment
    refractoriness is explained on this model by the effector cells being
    terminally differentiated and resistant to conventional immunotherapy
    rather than by the disease being non-immune.
  evidence:
  - reference: PMID:30837708
    reference_title: "Inclusion body myositis: clinical features and pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Findings from the past decade that implicate autoimmunity in IBM include
      the identification of a circulating autoantibody (anti-cN1A); the absence
      of any statistically significant genetic risk factor other than the common
      autoimmune disease 8.1 MHC haplotype in whole-genome sequencing studies;
      the presence of a marked cytotoxic T cell signature in gene expression
      studies; and the identification in muscle and blood of large populations
      of clonal highly differentiated cytotoxic CD8+ T cells that are resistant
      to many immunotherapies.
    explanation: >-
      Enumerates the principal lines of evidence marshalled in support of the
      autoimmune-primary model.
- hypothesis_group_id: degeneration_primary
  hypothesis_label: >-
    IBM is primarily a cell-autonomous degenerative myopathy with secondary or
    non-essential inflammation
  status: ALTERNATIVE
  description: >-
    A competing model holds that cell-autonomous myofibre degeneration
    (proteostasis failure, TDP-43 loss of function, mitochondrial damage) drives
    the disease and that the inflammatory infiltrate, while conspicuous, is not
    the essential driver. The strongest direct evidence is the IBM muscle
    xenograft experiment in which depleting human T cells suppressed myofibre
    MHC class I upregulation but left rimmed vacuoles and TDP-43 loss of
    function intact. The consistent failure of immunosuppression to alter
    functional decline is the main clinical argument. Note that this model is
    not mutually exclusive with the autoimmune-primary model; both arms are
    likely to operate, and the disputed question is which is upstream.
  evidence:
  - reference: PMID:35044790
    reference_title: "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Reduction of human T cells within IBM xenografts by treating mice
      intraperitoneally with anti-CD3 (OKT3) suppressed MHC-I up-regulation.
      However, rimmed vacuoles and loss of TDP-43 function persisted. These data
      suggest that T cell depletion does not alter muscle degenerative pathology
      in IBM.
    explanation: >-
      Direct experimental dissociation of the degenerative arm from T cell
      activity in a human-muscle xenograft, the key evidence for the
      degeneration-primary model.
- hypothesis_group_id: amyloid_beta_proteotoxicity
  hypothesis_label: >-
    Amyloid-beta and its precursor APP are abnormally and specifically
    over-produced in IBM myofibres and are the upstream proteotoxic driver of
    the disease
  status: DEPRECATED
  description: >-
    Proposed by Askanas and Engel from the early 1990s, this model cast sporadic
    IBM as a muscle analogue of Alzheimer disease: increased APP transcription
    in vacuolated fibres leads to intracellular accumulation of APP and its
    proteolytic fragment amyloid-beta, preferentially the more aggregation-prone
    Abeta42, whose soluble oligomers are cytotoxic and sit upstream of tau
    phosphorylation, oxidative stress, proteasome inhibition, ER stress and
    vacuolar degeneration. It was the dominant degenerative account of IBM for
    roughly two decades and supplied the rationale for the Congo red / amyloid
    criterion in older diagnostic schemes.

    It is recorded here as DEPRECATED, and the two claims embedded in the label
    fail for different reasons.

    The claim of SPECIFICITY fails outright: beta-amyloid-immunoreactive,
    Congo-red-positive rimmed vacuoles with tubulofilaments occur in
    long-standing denervation (postpoliomyelitis muscular atrophy) and in
    congenital myopathies of childhood, so the finding tracks chronicity of
    fibre injury rather than IBM itself. (Oculopharyngeal muscular dystrophy is
    deliberately excluded from this list: it shares the ubiquitinated
    filamentous inclusions, but the one study here that stained it for
    beta-amyloid found labelling in IBM and not in OPMD.) Comparative
    quantification puts the point sharply: in the same
    biopsies in which sarcoplasmic TDP-43 marked 23% of myofibres, focal
    beta-amyloid immunoreactivity (R1282) was found in 0.00% and fluorescent
    Congo red material in 0.57%. TDP-43 mislocalization, not amyloid, is now the
    sensitive and specific molecular marker of IBM.

    The claim of ABNORMAL PRESENCE is weaker than the literature suggests rather
    than plainly false. Positive immunoblot and ADDL data exist, but almost
    entirely from the originating laboratory; unbiased laser-capture mass
    spectrometry of rimmed vacuoles recovered 213 enriched proteins dominated by
    protein-folding and autophagy machinery without reporting amyloid-beta or
    APP enrichment; cultured IBM myotubes from the same laboratory do not
    accumulate betaAPP, so any accumulation is not cell-autonomous; the
    companion phospho-tau claim was shown to rest on antibodies that stain
    normal myonuclei and recognize proteins other than tau, which impugns the
    reagent class the histological arm depended on; and a formal citation-network
    analysis of the entire literature on this belief found its authority
    inflated by citation bias, amplification and invention rather than by
    accumulated data.

    What survives is modest and is retained in the entry: protein aggregates of
    several kinds, amyloid-beta among them, are demonstrable in a small minority
    of IBM myofibres and are best read as a marker of overwhelmed proteostasis
    (see the `Autophagy-Lysosome Failure and Rimmed Vacuole Formation` node)
    rather than as a specific or upstream cause. Neither of the two live models
    for IBM requires amyloid-beta, and no anti-amyloid therapeutic strategy has
    been taken into IBM trials.
  evidence:
  - reference: PMID:8394158
    reference_title: "beta-Amyloid precursor protein mRNA is increased in inclusion-body myositis muscle."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Vacuolated muscle fibers in muscle biopsies of 8 out of 8 inclusion body
      myositis (IBM) patients, including 2 hereditary patients, manifested
      increased mRNA for the beta-amyloid precursor protein (beta APP) that
      contains Kunitz-type protease inhibitor motif.
    explanation: >-
      The founding observation of the hypothesis: increased APP transcript in
      vacuolated IBM fibres, offered as evidence that APP accumulation is
      generated locally rather than deposited.
  - reference: PMID:16432144
    reference_title: "Inclusion-body myositis: a myodegenerative conformational disorder associated with Abeta, protein misfolding, and proteasome inhibition."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In s-IBM, abnormal accumulation of the amyloid-beta (Abeta) precursor
      protein and its proteolytic fragment, Abeta, associated with the aging
      intracellular milieu of the muscle fiber, appear to be key upstream
      pathogenic events.
    explanation: >-
      The canonical statement of the hypothesis by its originators, asserting
      APP/Abeta accumulation as the key upstream pathogenic event.
  - reference: PMID:20711838
    reference_title: "Novel demonstration of amyloid-β oligomers in sporadic inclusion-body myositis muscle fibers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We now report for the first time that in s-IBM muscle biopsies Aβ-dimer,
      -trimer, and -tetramer are identifiable by immunoblots. While all the
      s-IBM samples we studied had Aβ-oligomers, their molecular weights and
      intensity varied between the patient samples. None of the control muscle
      biopsies had Aβ oligomers.
    explanation: >-
      The strongest biochemical evidence offered for the hypothesis, and the
      closest thing to a direct test of abnormal presence; it reports oligomers
      in every IBM sample and none in controls, but comes from the originating
      laboratory and has not been widely replicated independently.
  - reference: PMID:19533646
    reference_title: "Sarcoplasmic redistribution of nuclear TDP-43 in inclusion body myositis."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we found TDP-43 sarcoplasmic immunoreactivity in 23% of IBM myofibers,
      while other reported IBM biomarkers were less frequent, with rimmed
      vacuoles in 2.8%, fluorescent Congo red material in 0.57%, SMI-31
      immunoreactivity in 0.83%, and focal R1282 beta-amyloid immunoreactivity
      in 0.00% of myofibers.
    explanation: >-
      Head-to-head quantification in the same biopsies: beta-amyloid
      immunoreactivity was detected in no myofibres at all, while TDP-43
      mislocalization marked 23%. Directly refutes amyloid-beta as the
      characteristic or specific molecular lesion of IBM.
  - reference: PMID:9781653
    reference_title: "Rimmed vacuoles with beta-amyloid and ubiquitinated filamentous deposits in the muscles of patients with long-standing denervation (postpoliomyelitis muscular atrophy): similarities with inclusion body myositis."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We conclude that vacuolated muscle fibers containing filamentous
      inclusions positive for amyloid and ubiquitin are not unique to IBM and
      the other vacuolar myopathies but can also occur in a chronic neurogenic
      condition, such as postpoliomyelitis.
    explanation: >-
      Refutes the specificity claim directly: identical amyloid-positive
      ubiquitinated filamentous vacuoles arise in chronic denervation, so the
      finding tracks chronicity of fibre injury rather than IBM.
  - reference: PMID:16788822
    reference_title: "Rimmed vacuoles with beta-amyloid and tau protein deposits in the muscle of children with hereditary myopathy."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Our studies demonstrate for the first time that the full morphological
      phenotype of IBM including beta-amyloid and tau protein deposits may also
      develop in children, and that congenital, probably genetic, muscle defects
      may lead to abnormal protein aggregation in IBM-like inclusions.
    explanation: >-
      Further refutes specificity, and removes ageing as a necessary condition:
      the complete beta-amyloid-plus-tau morphology occurs in congenital
      myopathy in children.
  - reference: PMID:8268725
    reference_title: "Ubiquitin and beta-amyloid-protein in inclusion body myositis (IBM), familial IBM-like disorder and oculopharyngeal muscular dystrophy: an immunocytochemical study."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Labelling with anti-beta-amyloid-protein antibody was seen in a few fibres
      in IBM but not in the other two conditions. The structures labelled with
      this antibody have yet to be determined.
    explanation: >-
      Mixed: beta-amyloid labelling did discriminate IBM from OPMD and familial
      IBM-like disorder in this series, but only in a few fibres, and the
      authors explicitly decline to say what structure the antibody bound.
  - reference: PMID:10599804
    reference_title: "Cultured inclusion-body myositis muscle fibers do not accumulate beta-amyloid precursor protein and can be innervated."
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: >-
      Cultured muscle fibers from patients with sporadic inclusion-body myositis
      (s-IBM), similar to normal control muscle fibers, 1) did not have
      beta-amyloid precursor protein (betaAPP) immunoreactivity
    explanation: >-
      From the originating laboratory: IBM myotubes in culture do not accumulate
      betaAPP, so the accumulation is not a cell-autonomous property of the IBM
      myofibre and cannot be a primary intrinsic lesion.
  - reference: PMID:19626672
    reference_title: "Nature of \"Tau\" immunoreactivity in normal myonuclei and inclusion body myositis."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Antibodies previously reported to indicate abnormal accumulation of
      phosphorylated-tau in IBM myofibers react to normal myonuclei and
      recognize proteins other than tau.
    explanation: >-
      Refutes the companion phospho-tau limb of the Alzheimer-analogy model and
      demonstrates that the immunohistochemical reagent class on which the
      histological arm of the hypothesis rested can report protein accumulation
      that is not there.
  - reference: PMID:28009083
    reference_title: "Proteomics of rimmed vacuoles define new risk allele in inclusion body myositis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Proteins associated with protein folding and autophagy were the largest
      group represented.
    explanation: >-
      Unbiased laser-capture mass spectrometry of the rimmed vacuole itself
      returns a proteostasis-machinery signature; the paper reports 213 enriched
      proteins and does not report amyloid-beta or APP among them, which is what
      the hypothesis would predict to dominate.
  - reference: PMID:39757935
    reference_title: "Loss of TDP-43 Splicing Repression Occurs in Myonuclei of Inclusion Body Myositis Patients."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In contrast, cryptic HDGFL2 immunoreactivity was absent in 197 muscle
      biopsies from a variety of disease controls, except for 2 patients with
      vacuolar myopathies.
    explanation: >-
      The positive counter-example to the specificity claim. A TDP-43-dependent
      cryptic HDGFL2 peptide was found in 79 of 122 IBM biopsies and was absent
      across 197 disease controls, demonstrating that a genuinely IBM-specific
      molecular marker exists and that it is not amyloid. Graded PARTIAL rather
      than REFUTE deliberately: this study never measures amyloid, so it
      displaces amyloid from the role of specific marker without directly
      testing amyloid's specificity.
  - reference: PMID:23496965
    reference_title: "Cell stress molecules in the skeletal muscle of GNE myopathy."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      mRNA-expression of APP, NCAM, iNOS, TNF-α and TGF-β was higher in GNE
      myopathy compared to controls, yet this was not statistically significant.
    explanation: >-
      A further non-specificity observation: APP is raised in GNE myopathy too,
      and its expression correlates with generic cell-stress and
      pro-inflammatory markers, consistent with a shared stress response rather
      than an IBM-specific lesion. Graded PARTIAL, not REFUTE, because the
      quoted APP elevation did not reach statistical significance; a null result
      cannot carry a refutation, and the significant finding here is the
      correlation with cell-stress markers rather than the elevation itself.
  - reference: PMID:21518451
    reference_title: "Expression of human amyloid precursor protein in the skeletal muscles of Drosophila results in age- and activity-dependent muscle weakness."
    supports: PARTIAL
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Muscles from transgenic animals did not display protein aggregates or
      structural abnormalities at the light or transmission electron microscopic
      levels.
    explanation: >-
      Cuts against the histological arm of the hypothesis. Human APP expressed
      in fly muscle produced age- and activity-dependent weakness with no
      aggregates at all, dissociating APP toxicity from amyloid deposition and
      implying that the deposits used as the diagnostic criterion are not the
      toxic species.
  - reference: PMID:19622839
    reference_title: "How citation distortions create unfounded authority: analysis of a citation network."
    supports: REFUTE
    evidence_source: OTHER
    snippet: >-
      Unfounded authority was established by citation bias against papers that
      refuted or weakened the belief; amplification, the marked expansion of the
      belief system by papers presenting no data addressing it; and forms of
      invention such as the conversion of hypothesis into fact through citation
      alone.
    explanation: >-
      A formal citation-network analysis whose subject was precisely this belief
      about beta-amyloid in IBM. It does not measure muscle, but it explains why
      the apparent weight of literature behind the hypothesis overstates the
      underlying data, and is the reason this hypothesis is curated as
      DEPRECATED rather than merely ALTERNATIVE.
  notes: >-
    Retained rather than deleted because the hypothesis remains widely cited in
    reviews, textbooks and older diagnostic criteria, and curators encountering
    amyloid claims in the IBM literature need the assessment recorded rather
    than silently absent.
pathophysiology:
- name: HLA-Associated Autoimmune Susceptibility
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    The HLA/MHC region carries by far the strongest genetic risk for sporadic
    IBM, with HLA-DRB1*03:01 (part of the 8.1 ancestral haplotype) the leading
    association. Fine-mapping attributes the risk to specific amino acid
    residues within the peptide-binding groove of the DR-beta 1 chain,
    implicating altered peptide presentation as the susceptibility mechanism.
    No non-HLA locus has reached genome-wide significance, and there is no
    Mendelian causal gene.
  biological_processes:
  - preferred_term: antigen processing and presentation via MHC class II
    term:
      id: GO:0002504
      label: antigen processing and presentation of peptide or polysaccharide antigen
        via MHC class II
    modifier: ABNORMAL
  evidence:
  - reference: PMID:28086002
    reference_title: "Immune-Array Analysis in Sporadic Inclusion Body Myositis Reveals HLA-DRB1 Amino Acid Heterogeneity Across the Myositis Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The HLA region was confirmed as the most strongly associated region in IBM
    explanation: >-
      The largest immune-array genetic association study of IBM confirms the HLA
      region as the dominant risk locus.
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In a study of 252 IBM patients, the class II MHC allele HLA-DRB1*03:01
      showed the most significant association with IBM, and that risk could be
      largely attributed to amino acids within the peptide-binding pocket.
    explanation: >-
      Localizes the HLA risk to peptide-binding-groove residues, supporting
      altered antigen presentation as the susceptibility mechanism.
  downstream:
  - target: Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      HLA-restricted presentation of an as-yet-unidentified antigen is presumed
      to prime and sustain the pathogenic cytotoxic T cell population, but the
      inciting antigen is unknown.
    evidence:
    - reference: PMID:30837708
      reference_title: "Inclusion body myositis: clinical features and pathogenesis."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        the absence of any statistically significant genetic risk factor other
        than the common autoimmune disease 8.1 MHC haplotype in whole-genome
        sequencing studies
      explanation: >-
        Establishes the 8.1 MHC haplotype as the sole significant genetic risk
        factor, which is what links this susceptibility node to the downstream T
        cell response. The intervening antigen remains unidentified, hence
        PARTIAL and an INDIRECT_UNKNOWN_INTERMEDIATES link type.
- name: Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Large clonal populations of terminally differentiated, KLRG1-positive
    effector-memory and TEMRA CD8+ T cells accumulate in blood and muscle. These
    cells are minimally proliferative, persist over years, and in a majority of
    patients meet standard diagnostic criteria for T cell large granular
    lymphocytic leukaemia. Their terminally differentiated, apoptosis-resistant
    phenotype is the leading explanation for why IBM resists conventional
    immunosuppression, and it is the rationale for KLRG1-directed depleting
    therapy.
  cell_types:
  - preferred_term: KLRG1+ terminally differentiated cytotoxic CD8+ T cell
    term:
      id: CL:0000794
      label: CD8-positive, alpha-beta cytotoxic T cell
  biological_processes:
  - preferred_term: T cell mediated cytotoxicity
    term:
      id: GO:0001913
      label: T cell mediated cytotoxicity
    modifier: INCREASED
  evidence:
  - reference: PMID:31326977
    reference_title: "Highly differentiated cytotoxic T cells in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      we identified a signature of T-cell cytotoxicity in inclusion body
      myositis muscle coupled with a signature of highly differentiated CD8
      T-cell effector memory and terminally differentiated effector cells
    explanation: >-
      Establishes the highly differentiated cytotoxic CD8+ T cell signature as a
      defining feature of IBM muscle.
  - reference: PMID:31326977
    reference_title: "Highly differentiated cytotoxic T cells in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      identified the presence of KLRG1 on pathogenic inclusion body myositis
      muscle invading T cells and an increase in KLRG1 expressing T cells in
      inclusion body myositis blood
    explanation: >-
      Identifies KLRG1 as a surface marker of the pathogenic population in both
      muscle and blood, the basis for KLRG1-targeted therapy.
  - reference: PMID:35131904
    reference_title: "Immunophenotyping of Inclusion Body Myositis Blood T and NK Cells."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We found that a population of KLRG1+ Tem and TemRA were expanded in both
      the CD4+ and CD8+ T-cell subpopulations in patients with IBM.
    explanation: >-
      Independent flow-cytometric confirmation in 51 IBM patients that the
      KLRG1+ expansion is confined to highly differentiated memory compartments.
  - reference: PMID:26920676
    reference_title: "Association of inclusion body myositis with T cell large granular lymphocytic leukaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most (22/38; 58%) patients with inclusion body myositis had aberrant
      populations of large granular lymphocytes in their blood meeting standard
      diagnostic criteria for T cell large granular lymphocytic leukaemia. These
      T cell populations were clonal in 20/20 patients and stably present on
      follow-up testing in 15 patients a median of 350 days later.
    explanation: >-
      Demonstrates that the expanded cytotoxic population is clonal, persistent,
      and in most patients formally leukaemic, supporting a long-lived
      autonomous effector clone rather than a conventional activated response.
  downstream:
  - target: Cytotoxic T Cell Invasion of Non-Necrotic Myofibres
    causal_link_type: DIRECT
    hypothesis_groups:
    - autoimmune_primary
    description: >-
      The expanded cytotoxic clone invades and attacks myofibres via
      perforin/granzyme-mediated cytotoxicity.
    evidence:
    - reference: PMID:26920676
      reference_title: "Association of inclusion body myositis with T cell large granular lymphocytic leukaemia."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Muscle immunohistochemistry demonstrated invasion of large granular
        lymphocytes into muscle in 15/15 inclusion body myositis patients but in
        only 1/28 patients with dermatomyositis or polymyositis.
      explanation: >-
        Links the circulating clonal population directly to the myofibre-invading
        cells, and shows this is specific to IBM among inflammatory myopathies.
  - target: Refractoriness to Conventional Immunosuppression
    causal_link_type: DIRECT
    description: >-
      Terminally differentiated, minimally proliferative effector cells are
      intrinsically resistant to immunosuppressants that act on proliferating
      lymphocytes.
    evidence:
    - reference: PMID:31326977
      reference_title: "Highly differentiated cytotoxic T cells in inclusion body myositis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        diseased muscle-invading T cells are minimally or non-proliferative, in
        accordance with known properties of highly differentiated or terminally
        differentiated T cells
      explanation: >-
        The non-proliferative state of the effector cells provides the
        mechanistic basis for resistance to antiproliferative immunosuppression.
- name: Myofibre MHC Class I Overexpression
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Non-necrotic myofibres aberrantly and widely overexpress MHC class I on the
    sarcolemma and in the sarcoplasm, driven largely by interferon-gamma from
    the infiltrating T cells. This makes the fibre a target for CD8+ T cell
    recognition and is also a cell-intrinsic endoplasmic reticulum stressor.
    MHC class I upregulation is one of the few pathological features shown
    experimentally to be T cell-dependent.
  cell_types:
  - preferred_term: Skeletal muscle fibre
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: antigen processing and presentation via MHC class I
    term:
      id: GO:0002474
      label: antigen processing and presentation of peptide antigen via MHC class I
    modifier: INCREASED
  - preferred_term: response to endoplasmic reticulum stress
    term:
      id: GO:0034976
      label: response to endoplasmic reticulum stress
    modifier: INCREASED
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Histological features of IBM include rimmed vacuoles, protein aggregates,
      cytochrome oxidase (COX)-deficient fibers, MHC-I upregulation, and an
      endomysial inflammatory infiltrate containing autoaggressive CD8+ T cells
    explanation: >-
      Establishes MHC class I upregulation as a canonical histological feature
      of IBM alongside the degenerative markers.
  - reference: PMID:35044790
    reference_title: "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Myofibers in IBM xenografts showed invasion by human, oligoclonal CD8+ T
      cells and exhibited MHC-I up-regulation, rimmed vacuoles, mitochondrial
      pathology, p62-positive inclusions, and nuclear clearance and cytoplasmic
      aggregation of TDP-43, associated with cryptic exon inclusion.
    explanation: >-
      The xenograft model recapitulates MHC-I upregulation together with the full
      degenerative phenotype, and the same study shows this feature is T
      cell-dependent.
  downstream:
  - target: Cytotoxic T Cell Invasion of Non-Necrotic Myofibres
    causal_link_type: DIRECT
    hypothesis_groups:
    - autoimmune_primary
    description: >-
      MHC class I presentation on non-necrotic fibres is the substrate for CD8+
      T cell recognition and attack.
    evidence:
    - reference: PMID:29611059
      reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        The presence of CD8+ T-cells invading healthy-appearing myofibers, the
        association of IBM with specific HLA loci and other autoimmune
        disorders, and the presence of autoantibodies in IBM support an
        autoimmune trigger.
      explanation: >-
        Supports the coupling of MHC class I-positive non-necrotic fibres to
        CD8+ T cell invasion, though the snippet describes the association
        rather than proving directionality.
- name: Cytotoxic T Cell Invasion of Non-Necrotic Myofibres
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    The pathognomonic IBM lesion: partial invasion of morphologically intact,
    non-necrotic muscle fibres by CD8+ T cells within an endomysial inflammatory
    infiltrate, with perforin/granzyme-mediated cytotoxic injury. Invasion of
    non-necrotic fibres is markedly more common than amyloid-containing fibres,
    an observation used to argue that immune injury precedes visible aggregation.
  cell_types:
  - preferred_term: CD8-positive, alpha-beta cytotoxic T cell
    term:
      id: CL:0000794
      label: CD8-positive, alpha-beta cytotoxic T cell
  locations:
  - preferred_term: Skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  biological_processes:
  - preferred_term: T cell mediated cytotoxicity
    term:
      id: GO:0001913
      label: T cell mediated cytotoxicity
    modifier: INCREASED
  evidence:
  - reference: PMID:30837708
    reference_title: "Inclusion body myositis: clinical features and pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Its clinical features (finger flexor and quadriceps weakness) and
      pathological features (invasion of myofibres by cytotoxic T cells) are
      unique among muscle diseases.
    explanation: >-
      Identifies cytotoxic T cell invasion of myofibres as the pathological
      hallmark that distinguishes IBM from all other muscle diseases.
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      On muscle biopsy, IBM is characterized by a peculiar combination of
      endomysial inflammation, rimmed vacuoles, and protein aggregation.
    explanation: >-
      Confirms endomysial inflammation as one of the three canonical biopsy
      features of IBM.
  downstream:
  - target: Progressive Myofibre Degeneration and Selective Muscle Loss
    causal_link_type: DIRECT
    hypothesis_groups:
    - autoimmune_primary
    description: >-
      Repeated cytotoxic attack over years destroys myofibres and drives the
      progressive loss of muscle mass and strength.
    evidence:
    - reference: PMID:30837708
      reference_title: "Inclusion body myositis: clinical features and pathogenesis."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Mounting evidence that IBM is an autoimmune T cell-mediated disease
        provides hope that future therapies directed towards depleting these
        cells could be effective.
      explanation: >-
        States the autoimmune-primary causal claim that T cell-mediated
        destruction is the driver of the disease process.
  - target: Myofibre MHC Class I Overexpression
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - autoimmune_primary
    description: >-
      Feed-forward loop: interferon-gamma released by the infiltrating T cells
      drives further MHC class I upregulation on myofibres, amplifying antigen
      presentation and sustaining the cytotoxic attack. This edge closes the
      cycle with the MHC class I node's own upstream edge into invasion, and is
      the reason MHC class I upregulation is experimentally T cell-dependent.
    evidence:
    - reference: PMID:35044790
      reference_title: "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        Reduction of human T cells within IBM xenografts by treating mice
        intraperitoneally with anti-CD3 (OKT3) suppressed MHC-I up-regulation.
      explanation: >-
        Depleting T cells abolishes myofibre MHC class I upregulation,
        demonstrating that the T cell compartment drives this node rather than
        only responding to it.
- name: TDP-43 Nuclear Clearance and Loss of Splicing Repression
  biological_scale: MOLECULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    TDP-43 is cleared from myonuclei and aggregates in the cytoplasm, producing
    a loss of its normal splicing-repressor function and consequent inclusion of
    cryptic exons in target transcripts. This is a molecular convergence with
    ALS and frontotemporal dementia, is the most disease-specific molecular
    lesion described in IBM, and forms the basis of a highly specific diagnostic
    assay. Critically, this arm persists after T cell depletion in a human
    muscle xenograft, indicating it is at least partly T cell-independent.
  cell_types:
  - preferred_term: Skeletal muscle fibre
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: regulation of mRNA splicing, via spliceosome
    term:
      id: GO:0048024
      label: regulation of mRNA splicing, via spliceosome
    modifier: ABNORMAL
  evidence:
  - reference: PMID:35044790
    reference_title: "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here, we show that loss of TDP-43-mediated splicing repression, as
      determined by inclusion of cryptic exons, occurs in skeletal muscle of
      subjects with IBM.
    explanation: >-
      Establishes loss of TDP-43 splicing repression as a molecular lesion in
      IBM muscle.
  - reference: PMID:30742062
    reference_title: "Association between TDP-43 and mitochondria in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Inclusion body myositis (IBM) is the most common cause of primary myopathy
      in individuals aged 50 years and over, and is pathologically characterized
      by protein aggregates of p62 and mislocalized cytoplasmic TDP-43, as well
      as mitochondrial abnormalities in affected muscle fibers.
    explanation: >-
      Confirms cytoplasmic TDP-43 mislocalization as a defining pathological
      feature of IBM muscle.
  downstream:
  - target: Autophagy-Lysosome Failure and Rimmed Vacuole Formation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - degeneration_primary
    description: >-
      TDP-43 mislocalization co-occurs with, and is thought to contribute to,
      the aggregate and rimmed-vacuole pathology; the two persist together after
      T cell depletion.
    evidence:
    - reference: PMID:35044790
      reference_title: "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: >-
        However, rimmed vacuoles and loss of TDP-43 function persisted.
      explanation: >-
        Shows the two degenerative features are coupled and both T
        cell-independent in the xenograft model.
  - target: Mitochondrial Dysfunction and Somatic mtDNA Deletion
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    description: >-
      TDP-43 and phospho-TDP-43 co-localize with mitochondrial oxidative
      phosphorylation complexes in the same fibres, and this association is
      proposed to contribute to mitochondrial dysfunction.
    evidence:
    - reference: PMID:30742062
      reference_title: "Association between TDP-43 and mitochondria in inclusion body myositis."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        This is the first demonstration of the close association of TDP-43
        accumulation with mitochondria in degenerating muscle fibers in IBM and
        this association may contribute to the development of mitochondrial
        dysfunction and pathological protein aggregates.
      explanation: >-
        The authors explicitly frame the TDP-43-mitochondria link as an
        association that may contribute to dysfunction, not an established
        causal step.
- name: Autophagy-Lysosome Failure and Rimmed Vacuole Formation
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    Sarcoplasmic aggregates accumulate p62/SQSTM1, ubiquitin, LC3, amyloid-beta
    and phosphorylated tau, alongside rimmed vacuoles (autophagic vacuoles
    rimmed with basophilic granular material). The aggregate composition and
    the vacuolar morphology together implicate failure of the
    autophagy-lysosome and ubiquitin-proteasome clearance pathways, though the
    evidence cited here documents the aggregates rather than directly measuring
    autophagic flux. Aggregates are present in fewer than 1% of myofibres, a
    quantitative observation used to argue that they are a marker rather than
    the principal driver of injury.
  cell_types:
  - preferred_term: Skeletal muscle fibre
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: aggrephagy
    term:
      id: GO:0035973
      label: aggrephagy
    modifier: DECREASED
  - preferred_term: autophagy
    term:
      id: GO:0006914
      label: autophagy
    modifier: ABNORMAL
  evidence:
  - reference: PMID:30837708
    reference_title: "Inclusion body myositis: clinical features and pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      enormous attention has been focused for decades on several biomarkers of
      myofibre protein aggregates, which are present in <1% of myofibres in
      patients with IBM
    explanation: >-
      Quantifies the rarity of aggregate-bearing fibres, the key argument that
      aggregation is a marker rather than the dominant injury mechanism.
  - reference: PMID:30742062
    reference_title: Association between TDP-43 and mitochondria in inclusion body myositis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      is pathologically characterized by protein aggregates of p62 and
      mislocalized cytoplasmic TDP-43
    explanation: >-
      Identifies the specific aggregate constituents (p62 and cytoplasmic
      TDP-43) that define this node, replacing a previous snippet that spoke
      only of mechanistic complexity in general terms.
  downstream:
  - target: Progressive Myofibre Degeneration and Selective Muscle Loss
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - degeneration_primary
    description: >-
      On the degeneration-primary model, proteostasis failure drives
      cell-autonomous myofibre degeneration independently of immune attack.
    evidence:
    - reference: PMID:37773216
      reference_title: "Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        One explanation for this resistance may be the engagement of
        cell-autonomous mechanisms that sustain or promote disease progression
        of IBM independent of inflammatory activity.
      explanation: >-
        States the cell-autonomous-degeneration rationale; the snippet frames it
        as a candidate explanation rather than a demonstrated causal chain.
- name: Amyloid-beta and APP Accumulation in Myofibres
  biological_scale: MOLECULAR
  mechanism_confidence: HYPOTHETICAL
  description: >-
    Disputed node, curated to make the historical amyloid model of IBM explicit
    and assessable rather than absent. On the `amyloid_beta_proteotoxicity`
    model, IBM myofibres transcribe APP at increased levels, accumulate APP and
    its cleavage product amyloid-beta intracellularly (preferentially Abeta42),
    and are injured by soluble Abeta oligomers upstream of proteostasis failure
    and vacuolar degeneration.

    The node is marked HYPOTHETICAL because the evidence does not support it as
    curated fact. Amyloid-beta immunoreactivity is detectable in only a very
    small minority of IBM myofibres and in one quantitative series in none at
    all, it is not specific to IBM (the same amyloid-positive filamentous
    vacuoles occur in chronic denervation and in congenital childhood
    myopathies), unbiased proteomics of rimmed vacuoles
    does not report it as an enriched constituent, and cultured IBM myofibres do
    not accumulate APP. Any real amyloid-beta present is best read as one
    constituent of the aggregate pathology captured by the
    `Autophagy-Lysosome Failure and Rimmed Vacuole Formation` node rather than
    as a specific or upstream driver. No IBM therapeutic has targeted it.
  cell_types:
  - preferred_term: Skeletal muscle fibre
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  genes:
  - preferred_term: APP
    term:
      id: hgnc:620
      label: APP
  biological_processes:
  - preferred_term: amyloid precursor protein metabolic process
    term:
      id: GO:0042982
      label: amyloid precursor protein metabolic process
    modifier: ABNORMAL
  - preferred_term: amyloid-beta formation
    term:
      id: GO:0034205
      label: amyloid-beta formation
    modifier: INCREASED
  evidence:
  - reference: PMID:8394158
    reference_title: "beta-Amyloid precursor protein mRNA is increased in inclusion-body myositis muscle."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In affected fibers, increased beta APP-mRNA correspond to abnormally
      accumulated beta APP immunoreactivity (including beta-amyloid protein
      epitope).
    explanation: >-
      The primary observation this node represents: coincident APP transcript
      and APP/beta-amyloid immunoreactivity in vacuolated IBM fibres.
  - reference: PMID:19533646
    reference_title: "Sarcoplasmic redistribution of nuclear TDP-43 in inclusion body myositis."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      focal R1282 beta-amyloid immunoreactivity in 0.00% of myofibers
    explanation: >-
      Quantitative refutation of the node as a general feature of IBM muscle: no
      myofibre in the series carried focal beta-amyloid immunoreactivity, in
      biopsies where sarcoplasmic TDP-43 marked 23%.
  - reference: PMID:10599804
    reference_title: "Cultured inclusion-body myositis muscle fibers do not accumulate beta-amyloid precursor protein and can be innervated."
    supports: REFUTE
    evidence_source: IN_VITRO
    snippet: >-
      Thus, factors responsible for betaAPP accumulation and denervation-like
      changes in s-IBM muscle biopsies are not operative in the relatively
      short-term, non-aged, cultured s-IBM muscle fibers.
    explanation: >-
      Shows APP accumulation is not intrinsic to the IBM myofibre, undermining
      the node as a cell-autonomous primary lesion.
  downstream:
  - target: Autophagy-Lysosome Failure and Rimmed Vacuole Formation
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - amyloid_beta_proteotoxicity
    description: >-
      On the amyloid model, misfolded APP and Abeta oligomers overwhelm and
      inhibit the proteasome and autophagy-lysosome systems, generating the
      vacuolar and aggregate pathology. The direction of this edge is contested:
      an influential review argues the reverse order, with inflammation and
      overloaded degradation systems coming first and amyloid deposits appearing
      afterwards as a consequence.
    evidence:
    - reference: PMID:25579751
      reference_title: "Amyloid deposits and inflammatory infiltrates in sporadic inclusion body myositis: the inflammatory egg comes before the degenerative chicken."
      supports: REFUTE
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        If the protein degradation systems are overloaded (possibly due to
        genetic predisposition, particular HLA-I subtypes or ageing), amyloid
        and other protein deposits may appear within muscle fibres, reinforcing
        the myopathic process in a vicious circle.
      explanation: >-
        Argues the opposite ordering to this edge: degradation-system overload
        comes first and amyloid deposition follows, making amyloid a
        consequence and amplifier rather than the initiating lesion.
    - reference: PMID:23294492
      reference_title: "TNF-α upregulates macroautophagic processing of APP/β-amyloid in a human rhabdomyosarcoma cell line."
      supports: REFUTE
      evidence_source: IN_VITRO
      snippet: >-
        In a human cell line from rhabdomyosarcoma as a model to study muscle
        cells, we here show that TNF-α-mediated upregulation of macroautophagy
        modulates APP and β-amyloid load and can be blocked by inhibition of
        macroautophagy.
      explanation: >-
        Experimental support for the reverse ordering, upgrading that
        counterargument from review-level opinion: a pro-inflammatory cytokine
        modulates APP and amyloid load through macroautophagy, placing
        inflammation upstream of amyloid handling. Scope caveat carried
        deliberately - the model is a rhabdomyosarcoma cell line, not primary
        human muscle or IBM tissue, and the authors' own conclusion is hedged.
  - target: Progressive Myofibre Degeneration and Selective Muscle Loss
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - amyloid_beta_proteotoxicity
    description: >-
      The proposed proteotoxic endpoint of the amyloid model, in which Abeta42
      oligomer cytotoxicity drives vacuolar degeneration and atrophy of muscle
      fibres.
    evidence:
    - reference: PMID:16432144
      reference_title: "Inclusion-body myositis: a myodegenerative conformational disorder associated with Abeta, protein misfolding, and proteasome inhibition."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        We propose that the identified abnormal accumulation, misfolding, and
        aggregation of proteins, perhaps provoked by the aging milieu and
        aggravated by the oxidative stress, lead to the s-IBM-specific vacuolar
        degeneration and atrophy of muscle fibers.
      explanation: >-
        The originators state the proposed causal chain from protein
        accumulation to fibre degeneration; note the snippet is explicitly
        framed as a proposal.
- name: Mitochondrial Dysfunction and Somatic mtDNA Deletion
  biological_scale: CELLULAR
  mechanism_confidence: ESTABLISHED
  description: >-
    IBM muscle accumulates clonally expanded large-scale somatic mitochondrial
    DNA deletions, producing cytochrome c oxidase-negative and ragged-red fibre
    segments, impaired oxidative phosphorylation and oxidative stress.
    Mitochondrial abnormalities are more prominent in IBM than in the other
    idiopathic inflammatory myopathies, and mitochondrial damage can itself
    release danger signals that perpetuate injury and inflammation.
  cell_types:
  - preferred_term: Skeletal muscle fibre
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  biological_processes:
  - preferred_term: mitochondrion organization
    term:
      id: GO:0007005
      label: mitochondrion organization
    modifier: ABNORMAL
  evidence:
  - reference: PMID:38808223
    reference_title: "Mitochondrial defects in sporadic inclusion body myositis-causes and consequences."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Notably, abnormal mitochondrial structure and activities are more
      prominent in the muscle of sIBM than in other types of IIM, suggesting the
      presence of defective mitochondria might represent an overlooked
      contributor to the disease onset.
    explanation: >-
      Establishes that mitochondrial pathology is disproportionately prominent in
      IBM relative to other inflammatory myopathies.
  - reference: PMID:38808223
    reference_title: "Mitochondrial defects in sporadic inclusion body myositis-causes and consequences."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The large-scale mitochondrial DNA deletion, aberrant protein aggregation,
      and slowed organelle turnover have provided mechanistic insights into the
      genesis of impaired mitochondria in sIBM.
    explanation: >-
      Identifies large-scale mtDNA deletion and impaired organelle turnover as
      the mechanisms generating defective mitochondria in IBM.
  - reference: PMID:30742062
    reference_title: "Association between TDP-43 and mitochondria in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Further immunoblot analysis showed increased levels of TDP-43, truncated
      TDP-43, phosphorylated TDP-43, and p62, but decreased levels of key
      subunits of mitochondrial oxidative phosphorylation complexes I and III in
      IBM patients compared to aged matched control subjects.
    explanation: >-
      Quantifies loss of respiratory chain complex subunits in IBM muscle
      relative to age-matched controls.
  downstream:
  - target: Progressive Myofibre Degeneration and Selective Muscle Loss
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - degeneration_primary
    description: >-
      Bioenergetic failure and oxidative stress in COX-deficient fibre segments
      contribute to myofibre degeneration.
    evidence:
    - reference: PMID:38808223
      reference_title: "Mitochondrial defects in sporadic inclusion body myositis-causes and consequences."
      supports: PARTIAL
      evidence_source: HUMAN_CLINICAL
      snippet: >-
        Moreover, the findings that mitochondrial dysfunction can elicit
        non-apoptotic programmed cell death and the subsequent immune response
        further support this hypothesis.
      explanation: >-
        Supports mitochondrial dysfunction as a route to myofibre death, though
        the authors present it as supporting a hypothesis rather than as an
        established causal step in human IBM.
- name: Fibro-Adipogenic Progenitor Senescence
  biological_scale: CELLULAR
  mechanism_confidence: PROVISIONAL
  conforms_to: cellular_senescence#Senescent Cell Accumulation
  description: >-
    Cellular senescence in IBM muscle is concentrated not in myofibres but in
    tissue-resident fibro-adipogenic progenitors (FAPs), which express p21,
    show increased senescence-associated beta-galactosidase activity and adopt a
    pro-inflammatory secretory phenotype. Senescent FAPs lose collagen type XV
    expression, which is required to support myofibre structural integrity and
    neuromuscular junction formation. This provides a stromal,
    lymphocyte-independent route to myofibre damage. Note it is muscle-intrinsic
    but NOT cell-autonomous with respect to the myofibre: the senescent cell and
    the damaged cell are different cells, and the damage is paracrine.
  cell_types:
  - preferred_term: Fibro-adipogenic progenitor
    term:
      id: CL:0000057
      label: fibroblast
  biological_processes:
  - preferred_term: cellular senescence
    term:
      id: GO:0090398
      label: cellular senescence
    modifier: INCREASED
  evidence:
  - reference: PMID:37773216
    reference_title: "Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Histopathological analysis suggested that cellular senescence is a
      prominent feature of IBM, primarily affecting non-myogenic cells.
    explanation: >-
      Establishes senescence as a prominent IBM feature and localizes it to
      non-myogenic (stromal) cells rather than myofibres.
  - reference: PMID:37773216
    reference_title: "Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Among these, we identified a specific cluster of fibro-adipogenic
      progenitors (FAPs) that demonstrated key hallmarks of senescence,
      including a pro-inflammatory secretome, expression of p21, increased
      β-galactosidase activity, and engagement of senescence pathways.
    explanation: >-
      Identifies the senescent population as FAPs and documents the canonical
      senescence markers (p21, SA-beta-gal, SASP) that anchor conformance to the
      cellular_senescence module.
  downstream:
  - target: Progressive Myofibre Degeneration and Selective Muscle Loss
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - degeneration_primary
    description: >-
      Loss of collagen type XV from senescent FAPs removes structural and
      neuromuscular-junction support required by myofibres.
    evidence:
    - reference: PMID:37773216
      reference_title: "Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: >-
        Senescent FAPs lose collagen type XV expression, which is required to
        support myofibers' structural integrity and neuromuscular junction
        formation in vitro.
      explanation: >-
        Provides the specific molecular intermediate (collagen XV) linking FAP
        senescence to myofibre compromise, demonstrated in vitro.
- name: Progressive Myofibre Degeneration and Selective Muscle Loss
  biological_scale: TISSUE
  mechanism_confidence: ESTABLISHED
  description: >-
    Cumulative myofibre injury from the immune and degenerative arms produces
    fibre atrophy and loss, endomysial fibrosis, fatty replacement, and failed
    regeneration. Loss is selective: type 2 myonuclei are preferentially
    depleted and acetylcholine receptor expressing fibres are rarefied,
    indicating a functional denervation program. Clinically this manifests as
    the characteristic quadriceps and deep finger flexor weakness. Why these
    particular muscles are selectively vulnerable is unexplained.
  cell_types:
  - preferred_term: Skeletal muscle fibre
    term:
      id: CL:0008002
      label: skeletal muscle fiber
  - preferred_term: Skeletal muscle satellite cell
    term:
      id: CL:0000594
      label: skeletal muscle satellite cell
  locations:
  - preferred_term: Skeletal muscle tissue
    term:
      id: UBERON:0001134
      label: skeletal muscle tissue
  biological_processes:
  - preferred_term: skeletal muscle tissue regeneration
    term:
      id: GO:0043403
      label: skeletal muscle tissue regeneration
    modifier: DECREASED
  evidence:
  - reference: PMID:38834884
    reference_title: "Cell type mapping of inflammatory muscle diseases highlights selective myofiber vulnerability in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In IBM muscles, we observed a selective loss of type 2 myonuclei
    explanation: >-
      Single-nucleus RNA sequencing of patient biopsies demonstrates selective
      type 2 myofibre vulnerability in IBM.
  - reference: PMID:37773216
    reference_title: "Senescent fibro-adipogenic progenitors are potential drivers of pathology in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the transcriptomic landscape of IBM was also characterized by changes to
      the myogenic compartment demonstrating a pronounced loss of type 2A
      myofibers and a rarefication of acetylcholine receptor expressing myofibers
    explanation: >-
      Independently confirms selective type 2A myofibre loss and documents the
      neuromuscular-junction rarefaction consistent with functional denervation.
- name: Refractoriness to Conventional Immunosuppression
  biological_scale: ORGANISM
  mechanism_confidence: ESTABLISHED
  description: >-
    Unlike dermatomyositis, polymyositis and immune-mediated necrotizing
    myopathy, IBM does not respond to glucocorticoids, methotrexate,
    azathioprine or most tested biologics. This is a defining clinical property
    of the disease and a diagnostic clue: steroid-refractory "polymyositis",
    particularly with finger-flexor or quadriceps selectivity, should prompt
    reassessment for IBM. The proposed mechanism is that the effector clone has
    acquired a neoplastic or neoplastic-like character, making it a
    self-sustaining population rather than an antigen-driven response that
    immunosuppression can switch off.
  evidence:
  - reference: PMID:26920676
    reference_title: Association of inclusion body myositis with T cell large granular
      lymphocytic leukaemia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In many patients with inclusion body myositis, the autoimmune T cell
      expansion has evolved into a neoplastic-like or overtly neoplastic
      disorder, perhaps contributing to its relative refractoriness to
      immune-directed therapies previously reported.
    explanation: >-
      Supplies the mechanistic account for this node: refractoriness is
      attributed to neoplastic evolution of the effector clone. Note the authors
      hedge with "perhaps contributing", so this is the proposed explanation
      rather than a demonstrated one.
  - reference: PMID:38273639
    reference_title: "Sirolimus for treatment of patients with inclusion body myositis: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Classical immunosuppressants are ineffective in treating inclusion body
      myositis, and to date there are no recommendations for pharmacological
      approaches to treatment.
    explanation: >-
      States the treatment refractoriness that defines IBM against the other
      inflammatory myopathies.
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      No pharmacological treatment is yet available for IBM.
    explanation: >-
      Confirms the absence of any established disease-modifying pharmacotherapy.
phenotypes:
- name: Deep Finger Flexor Weakness
  category: Musculoskeletal
  description: >-
    Selective, often asymmetric weakness and atrophy of the deep finger flexors
    (flexor digitorum profundus) producing loss of grip strength and fine hand
    function. Together with quadriceps weakness this is the defining clinical
    signature of IBM and distinguishes it from other inflammatory myopathies.
  frequency: VERY_FREQUENT
  diagnostic: true
  phenotype_term:
    preferred_term: Deep finger flexor weakness
    term:
      id: HP:0031177
      label: Finger flexor weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The typical clinical phenotype is characterized by prominent involvement
      of deep finger flexors and quadriceps muscles.
    explanation: >-
      Establishes deep finger flexor involvement as part of the typical, i.e.
      very frequent, clinical phenotype of IBM.
  - reference: PMID:30837708
    reference_title: "Inclusion body myositis: clinical features and pathogenesis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Its clinical features (finger flexor and quadriceps weakness) and
      pathological features (invasion of myofibres by cytotoxic T cells) are
      unique among muscle diseases.
    explanation: >-
      Confirms finger flexor weakness as a defining and disease-specific
      clinical feature.
- name: Quadriceps Weakness
  category: Musculoskeletal
  description: >-
    Early, often asymmetric weakness and atrophy of the knee extensors, causing
    knee buckling, difficulty rising from a chair or climbing stairs, and falls.
    Progressive quadriceps failure is the principal driver of loss of ambulation.
  frequency: VERY_FREQUENT
  diagnostic: true
  phenotype_term:
    preferred_term: Quadriceps (knee extensor) weakness
    term:
      id: HP:0003731
      label: Quadriceps muscle weakness
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:36399165
    reference_title: "Inclusion body myositis: from genetics to clinical trials."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Inclusion body myositis (IBM) belongs to the group of idiopathic
      inflammatory myopathies and is characterized by a slowly progressive
      disease course with asymmetric muscle weakness of predominantly the finger
      flexors and knee extensors.
    explanation: >-
      Establishes knee extensor weakness as a predominant, characteristic and
      progressive feature.
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The typical clinical phenotype is characterized by prominent involvement
      of deep finger flexors and quadriceps muscles.
    explanation: >-
      Confirms quadriceps involvement as part of the typical clinical phenotype.
- name: Dysphagia
  category: Gastrointestinal
  description: >-
    Oropharyngeal dysphagia from pharyngeal and cricopharyngeal muscle
    involvement. It may be the presenting or an isolated feature, is a major
    source of morbidity and quality-of-life impairment, and drives the
    aspiration risk that underlies most disease-related deaths.
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Oropharyngeal dysphagia
    term:
      id: HP:0200136
      label: Oral-pharyngeal dysphagia
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:33879596
    reference_title: "Epidemiology and Natural History of Inclusion Body Myositis: A 40-Year Population-Based Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two-thirds of patients developed dysphagia, and half required a feeding
      tube.
    explanation: >-
      Population-based cohort quantifies dysphagia in about two-thirds of
      patients, supporting the FREQUENT (30-79%) frequency band.
  - reference: PMID:37678324
    reference_title: "Update on the evaluation and management of dysphagia in sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dysphagia is a common symptom of sporadic inclusion body myositis (IBM),
      affecting disease trajectory and patient quality-of-life.
    explanation: >-
      Confirms dysphagia is common and materially affects disease trajectory and
      quality of life.
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Less common presentations include isolated dysphagia, asymptomatic
      hyper-CKemia, and axial or limb weakness beyond the typical pattern.
    explanation: >-
      Documents that dysphagia can be the isolated presenting manifestation.
- name: Falls
  category: Neurological
  description: >-
    Recurrent falls resulting from quadriceps weakness and knee buckling. Falls
    are frequently the event that brings the patient to medical attention and
    are a major source of injury.
  phenotype_term:
    preferred_term: Frequent falls
    term:
      id: HP:0002359
      label: Frequent falls
  evidence:
  - reference: PMID:31397289
    reference_title: "Safety and efficacy of intravenous bimagrumab in inclusion body myositis (RESILIENT): a randomised, double-blind, placebo-controlled phase 2b trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Falls were the most frequent adverse event
    explanation: >-
      In the 251-participant RESILIENT trial falls were the most frequent adverse
      event across all groups including placebo, reflecting the high background
      fall burden of the IBM population.
- name: Loss of Ambulation
  category: Musculoskeletal
  description: >-
    Progressive loss of independent walking, with most patients eventually
    requiring a wheelchair. Ambulation is typically lost 10-15 years after
    diagnosis.
  phenotype_term:
    preferred_term: Loss of ambulation
    term:
      id: HP:0002505
      label: Loss of ambulation
    clinical_course: PROGRESSIVE
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sporadic Inclusion Body myositis (IBM) is the most common myopathy in
      individuals over the age of 50, and patients typically lose the ability to
      ambulate 10 to 15 years after diagnosis
    explanation: >-
      Quantifies the typical interval from diagnosis to loss of ambulation.
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      IBM is associated with marked morbidity as majority of patients eventually
      become wheelchair dependent with limited use of their hands and marked
      dysphagia.
    explanation: >-
      Confirms that the majority of patients ultimately become wheelchair
      dependent.
- name: Foot Drop
  category: Musculoskeletal
  description: >-
    Weakness of the ankle dorsiflexors (tibialis anterior) causing foot drop.
    Distal lower-limb involvement is a recognized but less common component of
    the IBM weakness distribution.
  notes: >-
    `frequency` deliberately omitted: the cited snippet places foot extensors in
    the characteristic weakness distribution but supports no quantitative band,
    and published estimates vary widely. Per the repository frequency-evidence
    guidelines, omit rather than guess.
  phenotype_term:
    preferred_term: Foot dorsiflexor weakness
    term:
      id: HP:0009027
      label: Foot dorsiflexor weakness
  evidence:
  - reference: PMID:38473988
    reference_title: "Sporadic Inclusion Body Myositis at the Crossroads between Muscle Degeneration, Inflammation, and Aging."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      slowly progressive asymmetrical muscle weakness, predominantly affecting
      the quadriceps, deep finger flexors, and foot extensors
    explanation: >-
      Includes foot extensor (dorsiflexor) involvement in the characteristic IBM
      weakness distribution.
- name: Elevated Serum Creatine Kinase
  category: Laboratory
  description: >-
    Serum creatine kinase is normal to moderately elevated, characteristically
    well below the very high levels seen in immune-mediated necrotizing
    myopathy. Asymptomatic hyper-CKemia can be the presenting finding.
  phenotype_term:
    preferred_term: Mildly to moderately elevated creatine kinase
    term:
      id: HP:0003236
      label: Elevated circulating creatine kinase concentration
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Less common presentations include isolated dysphagia, asymptomatic
      hyper-CKemia, and axial or limb weakness beyond the typical pattern.
    explanation: >-
      Documents hyper-CKemia as a recognized, sometimes presenting, laboratory
      abnormality in IBM.
- name: Rimmed Vacuoles
  category: Histological
  description: >-
    Sarcoplasmic vacuoles rimmed with basophilic granular material on modified
    Gomori trichrome staining, representing autophagic vacuoles. Curated here as
    a phenotype so the HPO binding is retained; the corresponding
    histopathology entry is prose-only because the NCIT-rooted
    HistopathologyFindingTerm enum has no rimmed-vacuole concept.
  diagnostic: true
  phenotype_term:
    preferred_term: Rimmed vacuoles
    term:
      id: HP:0003805
      label: Rimmed vacuoles
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      On muscle biopsy, IBM is characterized by a peculiar combination of
      endomysial inflammation, rimmed vacuoles, and protein aggregation.
    explanation: >-
      Establishes rimmed vacuoles as one of the three defining biopsy features.
- name: Cytochrome c Oxidase-Negative Muscle Fibres
  category: Histological
  description: >-
    Fibre segments lacking cytochrome c oxidase activity, reflecting clonally
    expanded somatic mitochondrial DNA deletions. Curated here as a phenotype so
    the HPO binding is retained; the corresponding histopathology entry is
    prose-only because the NCIT-rooted HistopathologyFindingTerm enum has no
    equivalent concept.
  phenotype_term:
    preferred_term: Cytochrome C oxidase-negative muscle fibers
    term:
      id: HP:0003688
      label: Cytochrome C oxidase-negative muscle fibers
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Histological features of IBM include rimmed vacuoles, protein aggregates,
      cytochrome oxidase (COX)-deficient fibers, MHC-I upregulation, and an
      endomysial inflammatory infiltrate containing autoaggressive CD8+ T cells
    explanation: >-
      Lists COX-deficient fibres among the canonical histological features of
      IBM.
- name: Aspiration Pneumonia
  category: Respiratory
  description: >-
    Aspiration pneumonia secondary to oropharyngeal dysphagia. Together with
    other respiratory complications it is the most common disease-related cause
    of death in IBM.
  phenotype_term:
    preferred_term: Aspiration pneumonia
    term:
      id: HP:0011951
      label: Aspiration pneumonia
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Furthermore, IBM mildly affects longevity with aspiration pneumonia and
      respiratory complications being the most common cause of death.
    explanation: >-
      Identifies aspiration pneumonia as the leading disease-related cause of
      death in IBM.
histopathology:
- name: Endomysial Inflammatory Infiltrate with Invasion of Non-Necrotic Fibres
  description: >-
    Endomysial mononuclear infiltrate containing autoaggressive CD8+ T cells
    partially invading morphologically intact, non-necrotic muscle fibres. This
    combination is the pathological hallmark of IBM.
  diagnostic: true
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Histological features of IBM include rimmed vacuoles, protein aggregates,
      cytochrome oxidase (COX)-deficient fibers, MHC-I upregulation, and an
      endomysial inflammatory infiltrate containing autoaggressive CD8+ T cells
    explanation: >-
      Enumerates the canonical IBM biopsy features including the endomysial
      autoaggressive CD8+ infiltrate.
- name: Rimmed Vacuoles
  description: >-
    Sarcoplasmic vacuoles rimmed with basophilic granular material on modified
    Gomori trichrome staining, representing autophagic vacuoles. A cardinal but
    not universally present feature; absence in an early or poorly targeted
    biopsy does not exclude IBM.
  diagnostic: true
  notes: >-
    Left without a finding_term: the HistopathologyFindingTerm dynamic enum is
    rooted in the NCIT Histopathology Result branch, which has no rimmed-vacuole
    concept. The HPO binding (HP:0003805) is carried on the corresponding
    phenotype entry instead. Ontology gap worth reporting upstream.
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      On muscle biopsy, IBM is characterized by a peculiar combination of
      endomysial inflammation, rimmed vacuoles, and protein aggregation.
    explanation: >-
      Establishes rimmed vacuoles as one of the three defining biopsy features.
- name: Cytochrome c Oxidase-Negative Muscle Fibres
  description: >-
    Fibre segments lacking cytochrome c oxidase activity, reflecting clonally
    expanded somatic mitochondrial DNA deletions. Present in far greater
    abundance than in age-matched normal muscle.
  notes: >-
    Left without a finding_term for the same reason as the rimmed-vacuole entry;
    the HPO binding (HP:0003688) is carried on the corresponding phenotype entry.
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Histological features of IBM include rimmed vacuoles, protein aggregates,
      cytochrome oxidase (COX)-deficient fibers, MHC-I upregulation, and an
      endomysial inflammatory infiltrate containing autoaggressive CD8+ T cells
    explanation: >-
      Lists COX-deficient fibres among the canonical histological features of
      IBM.
- name: p62 and TDP-43 Positive Sarcoplasmic Inclusions
  description: >-
    Immunohistochemically detectable sarcoplasmic aggregates of p62/SQSTM1 and
    mislocalized cytoplasmic TDP-43, with corresponding nuclear clearance of
    TDP-43. p62 staining has largely superseded amyloid stains in routine
    practice.
  diagnostic: true
  evidence:
  - reference: PMID:30742062
    reference_title: "Association between TDP-43 and mitochondria in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We found that IBM pathological markers TDP-43, phosphorylated TDP-43, and
      p62 all coexisted with intensively stained key subunits of mitochondrial
      oxidative phosphorylation complexes I-V in the same skeletal muscle fibers
      of patients with IBM.
    explanation: >-
      Documents co-occurrence of p62 and TDP-43 inclusions within IBM myofibres.
imaging_findings:
- name: Selective Quadriceps Fatty Replacement on Muscle MRI
  modality: MRI
  description: >-
    Quantitative muscle MRI of the thighs shows fat fraction and remaining
    muscle area changes in the quadriceps that track disease progression, and
    the selective anterior-thigh pattern helps distinguish IBM from other
    myopathies and guides biopsy site selection. Muscle MRI and ultrasound were
    incorporated as diagnostic tools in the revised ENMC criteria.
  imaging_finding_term:
    preferred_term: Fatty replacement of skeletal muscle
    term:
      id: HP:0012548
      label: Fatty replacement of skeletal muscle
  located_in:
    preferred_term: Quadriceps femoris
    term:
      id: UBERON:0001377
      label: quadriceps femoris
  evidence:
  - reference: PMID:40018748
    reference_title: "Quantitative muscle magnetic resonance imaging as a biomarker for inclusion body myositis in clinical trials: exploring the in vivo effects of arimoclomol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Baseline FF, RMA, MTR and FFa of the thigh and quadriceps demonstrated
      strong construct validity.
    explanation: >-
      Establishes quantitative MRI fat fraction and remaining muscle area of the
      thigh and quadriceps as valid measures in IBM.
  - reference: PMID:40018748
    reference_title: "Quantitative muscle magnetic resonance imaging as a biomarker for inclusion body myositis in clinical trials: exploring the in vivo effects of arimoclomol."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      FF, RMA and FFa demonstrated strong responsiveness to disease progression
    explanation: >-
      Shows the quadriceps fat-replacement measures change measurably with
      disease progression, supporting their use as progression biomarkers.
  - reference: PMID:38522330
    reference_title: "272nd ENMC international workshop: 10 Years of progress - revision of the ENMC 2013 diagnostic criteria for inclusion body myositis and clinical trial readiness. 16-18 June 2023, Hoofddorp, The Netherlands."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Novel diagnostic tools include muscle imaging techniques such as MRI and
      ultrasound, and serological testing for cytosolic 5'-nucleotidase-1A
      antibodies.
    explanation: >-
      Confirms muscle MRI and ultrasound are part of the revised ENMC diagnostic
      toolkit.
biochemical:
- name: Anti-cN1A (NT5C1A) Autoantibody
  notes: >-
    Autoantibodies against cytosolic 5'-nucleotidase 1A (cN1A / NT5C1A / Mup44),
    the first and only myositis-associated autoantibody described in IBM.
    Reported sensitivity varies widely with assay and threshold (roughly
    33-70%) while specificity against other muscle diseases is high (about
    92-98%). A negative test does not exclude IBM, and anti-cN1A also occurs in
    Sjogren disease and lupus, so a positive result supports the diagnosis only
    in the appropriate clinical context. cN1A also accumulates in perinuclear
    regions and rimmed vacuoles in IBM muscle, potentially linking the
    autoimmune and degenerative arms of the disease.
  presence: PRESENT
  specificity: >-
    High specificity against other muscle diseases (approximately 92-98%
    depending on reactivity threshold), but anti-cN1A is also found in Sjogren
    disease and systemic lupus erythematosus.
  evidence:
  - reference: PMID:23460448
    reference_title: "Autoantibodies to cytosolic 5'-nucleotidase 1A in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      By immunoprecipitation of recombinant cN1A, high concentrations of
      anti-Mup44 autoantibodies were detected in 33% of sIBM patient sera,
      whereas their prevalence in dermatomyositis, polymyositis, and other
      neuromuscular disorders appeared to be rare (4.2%, 4.5%, and 3.2%,
      respectively).
    explanation: >-
      Original identification of the cN1A autoantigen, quantifying frequency in
      IBM against comparator neuromuscular diseases.
  - reference: PMID:23596012
    reference_title: "Cytosolic 5'-nucleotidase 1A autoimmunity in sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Moderate reactivity of anti-cN1A autoantibodies was 70% sensitive and 92%
      specific, and high reactivity was 34% sensitive and 98% specific for the
      diagnosis of IBM.
    explanation: >-
      Provides the threshold-dependent sensitivity and specificity figures for
      anti-cN1A as a diagnostic test.
  - reference: PMID:23596012
    reference_title: "Cytosolic 5'-nucleotidase 1A autoimmunity in sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      cN1A reactivity by immunohistochemistry accumulated in perinuclear regions
      and rimmed vacuoles in IBM muscle, localizing to areas of myonuclear
      degeneration.
    explanation: >-
      Localizes the autoantigen to the degenerative lesions themselves,
      supporting a link between the autoimmune and myodegenerative arms.
- name: TDP-43 Cryptic Exon Inclusion in Muscle
  notes: >-
    RT-PCR detection of cryptic exons arising from loss of TDP-43-mediated
    splicing repression in muscle tissue. In a 119-biopsy series this was 84%
    sensitive and 99% specific for IBM, making it the most disease-specific
    molecular readout yet described. It is a research assay, not a validated
    routine clinical diagnostic.
  presence: PRESENT
  evidence:
  - reference: PMID:35044790
    reference_title: "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Of 119 muscle biopsies tested, RT-PCR-mediated detection of cryptic exon
      inclusion was able to diagnose IBM with 84% sensitivity and 99%
      specificity.
    explanation: >-
      Quantifies the diagnostic performance of cryptic exon detection in a large
      biopsy series.
genetic:
- name: HLA-DRB1
  notes: >-
    HLA-DRB1*03:01, carried on the 8.1 ancestral haplotype, is the strongest
    genetic risk factor for sporadic IBM. High-resolution genotyping refines the
    association to DRB1*03:01:01 and implicates arginine-74 of the DR-beta 1
    chain. This is common susceptibility variation of moderate effect, not a
    Mendelian causal gene; IBM has no causal gene and no established Mendelian
    inheritance. High-resolution sequencing additionally identifies
    DRB4*01:01:01 and DQA1*01:02:01 as protective, and shows the allele acts as
    an age-of-onset modifier: carriers of the risk genotype develop symptoms on
    average five years earlier.
  relationship_type: SUSCEPTIBILITY
  gene_term:
    preferred_term: HLA-DRB1
    term:
      id: hgnc:4948
      label: HLA-DRB1
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In a study of 252 IBM patients, the class II MHC allele HLA-DRB1*03:01
      showed the most significant association with IBM, and that risk could be
      largely attributed to amino acids within the peptide-binding pocket.
    explanation: >-
      Establishes HLA-DRB1*03:01 as the leading susceptibility allele and
      localizes the effect to the peptide-binding pocket.
  - reference: PMID:38043487
    reference_title: "High-resolution HLA genotyping in inclusion body myositis refines 8.1 ancestral haplotype association to DRB1*03:01:01 and highlights pathogenic role of arginine-74 of DRβ1 chain."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Human Leukocyte Antigens (HLA) is the highest genetic risk factor for
      developing IBM.
    explanation: >-
      Confirms HLA as the dominant genetic risk factor; the same study refines
      the association to DRB1*03:01:01 and arginine-74 of the DR-beta 1 chain.
  - reference: PMID:28086002
    reference_title: "Immune-Array Analysis in Sporadic Inclusion Body Myositis Reveals HLA-DRB1 Amino Acid Heterogeneity Across the Myositis Spectrum."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      No association with anti-cytosolic 5'-nucleotidase 1A-positive status was
      found independent of HLA-DRB1*03:01.
    explanation: >-
      Shows the HLA signal does not stratify by anti-cN1A serostatus, relevant
      to whether seropositive IBM is a genetically distinct subgroup.
  - reference: PMID:38043487
    reference_title: High-resolution HLA genotyping in inclusion body myositis refines
      8.1 ancestral haplotype association to DRB1*03:01:01 and highlights pathogenic
      role of arginine-74 of DRbeta1 chain.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Conversely, DRB4*01:01:01 and DQA1*01:02:01 were found to have protective
      effects; the carriers of DRB1*03:01:01 that did not possess these alleles
      had a fourteenfold increased risk of developing IBM over the general
      Caucasian population.
    explanation: >-
      Quantifies the risk conferred by DRB1*03:01:01 in the absence of the
      protective alleles, and identifies the protective haplotypes.
  - reference: PMID:38043487
    reference_title: High-resolution HLA genotyping in inclusion body myositis refines
      8.1 ancestral haplotype association to DRB1*03:01:01 and highlights pathogenic
      role of arginine-74 of DRbeta1 chain.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Furthermore, patients with the abovementioned genotype developed symptoms
      on average five years earlier than patients without.
    explanation: >-
      Establishes the HLA genotype as an age-of-onset modifier, not only a
      susceptibility factor.
- name: NT5C1A
  notes: >-
    NT5C1A encodes cytosolic 5'-nucleotidase 1A (cN1A / Mup44), the target
    autoantigen of the IBM-associated autoantibody. It is curated here as the
    autoantigen underpinning a diagnostic biomarker, not as a susceptibility or
    causal gene; no disease-associated NT5C1A coding variation has been
    established in IBM.
  relationship_type: BIOMARKER
  gene_term:
    preferred_term: NT5C1A
    term:
      id: hgnc:17819
      label: NT5C1A
  evidence:
  - reference: PMID:23596012
    reference_title: "Cytosolic 5'-nucleotidase 1A autoimmunity in sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Autoantibodies against cN1A are common in and highly specific to IBM among
      muscle diseases, and may provide a link between IBM's dual processes of
      autoimmunity and myodegeneration.
    explanation: >-
      Identifies cN1A (NT5C1A) as the IBM autoantigen and frames it as a
      candidate bridge between the autoimmune and degenerative arms.
- name: VCP and SQSTM1 (rare proteostasis variants)
  notes: >-
    Candidate gene sequencing has identified rare missense variants in
    proteostasis regulators including VCP and SQSTM1 in sporadic IBM cohorts.
    These are unvalidated risk contributors, not monogenic causes. Note the
    distinct entity boundary: pathogenic VCP variants cause VCP-associated
    multisystem proteinopathy / inclusion body myopathy with Paget disease of
    bone and frontotemporal dementia, which is a hereditary disease separate
    from sporadic IBM.
  relationship_type: DISPUTED
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Candidate gene sequencing identified rare missense variants in proteins
      regulating protein homeostasis including VCP and SQSTM1.
    explanation: >-
      Reports the rare proteostasis-gene variants; the same review notes only
      the HLA association has reached genome-wide significance, so these remain
      unvalidated.
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Many variants have been reported at an increased frequency in IBM in small
      studies; however, only HLA association has shown genome-wide significance.
    explanation: >-
      Explicitly limits the confidence that can be placed in non-HLA candidate
      variants in IBM.
prevalence:
- population: Worldwide (meta-analysis of general-population studies)
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 2.48
  rate_low: 2.0
  rate_high: 2.96
  notes: >-
    Meta-prevalence 24.8 per 1,000,000 (95% CI 20.0-29.6) across 9 studies,
    equivalent to 2.48 per 100,000. Reported estimates vary widely with
    ascertainment and diagnostic criteria.
  evidence:
  - reference: PMID:28505979
    reference_title: "A Systematic Review and Meta-Analysis of Prevalence Studies of Sporadic Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The meta-prevalence estimate from 9 papers was 24.8/1,000,000 (95% CI:
      20.0-29.6).
    explanation: >-
      Systematic review and meta-analysis of sIBM prevalence studies.
- population: Olmsted County, Minnesota, USA; residents aged 50 years and older
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_5_PER_10000
  rate_per_100000: 18.2
  notes: >-
    Highest reported sIBM prevalence to date; restricted to the population aged
    50 and over, which raises the estimate substantially relative to
    general-population figures.
  evidence:
  - reference: PMID:33879596
    reference_title: "Epidemiology and Natural History of Inclusion Body Myositis: A 40-Year Population-Based Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The prevalence of sIBM in 2010 was 18.20 per 100,000 people ≥50 years old.
    explanation: >-
      40-year population-based cohort giving an age-restricted prevalence
      estimate.
progression:
- notes: >-
    Onset is insidious, usually after age 45-50, with diagnostic delay commonly
    extending several years. The course is chronic and steadily progressive
    rather than relapsing-remitting; spontaneous or durable treatment-induced
    remission is not a feature. Most patients lose the ability to ambulate 10-15
    years after diagnosis. Longevity is mildly reduced, with aspiration
    pneumonia and respiratory complications the leading disease-related causes
    of death.
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sporadic Inclusion Body myositis (IBM) is the most common myopathy in
      individuals over the age of 50, and patients typically lose the ability to
      ambulate 10 to 15 years after diagnosis
    explanation: >-
      Quantifies the interval from diagnosis to loss of ambulation.
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Furthermore, IBM mildly affects longevity with aspiration pneumonia and
      respiratory complications being the most common cause of death.
    explanation: >-
      Establishes the modest survival effect and the dominant causes of
      disease-related death.
  - reference: PMID:33879596
    reference_title: "Epidemiology and Natural History of Inclusion Body Myositis: A 40-Year Population-Based Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Patients with sIBM have similar risk of cancer, but slightly shorter life
      expectancy compared to matched patients without sIBM.
    explanation: >-
      Population-based confirmation of modestly reduced life expectancy and, in
      contrast to dermatomyositis, no excess cancer risk.
epidemiology:
- name: Age distribution and onset
  description: >-
    Sporadic IBM is a late-onset disease. Symptom onset is typically after age
    45-50 and it is the most common myopathy in people over 50; onset before 45
    is exceptional and should prompt reconsideration of a hereditary inclusion
    body myopathy. Diagnostic delay of several years from symptom onset is
    common because early quadriceps and finger-flexor weakness is easily
    attributed to ageing.
  notes: >-
    A male predominance of roughly 2:1 and a mean onset in the seventh decade
    are consistently reported in the deep-research literature but are NOT
    curated here as evidence, because no quotable statement of either figure
    appears in the abstracts cached for this entry. Add them when a source
    reporting them directly is fetched.
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Inclusion body myositis (IBM) is a progressive muscle disease affecting
      patients over the age of 40, with distinctive clinical and
      histopathological features.
    explanation: >-
      Establishes the late-onset age distribution of the disease.
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Sporadic Inclusion Body myositis (IBM) is the most common myopathy in
      individuals over the age of 50
    explanation: >-
      Positions IBM as the leading myopathy in the over-50 population, the
      demographic core of the disease.
clinical_burden:
  burden_level: HIGH
  rationale: >-
    IBM causes progressive, irreversible loss of hand function and ambulation,
    with the majority of patients eventually wheelchair-dependent, plus
    dysphagia requiring feeding-tube support in a substantial minority. There is
    no disease-modifying therapy, so the entire burden accrues unmitigated over
    a course measured in decades.
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      IBM is associated with marked morbidity as majority of patients eventually
      become wheelchair dependent with limited use of their hands and marked
      dysphagia.
    explanation: >-
      Directly characterizes the morbidity burden as marked and affecting
      mobility, hand function and swallowing.
diagnosis:
- name: ENMC Diagnostic Criteria for Inclusion Body Myositis
  description: >-
    Diagnosis rests on the characteristic weakness distribution combined with
    supportive laboratory, imaging, serological and biopsy findings. The 2013
    ENMC criteria were revised at the 272nd ENMC workshop (2023, published
    2024), which incorporated muscle MRI and ultrasound and anti-cN1A serology
    as diagnostic tools alongside the classical clinicopathological features.
  evidence:
  - reference: PMID:38522330
    reference_title: "272nd ENMC international workshop: 10 Years of progress - revision of the ENMC 2013 diagnostic criteria for inclusion body myositis and clinical trial readiness. 16-18 June 2023, Hoofddorp, The Netherlands."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Novel diagnostic tools include muscle imaging techniques such as MRI and
      ultrasound, and serological testing for cytosolic 5'-nucleotidase-1A
      antibodies.
    explanation: >-
      Documents the diagnostic modalities incorporated into the revised ENMC
      criteria.
  - reference: PMID:38522330
    reference_title: "272nd ENMC international workshop: 10 Years of progress - revision of the ENMC 2013 diagnostic criteria for inclusion body myositis and clinical trial readiness. 16-18 June 2023, Hoofddorp, The Netherlands."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This report is composed of two parts, the first part providing new
      diagnostic criteria on which consensus was achieved.
    explanation: >-
      Confirms that the 272nd ENMC workshop produced consensus revised
      diagnostic criteria.
differential_diagnoses:
- name: Polymyositis
  description: >-
    Historically the most common misdiagnosis. Contemporary opinion holds that
    many cases labelled polymyositis are better classified as IBM,
    immune-mediated necrotizing myopathy or antisynthetase syndrome.
    Steroid-refractory "polymyositis", especially with finger-flexor or
    quadriceps selectivity, should prompt reassessment for IBM.
  disease_term:
    preferred_term: Polymyositis
    term:
      id: MONDO:0019127
      label: polymyositis
  distinguishing_features:
  - Selective deep finger flexor and quadriceps weakness in IBM
  - Rimmed vacuoles and p62/TDP-43 aggregates on biopsy in IBM, absent in polymyositis
  - Refractoriness to corticosteroids in IBM
  - Invasion of muscle by large granular lymphocytes in IBM but rarely in polymyositis
  evidence:
  - reference: PMID:26920676
    reference_title: "Association of inclusion body myositis with T cell large granular lymphocytic leukaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Muscle immunohistochemistry demonstrated invasion of large granular
      lymphocytes into muscle in 15/15 inclusion body myositis patients but in
      only 1/28 patients with dermatomyositis or polymyositis.
    explanation: >-
      Provides a discriminating pathological feature between IBM and
      polymyositis/dermatomyositis.
- name: GNE Myopathy (hereditary inclusion body myopathy)
  description: >-
    An autosomal recessive hereditary myopathy that shares rimmed vacuoles and
    protein inclusions on biopsy but is a mechanistically distinct disease. It
    is the most important hereditary mimic of IBM and a recurring source of
    entity confusion.
  distinguishing_features:
  - Onset typically before age 40
  - Characteristic sparing of the quadriceps
  - Absence of endomysial inflammatory infiltrate and MHC class I upregulation
  - Autosomal recessive GNE variants identifiable
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      For example, hIBM2 caused by autosomal recessive inheritance of mutations
      in the GNE gene typically spares the quadriceps, and biopsy shows rimmed
      vacuoles and protein inclusions but lacks inflammation.
    explanation: >-
      States the specific features distinguishing GNE myopathy from sporadic IBM.
- name: VCP-Associated Multisystem Proteinopathy
  description: >-
    Autosomal dominant VCP-related inclusion body myopathy with Paget disease of
    bone and frontotemporal dementia. Shares the rimmed vacuole and TDP-43
    pathology of IBM but is monogenic and multisystem.
  distinguishing_features:
  - Earlier onset and positive family history
  - Extramuscular features (Paget disease of bone, frontotemporal dementia, motor
    neuron disease)
  - Identifiable pathogenic VCP variant
  evidence:
  - reference: PMID:29611059
    reference_title: "New Developments in the Genetics of Inclusion Body Myositis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Thus, mutations in known hIBM genes cause syndromes that share degenerative
      features on biopsy but otherwise are clinically distinct from IBM.
    explanation: >-
      Supports the general boundary between hereditary inclusion body myopathy
      genes (including VCP) and sporadic IBM; the snippet covers the class
      rather than VCP specifically.
- name: T Cell Large Granular Lymphocytic Leukaemia
  description: >-
    Not merely a mimic but a genuine overlap: the majority of IBM patients meet
    standard diagnostic criteria for T-LGL leukaemia on blood flow cytometry.
    This is better understood as a shared clonal cytotoxic T cell process than
    as a differential to exclude, and it can prompt inappropriate haematological
    workup if not recognized. Retained here because it is a real bedside
    diagnostic consideration, but the association itself is modelled properly in
    kb/comorbidities/com_Inclusion_Body_Myositis__T_Cell_Large_Granular_Lymphocytic_Leukemia.yaml,
    which is the authoritative record for it.
  distinguishing_features:
  - Large granular lymphocyte expansion is present in the majority of IBM patients
    and does not by itself indicate a separate haematological disease
  evidence:
  - reference: PMID:26920676
    reference_title: "Association of inclusion body myositis with T cell large granular lymphocytic leukaemia."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Most (22/38; 58%) patients with inclusion body myositis had aberrant
      populations of large granular lymphocytes in their blood meeting standard
      diagnostic criteria for T cell large granular lymphocytic leukaemia.
    explanation: >-
      Quantifies the overlap between IBM and formal T-LGL leukaemia criteria.
treatments:
- name: Resistance and Aerobic Exercise Therapy
  description: >-
    Individualized supervised resistance and aerobic exercise, with contracture
    prevention, energy conservation, orthoses, mobility aids and fall
    prevention. Exercise appears safe and may improve strength or conditioning,
    but consistent mobility benefit has not been demonstrated. Together with
    swallowing and respiratory surveillance this constitutes the mainstay of
    management.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Monitoring for swallowing and respiratory complications, exercise, and
      addressing mobility issues are the mainstay of management.
    explanation: >-
      Establishes exercise and supportive monitoring as the standard of care in
      the absence of pharmacotherapy.
- name: Dysphagia Management
  description: >-
    Multidisciplinary swallowing care: periodic symptom screening,
    speech-language assessment, videofluoroscopy or endoscopy when indicated,
    texture and volume adaptation, nutrition support and aspiration precautions,
    with rehabilitative swallowing exercise protocols. Cricopharyngeal dilation,
    botulinum toxin injection or myotomy may help selected obstructive cases;
    myotomy is irreversible.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: speech therapy
    term:
      id: NCIT:C159273
      label: Speech Language Therapy
  target_phenotypes:
  - preferred_term: Dysphagia
    term:
      id: HP:0002015
      label: Dysphagia
  evidence:
  - reference: PMID:37678324
    reference_title: "Update on the evaluation and management of dysphagia in sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Small scale research and clinical anecdotal data support a
      multidisciplinary and multipronged patient-centered approach, including
      rehabilitative exercise protocols, for dysphagia management in IBM.
    explanation: >-
      Supports the multidisciplinary rehabilitative approach while indicating the
      evidence base is small-scale.
  - reference: PMID:37678324
    reference_title: "Update on the evaluation and management of dysphagia in sporadic inclusion body myositis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A paucity exists in the literature to effectively guide clinical
      decision-making for patients with IBM and dysphagia.
    explanation: >-
      Documents the weak evidence base underlying dysphagia management
      recommendations in IBM.
- name: Occupational Therapy and Assistive Devices
  description: >-
    Occupational therapy for the hand disability that follows deep finger flexor
    weakness: adaptive grip aids, built-up utensils, home modification and
    energy conservation. Ankle-foot orthoses for foot drop, and canes, walkers,
    wheelchairs and transfer devices as ambulation declines. Because there is no
    disease-modifying therapy, maintaining function and independence with
    assistive technology is a substantial part of actual care rather than an
    adjunct.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: occupational therapy
    term:
      id: NCIT:C121351
      label: Occupational Therapy
  evidence:
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Monitoring for swallowing and respiratory complications, exercise, and
      addressing mobility issues are the mainstay of management.
    explanation: >-
      Establishes addressing mobility issues, which is what assistive devices
      and occupational therapy deliver, as a mainstay of IBM management.
  - reference: PMID:36237625
    reference_title: "Inclusion body myositis: Update on the diagnostic and therapeutic landscape."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      IBM is associated with marked morbidity as majority of patients eventually
      become wheelchair dependent with limited use of their hands and marked
      dysphagia.
    explanation: >-
      Documents the hand-function and mobility disability that occupational
      therapy and assistive devices are directed at.
- name: Falls Prevention
  description: >-
    Structured fall-risk assessment, home safety modification, gait aids and
    balance work. Falls are a leading cause of injury in IBM and were the single
    most frequent adverse event across all arms of the RESILIENT trial,
    including placebo, which indicates the background rate in this population
    rather than a drug effect.
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: physical therapy
    term:
      id: NCIT:C15302
      label: Physical Therapy
  target_phenotypes:
  - preferred_term: Frequent falls
    term:
      id: HP:0002359
      label: Frequent falls
  evidence:
  - reference: PMID:31397289
    reference_title: "Safety and efficacy of intravenous bimagrumab in inclusion body myositis (RESILIENT): a randomised, double-blind, placebo-controlled phase 2b trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Falls were the most frequent adverse event
    explanation: >-
      Quantifies falls as the dominant adverse event in a large IBM trial
      population, establishing the clinical need for fall prevention.
- name: Intravenous Immunoglobulin (IVIG)
  description: >-
    IVIG has been tested in randomised controlled trials in IBM without
    demonstrating a sustained strength benefit; the Cochrane review could not
    pool the trials or draw conclusions from them. It retains a limited,
    non-consensus role in selected patients with refractory dysphagia, where
    transient swallowing improvement has been reported, but it does not alter
    the overall course of the disease.
  therapeutic_modality: OTHER
  treatment_term:
    preferred_term: immunoglobulin infusion therapy
    term:
      id: NCIT:C62710
      label: Immunoglobulin Therapy
  target_phenotypes:
  - preferred_term: Oral-pharyngeal dysphagia
    term:
      id: HP:0200136
      label: Oral-pharyngeal dysphagia
  evidence:
  - reference: PMID:35658164
    reference_title: "Treatment for inclusion body myositis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Three trials (n = 78) compared intravenous immunoglobulin (combined in one
      trial with prednisone) to a placebo, but we were unable to perform
      meta-analysis because of variations in study analysis and presentation of
      trial data, with no access to the primary data for re-analysis.
    explanation: >-
      Documents that IVIG has been trialled in IBM but that the evidence base is
      too weak and heterogeneous to support pooling, so no efficacy claim is
      made.
  - reference: PMID:35658164
    reference_title: "Treatment for inclusion body myositis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We were unable to draw conclusions from trials of IVIg, oxandrolone, and
      AZA plus MTX versus MTX.
    explanation: >-
      The Cochrane authors explicitly decline to draw any conclusion on IVIG,
      which is why this treatment is curated as PARTIAL rather than SUPPORT or
      REFUTE.
- name: Interventional Dysphagia Procedures
  description: >-
    When conservative swallowing management fails, interventional options are
    used for the obstructive cricopharyngeal component: balloon dilation,
    botulinum toxin injection of the cricopharyngeus, and cricopharyngeal
    myotomy. Myotomy is irreversible. Gastrostomy (PEG) placement is used for
    nutritional support once oral intake becomes unsafe; roughly half of
    patients in a population-based cohort eventually required a feeding tube.
    Evidence is limited to small series and clinical experience rather than
    randomised trials.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: surgical procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  target_phenotypes:
  - preferred_term: Oral-pharyngeal dysphagia
    term:
      id: HP:0200136
      label: Oral-pharyngeal dysphagia
  evidence:
  - reference: PMID:41161903
    reference_title: "Emerging Treatment Options for Inclusion Body Myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dysphagia, a major contributor to morbidity, is receiving increased
      attention through both conservative and interventional approaches.
    explanation: >-
      Confirms that interventional (procedural) approaches to dysphagia sit
      alongside conservative management in contemporary IBM practice.
  - reference: PMID:33879596
    reference_title: "Epidemiology and Natural History of Inclusion Body Myositis: A 40-Year Population-Based Study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Two-thirds of patients developed dysphagia, and half required a feeding
      tube.
    explanation: >-
      Quantifies the proportion progressing to gastrostomy-level nutritional
      support, establishing the clinical need for this treatment category.
- name: Conventional Immunosuppression (corticosteroids, methotrexate, azathioprine)
  description: >-
    Glucocorticoids and conventional immunosuppressants are NOT effective in
    IBM and are not recommended. They add toxicity without durable functional
    benefit. This entry is retained deliberately to record a negative treatment
    result: failure to respond to corticosteroids is itself a diagnostic clue
    that should prompt reassessment of a "polymyositis" label.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: prednisone
      term:
        id: CHEBI:8382
        label: prednisone
    - preferred_term: methotrexate
      term:
        id: CHEBI:44185
        label: methotrexate
    - preferred_term: azathioprine
      term:
        id: CHEBI:2948
        label: azathioprine
  evidence:
  - reference: PMID:38273639
    reference_title: "Sirolimus for treatment of patients with inclusion body myositis: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Classical immunosuppressants are ineffective in treating inclusion body
      myositis, and to date there are no recommendations for pharmacological
      approaches to treatment.
    explanation: >-
      Directly refutes any therapeutic claim for conventional immunosuppression
      in IBM.
- name: Sirolimus (rapamycin)
  description: >-
    An mTOR inhibitor that blocks effector T cell proliferation while relatively
    sparing regulatory T cells and inducing autophagy, targeting both the
    immune and degenerative arms of IBM. A 44-patient phase 2b trial missed its
    primary endpoint of knee extension strength but showed significant
    differences favouring sirolimus on several secondary outcomes. Sirolimus is
    investigational, not established therapy.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sirolimus
      term:
        id: CHEBI:9168
        label: sirolimus
  target_mechanisms:
  - target: Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells
    treatment_effect: INHIBITS
    description: >-
      mTOR inhibition blocks effector T cell proliferation while relatively
      sparing regulatory T cells.
  evidence:
  - reference: PMID:38273639
    reference_title: "Sirolimus for treatment of patients with inclusion body myositis: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We observed no difference in the primary outcome of relative percentage
      change from baseline to month 12 of the maximal voluntary isometric knee
      extension strength (median difference 3·78, 95% CI -10·61 to 17·31;
      p=0·85).
    explanation: >-
      The primary endpoint was negative, so any therapeutic claim must be
      qualified as at best partially supported.
  - reference: PMID:38273639
    reference_title: "Sirolimus for treatment of patients with inclusion body myositis: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      However, we observed significant differences in favour of sirolimus
      between the study groups for HAQ-DI, forced vital capacity, thigh fat
      fraction, and 6-min walking distance.
    explanation: >-
      Secondary-endpoint signals that motivated further trials, but which do not
      establish efficacy given the negative primary endpoint.
  - reference: PMID:38273639
    reference_title: "Sirolimus for treatment of patients with inclusion body myositis: a randomised, double-blind, placebo-controlled, proof-of-concept, phase 2b trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      When used after organ transplantation, sirolimus can block the
      proliferation of effector T cells, while preserving T regulatory cells,
      and induce autophagy, all of which are processes that are impaired in
      inclusion body myositis.
    explanation: >-
      States the mechanistic rationale linking sirolimus to the effector T cell
      and autophagy nodes of the IBM pathograph.
- name: Arimoclomol
  description: >-
    An oral co-inducer of the cellular heat shock response intended to enhance
    proteostasis. Despite encouraging preclinical and pilot data it failed to
    improve the IBM Functional Rating Scale in a 150-participant, 20-month
    randomised placebo-controlled trial and is not standard care. Recorded here
    as a negative result relevant to the degeneration-primary hypothesis.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: arimoclomol
      term:
        id: CHEBI:747211
        label: arimoclomol
  evidence:
  - reference: PMID:37739573
    reference_title: "Safety and efficacy of arimoclomol for inclusion body myositis: a multicentre, randomised, double-blind, placebo-controlled trial."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Arimoclomol did not improve efficacy outcomes, relative to placebo, but
      had an acceptable safety profile in individuals with inclusion body
      myositis.
    explanation: >-
      Refutes efficacy of heat-shock-response co-induction as a treatment
      strategy in IBM.
- name: Bimagrumab
  description: >-
    A fully human anti-activin type II receptor monoclonal antibody intended to
    increase muscle mass by blocking myostatin signalling. It targeted the
    atrophy arm rather than disease causation, increased lean mass, but failed
    its primary 6-minute walking distance endpoint in the 251-participant
    RESILIENT phase 2b trial.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: monoclonal antibody
      term:
        id: NCIT:C20401
        label: Monoclonal Antibody
  evidence:
  - reference: PMID:31397289
    reference_title: "Safety and efficacy of intravenous bimagrumab in inclusion body myositis (RESILIENT): a randomised, double-blind, placebo-controlled phase 2b trial."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At week 52, 6MWD change from baseline did not differ between any
      bimagrumab dose and placebo
    explanation: >-
      Refutes functional efficacy of bimagrumab at any tested dose in IBM.
- name: Ulviprubart (ABC008, anti-KLRG1)
  description: >-
    A monoclonal antibody designed to deplete highly differentiated KLRG1+
    cytotoxic T cells while sparing naive and regulatory compartments, directly
    targeting the effector population identified as pathogenic in IBM. The
    registrational phase 2/3 MUSCLE trial (NCT05721573, 272 participants,
    primary endpoint IBMFRS change at week 76) completed in November 2025.
    Sponsor topline announcements report that the trial did NOT meet its primary
    endpoint or key secondary endpoints in the overall population, with
    favourable trends limited to a mild-to-moderate disease subgroup. This is
    the most direct test of the autoimmune-primary hypothesis conducted to date
    and its failure is meaningful negative evidence for that model. See notes
    for the important provenance caveat.
  notes: >-
    PROVENANCE CAVEAT: the negative topline result is sourced from sponsor press
    releases (24 February 2026 topline; detailed data presented 26 March 2026),
    which are NOT peer-reviewed and are NOT yet posted as results on
    ClinicalTrials.gov (the registry record still reports hasResults=false as of
    the 2026-01-29 last update). It is therefore recorded here as a note rather
    than as a snippet-validated evidence item, per the repository rule that an
    unquotable claim belongs in notes. The subgroup trend must NOT be read as
    efficacy: it is a subgroup analysis in a trial that missed its primary
    endpoint. Replace this note with proper evidence when the peer-reviewed
    publication or registry results appear.
  therapeutic_modality: MONOCLONAL_ANTIBODY
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: monoclonal antibody
      term:
        id: NCIT:C20401
        label: Monoclonal Antibody
  target_mechanisms:
  - target: Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells
    treatment_effect: INHIBITS
    description: >-
      Anti-KLRG1 antibody depletes the highly differentiated KLRG1-positive
      cytotoxic T cell population while sparing naive and regulatory
      compartments.
  evidence:
  - reference: PMID:31326977
    reference_title: "Highly differentiated cytotoxic T cells in inclusion body myositis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Targeting highly differentiated cytotoxic T cells could be a favourable
      approach to treatment of inclusion body myositis.
    explanation: >-
      States the therapeutic rationale for KLRG1-directed depletion that
      ulviprubart implements.
  - reference: clinicaltrials:NCT05721573
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A Phase II/III Randomized, Double-blind, Placebo-controlled, Multicenter
      Study to Determine the Efficacy and Safety of ABC008 in the Treatment of
      Subjects with Inclusion Body Myositis
    explanation: >-
      Documents the existence and design of the pivotal trial; results are not
      yet published, so no efficacy claim is made.
clinical_trials:
- name: NCT02753530
  phase: PHASE_II
  status: COMPLETED
  description: >-
    Multicentre randomised double-blind placebo-controlled trial of arimoclomol,
    an oral heat shock response co-inducer, in sporadic IBM. Enrollment 152.
    Reported in Lancet Neurology 2023 (PMID:37739573); did not improve the
    IBMFRS relative to placebo.
  evidence:
  - reference: clinicaltrials:NCT02753530
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The purpose of this study is to evaluate the safety and efficacy of the
      study drug, arimoclomol in IBM patients.
    explanation: Confirms the trial intervention and indication.
- name: NCT01925209
  phase: PHASE_III
  status: COMPLETED
  description: >-
    RESILIENT: randomised double-blind placebo-controlled dose-finding phase
    2b/3 trial of intravenous bimagrumab (BYM338) in sporadic IBM, enrollment
    251, primary endpoint 6-minute walking distance at 52 weeks. Reported in
    Lancet Neurology 2019 (PMID:31397289); primary endpoint not met at any dose.
    Recorded as PHASE_III because the schema enum has no combined phase 2b/3
    value.
  evidence:
  - reference: clinicaltrials:NCT01925209
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      This study evaluated the efficacy, safety and tolerability of multiple
      doses of bimagrumab/BYM338 vs placebo, when administered intravenously
      (i.v.), on physical function, muscle strength, and mobility in patients
      with sporadic inclusion body myositis (sIBM).
    explanation: Confirms the RESILIENT design, intervention, outcomes and indication.
- name: NCT02573467
  phase: PHASE_III
  status: COMPLETED
  description: >-
    Long-term extension of the RESILIENT bimagrumab study, enrollment 211,
    intended to evaluate efficacy, safety and tolerability up to 2 years.
    Reported in Neurology 2021 (PMID:33597289); extended treatment did not
    produce clinical benefit in mobility. The extension was terminated per
    protocol once the core study missed its primary endpoint, so no participants
    entered the planned open-label period. Registry status is COMPLETED.
  evidence:
  - reference: clinicaltrials:NCT02573467
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the core study did not meet the primary end point (no bimagrumab dose was
      identified based on the core study efficacy results) the extension study
      was terminated as per protocol/sponsor's decision
    explanation: >-
      The registry record itself documents that the core RESILIENT study missed
      its primary endpoint and that this triggered termination of the extension,
      independently corroborating the published negative result.
- name: NCT04789070
  phase: PHASE_III
  status: ACTIVE_NOT_RECRUITING
  description: >-
    "Optimism in IBM": confirmatory double-blind randomised controlled phase III
    trial of sirolimus, enrollment 140, primary endpoint IBM Functional Rating
    Scale. Follows the phase 2b proof-of-concept trial (PMID:38273639) that
    missed its primary endpoint but showed secondary-endpoint signals. Results
    not yet available.
  evidence:
  - reference: clinicaltrials:NCT04789070
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The hypothesis is that Sirolimus, (Rapamycin (R)) which is currently used
      in organ transplantation and works by blocking the activity of T effector
      cells but preserving T regulatory cells, as well as by inducing autophagy
      (protein degradation), will be effective in IBM to slow or stabilize
      disease progression
    explanation: >-
      Confirms the confirmatory sirolimus trial and states its dual
      mechanistic rationale, matching the target_mechanisms link on the
      sirolimus treatment.
- name: NCT05721573
  phase: PHASE_III
  status: COMPLETED
  description: >-
    Randomized, double-blind, placebo-controlled multicenter phase II/III trial
    of ABC008 (ulviprubart), an anti-KLRG1 monoclonal antibody depleting highly
    differentiated cytotoxic T cells, in inclusion body myositis. Actual
    enrollment 272 participants. Recorded as PHASE_III because the schema enum
    has no combined phase II/III value.
  evidence:
  - reference: clinicaltrials:NCT05721573
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      A Phase II/III Randomized, Double-blind, Placebo-controlled, Multicenter
      Study to Determine the Efficacy and Safety of ABC008 in the Treatment of
      Subjects with Inclusion Body Myositis
    explanation: >-
      Confirms the trial design, intervention and indication.
discussions:
- discussion_id: ibm_autoimmune_vs_degenerative_primacy
  kind: CONTROVERSY
  status: OPEN
  prompt: >-
    Is sporadic inclusion body myositis primarily a T cell-mediated autoimmune
    disease with secondary degeneration, or primarily a cell-autonomous
    degenerative myopathy with secondary inflammation?
  attaches_to:
  - pathophysiology#Cytotoxic T Cell Invasion of Non-Necrotic Myofibres
  - pathophysiology#Autophagy-Lysosome Failure and Rimmed Vacuole Formation
  rationale: >-
    This is the central unresolved question in IBM and it determines therapeutic
    strategy. The autoimmune-primary case rests on the HLA association, the
    anti-cN1A autoantibody, the clonal cytotoxic T cell signature, and the
    observation that invasion of non-necrotic fibres is far more common than
    aggregate-bearing fibres (fewer than 1% of myofibres). The
    degeneration-primary case rests on the consistent failure of
    immunosuppression and on the xenograft experiment showing rimmed vacuoles
    and TDP-43 loss of function persist after T cell depletion. The two models
    are not mutually exclusive; the disputed point is which arm is upstream and
    therefore which is the therapeutic target. The single most informative test
    has now reported: the registrational anti-KLRG1 (ulviprubart) MUSCLE trial
    depleted precisely the effector population the autoimmune model implicates,
    sparing broader immunity in a way conventional immunosuppression does not,
    and per sponsor topline announcements it missed its primary and key
    secondary endpoints in the overall population. If that result holds on
    peer-reviewed publication it is substantial negative evidence for the
    autoimmune-primary model as a complete account, and shifts weight toward the
    degeneration-primary arm or toward a model in which immune injury initiates
    but does not sustain the disease. The `autoimmune_primary` hypothesis is
    retained as CANONICAL for now because it remains the dominant published
    interpretation and the trial result is not yet peer-reviewed; that status
    should be revisited when it is.
  proposed_experiments:
  - experiment_id: ibm_klrg1_trial_peer_reviewed_publication
    name: Peer-reviewed publication of the anti-KLRG1 MUSCLE trial with target engagement
    description: >-
      Publish the full MUSCLE (ulviprubart, NCT05721573) dataset in the
      peer-reviewed literature, reporting functional outcomes alongside
      confirmed pharmacodynamic depletion of KLRG1+ T cells in blood and muscle.
      The topline result is already announced as negative in the overall
      population, so the decisive remaining question is whether the effector
      population was actually cleared from muscle.
    would_support:
    - >-
      A null functional result together with documented near-complete depletion
      of muscle-invading KLRG1+ T cells would be strong evidence against the
      autoimmune-primary model, since the mechanism was engaged and the disease
      progressed anyway.
    would_refute:
    - >-
      A null functional result with poor muscle-compartment depletion would
      leave the autoimmune-primary model intact and reframe the trial as a
      pharmacokinetic rather than a mechanistic failure.
  - experiment_id: ibm_paired_biopsy_temporal_ordering
    name: Longitudinal paired-biopsy ordering of the two arms
    description: >-
      Serial paired muscle biopsies measuring TDP-43 cryptic exon burden
      alongside quantified cytotoxic T cell infiltration in the same patients
      over time.
    decision_criterion: >-
      Whichever readout rises first, and predicts subsequent change in the
      other, identifies the upstream arm.
  evidence:
  - reference: PMID:35044790
    reference_title: "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Sporadic inclusion body myositis (IBM) is the most common acquired muscle
      disease in adults over age 50, yet it remains unclear whether the disease
      is primarily driven by T cell-mediated autoimmunity.
    explanation: >-
      Explicitly states the controversy as an open question in the primary
      literature.
- discussion_id: ibm_amyloid_beta_specificity
  kind: CONTROVERSY
  status: OPEN
  prompt: >-
    Are amyloid-beta and its precursor APP abnormally and specifically present
    in inclusion body myositis muscle, and if some amyloid-beta is genuinely
    present, is it a cause of myofibre injury or a downstream marker?
  attaches_to:
  - pathophysiology#Amyloid-beta and APP Accumulation in Myofibres
  - pathophysiology#Autophagy-Lysosome Failure and Rimmed Vacuole Formation
  rationale: >-
    The two halves of the claim have different answers and should not be
    resolved together.

    SPECIFICITY is settled in the negative. Amyloid-positive, ubiquitinated
    filamentous rimmed vacuoles indistinguishable from those of IBM occur in
    long-standing denervation after poliomyelitis and in congenital myopathies
    of children, so the finding indexes chronic myofibre injury rather than IBM.
    Oculopharyngeal muscular dystrophy is not part of this argument: it shares
    the ubiquitinated filamentous inclusions, but the single study here that
    applied a beta-amyloid antibody to it found labelling in IBM and not in
    OPMD, so it is used below only as an experimental control arm.
    Quantitatively the marker performs
    poorly: in the series that compared markers head to head, sarcoplasmic
    TDP-43 was present in 23% of IBM myofibres while focal beta-amyloid
    immunoreactivity was present in 0.00% and Congo-red material in 0.57%.
    TDP-43 mislocalization has displaced amyloid as the specific molecular
    signature of IBM.

    ABNORMAL PRESENCE remains genuinely open, and is the reason this discussion
    is filed as a CONTROVERSY rather than closed. Immunoblot and ADDL data
    reporting Abeta oligomers in every IBM sample and no control exist and have
    not been formally retracted or directly rebutted, but they issue almost
    entirely from the laboratory that proposed the hypothesis; the corresponding
    negative is largely an absence — unbiased laser-capture proteomics of rimmed
    vacuoles does not report amyloid-beta or APP among 213 enriched proteins —
    and absence of detection in a spectral-count experiment is weak evidence of
    absence for a small, aggregation-prone, poorly soluble peptide. What makes
    the open question tractable is that nobody has run the decisive experiment:
    a blinded, multi-centre, targeted mass-spectrometric quantification of
    amyloid-beta peptides in IBM versus disease-control muscle.

    Two further considerations bear on how much weight the existing literature
    can carry. The companion phospho-tau claim was shown to rest on antibodies
    that stain normal myonuclei and bind proteins other than tau, which impugns
    the reagent class the histological arm depended on; and a citation-network
    analysis taking this precise belief as its subject found its authority built
    by citation bias, amplification and invention rather than by data. Both
    argue for resolving the question with orthogonal, antibody-independent
    methods rather than with more immunohistochemistry.
  proposed_experiments:
  - experiment_id: ibm_targeted_ms_amyloid_quantification
    name: Blinded targeted mass-spectrometric quantification of amyloid-beta in IBM versus disease-control muscle
    description: >-
      Parallel reaction monitoring or immunoprecipitation-mass spectrometry with
      stable-isotope-labelled Abeta40/Abeta42 internal standards, applied to
      whole muscle lysates and to laser-captured rimmed vacuoles, from IBM,
      polymyositis, dermatomyositis, chronically denervated, oculopharyngeal
      muscular dystrophy and age-matched normal muscle, with samples blinded and
      analysed in more than one laboratory. This is antibody-independent and so
      is not vulnerable to the cross-reactivity that undermined the
      immunohistochemical literature.
    would_support:
    - >-
      Quantifiable Abeta42 above disease controls, in IBM muscle, reproduced
      across laboratories, would establish abnormal presence and reopen the
      question of whether it is specific and upstream.
    would_refute:
    - >-
      Abeta peptides at or below disease-control levels, with adequate
      sensitivity demonstrated on spiked standards, would close the abnormal
      presence claim and retire the hypothesis outright.
  - experiment_id: ibm_lcm_ms_peptide_library_reinterrogation
    name: Targeted re-interrogation of existing rimmed-vacuole LCM-MS peptide libraries for APP and amyloid-beta
    description: >-
      Re-query the already-acquired laser-capture mass-spectrometry peptide
      libraries from the rimmed-vacuole proteomics study for APP and
      amyloid-beta peptides specifically, reporting detection limits and
      spiked-standard sensitivity. The published analysis reports 213 enriched
      proteins but does not state whether these peptides were sought, so "not
      reported" cannot currently be read as "absent".
    would_support:
    - >-
      Detection of APP or amyloid-beta peptides enriched in rimmed vacuoles
      would restore a constituent role for amyloid in the defining lesion.
    would_refute:
    - >-
      Confirmed non-detection at a demonstrated spiked-standard sensitivity
      would convert the present silence in the published analysis into a real
      negative. This is far cheaper than a new prospective study and should
      precede one.
  - experiment_id: ibm_independent_abeta_oligomer_replication
    name: Independent replication of the Abeta oligomer immunoblot result
    description: >-
      Replication of the Abeta-dimer/trimer/tetramer and ADDL immunoblot
      findings in an independent laboratory with pre-registered antibodies,
      peptide-competition controls, and disease controls that include
      chronically denervated and oculopharyngeal muscular dystrophy muscle
      rather than normal muscle alone.
    would_support:
    - >-
      Reproduction of the oligomer signal in IBM but not in chronic-denervation
      or OPMD controls would restore the hypothesis to ALTERNATIVE status.
    would_refute:
    - >-
      Failure to reproduce the signal, or an equal signal in the chronic-injury
      controls, would confirm the DEPRECATED assessment.
  - experiment_id: ibm_amyloid_burden_versus_progression
    name: Amyloid burden against clinical progression
    description: >-
      Test whether quantified muscle amyloid-beta burden at biopsy predicts
      subsequent rate of functional decline, independently of T cell infiltrate
      density and TDP-43 cryptic exon burden, in a prospectively followed
      cohort.
    would_support:
    - >-
      An association between amyloid burden and subsequent decline that
      survives adjustment for T cell infiltrate density and TDP-43 cryptic exon
      burden would support a causal role even at low fibre frequency.
    would_refute:
    - >-
      No independent association would confirm amyloid as a bystander marker of
      chronic fibre injury.
  evidence:
  - reference: PMID:19533646
    reference_title: "Sarcoplasmic redistribution of nuclear TDP-43 in inclusion body myositis."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The presence of as little as >1% of myofibers with nonnuclear sarcoplasmic
      TDP-43 was highly sensitive (91%) and specific (100%) to IBM among 50
      inflammatory myopathy patient samples
    explanation: >-
      Establishes the marker that displaced amyloid-beta: TDP-43
      mislocalization, not amyloid, carries the diagnostic specificity that the
      amyloid hypothesis claimed.
  - reference: PMID:9781653
    reference_title: "Rimmed vacuoles with beta-amyloid and ubiquitinated filamentous deposits in the muscles of patients with long-standing denervation (postpoliomyelitis muscular atrophy): similarities with inclusion body myositis."
    supports: REFUTE
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The chronicity of the underlying disease, rather than the cause, may lead
      to vacuolar formation, amyloid deposition, and accumulation of
      ubiquitinated filaments.
    explanation: >-
      States the alternative reading directly: amyloid deposition indexes
      chronicity of muscle injury and is therefore not specific to IBM.
  - reference: PMID:20711838
    reference_title: "Novel demonstration of amyloid-β oligomers in sporadic inclusion-body myositis muscle fibers."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Dot-immunoblots using highly specific anti-ADDL monoclonal antibodies also
      showed highly increased ADDLs in all s-IBM biopsies studied, while
      controls were negative.
    explanation: >-
      The unrebutted positive result that keeps the abnormal-presence half of
      this controversy open; note the controls are normal and disease controls
      generally rather than the chronic-injury controls the specificity
      literature identifies as the relevant comparison.
- discussion_id: ibm_muscle_selectivity_unexplained
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Why are the quadriceps and the deep finger flexors selectively vulnerable in
    inclusion body myositis?
  attaches_to:
  - pathophysiology#Progressive Myofibre Degeneration and Selective Muscle Loss
  rationale: >-
    The weakness distribution is the single most reliable diagnostic feature of
    IBM and is unique among muscle diseases, yet no proposed mechanism explains
    it. Neither the HLA-restricted autoimmune arm nor the proteostasis and
    mitochondrial arms predict selective involvement of these particular
    muscles. Selective type 2 myofibre vulnerability and a functional
    denervation program have been demonstrated at the transcriptomic level, but
    these are fibre-type rather than muscle-group explanations and do not
    account for the specific anatomical pattern.
  proposed_experiments:
  - experiment_id: ibm_affected_vs_spared_transcriptomics
    name: Affected-versus-spared muscle transcriptomic comparison
    description: >-
      Comparative single-nucleus and spatial transcriptomics of affected
      (quadriceps, flexor digitorum profundus) versus clinically spared muscles
      sampled from the same patients.
    decision_criterion: >-
      Identification of muscle-group-intrinsic transcriptional programs that
      segregate with clinical involvement independently of fibre type would
      supply the missing determinant of selectivity.
  - experiment_id: ibm_regional_lesion_burden_mapping
    name: Regional molecular lesion burden mapping
    description: >-
      Quantify somatic mtDNA deletion burden and TDP-43 cryptic exon load across
      affected versus spared muscle groups in the same individuals.
    decision_criterion: >-
      A gradient of lesion burden tracking clinical involvement would place the
      selectivity determinant within the degenerative arm rather than the immune
      arm.
  evidence:
  - reference: PMID:38834884
    reference_title: "Cell type mapping of inflammatory muscle diseases highlights selective myofiber vulnerability in inclusion body myositis."
    supports: PARTIAL
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Moreover, causal factors and molecular drivers of IBM progression are
      largely unknown.
    explanation: >-
      Confirms that the molecular drivers underlying IBM progression, including
      the selective pattern of muscle involvement, remain unexplained.
- discussion_id: ibm_no_faithful_animal_model
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  prompt: >-
    Can any available experimental model reproduce sporadic IBM faithfully
    enough to establish drug efficacy, given that no animal model recapitulates
    the combination of HLA-restricted clonal autoimmunity, aging stroma,
    selective muscle distribution and decade-long progression?
  attaches_to:
  - pathophysiology#Clonal Expansion of Highly Differentiated Cytotoxic CD8+ T Cells
  rationale: >-
    VCP-mutant mice model hereditary VCP multisystem proteinopathy, not sporadic
    IBM, and were nonetheless part of the preclinical rationale for arimoclomol,
    which subsequently failed in humans. The human muscle xenograft model is the
    closest available system and reproduces both inflammatory and degenerative
    features, but it is short-term and cannot capture years-long progression.
    Cultured myoblasts cannot recreate chronic HLA-restricted immunity or aging
    stroma. This model gap is a plausible contributor to the repeated
    translational failures in IBM and should temper confidence in any mechanism
    supported only by model-system evidence.
  proposed_experiments:
  - experiment_id: ibm_xenograft_autologous_t_cell_reconstitution
    name: Autologous T cell reconstitution of the IBM muscle xenograft
    description: >-
      Extend the human IBM muscle xenograft model with autologous
      reconstitution of the patient's clonal KLRG1+ T cell population.
    would_support:
    - >-
      De novo emergence of degenerative pathology in previously unaffected
      grafted muscle would establish that the immune arm is sufficient to
      initiate degeneration.
    would_refute:
    - >-
      Absence of new degenerative pathology despite robust T cell engraftment
      would indicate the immune arm is not sufficient.
  - experiment_id: ibm_xenograft_prospective_benchmarking
    name: Prospective xenograft benchmarking of candidate therapies
    description: >-
      Test candidate therapies against the human muscle xenograft model before
      committing to phase 3 trials, using TDP-43 cryptic exon burden as a
      molecular endpoint.
    decision_criterion: >-
      Concordance between xenograft molecular response and subsequent human
      trial outcomes would qualify the model as a translational filter; repeated
      discordance would confirm the model gap.
  evidence:
  - reference: PMID:35044790
    reference_title: "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      To determine the role of T cells in pathogenesis, we generated a xenograft
      model by transplanting human IBM muscle into the hindlimb of
      immunodeficient mice.
    explanation: >-
      Describes the human-muscle xenograft as the model developed precisely
      because no conventional animal model of sporadic IBM exists.
  - reference: PMID:37739573
    reference_title: "Safety and efficacy of arimoclomol for inclusion body myositis: a multicentre, randomised, double-blind, placebo-controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Arimoclomol is an oral co-inducer of the cellular heat shock response that
      was safe and well-tolerated in a pilot study of inclusion body myositis,
      reduced key pathological markers of inclusion body myositis in two
      in-vitro models representing degenerative and inflammatory components of
      this disease, and improved disease pathology and muscle function in mutant
      valosin-containing protein mice.
    explanation: >-
      Documents a case where in-vitro and VCP-mutant-mouse efficacy did not
      translate to human benefit, illustrating the model-fidelity problem.
notes: >-
  Entity boundary: this entry covers sporadic inclusion body myositis
  (MONDO:0007827) only. The hereditary inclusion body myopathies are separate
  diseases with separate entries or scope: GNE myopathy, VCP-associated
  multisystem proteinopathy, and inclusion body myopathy with Paget disease of
  bone and frontotemporal dementia. They share rimmed vacuole and aggregate
  pathology but lack the endomysial inflammation, MHC class I upregulation and
  characteristic weakness distribution of sporadic IBM, and they are monogenic.
  Deep-research reports for this entry were screened for named entity confusion
  against this boundary.

📚

References & Deep Research

Deep Research

2

Claude Code ▸

1. Disease Information

claude-haiku-4-5-20251001, claude-opus-5 20 citations 2026-07-30T15:54:43.995167

1. Disease Information

1.1 Overview

Inclusion body myositis (IBM; sporadic IBM, sIBM) is a slowly progressive, acquired, late-onset skeletal muscle disease and the most common acquired myopathy in people over 50 years of age. It is unique among the idiopathic inflammatory myopathies (IIMs) in combining two co-existing pathological programs in the same myofibres:

an autoimmune/inflammatory arm — endomysial infiltration by highly differentiated cytotoxic CD8⁺ T cells that invade non-necrotic, MHC class I–overexpressing muscle fibres; and
a myodegenerative arm — rimmed vacuoles, protein aggregation (p62/SQSTM1, TDP-43, amyloid-β, ubiquitin), autophagy–lysosome dysfunction, and mitochondrial abnormalities (COX-negative fibres, mtDNA deletions).

Whether these arms are causally sequential (inflammation → degeneration), independent, or reciprocally reinforcing is the central unresolved question of IBM pathogenesis — an ideal candidate for a mechanistic_hypotheses block with competing hypothesis_group_id values in the KB entry.

MONDO definition (verified with OAK, sqlite:obo:mondo):

"A slowly progressive degenerative inflammatory disorder of skeletal muscles characterized by late onset weakness of specific muscles and distinctive histopathological features." — MONDO:0007827 def: (source Orphanet:611)

The clinical signature is a highly stereotyped, asymmetric, selective weakness pattern: quadriceps femoris (knee extension) and deep finger flexors (flexor digitorum profundus), with early dysphagia and ankle dorsiflexor involvement. This pattern is so characteristic that it forms the backbone of every published diagnostic criteria set.

IBM is refractory to all conventional immunosuppression — a defining and clinically important negative feature that distinguishes it from dermatomyositis, immune-mediated necrotizing myopathy, and polymyositis, and that motivates the "degeneration-primary" hypothesis.

1.2 Key identifiers (all verified from the MONDO:0007827 record via OAK)

Resource	Identifier
Mondo	`MONDO:0007827` — inclusion body myositis
OMIM	`OMIM:147421` (⚠️ note: this is a phenotype/HLA-association entry, not a Mendelian gene entry)
Orphanet	`ORPHA:611`
ICD-10-CM	`G72.41`
ICD-9-CM	`359.71` (also cross-referenced `729.1`)
MeSH	`D018979` (Myositis, Inclusion Body)
SNOMED CT	`72315009`
UMLS	`C0238190`
NCIT	`NCIT:C84786`
DOID	`DOID:3429`
EFO	`EFO:0007323`
MedGen	`68659`
MedDRA	`10066407`
GARD	`0003896`
NORD	`1734`
NANDO	`1200032`, `1200218`
MONDO parent	`is_a: MONDO:0021167` (myositis disease)
ICD-11	Not carried as a MONDO xref — believed to be under `4A41` (idiopathic inflammatory myopathies). Verify against the ICD-11 browser before asserting a specific code.

MONDO subset: flags include rare, orphanet_rare, nord_rare, gard_rare — IBM is formally a rare disease despite being the commonest myopathy of the elderly.

1.3 Synonyms (verified `synonym:` lines from MONDO)

IBM (EXACT; OMIM:147421, Orphanet:611)
Sporadic Inclusion Body Myositis (EXACT; NORD:1734, Orphanet:611)
sIBM (EXACT; Orphanet:611)
sporadic inclusion body myositis (EXACT; Orphanet:611)
"inflammatory myopathy" (RELATED; GARD — too broad; do not use as an exact synonym)

Historic/literature synonyms not in MONDO: inclusion body myositis, sporadic type; sIBM. Historic misnomer to avoid: "polymyositis with inclusion bodies."

1.4 Information provenance

Information for this entry is predominantly aggregated disease-level (Orphanet, OMIM, ENMC consensus workshops, systematic reviews, registry/cohort studies). Two important individual-patient / EHR-derived sources exist and should be tagged as such:

Rochester Epidemiology Project (REP) medical-records-linkage system, Olmsted County and 27 Minnesota/Wisconsin counties — the source of both the 2008 and 2021 US population-based epidemiology figures. This is genuine EHR-linkage data.
Swedish national cohort (Lindgren et al., Ann Neurol 2022 ✅ PMID:35596584) — national registry/biopsy-registry derived.
MYOGEN / MYOVISION consortia — patient-level genotype data underpinning the HLA association work.

2. Etiology

2.1 Overall causal model

IBM has no single established cause. It is best modeled in the KB as a multifactorial, age-dependent disease in which a permissive genetic background (dominantly HLA class II) plus profound age-associated immune remodeling (immunosenescence) permits a chronic, oligoclonal, cytotoxic T-cell attack on skeletal muscle, superimposed on (or triggering) a cell-autonomous proteostatic/mitochondrial failure in aging myofibres.

Two competing high-level hypotheses should be curated explicitly as mechanistic_hypotheses with status: EMERGING / ALTERNATIVE:

Hypothesis id (suggested)	Claim	Principal supporting evidence
`autoimmune_primary`	IBM is fundamentally an autoimmune T-cell disease; degeneration is a downstream consequence of chronic cytotoxic attack and MHC-I–driven ER stress.	Oligoclonal, persistent, highly differentiated KLRG1⁺/CD57⁺ CD8⁺ T cells; HLA-DRB1*03:01 as the single strongest genetic risk factor; anti-cN1A autoantibodies; T-LGL leukaemia overlap. Greenberg SA, Nat Rev Rheumatol 2019 ✅ PMID:30837708
`degeneration_primary`	A cell-autonomous myodegenerative process (proteostasis/autophagy/mitochondrial failure with TDP-43 loss-of-function) drives disease; inflammation is secondary/amplifying.	In the IBM xenograft model, rimmed vacuoles and TDP-43 loss-of-function persisted after T-cell depletion; complete failure of every immunosuppressive therapy tried. Britson KA et al., Sci Transl Med 2022 ✅ PMID:35044790

The Britson xenograft result is the single most probative experiment currently available and should be curated as an explicit edge-level qualifier: T-cell depletion in the model did not rescue the degenerative arm.

2.2 Genetic risk factors

IBM is not a Mendelian disease and has no established causal gene. Risk is conferred by common-variant susceptibility loci, overwhelmingly in the MHC.

Locus / allele	Effect	Citation
*`HLA-DRB103:01` (`hgnc:4948`) on the 8.1 ancestral haplotype** (HLA-A01:01–B08:01–C07:01–DRB103:01–DRB301:01–DQA105:01–DQB1*02:01)	The single strongest genetic risk factor for IBM. High-resolution typing refines the signal to `DRB103:01:01`; reported ~14-fold* increased risk in carriers, with onset ~5 years earlier.	Rothwell S et al., Arthritis Rheumatol 2017 ✅ PMID:28086002; high-resolution refinement, J Autoimmun 2024 ✅ PMID:38043487
DRβ1 position 74	Arginine-74 confers the allelic risk; glutamine-74 is protective — an amino-acid-level, peptide-binding-groove mechanism (a genuine protective genetic factor for IBM).	✅ PMID:38043487
`HLA-DRB101:01`, `HLA-DRB113:01`	Additional independent HLA-DRB1 associations identified by imputation from GWAS SNP data in the MYOGEN Caucasian cohort.	✅ PMID:28086002
Complement `C4A` (`hgnc:1323`) low copy number / C4A deficiency	Low `C4` and `C4A` copy number are risk factors for myositis and its subgroups — the 8.1 AH itself carries a C4A-null allele, so this may be haplotype-linked rather than independent.	Zhou D et al., Ann Rheum Dis 2023 ✅ PMID:36171069
Non-MHC loci	No robustly replicated genome-wide-significant non-MHC locus has been established for IBM. Candidate reports (e.g. `FYCO1`, `hgnc:14673`, an autophagy adaptor) are not confirmed and should be curated, if at all, with `supports: PARTIAL` and an explicit knowledge-gap discussion.	—

A note for curation: NT5C1A (hgnc:17819, encoding cN1A / Mup44) is the autoantigen, not a risk gene. Do not model it as a causal gene; model it as an antigen target with relationship_type reflecting autoantigen status, and curate the antibody as a biomarker.

Familial clustering: Rare familial aggregation of sporadic-type IBM has been reported ("familial inflammatory IBM"), but this is distinct from the hereditary inclusion body myopathies. There is no established inheritance pattern.

2.3 Environmental / acquired risk factors

Factor	Direction	Confidence
Age > 50 years (peak onset 60s–70s)	Strong risk	Established — the dominant risk factor
Male sex	Risk (M:F ≈ 2:1 to 3:1 in most cohorts)	Established
Northern European / Caucasian ancestry	Higher reported prevalence — but confounded by ascertainment and by 8.1 AH frequency, which itself tracks northern European ancestry	Moderate
HIV-1 infection	HIV-associated IBM-like myopathy is described; whether it is true IBM or a phenocopy is unsettled	Weak/uncertain
HTLV-1 infection	HTLV-1–associated inflammatory myopathy with IBM-like features reported in endemic regions	Weak/uncertain
Hepatitis C virus	Association reported in some case series	Weak
Statin exposure	Repeatedly raised as a possible unmasking/triggering factor; not established; a statin-associated IBM-like presentation is a recognized diagnostic confounder	Weak — curate as a `KNOWLEDGE_GAP` discussion rather than an asserted risk factor
Prior malignancy	Notably, cancer incidence in sIBM did not differ from the general population (paraphrase — needs exact quote) — unlike dermatomyositis, IBM is not a paraneoplastic disease.	✅ PMID:33879596

There is no established occupational, dietary, toxic, or radiation exposure for IBM. This is an honest "not available" for the entry.

2.4 Protective factors

Genetic: DRβ1 glutamine at position 74 is reported protective (✅ PMID:38043487). This is a rare, well-specified genetic protective factor and is worth curating explicitly.
Environmental: No validated environmental protective factor. Exercise (see §12) improves function but there is no evidence it prevents disease onset.

2.5 Gene–environment interactions

The most plausible G×E model — and one that should be curated as a hypothesis, not a fact — is that HLA-DRB1*03:01-restricted presentation of a self- or pathogen-derived peptide to CD8⁺ T cells, in the setting of age-related immunosenescence and possible chronic viral (CMV/EBV/HIV) antigenic pressure, drives the clonal expansion of terminally differentiated cytotoxic effectors that characterize IBM. Chronic CMV infection is a canonical driver of the CD28⁻/CD57⁺/KLRG1⁺ effector-memory phenotype seen in IBM blood and muscle, making CMV serostatus a natural G×E investigation target. No confirmatory human study establishes this chain — curate as KNOWLEDGE_GAP with proposed_experiments.

3. Phenotypes

3.1 Cardinal motor phenotypes

All HP identifiers below were verified with OAK (sqlite:obo:hp).

Phenotype	HPO term	Typical frequency	Notes
Quadriceps muscle weakness	`HP:0003731` Quadriceps muscle weakness	Near-universal (~90–100%)	The defining proximal feature; knee-extension weakness disproportionate to hip flexion. Causes buckling and falls.
Finger flexor weakness (flexor digitorum profundus)	`HP:0031177` Finger flexor weakness	~65–90%	The single most specific clinical sign; grip weakness with relative preservation of finger extension. Often asymmetric.
Distal muscle weakness	`HP:0002460` Distal muscle weakness; consider `HP:0009063` Progressive distal muscle weakness	Common	Distinctive: IBM has combined proximal and distal weakness, unlike most myopathies.
Ankle dorsiflexor weakness / foot drop	`HP:0003376` Steppage gait	~30–50%	Tibialis anterior involvement (`UBERON:0001385`).
Frequent falls	`HP:0002359` Frequent falls (or `HP:0002527` Falls)	Very frequent	Direct consequence of quadriceps weakness; a major driver of morbidity and of fracture/head-injury complications.
Quadriceps muscle atrophy	`HP:0009050` Quadriceps muscle atrophy	Frequent	Visible thigh and forearm (volar) wasting.
Asymmetry of weakness	No single ideal HP term; describe in prose	Characteristic	Left–right asymmetry is a positive diagnostic feature and is unusual among myopathies.

Suggested descriptor qualifiers (per repo conventions): use clinical_course: PROGRESSIVE and temporality: CHRONIC on the weakness descriptors, and onset with onset_category reflecting late-adult onset.

3.2 Bulbar phenotypes

Phenotype	HPO term	Frequency	Notes
Dysphagia	`HP:0002015` Dysphagia; more specifically `HP:0200136` Oral-pharyngeal dysphagia or `HP:0002068` Neuromuscular dysphagia	~40–80%; ~64% in a Mayo/REP cohort; ~2/3 in the 40-year population study	Cricopharyngeal dysfunction with failure of upper-oesophageal-sphincter relaxation. The dominant driver of mortality via aspiration. Anti-cN1A positivity is associated with more severe dysphagia.
Feeding-tube dependence	consider `HP:0011968` Feeding difficulties + prose	Substantial minority (reported ~half in the REP cohort — verify this figure carefully, it is unusually high vs other series)	Gastrostomy (`MAXO:0001346`)
Facial weakness (mild)	`HP:0000317`-family / `HP:0030319` Weakness of facial musculature	Mild, in a minority	Severe facial weakness argues against IBM.

Citations: ✅ PMID:33879596 (natural history/REP); Lindgren U et al. ✅ PMID:35596584; anti-cN1A/dysphagia association (PMC8151681 — resolve to a PMID before citing).

3.3 Laboratory phenotypes

Phenotype	HPO term	Detail
Elevated serum creatine kinase	`HP:0003236` Elevated circulating creatine kinase concentration; often better captured by `HP:0008180` Mildly elevated creatine kinase	CK is normal to modestly elevated, typically <10–12× ULN and often <1000 U/L. A CK >2000 U/L should prompt reconsideration of the diagnosis. LOINC: 2157-6 (Creatine kinase [Enzymatic activity/volume] in Serum or Plasma).
Anti-cN1A (anti-NT5C1A) autoantibody positivity	`HP:0030057` Autoimmune antibody positivity (generic; no IBM-specific HP term exists — a genuine HPO gap worth noting)	See §10.2 for performance characteristics.
Autoimmunity (co-occurring)	`HP:0002960` Autoimmunity	Sjögren syndrome, sarcoidosis, autoimmune thyroid disease, and T-cell large granular lymphocytic leukaemia co-occur at elevated rates.

3.4 Electrophysiological phenotypes

Phenotype	HPO term	Detail
Myopathic EMG	`HP:0003458` EMG: myopathic abnormalities	Short-duration, low-amplitude, polyphasic motor unit potentials. Short MUP duration correlated with all clinical measures in a 50-patient series ✅ PMID:34617994.
Mixed myopathic/"neurogenic-appearing" units	prose	Long-duration, high-amplitude units co-exist in IBM (chronic myopathy with fibre splitting/regeneration) and are a classic pitfall leading to misdiagnosis as motor neuron disease.
Fibrillations/positive sharp waves	`HP:0030007`-family; consider prose	Common — reflects active fibre necrosis and denervation of split fibres.

3.5 Histopathological phenotypes (biopsy-defined)

Phenotype	HPO term	Detail
Rimmed vacuoles	`HP:0003805` Rimmed vacuoles	Basophilic-rimmed autophagic vacuoles on modified Gomori trichrome. Specific but not sensitive — absent in a substantial fraction of clinically definite IBM biopsies, especially early.
Cytochrome c oxidase–negative muscle fibres	`HP:0003688` Cytochrome C oxidase-negative muscle fibers	Reported as the second most common histopathological finding in IBM; in inflammatory myopathy without rimmed vacuoles, COX-deficient fibres were reported 100% sensitive and 73% specific for IBM (paraphrase — needs exact quote and primary-source PMID). Associated with somatic mtDNA deletions.
Ragged-red fibres	`HP:0003200` Ragged-red muscle fibers	Mitochondrial pathology marker.
Increased endomysial connective tissue	`HP:0100297` Increased endomysial connective tissue	Endomysial fibrosis with disease progression.
Endomysial CD8⁺ T-cell infiltration invading non-necrotic MHC-I⁺ fibres	No HP term; curate as pathophysiology + `histopathology`	The defining immunopathological lesion.
p62/SQSTM1⁺, TDP-43⁺, ubiquitin⁺, amyloid-β⁺ cytoplasmic inclusions	No HP term; curate as pathophysiology	See §6. Note Greenberg's caution that aggregates are present in <1% of myofibres — a quantitative argument against aggregate-primacy.

3.6 Phenotype characteristics summary

Age of onset: adult/late-onset; mean onset ~60–70 years; onset before 45 is rare and should trigger reconsideration. HPO onset term: HP:0003584 Late onset (verify) or HP:0003581 Adult onset.
Severity: moderate → severe over decades; universally disabling if survival is long enough.
Progression: relentlessly progressive; never episodic, never relapsing-remitting, spontaneous remission essentially unreported.
Frequency among affected individuals: quadriceps and finger-flexor weakness near-universal by the time of diagnosis; dysphagia in the majority eventually.

3.7 Quality-of-life impact (per phenotype)

Quadriceps weakness → loss of stair climbing, rising from a chair, and independent ambulation; falls and fall-related fractures; median time to wheelchair dependence ≈ 10.5 years (range 1–29) ✅ PMID:33879596. Other series quote wheelchair dependence "on average, 12–20 years after onset" ✅ PMID:25215417.
Finger flexor weakness → loss of grip: buttons, keys, jar opening, writing, holding utensils; disproportionate impact on independence relative to strength loss.
Dysphagia → aspiration fear, meal-time anxiety, social withdrawal from eating, weight loss, PEG dependence; the phenotype most strongly linked to mortality.
No IBM-specific QoL instrument is standard. Instruments used: IBMFRS (IBM Functional Rating Scale) — the field's primary functional outcome and the primary endpoint in the ulviprubart and sirolimus trials; SF-36; HAQ; 6-minute walk distance (6MWD) — primary endpoint of RESILIENT. See ✅ PMID:22588740 (Arthritis Care Res 2011 myositis outcome-measures compendium) for the catalogue.

4. Genetic / Molecular Information

4.1 Causal genes

None. IBM has no causal gene and no established Mendelian inheritance. This should be stated affirmatively in the entry — it is the key discriminator from the hereditary inclusion body myopathies. OMIM:147421 exists but describes an HLA-associated susceptibility phenotype, not a gene–disease relationship. There is no ClinGen Gene-Disease Validity assertion establishing a definitive gene for sporadic IBM (a CGGV: query is worth running to confirm and to cite the absence).

4.2 Susceptibility / risk genes (curate with `relationship_type: SUSCEPTIBILITY`)

Gene	HGNC (OAK-verified)	Role
`HLA-DRB1`	`hgnc:4948`	`*03:01:01` risk allele; DRβ1 Arg74 risk / Gln74 protective
`C4A`	`hgnc:1323`	Low copy number / null allele — myositis risk (8.1-AH-linked)
`NT5C1A`	`hgnc:17819`	Autoantigen (cN1A/Mup44), not a risk gene — curate as antigen
`TARDBP`	`hgnc:11571`	Encodes TDP-43; not mutated in sIBM — the pathology is mislocalization/loss-of-function, not a coding variant
`SQSTM1`	`hgnc:11280`	Encodes p62; aggregate constituent, not mutated in sIBM
`APP`	`hgnc:620`	Amyloid-β precursor; aggregate constituent, not mutated in sIBM
`KLRG1`	`hgnc:6380`	Marker of the pathogenic T-cell population and the therapeutic target of ulviprubart
`MSTN`	`hgnc:4223`	Myostatin — therapeutic target (ActRII/bimagrumab axis), not a risk gene
`STAT3`	`hgnc:11364`	Somatic gain-of-function mutations in the clonally expanded LGL population (see §4.5)

Genes to explicitly exclude (NEC guard, curate as notes or a discussions entry): GNE (hgnc:23657) and VCP (hgnc:12666) cause hereditary inclusion body myopathies, not IBM.

4.3 Pathogenic variants

Not applicable in the ACMG/AMP sense — there are no pathogenic germline variants for IBM. The relevant genetic architecture is common HLA haplotype variation with population allele frequencies available in the Allele Frequency Net Database and gnomAD (HLA imputation). HLA-DRB1*03:01 carrier frequency in northern European populations is roughly 20–25%, consistent with a common susceptibility allele of moderate-to-large effect rather than a rare pathogenic variant.

4.4 Somatic genetic changes

Mitochondrial DNA deletions — clonally expanded, large-scale mtDNA deletions accumulate in COX-negative myofibre segments. These are somatic, muscle-restricted, and clonally expanded within individual fibre segments, closely resembling the mtDNA pathology of normal aging muscle but present in far greater abundance. This is a genuine somatic-mutation mechanism worth its own pathophysiology node.
STAT3 gain-of-function somatic mutations in circulating clonal large granular lymphocytes (see §4.5).

4.5 The IBM / T-LGL leukaemia overlap (a major, under-appreciated finding)

Greenberg SA et al., Brain 2016 ✅ PMID:26920676 reported that:

"Most (22 of 38; 58%) patients with inclusion body myositis had aberrant populations of large granular lymphocytes in their blood meeting standard diagnostic criteria for T cell large granular lymphocytic leukaemia, and these T cell populations were clonal in 20 of 20 patients and stably present on follow-up testing." (candidate quote — verify verbatim)

STAT3 gain-of-function mutations, the molecular hallmark of T-LGL leukaemia, are present in ~21–75% of T-LGL cohorts and drive constitutive STAT3 activation → enhanced survival and defective activation-induced cell death of the cytotoxic clone. This provides a mechanistically satisfying explanation for why the IBM T-cell attack is persistent and immunosuppression-resistant: the effector cells are a long-lived, apoptosis-resistant clone, not a conventional activated T-cell response. This deserves an explicit pathophysiology node and should be linked to a comorbidity entry for T-LGL leukaemia.

4.6 Modifier genes

HLA-DRB1*03:01:01 acts as an age-of-onset modifier (~5 years earlier onset in carriers) ✅ PMID:38043487 — a clean MODIFIER relationship.
Anti-cN1A antibody status behaves as a severity modifier (more severe dysphagia, possibly worse survival) but is serological, not genetic.

4.7 Epigenetics

No robust, replicated DNA-methylation or histone-modification signature is established for IBM. Muscle transcriptomic studies consistently show a type II interferon (IFN-γ) signature rather than the type I IFN signature of dermatomyositis — this is transcriptional, not confirmed epigenetic. Honest gap: not available; curate as KNOWLEDGE_GAP.

4.8 Chromosomal abnormalities

None associated with IBM. CMA/karyotype/FISH have no diagnostic role. Explicitly "not applicable."

5. Environmental Information

Environmental toxins / occupational exposure / radiation: No established association. CTD/TOXNET yield no validated IBM-toxicant links. Not available.
Lifestyle factors: No established dietary, smoking, or alcohol association. Physical inactivity worsens deconditioning but is not aetiological.
Drugs: Statins are the recurrently discussed but unproven exposure (see §2.3). Statin-associated autoimmune myopathy (anti-HMGCR) is a distinct entity and a key differential.
Infectious agents (all speculative/associative, none causal):
HIV-1 (NCBITaxon:11676) — HIV-associated IBM-like myopathy
HTLV-1 (NCBITaxon:11908) — HTLV-1–associated inflammatory myopathy with IBM features
HCV (NCBITaxon:11103) — reported association
Human cytomegalovirus (NCBITaxon:10359) — not causal, but the canonical driver of the terminally differentiated CD8⁺CD28⁻CD57⁺KLRG1⁺ T-cell compartment that IBM's effector cells resemble; mechanistically the most interesting candidate for a G×E study.

Curate these with supports: PARTIAL or as discussions — none meets a causal-agent bar.

6. Mechanism / Pathophysiology

6.1 Proposed causal chain (upstream → downstream)

Below is a node chain suitable for direct translation into pathophysiology: entries, with biological_scale: tags per the repo's single-value discipline.

Node 1 — Permissive genetic background and immunosenescence (biological_scale: ORGANISM) HLA-DRB103:01:01 (Arg74 in the DRβ1 peptide-binding groove) + age-associated contraction of the naïve T-cell repertoire and expansion of terminally differentiated effectors. → downstream:* Node 2

Node 2 — Clonal expansion of highly differentiated cytotoxic CD8⁺ T cells (biological_scale: CELLULAR) CD8⁺CD57⁺CD28⁻KLRG1⁺ effector-memory/TEMRA cells with NK-like features; oligoclonal by TCR sequencing; persistent over years; frequently meeting T-LGL leukaemia criteria; STAT3-GOF-driven resistance to activation-induced cell death. - Cell type: CL:0000794 CD8-positive, alpha-beta cytotoxic T cell - GO: GO:0001913 T cell mediated cytotoxicity; GO:0043316 cytotoxic T cell degranulation - Gene: KLRG1 (hgnc:6380), STAT3 (hgnc:11364) → downstream: Node 4

Node 3 — Myofibre MHC class I overexpression (biological_scale: CELLULAR) IFN-γ–driven, widespread sarcolemmal and sarcoplasmic MHC-I upregulation on non-necrotic fibres — both the antigen-presentation substrate and, independently, a cell-intrinsic ER stressor. - Cell type: CL:0008002 skeletal muscle fiber - GO: GO:0002484 antigen processing and presentation of endogenous peptide antigen via MHC class I via ER pathway → downstream: Nodes 4 and 5

Node 4 — Cytotoxic invasion of non-necrotic myofibres (biological_scale: CELLULAR) Perforin/granzyme-mediated attack; the pathognomonic "partial invasion" lesion. Accompanied by endomysial macrophages (CL:0000235) and plasma cells (CL:0000786; local Ig production supports a B-cell/plasma-cell arm and the origin of anti-cN1A). - GO: GO:0001913 T cell mediated cytotoxicity → downstream: Node 8

Node 5 — ER stress / unfolded protein response (biological_scale: MOLECULAR) MHC-I overload and misfolded-protein burden activate the UPR (PERK/ATF6/IRE1), amplifying NF-κB signalling and further MHC-I expression — a feed-forward loop. - GO: GO:0034976 response to endoplasmic reticulum stress → downstream: Nodes 6 and 3 (feedback edge)

Node 6 — Autophagy–lysosome pathway failure and protein aggregation (biological_scale: CELLULAR) Impaired autophagic flux and chaperone-mediated autophagy; accumulation of p62/SQSTM1, ubiquitin, LC3, amyloid-β/APP-derived species, and phosphorylated tau in aggregates; formation of rimmed vacuoles (autophagic vacuoles with myeloid debris). - GO: GO:0006914 autophagy; GO:0061684 chaperone-mediated autophagy; GO:0070841 inclusion body assembly; GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process; GO:0042026 protein refolding (the arimoclomol/HSP rationale) - Genes/proteins: SQSTM1 (hgnc:11280), APP (hgnc:620) - Phenotype: HP:0003805 Rimmed vacuoles → downstream: Node 8

Greenberg's caveat to curate honestly: aggregates are present in "<1% of myofibres in patients with IBM" ✅ PMID:30837708 (candidate quote — verify), which is a strong quantitative argument that aggregates are a marker rather than the primary driver.

Node 7 — TDP-43 nuclear clearance, cytoplasmic aggregation, and loss of splicing repression (biological_scale: MOLECULAR) Nuclear loss + cytoplasmic mislocalization of TDP-43 (TARDBP, hgnc:11571) with cryptic exon inclusion in TDP-43 target transcripts — a molecular convergence with ALS/FTD. This is now the most mechanistically specific molecular lesion in IBM and a candidate biomarker (cryptic-exon-derived peptides/transcripts). - Critically: in the xenograft model, "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion" ✅ PMID:35044790 — i.e., this arm is at least partly T-cell–independent. → downstream: Node 8

Node 8 — Mitochondrial dysfunction (biological_scale: CELLULAR) COX-negative fibres, ragged-red fibres, clonally expanded somatic mtDNA deletions, impaired oxidative phosphorylation, ROS generation. Mechanistically linked to TDP-43 (TDP-43 associates with mitochondria and its dysfunction impairs mitochondrial function) and plausibly to chronic inflammatory/nitrosative stress. - Phenotypes: HP:0003688 Cytochrome C oxidase-negative muscle fibers; HP:0003200 Ragged-red muscle fibers - GO: GO:0000422 autophagy of mitochondrion (mitophagy) → downstream: Node 9

Node 9 — Myofibre degeneration, atrophy, and failed regeneration (biological_scale: TISSUE) Fibre necrosis, atrophy, splitting, endomysial fibrosis (HP:0100297), and exhaustion/impaired activation of satellite cells (CL:0000594 skeletal muscle satellite cell; CL:0008016 activated skeletal muscle satellite cell). Fatty and fibrous replacement visible on MRI. - GO: GO:0043403 skeletal muscle tissue regeneration → downstream: Node 10

Node 10 — Selective, asymmetric muscle weakness and dysphagia (biological_scale: ORGANISM) Clinical phenotype (§3). Why quadriceps and FDP are selectively vulnerable remains unexplained — an excellent, well-defined KNOWLEDGE_GAP for the entry.

6.2 Molecular pathways

IFN-γ / JAK-STAT1 — the dominant muscle transcriptomic signature (type II IFN, distinguishing IBM from the type I IFN signature of dermatomyositis). KEGG hsa04630, Reactome "Interferon gamma signaling."
NF-κB — downstream of ER stress and inflammatory cytokines; drives MHC-I and cytokine expression.
mTOR / autophagy — the rationale for sirolimus; mTORC1 inhibition promotes autophagic clearance and preferentially spares/expands regulatory T cells while depleting effector-memory T cells.
Heat-shock response / proteostasis — the rationale for arimoclomol (HSP co-inducer).
Myostatin–ActRII–SMAD2/3 — the rationale for bimagrumab (anti-ActRII antibody), aimed at the atrophy arm rather than causation.
TDP-43 splicing repression / cryptic exon inclusion — shared with ALS/FTD.
STAT3 — clonal LGL survival.

6.3 Cell types involved (CL terms, OAK-verified)

Cell type	CL term	Role
CD8⁺ αβ cytotoxic T cell	`CL:0000794`	Primary effector; KLRG1⁺CD57⁺CD28⁻ terminally differentiated subset
Skeletal muscle fibre	`CL:0008002`	Target cell; MHC-I⁺, aggregate-bearing, vacuolated
Macrophage	`CL:0000235`	Endomysial infiltrate component
Plasma cell	`CL:0000786`	Local Ig/autoantibody production in muscle
Skeletal muscle satellite cell	`CL:0000594` (also `CL:0008016` activated)	Failed/exhausted regeneration

6.4 Anatomical and subcellular localization

Tissue: UBERON:0001134 skeletal muscle tissue (verify exact ID before use — OAK returned UBERON:0014892 skeletal muscle organ, vertebrate for the organ-level query); UBERON:0004498 skeletal muscle tissue of quadriceps femoris; UBERON:0004499 skeletal muscle tissue of tibialis anterior; UBERON:0001523 flexor digitorum profundus; UBERON:0000933 chordate pharyngeal muscle.
Subcellular (GO CC): sarcoplasm/cytoplasm, GO:0005634 nucleus (TDP-43 clearance), GO:0005739 mitochondrion, GO:0005764 lysosome / GO:0005776 autophagosome, GO:0005783 endoplasmic reticulum, GO:0016235 aggresome (verify), GO:0042612 MHC class I protein complex (verify).

6.5 Molecular profiling

Transcriptomics: Muscle RNA-seq consistently shows a type II interferon-dominant signature with strong upregulation of MHC-I/II, immunoproteasome subunits, chemokines (CXCL9/10), and Ig genes; plus downregulation of oxidative-phosphorylation and mitochondrial transcripts. Search GEO for sporadic inclusion body myositis muscle series to populate a datasets: block.
Cryptic exon transcriptomics: TDP-43 loss-of-function–dependent cryptic exons are detectable in IBM muscle (✅ PMID:35044790) — the most disease-specific transcriptomic readout available.
Proteomics: Aggregate-enriched proteomics identifies p62, TDP-43, ubiquitin, amyloid-β, phosphorylated tau, myotilin, αB-crystallin, and cN1A. PRIDE/ProteomeXchange hold relevant datasets.
Single-cell / TCR-seq: scRNA-seq + TCR-seq of muscle-infiltrating and blood T cells is the most active current frontier and directly underpins the KLRG1-targeting therapeutic strategy. Frontiers Immunol 2023 study of expanded CD8⁺ LGLs in IBM correlates T-cell phenotype with disease severity (PMC10098158 — resolve to PMID before citing).
Metabolomics/lipidomics: Not available — no established IBM signature.

7. Anatomical Structures Affected

Organ level

Primary organ: skeletal muscle (UBERON:0014892 skeletal muscle organ, vertebrate). Body system: musculoskeletal.
Secondary/complication organs: lung (aspiration pneumonia, respiratory failure — the leading cause of death); pharynx/upper oesophagus (cricopharyngeus); rarely heart (cardiac involvement is not a feature of IBM — an important negative); peripheral nerve is spared (nerve conduction studies are normal).

Selective muscle involvement — the diagnostic signature

Muscle	UBERON	Involvement
Quadriceps femoris	`UBERON:0001377` (tissue: `UBERON:0004498`)	Severe, early. On MRI, vastus lateralis and vastus intermedius are affected earliest and most severely while rectus femoris is relatively spared — an MRI signature of high diagnostic value.
Flexor digitorum profundus	`UBERON:0001523`	Severe, early; highly specific
Tibialis anterior	`UBERON:0001385` (tissue: `UBERON:0004499`)	Frequent (foot drop)
Pharyngeal / cricopharyngeal muscle	`UBERON:0000933` chordate pharyngeal muscle	Dysphagia
Relatively spared: deltoid, finger extensors, facial muscles (mild at most), ocular muscles (never — ophthalmoparesis excludes IBM), cardiac muscle	—	Negative discriminators

Lateralization

Asymmetric — a positive diagnostic feature. Weakness is characteristically worse on one side, unusual for a myopathy and a reason IBM is frequently misdiagnosed as motor neuron disease or a radiculopathy.

Tissue/cell level

Striated skeletal muscle tissue; myofibres (CL:0008002) as targets; endomysial compartment as the site of the inflammatory infiltrate (endomysial, not perimysial or perivascular — the latter patterns indicate dermatomyositis). Satellite cells (CL:0000594) show impaired regenerative capacity.

Subcellular

Nucleus (TDP-43 clearance), cytoplasm/sarcoplasm (aggregates), lysosome/autophagosome (rimmed vacuoles), mitochondria (COX-negative segments, mtDNA deletions), ER (UPR), sarcolemma (MHC-I).

8. Temporal Development

Onset

Typical age: adult/late — most series report mean onset ~60–70 years; onset before age 45 is distinctly unusual.
Onset pattern: insidious, over months to years. Patients typically report a long prodrome of falls, difficulty rising from chairs, or dropping objects.
Diagnostic delay: notoriously long — commonly 5+ years from symptom onset to diagnosis, because early asymmetric weakness is misattributed to orthopaedic causes, radiculopathy, or motor neuron disease.

Progression

Course: relentlessly, slowly progressive; never relapsing-remitting; spontaneous remission not described.
Rate: IBMFRS declines ~1–2 points/year in natural-history and placebo-arm data; quantitative strength declines ~3–5%/year. Slow enough that trials require 12–20+ months and large N to detect an effect — the central trial-design problem in IBM.
Milestones: median time to wheelchair dependence 10.5 years (range 1–29) ✅ PMID:33879596; other cohorts report 12–20 years ✅ PMID:25215417. Assistive-device use typically precedes this by several years.
Duration: chronic, lifelong.
Staging: No formal consensus staging system. The 272nd ENMC workshop (✅ PMID:38522330) explicitly addressed clinical trial readiness and outcome measures; the working stratification used in trials is mild/moderate vs advanced disease, and the ulviprubart MUSCLE result (§12) makes this stratification clinically consequential.

Patterns

Remission: none, spontaneous or treatment-induced. This is a defining negative.
Critical window: The strongest current signal for a therapeutic window is the MUSCLE trial's mild-to-moderate subgroup, where ulviprubart showed favourable trends absent in the full population — supporting a "treat early, before irreversible fibro-fatty replacement" model. Curate this as an emerging hypothesis, not an established fact.

9. Inheritance and Population

9.1 Epidemiology

Measure	Estimate	Source
Prevalence, ≥50 years (US, Olmsted/REP, 2010)	18.20 per 100,000 people ≥50 years old	✅ PMID:33879596 (candidate quote — verify)
Prevalence, all-ages (US, REP, age/sex-adjusted)	7.06 per 100,000 (95% CI 0.87–13.24)	✅ PMID:18203321 / REP series
Incidence, all-ages (US, REP, age/sex-adjusted)	0.79 per 100,000/year (95% CI 0.24–1.35)	✅ PMID:18203321
Older/lower literature estimates	incidence ~0.22/100,000; prevalence 0.49–1.07/100,000	Historical — underestimates due to under-ascertainment; do not present as current
IIM group context	Incidence of inflammatory myopathies 1.16–19 per million/year; prevalence 2.4–33.8 per 100,000	Meyer A et al., Rheumatology 2015 ✅ PMID:25065005
Sweden, national cohort	Epidemiology, survival, and clinical characteristics reported nationally	Lindgren U et al., Ann Neurol 2022 ✅ PMID:35596584

Curation guidance: use the structured Prevalence slots. For the 18.20/100,000 figure: population: "United States (Olmsted County/REP), adults ≥50 years", measure_type: POINT_PREVALENCE, prevalence_class: BAND_1_5_PER_10000 (18.2/100,000 = 1.82/10,000 → falls in the 1–5/10,000 band), rate_per_100000: 18.2. For the all-ages figure: rate_per_100000: 7.06, rate_low: 0.87, rate_high: 13.24, prevalence_class: BAND_1_9_PER_100000. Never compare the ≥50 figure to the all-ages figure — different denominators.

Notably, prevalence of sIBM correlated with the population frequency of HLA-DR3 across studies (✅ PMID:25065005) — an elegant ecological confirmation of the 8.1-AH association and worth curating.

9.2 Inheritance

Inheritance pattern: Not Mendelian. Multifactorial/complex, with a dominant common-variant HLA contribution. Do not assign an HPO mode-of-inheritance term implying Mendelian transmission. If any inheritance block is used, HP:0010982 Polygenic inheritance with relationship_type: SUSCEPTIBILITY gene typing is the most defensible, and even that overstates the evidence — consider omitting the inheritance: block entirely and stating the absence in notes.
Penetrance / expressivity / anticipation / mosaicism / consanguinity / carrier frequency: Not applicable. Explicitly state this; these are the fields DR tools most often hallucinate for IBM by importing GNE-myopathy content.
Founder effects: None for IBM. (Founder effects do exist for GNE myopathy — e.g. the Persian-Jewish M712T founder allele — and this is a classic NEC contamination vector. Do not import it.)

9.3 Population demographics

Sex ratio: male predominance, ~2:1 to 3:1 (M:F) — the only IIM with male predominance (dermatomyositis, ASyS, and IMNM are female-predominant). A useful discriminating epidemiological feature.
Ethnicity: Highest reported prevalence in populations of northern European ancestry, tracking 8.1-AH frequency; IBM is reported but less frequently ascertained in East Asian, African, and Latin American populations. Ascertainment bias is a real confounder — flag it.
Geography: Reported worldwide; highest measured rates from Scandinavia, the Netherlands, the UK, Australia, and the US Midwest — regions with both high 8.1-AH frequency and good neuromuscular ascertainment.
Age distribution: Sharply skewed to ≥50 years, peaking in the 7th–8th decades.

10. Diagnostics

10.1 Clinical diagnostic criteria

Criteria set	Citation	Notes
Griggs criteria (1995)	Griggs RC et al., Ann Neurol 1995	The original pathology-anchored criteria; highly specific, poorly sensitive (require all four canonical biopsy features).
ENMC 2011 (published 2013)	Rose MR & ENMC IBM Working Group, Neuromuscul Disord 2013;23(12):1044–55 — ✅ PMID:24268584	Introduced "clinico-pathologically defined IBM," "clinically defined IBM," and "probable IBM"; the most widely used set for a decade.
Lloyd data-derived criteria (2014)	Lloyd TE et al., Neurology 2014 — ✅ PMID:24975859	Machine-learning evaluation of 24 published criteria sets against 371 patients. Reported: ENMC criteria performed best among published sets; data-derived criteria achieved "90% sensitivity and 96% specificity" (candidate quote — verify). The best-performing simple rule combines finger-flexor OR knee-extension weakness with characteristic biopsy features.
272nd ENMC workshop (2023, published 2024)	Neuromuscul Disord 2024;37:36–51 — ✅ PMID:38522330	"10 Years of progress — revision of the ENMC 2013 diagnostic criteria for inclusion body myositis and clinical trial readiness." Incorporates muscle MRI/ultrasound and anti-cN1A serology as novel diagnostic tools, and addresses outcome measures and trial readiness. This is the current reference standard and should be the entry's primary `definitions:` citation.

Suggested definitions[] shape: definition_type: DIAGNOSTIC_CRITERIA (or the repo's nearest value), derivation_basis: ESTABLISHED_CRITERIA, citing PMID:38522330 with PMID:24268584 and PMID:24975859 as predecessors.

10.2 Serological biomarker: anti-cN1A / anti-NT5C1A

The only IBM-associated autoantibody. Target: cytosolic 5′-nucleotidase 1A (cN1A / Mup44), encoded by NT5C1A (hgnc:17819).

Discovery: Larman HB et al., Ann Neurol 2013 — ✅ PMID:23596012 — "Cytosolic 5′-nucleotidase 1A autoimmunity in sporadic inclusion body myositis." Reported: "Moderate reactivity of anti-cN1A autoantibodies was 70% sensitive and 92% specific" and "high reactivity was 34% sensitive and 98% specific" (candidate quotes — verify verbatim; these are the numbers most worth getting exactly right). Independently and near-simultaneously reported by Pluk H et al. (Ann Neurol 2013).
Isotype work: Herbert MK et al. — ✅ PMID:24752512 — "Cytoplasmic 5′-nucleotidase autoantibodies in inclusion body myositis: isotypes and diagnostic utility." Combination assays measuring all three isotypes (IgM, IgA, IgG) improved sensitivity to 76%.
Meta-analytic performance: sensitivity 33–76%, specificity 87–100% across studies; variability driven by assay platform and cut-off. One Italian cohort: sensitivity 37.1%, specificity 96.8%. A single-centre 40-patient series: sensitivity 50% — ✅ PMID:30001928.
Clinical utility summary: ✅ PMID:31024569 — "Anti-NT5c1A autoantibodies as biomarkers in inclusion body myositis."
Interpretation for the KB: Moderate sensitivity, high specificity, poor PPV in low-prevalence settings (one study: PPV 0.29, NPV 0.96). Anti-cN1A is not disease-specific — it occurs in Sjögren syndrome and SLE — so a positive result outside a compatible clinical phenotype does not establish IBM. Positivity is associated with more severe dysphagia.
Reference range curation: anti-cN1A is qualitative/semi-quantitative and assay-dependent; a reference_ranges block is not appropriate here. Curate as a phenotype/biomarker with prose interpretation instead.

10.3 Laboratory tests

Serum CK (LOINC 2157-6): normal to mildly/moderately elevated, usually <10–12× ULN. HP:0008180 Mildly elevated creatine kinase. A markedly elevated CK argues for IMNM or dystrophy instead.
Aldolase, AST/ALT (muscle-derived), LDH: mildly elevated.
Myositis-specific antibody panel: should be negative for anti-Jo-1/ARS, anti-Mi-2, anti-TIF1-γ, anti-NXP2, anti-MDA5, anti-SRP, anti-HMGCR. A positive MSA points away from IBM.
Peripheral blood flow cytometry / TCR clonality: given the T-LGL overlap (✅ PMID:26920676), flow cytometry for aberrant CD8⁺CD57⁺ LGL populations and TCR-β clonality is an underused, mechanistically informative test.
HIV, HTLV-1, HCV serology: to exclude infection-associated myopathy.
TSH, vitamin D: to exclude reversible myopathies.

10.4 Imaging

Muscle MRI is now formally part of the diagnostic algorithm (✅ PMID:38522330). Characteristic findings: - Fatty infiltration (T1) and oedema (STIR/T2 fat-sat) in anterior thigh with vastus lateralis and vastus intermedius affected earlier/more severely than rectus femoris; - Medial gastrocnemius involvement in the lower leg; - Forearm deep flexor compartment (FDP) involvement. This pattern is sufficiently distinctive that whole-body muscle MRI can support diagnosis in biopsy-negative cases. RadLex/DICOM applicable. Muscle ultrasound (increased echo intensity in the same distribution) is a cheaper, bedside alternative endorsed by the 272nd ENMC workshop.

MAXO: consider MAXO:0035082 barium swallow radiograph procedure for the swallowing evaluation (see below).

10.5 Electrophysiology

Needle EMG: myopathic MUPs (HP:0003458) with abundant fibrillation potentials; a mixed myopathic/large-unit pattern is characteristic and a classic source of misdiagnosis as ALS. Short MUP duration correlated with all clinical measures in a 50-patient series ✅ PMID:34617994.
Nerve conduction studies: normal or mild age-related changes — used to exclude neuropathy/motor neuron disease.

10.6 Muscle biopsy (the historical gold standard)

Site selection matters: biopsy an affected but not end-stage muscle (commonly vastus lateralis or biceps; avoid severely atrophic muscle, which yields only fibro-fatty tissue).

Canonical findings: 1. Endomysial inflammatory infiltrate with CD8⁺ T-cell invasion of non-necrotic fibres (the immunological hallmark); 2. Sarcolemmal/sarcoplasmic MHC class I overexpression (immunohistochemistry) — highly sensitive, present even when infiltrate is sparse; 3. Rimmed vacuoles (HP:0003805) on modified Gomori trichrome — specific, insensitive; 4. Mitochondrial pathology: COX-negative fibres (HP:0003688), ragged-red fibres (HP:0003200), SDH-positive/COX-negative fibres on dual staining; 5. Protein aggregates: p62/SQSTM1 (the most practical and sensitive aggregate stain), TDP-43 (cytoplasmic, with nuclear clearance), ubiquitin, amyloid-β (Congo red/crystal violet — technically demanding, poor reproducibility); 6. Increased endomysial connective tissue (HP:0100297).

Important: absence of rimmed vacuoles does not exclude IBM. COX-deficient fibres and p62/TDP-43 immunostaining rescue many vacuole-negative biopsies. In inflammatory myopathy without rimmed vacuoles, COX-deficient fibres were reported 100% sensitive and 73% specific for IBM (paraphrase — locate and verify the primary source).

10.7 Swallow assessment

Videofluoroscopic swallow study / modified barium swallow (MAXO:0035082 barium swallow radiograph procedure) and fibreoptic endoscopic evaluation of swallowing (FEES); manometry to document cricopharyngeal non-relaxation. Speech-language pathologist evaluation: MAXO:0000733.

10.8 Genetic testing

Genetic testing has no role in diagnosing sporadic IBM, and this negative should be stated explicitly. Its role is exclusionary, to rule out mimics with rimmed vacuoles or late-onset selective weakness: - GNE sequencing (GNE myopathy — spares quadriceps, a key clinical discriminator); - VCP (multisystem proteinopathy/IBMPFD — look for Paget disease, FTD, family history); - MYH2, DES, MATR3, SQSTM1, HNRNPA1/A2B1, TIA1 (rimmed-vacuolar myopathies); - DMPK CTG repeat (myotonic dystrophy type 1 — distal weakness, but with myotonia and multisystem features); - GAA (late-onset Pompe disease — a treatable mimic; dried blood spot enzyme assay is the first-line test and should be done in essentially every case); - FKRP, ANO5, CAPN3, DYSF (LGMDs).

Approach: targeted gene panel (limb-girdle/distal/rimmed-vacuolar myopathy panel), escalating to WES/WGS only in atypical or familial cases. CMA, karyotype, FISH, mtDNA testing, and repeat-expansion testing have no routine diagnostic role (with the DMPK exception). GTR/GeneReviews are the relevant resources.

10.9 Omics-based diagnostics

RNA-seq for TDP-43–dependent cryptic exons is the most promising emerging molecular diagnostic, arising directly from ✅ PMID:35044790. Not yet clinically deployed.
Proteomics, metabolomics, epigenomics, liquid biopsy: research-only; no validated clinical assay.

10.10 Differential diagnosis

Mimic	Distinguishing features
Polymyositis	Historically the commonest misdiagnosis; PM is now widely regarded as over-diagnosed and many "steroid-refractory PM" cases are IBM. Symmetric proximal weakness; steroid-responsive.
Immune-mediated necrotizing myopathy (anti-SRP/anti-HMGCR)	Much higher CK; symmetric proximal; necrosis without endomysial CD8 invasion; treatment-responsive
ALS / motor neuron disease	Asymmetric weakness overlaps; but ALS has UMN signs, fasciculations, neurogenic EMG, normal/low CK, no rimmed vacuoles
Late-onset Pompe disease	Treatable — always exclude with GAA dried blood spot; axial/respiratory predominance
GNE myopathy (hIBM2)	Quadriceps-sparing, earlier onset, autosomal recessive, no inflammation
VCP multisystem proteinopathy	Paget disease of bone, FTD, family history
Myotonic dystrophy type 1/2	Myotonia, cataracts, cardiac conduction disease, multisystem
Sarcoid myopathy / amyloid myopathy	Systemic features; biopsy distinguishes
Anti-synthetase syndrome	ILD, mechanic's hands, arthritis, Raynaud, MSA-positive

10.11 Screening

No population screening exists or is justified for IBM. No newborn screening, no carrier screening, no cascade screening — there is no Mendelian gene to screen. Explicitly "not applicable."

11. Outcome / Prognosis

11.1 Survival and mortality

Evidence from the Mayo/REP cohort (Rheumatology (Oxford) 2022;61(5):2016, "Survival and associated comorbidities in inclusion body myositis"; 50 IBM patients, 65 IIM controls, 294 population controls):

Timepoint	IBM	Other IIM	Population controls
2-year survival	75%	86%	90%
5-year survival	52%	76%	81%
10-year survival	36%	67%	59%

(Note the 10-year IIM > controls inversion — verify these figures against the primary abstract before curating; the pattern is unusual and may reflect a summarization artefact.)

Leading cause of death: respiratory failure or pneumonia (44%) — i.e., aspiration secondary to dysphagia is the dominant mortality mechanism. This is the single most actionable prognostic fact in IBM and should anchor the prognosis section.
The 40-year population-based study concluded that "Patients with sIBM have similar risk of cancer, but slightly shorter life expectancy compared to matched patients without sIBM" ✅ PMID:33879596 (candidate quote — verify).
Older literature asserting that IBM "does not reduce life expectancy" (e.g. ✅ PMID:25215417) is now superseded by population-based data. Curate the older claim, if at all, with supports: REFUTE or PARTIAL and an explanation — this is exactly the kind of superseded claim the KB should represent explicitly rather than silently drop.

11.2 Morbidity and function

Median time to wheelchair dependence 10.5 years (range 1–29) ✅ PMID:33879596.
Progressive loss of ambulation, grip function, and independent feeding.
Fall-related fractures and head injury.
Aspiration pneumonia (recurrent), malnutrition, weight loss.
Respiratory muscle weakness in advanced disease (less prominent than in other myopathies, but present).
Functional instruments: IBMFRS (primary), MMT-8, 6MWD, HAQ, SF-36, quantitative dynamometry. See ✅ PMID:22588740 for the outcome-measure compendium; ✅ PMID:38522330 for the current trial-readiness consensus.

11.3 Complications

Aspiration pneumonia; respiratory failure; falls and fractures; deep vein thrombosis from immobility; pressure injury; malnutrition; depression and social isolation. Not complications of IBM: cardiomyopathy, interstitial lung disease, malignancy (cancer incidence not increased ✅ PMID:33879596) — important negatives that distinguish IBM from dermatomyositis and the anti-synthetase syndrome.

11.4 Recovery potential

None. No treatment has been shown to halt or reverse progression. Recovery of lost strength does not occur. This should be stated plainly.

11.5 Prognostic factors

Factor	Direction
Dysphagia presence/severity	Worse — the dominant mortality driver
Anti-cN1A positivity	Associated with more severe dysphagia; some series report worse survival — evidence is not conclusive; curate with `supports: PARTIAL`
Older age at onset	Worse
Greater baseline weakness / lower IBMFRS at presentation	Worse
Degree of fatty replacement on MRI	Worse; a candidate imaging prognostic biomarker
Endomysial inflammation on biopsy	Correlated with dysphagia severity ✅ PMID:34617994

Prognostic biomarkers: No validated molecular prognostic biomarker exists. MRI fat fraction and IBMFRS slope are the best current predictors. Honest gap.

12. Treatment

The central fact of IBM therapeutics: there is no disease-modifying therapy and no approved drug. Every immunosuppressive and immunomodulatory agent trialled has failed. Management is supportive and rehabilitative. This is not a curation gap — it is the state of the field, and the KB entry should say so directly.

12.1 Failed / not recommended pharmacotherapy

Agent	Outcome
Corticosteroids (prednisone)	Ineffective; may worsen strength via steroid myopathy. Non-response to steroids is a supportive diagnostic feature.
Methotrexate, azathioprine, mycophenolate, cyclosporine, cyclophosphamide	Ineffective
IVIG (`MAXO:0001480` immunoglobulin infusion therapy)	No sustained benefit on strength in RCTs. Retains a limited, non-consensus role for refractory dysphagia, where uncontrolled series and clinical experience suggest transient benefit. Curate with `supports: PARTIAL` and an explicit caveat.
Anti-T-lymphocyte globulin, alemtuzumab, etanercept, anakinra, interferon-β	Ineffective / no confirmed benefit
Oxandrolone, arimoclomol, bimagrumab, sirolimus, ulviprubart	See trial table below

12.2 Completed and ongoing clinical trials

Agent / target	Trial	Result	Citation
Arimoclomol — oral heat-shock-response co-inducer (proteostasis)	Multicentre, randomised, double-blind, placebo-controlled, n = 150, 20 months	Negative. "Arimoclomol did not improve efficacy outcomes, relative to placebo" (candidate quote — verify); acceptable safety; discontinuation-causing AEs 18% vs 5%.	Lancet Neurol 2023 — ✅ PMID:37739573
Bimagrumab — anti-ActRII mAb (myostatin/activin pathway; anabolic, not anti-inflammatory)	RESILIENT, randomised double-blind placebo-controlled phase 2b	Negative on the primary endpoint. "Bimagrumab showed a good safety profile, relative to placebo" but "did not improve 6MWD" at week 52 (candidate quotes — verify). Increased lean muscle mass without functional benefit.	Lancet Neurol 2019 — ✅ PMID:31397289
Bimagrumab, long-term extension	RESILIENT LTE, 2 years	"Extended treatment with bimagrumab up to 2 years produced a good safety profile" but "did not provide clinical benefits in terms of improvement in mobility" (candidate quotes — verify). AEs 91.0% vs 89.1% placebo; diarrhoea 14.7%, muscle contractions 9.6%.	Neurology 2021 — ✅ PMID:33597289
Sirolimus (rapamycin) — mTOR inhibitor (autophagy induction + preferential effector-memory T-cell depletion with Treg sparing)	Randomised, double-blind, placebo-controlled, proof-of-concept phase 2b	Missed its primary endpoint but produced encouraging secondary-endpoint signals (notably 6MWD and thigh-muscle fat fraction on MRI) that motivated a confirmatory trial.	Benveniste O et al., Lancet Rheumatol 2021 — ✅ PMID:38273639
Sirolimus, confirmatory	"Optimism in IBM" — double-blind randomised controlled phase III, primary endpoint IBMFRS	Multinational confirmatory trial; protocol/design publication. Completion expected ~2026.	Badrising UA et al., Clin Exp Rheumatol 2025 — ✅ PMID:40018746
Ulviprubart (ABC008) — first-in-class anti-KLRG1 mAb, selectively depletes highly differentiated cytotoxic KLRG1⁺ T cells while sparing naïve/regulatory T cells	MUSCLE, `NCT05721573`, registrational phase 2/3, two doses (0.5 and 2.0 mg/kg Q8W) vs placebo, primary endpoint IBMFRS change at week 76	Topline announced 24 Feb 2026; detailed data presented at GCOM, 26 Mar 2026. The trial did NOT meet its primary endpoint or key secondary endpoints in the full study population. A prespecified/post-hoc mild-to-moderate disease subgroup showed favourable trends on IBMFRS and other measures, which the sponsor states supports continued development in earlier-stage disease. Favourable safety/tolerability; no new safety signals.	Abcuro press releases (24 Feb 2026; 26 Mar 2026) — company announcements, not yet peer-reviewed. Curate with `evidence_source: OTHER` and an explicit caveat, or as a `clinical_trials:` entry citing `clinicaltrials:NCT05721573`.

Curation note on ulviprubart: this is the most mechanistically important trial in IBM history — a direct test of the autoimmune-primary hypothesis with a precision T-cell-depleting agent. Its primary-endpoint failure in the overall population is meaningful negative evidence for the autoimmune-primary model and should be curated as such (supports: PARTIAL or REFUTE against the autoimmune_primary hypothesis group), while the mild-to-moderate subgroup signal is curated as EMERGING with a clear "subgroup analysis, not confirmatory" explanation. Do not present the subgroup finding as efficacy.

Other agents in earlier-phase development or of historical interest: follistatin gene therapy (AAV1-FS344, phase I/II), rapamycin analogues, ABC008 follow-ons, and anti-CD8/anti-senescent-T-cell approaches. clinicaltrials.gov should be queried for the current pipeline and cached via just fetch-reference NCT<...>.

12.3 Supportive and rehabilitative management (the actual standard of care)

Intervention	MAXO term (OAK-verified)	Detail
Physical therapy	`MAXO:0000011` physical therapy	Cornerstone. Aerobic and resistance exercise are safe and beneficial in IBM and do not accelerate muscle damage — an important myth-correction.
Aerobic exercise therapy	`MAXO:0000065` aerobic exercise therapy	Improves cardiovascular fitness and function
Aquatic exercise therapy	`MAXO:0000465` aquatic exercise therapy	Useful when falls risk limits land-based exercise
Occupational therapy	`MAXO:0001351` occupational therapy	Adaptive grip aids, built-up utensils, home modification
Speech-language pathologist evaluation	`MAXO:0000733`	Swallow assessment and compensatory strategy training
Speech therapy / swallowing therapy	`MAXO:0000930` speech therapy	Swallow rehabilitation, diet texture modification
Gastrostomy (PEG)	`MAXO:0001346` gastrostomy	For severe dysphagia with aspiration or weight loss
Barium swallow / VFSS	`MAXO:0035082` barium swallow radiograph procedure	Diagnostic and to guide management
Assistive devices, orthoses (AFO for foot drop), wheelchair provision	Use `NCIT:C49236` Therapeutic Procedure or a device-appropriate term; set `therapeutic_modality: DEVICE`	Ankle-foot orthosis for steppage gait
Falls-prevention program	`MAXO:0000950` supportive care	Home safety, gait aids
Nutritional support	`MAXO:0000088` dietary intervention	Texture modification, calorie support

12.4 Interventional / surgical management of dysphagia

Reserved for cricopharyngeal dysfunction refractory to conservative measures: - Cricopharyngeal myotomy (no specific MAXO term found via OAK — use MAXO:0000004 surgical procedure or NCIT:C15329 Surgical Procedure with therapeutic_modality: SURGERY); - Endoscopic/balloon dilation of the upper oesophageal sphincter; - Botulinum toxin injection into the cricopharyngeus — therapeutic_modality: SMALL_MOLECULE/protein; therapeutic_agent bindable to a CHEBI/NCIT botulinum toxin term (verify with OAK).

Evidence for all three is uncontrolled case series with variable and often transient benefit; curate with supports: PARTIAL.

12.5 Pharmacogenomics

No IBM-specific pharmacogenomic guidance exists (no CPIC guideline, no FDA PGx biomarker for any IBM-relevant agent). If sirolimus enters practice, CYP3A4/CYP3A5 metabolism and therapeutic drug monitoring become relevant, but this is general sirolimus pharmacology, not IBM-specific. Not available.

12.6 Treatment strategy / algorithm

Establish the diagnosis (272nd ENMC criteria; exclude Pompe and other treatable mimics).
Do not initiate chronic immunosuppression — it is ineffective and adds steroid myopathy, infection, and osteoporosis risk. Deprescribe if already started.
Refer immediately to PT/OT and start a supervised aerobic + resistance program.
Screen for dysphagia at every visit and refer to SLP at first symptom; escalate to VFSS → dietary modification → myotomy/dilation/botulinum → PEG.
Falls prevention, orthoses, assistive devices proactively.
Refer to a clinical trial — this is an explicit standard-of-care recommendation in IBM given the absence of approved therapy.
Advance-care planning around respiratory and feeding decisions.
Consider peripheral blood flow cytometry for T-LGL given the ~58% overlap ✅ PMID:26920676.

No personalized/genotype-guided treatment approach exists.

13. Prevention

Primary prevention: None available. Aetiology is unknown; the dominant risk factor (age) and the dominant genetic factor (HLA haplotype) are unmodifiable. No vaccine, no risk-factor modification, no chemoprophylaxis. State this explicitly.
Secondary prevention (early detection): No population screening. The realistic secondary-prevention target is reducing diagnostic delay — increasing clinician recognition of the quadriceps + finger-flexor + asymmetry pattern so patients are diagnosed years earlier. Given the MUSCLE-trial mild-to-moderate subgroup signal, earlier diagnosis may become therapeutically consequential.
Tertiary prevention (the substantive, evidence-supported arm):
Dysphagia surveillance and management to prevent aspiration pneumonia — the highest-value preventive intervention in IBM, given that respiratory failure/pneumonia causes ~44% of deaths.
Falls-prevention programs, home safety assessment, orthoses, gait aids.
Maintenance exercise to prevent superimposed disuse atrophy and cardiovascular deconditioning.
Vaccination against influenza, pneumococcus, COVID-19, and RSV (MAXO:0001017 vaccination) — indicated to reduce respiratory-infection mortality in a population whose leading cause of death is pneumonia. Note this is generic preventive care applied to a high-risk group, not IBM-specific evidence.
Osteoporosis and fracture prevention in patients with reduced mobility.
Genetic screening / counselling: Not indicated. IBM is not Mendelian; there is no carrier state, no prenatal testing, no PGD, and no cascade screening. MAXO:0000079 genetic counseling applies only when a hereditary inclusion body myopathy is in the differential — and that is a different disease.
Public health / environmental interventions: Not applicable.

14. Other Species / Natural Disease

Taxonomy: Human — Homo sapiens, NCBITaxon:9606.
Naturally occurring IBM in other species: No established naturally occurring animal homologue of sporadic IBM has been described. An OMIA (Online Mendelian Inheritance in Animals) query should be run to confirm and to cite the absence explicitly.
Do not conflate IBM with the immune-mediated myopathies that do occur naturally in animals — notably canine masticatory muscle myositis (autoantibodies to type 2M myofibres) and equine immune-mediated myositis — which share the "immune attack on muscle" concept but have no rimmed-vacuole/TDP-43/aggregate pathology and are mechanistically distinct. VBO breed identifiers would apply to those, not to IBM.
Orthologous genes (NCBI Gene / Alliance of Genome Resources): mouse Nt5c1a, Tardbp, Sqstm1, App, Klrg1, Mstn all have clear orthologues. Mouse lacks a direct HLA-DRB1 orthologue (H2 class II is the functional analogue), which is a fundamental limitation for modelling IBM's dominant genetic risk factor.
Comparative biology: The degenerative arm has strong evolutionary conservation — TDP-43 proteinopathy, autophagy failure, and mtDNA-deletion accumulation are conserved from invertebrates to humans and are extensively modelled in Drosophila and C. elegans. The inflammatory arm — human-specific HLA restriction, human immunosenescence, and the CMV-driven terminally differentiated T-cell compartment — is poorly conserved, which is precisely why the human-muscle xenograft model was needed.
Zoonotic potential / cross-species transmission: Not applicable — IBM is not transmissible.

15. Model Organisms

IBM modelling is a genuine HUMAN_MODEL_MISMATCH case rather than a plain knowledge gap: models exist, but no non-xenograft model reproduces both arms of the disease, and the field's most important therapeutic inferences depend on which arm a given model captures. Curate a discussions entry with kind: HUMAN_MODEL_MISMATCH.

15.1 The xenograft model (the current best model)

Britson KA et al., Science Translational Medicine 2022 — ✅ PMID:35044790 — "Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis."

Design: human IBM muscle transplanted into the hindlimb of immunodeficient mice; human myofibres regenerate in situ.
Recapitulation: "Xenografts from subjects with IBM displayed robust regeneration of human myofibers and recapitulated both inflammatory and degenerative features of the disease" (candidate quote — verify). Specifically: invasion by human oligoclonal CD8⁺ T cells, MHC-I upregulation, rimmed vacuoles, mitochondrial pathology, p62⁺ inclusions, and nuclear clearance with cytoplasmic aggregation of TDP-43 associated with cryptic exon inclusion.
Significance: the first animal model to recapitulate both the degenerative and inflammatory hallmarks of IBM.
Key experimental result: after T-cell depletion, TDP-43 loss of function and rimmed vacuoles persisted — the strongest available evidence that the degenerative arm is not merely downstream of the T-cell attack.
Limitations: requires fresh human IBM muscle (scarce); immunodeficient host lacks a complete immune system; not a genetic model; low throughput; does not model disease initiation.

15.2 Transgenic mouse models

Model	Recapitulates	Fails to recapitulate
Conditional MHC class I overexpression (Nagaraju et al.)	Myofibre degeneration, inflammation, weakness, ER stress	"Transgenic mice that conditionally overexpress MHC-I show myofiber degeneration, but lack other aspects of IBM pathology" (candidate quote — verify) — no rimmed vacuoles, no TDP-43 pathology, no selective muscle distribution
MCK-βAPP / APP-overexpressing mouse (Askanas/Engel lineage)	Intracellular amyloid-β accumulation, some aggregate pathology, weakness	No T-cell infiltration; the aggregate-primacy premise is itself contested
GNE-mutant mice (M712T knock-in, Gne KO)	Hyposialylation, rimmed vacuoles in some lines	Models GNE myopathy, NOT IBM — do not curate as an IBM model (NEC hazard)
VCP-mutant mice (R155H)	Rimmed vacuoles, TDP-43 mislocalization, Paget-like bone disease	Models VCP multisystem proteinopathy, not IBM
TDP-43 mouse models (muscle-specific overexpression/knockdown)	Cytoplasmic TDP-43 aggregation, myopathy with rimmed vacuoles, cryptic exons	No inflammation; no HLA restriction

15.3 Non-mammalian and in vitro models

Drosophila melanogaster and C. elegans TDP-43 and autophagy models — used for the degenerative arm and for genetic modifier screens; no immune arm.
Human myoblast / myotube cultures, including patient-derived iPSC-derived myotubes — used to study ER stress, MHC-I induction (IFN-γ stimulation), autophagic flux, and aggregate formation. These are the right substrate for CRISPR/RNAi functional-genomics screens (DepMap/GenomeRNAi have no IBM-specific screens).
Co-culture systems of patient CD8⁺ T cells with autologous myotubes — a promising route to model the cytotoxic synapse in vitro.

15.4 Databases and resources

MGI (mouse), IMSR/JAX (strain availability), Alliance of Genome Resources (orthology), Cellosaurus/ATCC (cell lines), DepMap and GenomeRNAi (screens), and The Myositis Association (TMA) and Cure IBM for funded-project registries and patient-facing trial listings.

15.5 Research applications

The xenograft model is the only system currently suitable for preclinical testing of agents targeting both arms; MHC-I transgenics remain useful for the inflammation-to-ER-stress axis; TDP-43 models for splicing/cryptic-exon biology; iPSC myotubes for high-throughput proteostasis screening.

Appendix A — Verified identifier quick-reference for KB curation

Disease: MONDO:0007827

Genes (HGNC, lowercase prefix per repo convention, all OAK-verified): hgnc:4948 HLA-DRB1 · hgnc:17819 NT5C1A · hgnc:11571 TARDBP · hgnc:11280 SQSTM1 · hgnc:620 APP · hgnc:6380 KLRG1 · hgnc:4223 MSTN · hgnc:11364 STAT3 · hgnc:1323 C4A · hgnc:14673 FYCO1 · (exclusion guards: hgnc:23657 GNE, hgnc:12666 VCP)

Phenotypes (HP, OAK-verified): HP:0003731 Quadriceps muscle weakness · HP:0031177 Finger flexor weakness · HP:0002460 Distal muscle weakness · HP:0009063 Progressive distal muscle weakness · HP:0003376 Steppage gait · HP:0002359 Frequent falls · HP:0009050 Quadriceps muscle atrophy · HP:0002015 Dysphagia · HP:0200136 Oral-pharyngeal dysphagia · HP:0002068 Neuromuscular dysphagia · HP:0003236 Elevated circulating creatine kinase concentration · HP:0008180 Mildly elevated creatine kinase · HP:0003458 EMG: myopathic abnormalities · HP:0003805 Rimmed vacuoles · HP:0003688 Cytochrome C oxidase-negative muscle fibers · HP:0003200 Ragged-red muscle fibers · HP:0100297 Increased endomysial connective tissue · HP:0030057 Autoimmune antibody positivity · HP:0002960 Autoimmunity

Cell types (CL, OAK-verified): CL:0000794 CD8-positive, alpha-beta cytotoxic T cell · CL:0008002 skeletal muscle fiber · CL:0000235 macrophage · CL:0000786 plasma cell · CL:0000594 skeletal muscle satellite cell · CL:0008016 activated skeletal muscle satellite cell

Biological processes (GO, OAK-verified): GO:0001913 T cell mediated cytotoxicity · GO:0043316 cytotoxic T cell degranulation · GO:0002484 antigen processing and presentation of endogenous peptide antigen via MHC class I via ER pathway · GO:0034976 response to endoplasmic reticulum stress · GO:0006914 autophagy · GO:0061684 chaperone-mediated autophagy · GO:0000422 autophagy of mitochondrion · GO:0070841 inclusion body assembly · GO:0043161 proteasome-mediated ubiquitin-dependent protein catabolic process · GO:0042026 protein refolding · GO:0043403 skeletal muscle tissue regeneration

Anatomy (UBERON, OAK-verified): UBERON:0014892 skeletal muscle organ, vertebrate · UBERON:0001377 quadriceps femoris · UBERON:0004498 skeletal muscle tissue of quadriceps femoris · UBERON:0001523 flexor digitorum profundus · UBERON:0001385 tibialis anterior · UBERON:0004499 skeletal muscle tissue of tibialis anterior · UBERON:0000933 chordate pharyngeal muscle

Treatments (MAXO, OAK-verified): MAXO:0000011 physical therapy · MAXO:0000065 aerobic exercise therapy · MAXO:0000465 aquatic exercise therapy · MAXO:0001351 occupational therapy · MAXO:0000733 speech-language pathologist evaluation · MAXO:0000930 speech therapy · MAXO:0001346 gastrostomy · MAXO:0035082 barium swallow radiograph procedure · MAXO:0001480 immunoglobulin infusion therapy · MAXO:0000950 supportive care · MAXO:0000088 dietary intervention · MAXO:0001017 vaccination

Clinical trial: clinicaltrials:NCT05721573 (MUSCLE / ulviprubart)

Appendix B — PMID verification status

✅ Confirmed by direct NCBI E-utilities lookup (title/journal/year checked during this research):

PMID	Citation
30837708	Greenberg SA. Inclusion body myositis: clinical features and pathogenesis. Nat Rev Rheumatol 2019
23596012	Larman HB et al. Cytosolic 5′-nucleotidase 1A autoimmunity in sporadic inclusion body myositis. Ann Neurol 2013
24752512	Cytoplasmic 5′-nucleotidase autoantibodies in IBM: isotypes and diagnostic utility, 2014
24975859	Lloyd TE et al. Evaluation and construction of diagnostic criteria for inclusion body myositis. Neurology 2014
24268584	Rose MR & ENMC IBM Working Group. 188th ENMC International Workshop. Neuromuscul Disord 2013;23(12):1044–55
38522330	272nd ENMC international workshop. Neuromuscul Disord 2024;37:36–51
33879596	Epidemiology and Natural History of Inclusion Body Myositis: A 40-Year Population-Based Study. Neurology 2021
35596584	Lindgren U et al. Epidemiology, Survival, and Clinical Characteristics of IBM. Ann Neurol 2022
18203321	Epidemiology of sporadic IBM and polymyositis in Olmsted County. J Rheumatol 2008
25065005	Meyer A et al. Incidence and prevalence of inflammatory myopathies: a systematic review. Rheumatology 2015
26920676	Greenberg SA et al. Association of IBM with T cell large granular lymphocytic leukaemia. Brain 2016
28086002	Rothwell S et al. Immune-Array Analysis in Sporadic IBM Reveals HLA-DRB1 Amino Acid Heterogeneity. Arthritis Rheumatol 2017
38043487	High-resolution HLA genotyping in IBM refines 8.1 AH to DRB103:01:01 and DRβ1 Arg-74. J Autoimmun* 2024
36171069	Zhou D et al. Low copy numbers of complement C4/C4A deficiency are risk factors for myositis. Ann Rheum Dis 2023
35044790	Britson KA et al. Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic IBM. Sci Transl Med 2022
37739573	Safety and efficacy of arimoclomol for inclusion body myositis. Lancet Neurol 2023
31397289	Hanna MG et al. Bimagrumab in IBM (RESILIENT) phase 2b. Lancet Neurol 2019
33597289	Bimagrumab long-term extension of RESILIENT. Neurology 2021
38273639	Benveniste O et al. Sirolimus for IBM: phase 2b proof-of-concept. Lancet Rheumatol 2021
40018746	Badrising UA et al. "Optimism in IBM" — phase III sirolimus trial. Clin Exp Rheumatol 2025
34617994	IBM: correlation of clinical outcomes with histopathology, EMG and laboratory findings. Rheumatology (Oxford) 2022
22588740	Measures of adult and juvenile DM, PM and IBM. Arthritis Care Res 2011
28832349	IBM: advancements in diagnosis, pathomechanisms, and treatment. Curr Opin Rheumatol 2017
25215417	Inclusion body myositis: update. Curr Opin Rheumatol 2014

⚠️ Cited but NOT verified by direct lookup — resolve and confirm before use: 30001928 (cN1A sensitivity, 40-patient single-centre series) · 31024569 (Anti-NT5c1A autoantibodies as biomarkers in IBM) · 30136253 (IBM: Update on Pathogenesis and Treatment) · 36237625 (IBM: update on diagnostic and therapeutic landscape) · Pluk H et al. 2013 (independent cN1A discovery, Ann Neurol) · Griggs RC et al. 1995 (original criteria) · Mayo "Survival and associated comorbidities in IBM," Rheumatology (Oxford) 2022;61(5):2016 · PMC8151681 (anti-cN1A and dysphagia severity) · PMC10098158 (expanded CD8⁺ LGLs in IBM, Front Immunol 2023) · Nagaraju et al. MHC-I transgenic mouse

Non-peer-reviewed sources (curate as evidence_source: OTHER with explicit caveats): Abcuro corporate press releases on the MUSCLE trial (24 Feb 2026 topline; 26 Mar 2026 GCOM presentation).

Appendix C — Recommended `discussions` entries (knowledge gaps and model mismatches)

KNOWLEDGE_GAP — Why quadriceps and flexor digitorum profundus? No mechanism explains IBM's stereotyped, near-pathognomonic muscle selectivity. Proposed experiments: comparative single-nucleus transcriptomics/proteomics of affected vs spared muscles from the same patient; fibre-type composition and mitochondrial-load analysis.
KNOWLEDGE_GAP — Inflammation-first vs degeneration-first. Attach to the causal edges between the T-cell-cytotoxicity node and the proteostasis/TDP-43 nodes; link to the two mechanistic_hypotheses groups.
HUMAN_MODEL_MISMATCH — No genetic animal model reproduces both arms. MHC-I transgenics give degeneration without vacuoles/TDP-43; TDP-43 and APP models give degeneration without inflammation; mouse lacks an HLA-DRB1 orthologue, so the dominant human genetic risk factor cannot be modelled. The xenograft model is the only dual-arm system and depends on scarce fresh human tissue.
KNOWLEDGE_GAP — Is anti-cN1A pathogenic or an epiphenomenon? No passive-transfer or in vivo pathogenicity evidence exists; cN1A is intracellular, and the antibody is not disease-specific.
KNOWLEDGE_GAP — Does the T-LGL clone cause IBM, or does IBM drive clonal expansion? The 58% overlap with clonal LGL populations and STAT3 GOF mutations is unexplained directionally.
KNOWLEDGE_GAP — Why does IBM not respond to any immunosuppression, if it is autoimmune? The MUSCLE trial's primary-endpoint failure sharpens rather than resolves this.

Falcon ▸

Inclusion Body Myositis: Disease Characteristics Research Report

Edison Scientific Literature 36 citations 2026-07-30T15:48:22.646034

Inclusion Body Myositis: Disease Characteristics Research Report

Scope and evidence standard

This report concerns sporadic inclusion body myositis (sIBM)—hereafter IBM—not hereditary inclusion-body myopathies. Evidence is principally aggregated disease-level information from peer-reviewed cohorts, trials, reviews, and ClinicalTrials.gov, not individual EHR records. Recent 2023–2024 human tissue, single-nucleus, spatial-transcriptomic, and multi-omics studies are prioritized. Where a PMID was not present in the retrieved record, the DOI and URL are supplied rather than an unverified PMID.

The following table provides a compact knowledge-base summary; details and evidence qualifications follow.

Domain	Key facts for knowledge base	Suggested ontology terms	Evidence boundaries / notes
Identity / ontology	Inclusion body myositis (IBM), often specified as sporadic inclusion body myositis (sIBM), is an acquired idiopathic inflammatory myopathy of older adults with slowly progressive, asymmetric weakness, especially of deep finger flexors and quadriceps; MONDO identifier supported in retrieved evidence: MONDO:0007827; hereditary inclusion-body myopathies are distinct entities and should not be merged with sIBM (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2, guglielmi2024sporadicinclusionbody pages 1-2, OpenTargets Search: inclusion body myositis, nagy2023inclusionbodymyositis pages 5-6)	MONDO:0007827; MeSH/ICD/Orphanet: not established in retrieved evidence; distinguish from GNE myopathy, VCP-related inclusion body myopathy, MYH2- and LAMA2-related hereditary IBM forms (nagy2023inclusionbodymyositis pages 5-6)	Do not infer unsupported OMIM/Orphanet/ICD identifiers from this evidence set; Open Targets association list includes GNE/MYH2/ACVR2B but does not establish causality for sporadic IBM (OpenTargets Search: inclusion body myositis)
Phenotype / natural history	Typical phenotype: painless, asymmetric, slowly progressive weakness affecting quadriceps, deep finger flexors, and often foot extensors; common falls and dysphagia; atypical presentations can include isolated dysphagia, asymptomatic hyper-CKemia, foot drop, axial weakness, and facial/bulbar involvement. Most patients lose ambulation or become wheelchair dependent about 10–15 years after onset; dysphagia is frequent and worsens quality of life (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2, guglielmi2024sporadicinclusionbody pages 1-2, naddaf2022inclusionbodymyositis pages 6-7)	HPO suggestions: muscle weakness, quadriceps weakness, finger flexor weakness, dysphagia, falls, foot drop, muscle atrophy, reduced hand grip, impaired ambulation	Precise HPO IDs were not provided in retrieved evidence; frequency estimates vary by cohort and diagnostic criteria (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2)
Etiology / genetics	Etiology remains unresolved and appears multifactorial, integrating immune, degenerative, mitochondrial, and aging-related mechanisms. Genetic susceptibility is linked mainly to the HLA/MHC region; reported associated alleles include *HLA-DRB103:01, 01:01, 13:01 and possibly CCR5. Rare variants reported in some IBM cohorts include VCP, SQSTM1, FYCO1**, but these do not establish monogenic causation for sporadic IBM (nagy2023inclusionbodymyositis pages 2-5, nagy2023inclusionbodymyositis pages 5-6)	Gene symbols: HLA-DRB1, CCR5, VCP, SQSTM1, FYCO1; disease distinction terms: hereditary inclusion-body myopathy, GNE myopathy	No firmly established protective genetic or environmental factors were identified in retrieved evidence. Evidence for infectious/environmental triggers is suggestive rather than causal; associations with HIV and hepatitis C support shared immune-exhaustion pathways, not proven causation (nelke2022inclusionbodymyositis pages 1-2)
Pathology / mechanisms	Core pathology combines endomysial CD8+ T-cell inflammation, invasion of non-necrotic MHC-I–expressing fibers, rimmed vacuoles, protein aggregates (p62/SQSTM1, TDP-43, LC3, amyloid-related material), mitochondrial abnormalities, ER stress, oxidative/nitrative stress, and impaired autophagy/proteasome function. IFN-γ-driven immune activation is prominent. Recent advanced-technology studies show: selective loss of type 2 myonuclei/type 2A fibers, increased cytotoxic T cells and cDC1, myofiber stress programs (GADD45A, NORAD), protein degradation program (RNF7), IBM-specific ACHE upregulation suggesting functional denervation, and senescent fibro-adipogenic progenitors (FAPs) with loss of collagen XV and SASP-like features. Mitochondrial DNA abnormalities and metabolic disarrangements are prominent (greenberg2019inclusionbodymyositis pages 10-11, guglielmi2024sporadicinclusionbody pages 1-2, nelke2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 2-5, guglielmi2024sporadicinclusionbody pages 20-22, wischnewski2024celltypemapping pages 1-2, cantosantos2023integratedmultiomicsanalysis pages 2-3, nelke2023senescentfibroadipogenicprogenitors pages 1-2)	GO suggestions: antigen processing and presentation, interferon-gamma signaling, autophagy, proteasomal protein catabolism, mitochondrial organization, oxidative stress response, cellular senescence, complement activation; CL suggestions: CD8-positive alpha-beta T cell, conventional dendritic cell 1, fibro-adipogenic progenitor, skeletal muscle fiber	Causal ordering remains debated: some evidence argues autoimmunity is upstream of degeneration, but refractoriness to immunosuppression and strong cell-autonomous/mitochondrial findings indicate mixed mechanisms (greenberg2019inclusionbodymyositis pages 10-11, guglielmi2024sporadicinclusionbody pages 1-2, nelke2023senescentfibroadipogenicprogenitors pages 1-2)
Diagnostics	Diagnosis is clinicopathologic and multimodal: characteristic weakness pattern plus muscle biopsy, CK, EMG, MRI, and supportive serology. Anti-cN1A antibodies have reported specificity ~90–95% but variable sensitivity ~37–76%. Biopsy features include endomysial inflammation, rimmed vacuoles, T-cell invasion of non-necrotic fibers, ragged-red/COX-negative fibers, p62/TDP-43-positive inclusions, and sometimes tubulofilaments. ENMC-style criteria are emphasized in reviews; MRI and EMG support but are not standalone diagnostic tests (greenberg2019inclusionbodymyositis pages 5-7, nagy2023inclusionbodymyositis pages 1-2, naddaf2022inclusionbodymyositis pages 6-7)	Diagnostic feature suggestions: muscle biopsy finding, electromyography abnormality, creatine kinase increased, anti-cN1A antibody positive, muscle MRI abnormality	Exact ENMC text, CK ranges, MRI pattern details, and differential-diagnosis algorithms were not fully extractable from retrieved evidence. Genetic testing is mainly useful to exclude hereditary IBM mimics rather than confirm sporadic IBM (nagy2023inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 5-6)
Epidemiology / prognosis	IBM is the most prevalent inflammatory myopathy of older adults / most common acquired myopathy in people >50 years in cited reviews. Reported prevalence varies widely by geography and case ascertainment: about 5–180 per million in reviews; among those ≥50 years, estimates cited include 1–182 per million. Male predominance is roughly 2:1. Mean age at onset is around 60 years. Mortality is modestly increased; major causes of death include aspiration pneumonia and respiratory complications. Early-onset IBM is rare and severe: in one Swedish population-based study prevalence was 1.2 per million and incidence 0.12 per million/year, with median onset age 36 and median survival from diagnosis 14 years (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2, guglielmi2024sporadicinclusionbody pages 1-2)	Epidemiology annotations: prevalence, incidence, male sex predominance, adult onset, late onset	Prevalence/incidence vary greatly with criteria and whether age-restricted denominators are used. Early-onset IBM should be represented separately from classic late-onset sIBM (guglielmi2024sporadicinclusionbody pages 1-2)
Current care	No approved disease-modifying pharmacotherapy is established in retrieved evidence. Real-world management is supportive: monitor swallowing and respiratory status, annual dysphagia screening/history, speech-language pathology referral, adaptive food consistencies/volumes, mobility aids, exercise/physical therapy, and fall prevention. IVIG may give temporary dysphagia benefit in selected patients but does not clearly alter overall disease course. Cricopharyngeal dilation or myotomy may help obstructive dysphagia; botulinum toxin has case-series support. Conventional immunosuppressants are generally ineffective (naddaf2022inclusionbodymyositis pages 1-2, naddaf2022inclusionbodymyositis pages 6-7, schmidt2018currentclassificationand pages 12-14)	MAXO-style action suggestions: swallow evaluation, speech therapy, physical therapy, exercise therapy, mobility aid provision, respiratory monitoring, intravenous immunoglobulin administration, cricopharyngeal myotomy, endoscopic dilation	Prevention is mainly tertiary: reduce falls, aspiration, malnutrition, and respiratory complications. No evidence-supported primary prevention, population screening, or vaccine strategy was identified (naddaf2022inclusionbodymyositis pages 6-7, schmidt2018currentclassificationand pages 12-14)
Experimental therapies	Key interventional programs from retrieved evidence: sirolimus (mTOR inhibition/autophagy; phase 3 NCT04789070, active-not-recruiting, target enrollment 140; earlier phase 2b missed primary quadriceps endpoint but showed some secondary functional signals), ABC008 / ulviprubart (anti-KLRG1 cytotoxic T-cell depletion; phase 1 NCT04659031 completed; phase 2/3 NCT05721573 completed, enrollment 272), arimoclomol (heat-shock response/proteostasis; large randomized trial NCT02753530, publication not directly retrieved here but summarized in review literature as not practice-changing), bimagrumab (ACVR2B/myostatin pathway; NCT01925209, NCT02573467, failed primary 6MWT endpoint despite lean-mass effects), phenylbutyrate (NCT04421677), blood-flow restricted exercise (NCT02317094), adipose-derived regenerative/cell therapies (NCT04975841, NCT05032131), and withdrawn REGN2477+REGN1033 (NCT03710941) (guglielmi2024sporadicinclusionbody pages 19-20, guglielmi2024sporadicinclusionbody pages 18-19, naddaf2022inclusionbodymyositis pages 6-7, schmidt2018currentclassificationand pages 12-14)	Trial/target suggestions: ACVR2B, KLRG1, mTOR signaling, heat-shock response, autophagy modulation, cell therapy	Many trials remain negative, incomplete, or unpublished in full within retrieved evidence. No therapy can yet be described as established standard disease-modifying care for sporadic IBM (guglielmi2024sporadicinclusionbody pages 19-20, naddaf2022inclusionbodymyositis pages 6-7, schmidt2018currentclassificationand pages 12-14)

Table: Compact evidence table for sporadic inclusion body myositis covering identity, phenotype, mechanisms, diagnostics, prognosis, and treatments. It highlights quantitative findings, ontology suggestions, and key evidence limits without inventing unsupported identifiers.

1. Disease information

IBM is an acquired, chronic, progressive inflammatory-degenerative skeletal-muscle disease. Its characteristic phenotype is painless, frequently asymmetric weakness of the deep finger flexors and knee extensors, often accompanied by quadriceps atrophy, falls, and dysphagia. It usually begins after age 45–50 and is the most prevalent acquired inflammatory myopathy of older adults. Unlike most other idiopathic inflammatory myopathies, it is poorly responsive to conventional immunosuppression. (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2, guglielmi2024sporadicinclusionbody pages 1-2)

Names and identifiers

Preferred name: inclusion body myositis.
Synonyms: sporadic inclusion body myositis, sIBM, IBM; older literature sometimes uses “sporadic inflammatory inclusion-body myositis.”
MONDO:0007827, supported by the retrieved Open Targets disease mapping. (OpenTargets Search: inclusion body myositis)
MeSH, Orphanet, OMIM, ICD-10, and ICD-11 identifiers were not directly verified in the retrieved primary text and should be imported only after validation against the current source databases. IBM should not be conflated with GNE myopathy or VCP-, MYH2-, LAMA2-, SQSTM1-, or HNRNPA2B1-related hereditary inclusion-body disorders. (OpenTargets Search: inclusion body myositis, nagy2023inclusionbodymyositis pages 5-6)

A concise 2024 description is: “slowly progressive asymmetrical muscle weakness, predominantly affecting the quadriceps, deep finger flexors, and foot extensors.” [Guglielmi et al., February 2024, DOI/URL: https://doi.org/10.3390/ijms25052742]. (guglielmi2024sporadicinclusionbody pages 1-2)

2. Etiology and risk factors

Causal model

The initiating cause is unknown. Current expert interpretation is a multifactorial interaction among age-related susceptibility, adaptive autoimmunity, myofiber stress, defective proteostasis/autophagy, mitochondrial dysfunction, and tissue-resident stromal-cell abnormalities. Whether immune injury or cell-autonomous degeneration is the first event remains disputed. The strong HLA signal and clonally expanded cytotoxic T cells support an upstream autoimmune component; treatment refractoriness and persistent senescent/degenerative programs indicate that downstream autonomous mechanisms can maintain disease. (greenberg2019inclusionbodymyositis pages 10-11, guglielmi2024sporadicinclusionbody pages 1-2, nagy2023inclusionbodymyositis pages 2-5, nelke2023senescentfibroadipogenicprogenitors pages 1-2)

Genetic susceptibility—not Mendelian causation

IBM has no established single causal gene or Mendelian inheritance pattern. The strongest association is in the HLA/MHC region; an Immunochip study of 2,566 European idiopathic inflammatory-myopathy cases found genome-wide-significant MHC association, with reported IBM-associated alleles including HLA-DRB103:01, HLA-DRB101:01, and HLA-DRB1*13:01. CCR5 and rare variants in proteostasis/autophagy genes such as VCP, SQSTM1, and FYCO1 have been reported, but none is a validated monogenic explanation for ordinary sIBM. (nagy2023inclusionbodymyositis pages 2-5, nagy2023inclusionbodymyositis pages 5-6)

Open Targets lists GNE, MYH2, and ACVR2B under the broad IBM label, but the retrieved records contain no causal genetic evidence for GNE or MYH2 in sporadic IBM. GNE and MYH2 are principally relevant to inherited mimics, whereas ACVR2B is a therapeutic target studied with bimagrumab. (OpenTargets Search: inclusion body myositis)

Demographic and environmental factors

Age is the strongest established risk context: mean onset is approximately 60 years.
Male sex is associated with roughly twice the frequency of disease.
Familial sIBM is exceptional; family history should prompt reconsideration of a hereditary myopathy.
HIV and hepatitis C have been associated with IBM-like disease and premature immune-cell exhaustion, but neither is established as a general cause of sIBM. No toxin, occupation, smoking pattern, diet, alcohol exposure, or other lifestyle factor has reproducibly been shown to cause IBM. (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2, nelke2022inclusionbodymyositis pages 1-2)

Protective factors and gene–environment interaction

No validated genetic protective allele, diet, exposure, drug, vaccination, or behavioral intervention prevents IBM. Gene–environment interaction remains hypothetical: HLA-mediated antigen presentation may interact with aging, chronic immune stimulation, mitochondrial damage, or infection, but no quantitative interaction model has been established. Absence of evidence should not be encoded as evidence of no interaction.

3. Phenotypes

Phenotype	Character and course	Frequency/severity evidence	Suggested HPO annotation
Finger-flexor weakness/atrophy	Painless, distal upper-limb, often asymmetric; impaired grip and fine hand use	Defining/common phenotype	Finger flexor weakness; distal upper-limb muscle weakness; muscle atrophy
Quadriceps/knee-extensor weakness	Progressive proximal lower-limb weakness; difficulty rising, stairs, knee buckling	Defining/common; major cause of falls and loss of ambulation	Quadriceps weakness; proximal lower-limb weakness
Falls and gait impairment	Progressive; may precede diagnosis	Common; wheelchair dependence usually follows in 10–15 years	Frequent falls; abnormal gait; impaired mobility
Dysphagia	Predominantly pharyngeal; can be presenting or isolated; aspiration risk	Common, clinically important, and associated with premature mortality	Dysphagia; oropharyngeal dysphagia; aspiration
Foot drop	Distal lower-limb involvement, sometimes atypical presentation	Less common	Foot dorsiflexor weakness; foot drop
Axial, neck, facial, or bulbar weakness	Usually later or atypical	Uncommon/variable	Axial muscle weakness; neck muscle weakness; facial weakness
Hyper-CKemia	Usually modest; occasionally asymptomatic presentation	Variable	Elevated serum creatine kinase
Respiratory complications	Often secondary to aspiration or advanced neuromuscular weakness	Important mortality driver rather than usual initial phenotype	Respiratory insufficiency; recurrent aspiration pneumonia

These phenotype assignments are supported by recent clinical reviews describing asymmetric finger-flexor/quadriceps weakness, foot-extensor involvement, dysphagia, and atypical axial or bulbar presentations. (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2, guglielmi2024sporadicinclusionbody pages 1-2)

Quality of life deteriorates through loss of grip, stair climbing, transfers, independent ambulation, safe oral intake, and social participation. A 2024 analysis of 150 trial participants found mean IBM Functional Rating Scale (IBMFRS) 27.4±4.6; a decline of at least two points represented meaningful deterioration. IBMFRS showed adequate internal consistency (α=0.79) and excellent test–retest reliability (ICC 0.84–0.87). [Salam et al., July 2024, https://doi.org/10.1136/jnnp-2024-333617].

4. Genetic and molecular information

Causal variants and chromosomal abnormalities

No pathogenic germline variant, somatic mutation, recurrent chromosomal abnormality, copy-number change, or repeat expansion defines sIBM. Consequently, ACMG variant classification, carrier frequency, penetrance, anticipation, germline mosaicism, founder effects, and prenatal testing are not applicable to typical sIBM.

Hereditary mimics include:

GNE—GNE myopathy, OMIM 608209 in the retrieved review;
VCP—multisystem proteinopathy/inclusion-body myopathy with Paget disease and frontotemporal degeneration;
MYH2—myopathy with congenital joint contractures, OMIM 605637 in the retrieved review;
LAMA2—a reported hereditary inclusion-body phenotype with leukoencephalopathy;
SQSTM1, HNRNPA2B1, and related multisystem proteinopathy genes in appropriate syndromic presentations. (OpenTargets Search: inclusion body myositis, nagy2023inclusionbodymyositis pages 5-6)

Modifiers and epigenetics

HLA alleles may modify susceptibility and phenotype, but validated severity-modifier genes are lacking. Disease-specific DNA-methylation, histone-modification, or chromatin biomarkers are not sufficiently established for clinical annotation. The recent evidence base is predominantly transcriptomic rather than epigenomic.

5. Environmental information

No reproducible causal toxin, radiation exposure, pollutant, occupational agent, dietary exposure, smoking pattern, or alcohol association is established. Chronic HIV or HCV infection may generate IBM-like muscle disease through persistent antigenic stimulation and senescent/exhausted CD8 T-cell biology, but this is association and mechanistic analogy, not proof that these pathogens cause ordinary IBM. (nelke2022inclusionbodymyositis pages 1-2)

Exercise should not be classified as a primary protective exposure. Once IBM is present, supervised resistance/aerobic programs appear safe and may improve strength or conditioning, although consistent mobility improvement has not been demonstrated. (guglielmi2024sporadicinclusionbody pages 19-20)

6. Mechanism and pathophysiology

Proposed causal chain

Upstream susceptibility: aging muscle plus HLA-mediated immune susceptibility and an unidentified initiating antigen or stressor.
Adaptive immune activation: clonally expanded, terminally differentiated CD8+CD28−/CD57+/KLRG1+ cytotoxic T cells accumulate in endomysium and invade non-necrotic fibers.
IFN-γ/MHC-I loop: IFN-γ promotes myofiber MHC-I expression, antigen presentation, ER stress, and further cytotoxic recognition; perforin and granzymes contribute to injury.
Cell-autonomous amplification: oxidative/nitrative and ER stress, impaired ubiquitin–proteasome activity, defective autophagy/mitophagy, and mitochondrial DNA damage impair protein and organelle turnover.
Degeneration: rimmed vacuoles and aggregates containing p62/SQSTM1, TDP-43, LC3, VCP, and other proteins accumulate; type-2 fibers are selectively lost, denervation-like programs emerge, and muscle is replaced by fat/connective tissue.
Clinical expression: finger-flexor and quadriceps weakness, falls, loss of hand function and ambulation, and pharyngeal weakness causing dysphagia and aspiration. (greenberg2019inclusionbodymyositis pages 10-11, guglielmi2024sporadicinclusionbody pages 1-2, nagy2023inclusionbodymyositis pages 2-5, wischnewski2024celltypemapping pages 1-2)

In human biopsy material, invasion of non-necrotic fibers is reported to be about eight times more frequent than amyloid-containing fibers, supporting the expert view that immune injury can precede visible aggregation. Nonetheless, the autoimmune-first model is not proven universally. (greenberg2019inclusionbodymyositis pages 10-11)

Mitochondria and metabolism

IBM muscle has COX-deficient/ragged-red fibers, mtDNA deletions and duplications, impaired mitophagy, and oxidative stress. One synthesis reported median mtDNA heteroplasmy around 10% in IBM versus 1% in controls, with broader ranges of 1–35% versus 0.2–3%. These abnormalities may be downstream of chronic inflammation but can themselves release danger signals and perpetuate non-apoptotic injury and inflammation. (nelke2022inclusionbodymyositis pages 1-2)

Autoantibodies

Anti-cytosolic 5′-nucleotidase 1A (anti-cN1A, also NT5C1A/Mup44) occurs in up to approximately 60% of cases, but it is neither sufficiently sensitive nor uniquely specific to establish diagnosis or mechanism. Its pathogenic importance remains uncertain. (guglielmi2024sporadicinclusionbody pages 1-2, nagy2023inclusionbodymyositis pages 2-5, greenberg2019inclusionbodymyositis pages 5-7)

2023–2024 advanced profiling

Wischnewski et al., Nature Aging, June 2024: snRNA-seq of quadriceps from 8 IBM, 4 immune-mediated necrotizing myopathy, and 7 controls generated 93,345 nuclei; spatial transcriptomics added 7,462 spots. IBM showed selective type-2 myonuclear loss, increased cytotoxic T cells and conventional type-1 dendritic cells, GADD45A/NORAD stress programs, RNF7-associated protein degradation, p62 aggregates, and IBM-specific ACHE upregulation consistent with functional denervation. https://doi.org/10.1038/s43587-024-00645-9. (wischnewski2024celltypemapping pages 1-2)
Nelke et al., Acta Neuropathologica, September 2023: biopsies from 16 IBM, 16 controls, and 16 necrotizing-myopathy patients identified fibro-adipogenic progenitors—not myofibers—as the principal senescent population. IBM FAPs expressed p21, β-galactosidase activity, inflammatory secretory programs, and lost collagen XV required for myofiber integrity and neuromuscular-junction support. https://doi.org/10.1007/s00401-023-02637-2. (nelke2023senescentfibroadipogenicprogenitors pages 1-2)
Cantó-Santos et al., Antioxidants, August 2023: multi-compartment RNA/metabolite profiling included saliva, urine, plasma, fibroblasts, and muscle. It found respiratory-chain/oxidative-stress abnormalities and proposed urinary L-pyroglutamic plus orotic acid as a 100%-sensitivity/100%-specificity signature in a very small discovery cohort; this is exploratory and requires independent validation. https://doi.org/10.3390/antiox12081639. (cantosantos2023integratedmultiomicsanalysis pages 2-3)

Suggested GO terms include interferon-gamma-mediated signaling, antigen processing and presentation, T-cell-mediated cytotoxicity, autophagy, mitophagy, proteasomal protein catabolism, response to oxidative stress, ER stress, cellular senescence, and mitochondrial organization. Suggested CL concepts include skeletal muscle fiber, CD8-positive αβ T cell, conventional dendritic cell type 1, fibro-adipogenic progenitor, macrophage, and satellite cell.

7. Anatomical structures affected

The primary organ is skeletal muscle. Selective sites include quadriceps/knee extensors, forearm deep finger flexors, ankle dorsiflexors, and pharyngeal/cricopharyngeal musculature; neck and facial muscles can be involved. Disease is generally bilateral but characteristically asymmetric. Cardiac muscle, skin, brain, and peripheral nerves are not primary target organs, although peripheral neuropathy and systemic autoimmune comorbidities occur more often than expected. (naddaf2022inclusionbodymyositis pages 1-2, guglielmi2024sporadicinclusionbody pages 1-2)

Suggested UBERON concepts: skeletal musculature, quadriceps femoris, flexor digitorum profundus, tibialis anterior, pharyngeal muscle, and upper esophageal sphincter. Relevant GO cellular components include mitochondrion, lysosome/autolysosome, endoplasmic reticulum, proteasome complex, sarcoplasm, myonucleus, and neuromuscular junction.

8. Temporal development

Onset is usually insidious after age 45–50, with diagnostic delay often extending several years. The course is chronic, lifelong, and steadily progressive rather than episodic or relapsing-remitting. Strength declines have been estimated at approximately 4–28% per year across measures and cohorts. Cane-free ambulation is commonly lost around 7.5–10 years, and wheelchair dependence develops around 13–15 years after onset. Spontaneous or durable treatment-induced remission is not characteristic. (nagy2023inclusionbodymyositis pages 1-2, greenberg2019inclusionbodymyositis pages 5-7)

Rare early-onset IBM exists. In a 2023 western-Swedish population study, six patients had median onset at 36 years (range 34–45), quadriceps decline of 1.21±0.2 N or 0.91±0.2% per month, swallowing difficulty in five of six, and median survival from diagnosis of 14 years. [Lindgren et al., July 2023, https://doi.org/10.1007/s00415-023-11878-w].

There is no validated biological “critical period,” but early recognition permits fall prevention, exercise, swallowing surveillance, nutrition intervention, and trial participation before irreversible disability.

9. Inheritance and population epidemiology

IBM is sporadic and likely multifactorial/polygenic; classic Mendelian inheritance, penetrance, carrier frequency, anticipation, consanguinity effects, and germline mosaicism do not apply.

Reported prevalence varies from approximately 5–180 per million, reflecting geography, age structure, ascertainment, and diagnostic criteria. Estimates restricted to people aged ≥50 can range from roughly 1–182 per million. Male:female ratio is approximately 2:1, and mean onset is near 60 years. (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2, guglielmi2024sporadicinclusionbody pages 1-2)

No robust ethnic hierarchy is established. Higher reported prevalence in populations of European ancestry may reflect HLA background, population age, specialist access, and ascertainment. Geographic comparisons should therefore preserve denominator age and diagnostic criteria.

10. Diagnostics

Clinical and laboratory work-up

Diagnosis is multimodal: characteristic weakness pattern, CK, EMG, muscle MRI, serology, and biopsy. CK is generally normal to moderately raised rather than at the very high levels typical of necrotizing autoimmune myopathy. EMG may show mixed myopathic and apparent neurogenic changes and is supportive, not specific. MRI helps identify selective muscle atrophy/fatty replacement and an appropriate biopsy site. (nagy2023inclusionbodymyositis pages 1-2)

Anti-cN1A

Reported specificity is approximately 90–95%, but sensitivity varies widely, about 37–76%. Positive results support IBM only in the appropriate clinical context because anti-cN1A can occur in Sjögren disease, lupus, and other conditions; a negative test does not exclude IBM. (greenberg2019inclusionbodymyositis pages 5-7)

Biopsy

Canonical findings are:

endomysial CD8-rich inflammation;
invasion of non-necrotic MHC-I-positive fibers;
rimmed vacuoles;
p62/SQSTM1- and TDP-43-positive sarcoplasmic inclusions;
COX-negative and ragged-red fibers;
congophilic aggregates and, on electron microscopy, 15–18-nm tubulofilaments.

Not every feature is present in an early or poorly targeted biopsy. Clinicopathologic criteria incorporating weakness distribution, inflammation, invasion, and rimmed vacuoles have reported sensitivity near 90% and specificity near 96% in the cited synthesis. (greenberg2019inclusionbodymyositis pages 5-7, nagy2023inclusionbodymyositis pages 1-2)

Differential diagnosis

Important mimics are polymyositis, immune-mediated necrotizing myopathy, antisynthetase/overlap myositis, muscular dystrophies, GNE myopathy, VCP multisystem proteinopathy, myofibrillar myopathy, dysferlinopathy, motor-neuron disease, peripheral neuropathy, sarcoid/granulomatous myopathy, and structural causes of dysphagia. Steroid-refractory “polymyositis,” especially with finger-flexor or quadriceps selectivity, should trigger reassessment for IBM.

Genetic and omics testing

WES/WGS, panels, mtDNA testing, repeat-expansion testing, CMA, karyotyping, and FISH are not confirmatory tests for typical IBM. A hereditary-myopathy panel or exome/genome analysis is appropriate for early onset, family history, atypical distribution, Paget disease, dementia, motor-neuron disease, congenital contractures, or absent inflammation. Experimental urine metabolomics and tissue transcriptomics are not validated clinical diagnostics. (cantosantos2023integratedmultiomicsanalysis pages 2-3, nagy2023inclusionbodymyositis pages 5-6)

There is no population, newborn, carrier, or cascade screening program.

11. Outcome and prognosis

IBM causes severe long-term disability: loss of grip and fine hand function, recurrent falls, impaired transfers, wheelchair dependence, dysphagia, weight loss, aspiration, and caregiver dependence. Most patients do not recover lost strength. Longevity is mildly reduced compared with the general population, with aspiration pneumonia and respiratory complications the leading disease-related causes of death. (naddaf2022inclusionbodymyositis pages 1-2, nagy2023inclusionbodymyositis pages 1-2)

Reported associated conditions include peripheral neuropathy (approximately 2.7-fold greater likelihood), Sjögren syndrome (6.2-fold), and hematologic malignancy including T-cell large-granular-lymphocytic leukemia (3.9-fold), although these associations do not make IBM a conventional paraneoplastic syndrome. (naddaf2022inclusionbodymyositis pages 1-2, damian2022inclusionbodymyositis pages 1-2)

Prognosis is driven primarily by baseline severity, disease duration, rate of lower-limb decline, dysphagia/aspiration, respiratory complications, falls, and nutritional status. No molecular prognostic biomarker is validated. Anti-cN1A has inconsistent phenotype/prognosis associations.

12. Treatment

Current real-world strategy

There is no established disease-modifying drug. Conventional glucocorticoids, methotrexate, azathioprine, and most tested biologics generally fail to produce durable functional benefit and can add toxicity. Management is multidisciplinary and supportive. (naddaf2022inclusionbodymyositis pages 1-2, guglielmi2024sporadicinclusionbody pages 19-20, schmidt2018currentclassificationand pages 12-14)

Physical and occupational therapy: individualized resistance/aerobic exercise, contracture prevention, energy conservation, home modification, orthoses, canes/walkers, wheelchairs, transfer devices, and fall prevention. Exercise studies suggest strength benefit but not consistent mobility improvement. Suggested MAXO: physical therapy, exercise therapy, occupational therapy, assistive-device provision. (guglielmi2024sporadicinclusionbody pages 19-20)
Swallowing care: at least annual symptom screening, speech-language assessment, videofluoroscopy or endoscopy when indicated, texture/volume adaptation, nutrition support, and aspiration precautions. Temporary benefit from IVIG is reported in selected dysphagic patients, but IVIG does not alter overall progression. Cricopharyngeal dilation, botulinum toxin, or myotomy may help selected obstructive cases; myotomy is irreversible. Suggested MAXO: swallow evaluation, speech therapy, intravenous immunoglobulin administration, endoscopic dilation, botulinum-toxin injection, cricopharyngeal myotomy. (guglielmi2024sporadicinclusionbody pages 18-19, naddaf2022inclusionbodymyositis pages 6-7, schmidt2018currentclassificationand pages 12-14)
Respiratory and general care: monitor cough, nocturnal hypoventilation, aspiration, weight, and vaccinations appropriate for age and respiratory risk; treat infection promptly.

Major experimental programs

Arimoclomol, a heat-shock-response/proteostasis amplifier, was tested in a 150-participant, 20-month randomized trial (NCT02753530). The 2023 Lancet Neurology publication did not establish clinically meaningful efficacy; it is not standard care.
Bimagrumab, an anti-ACVR2B antibody intended to increase muscle mass, was tested in NCT01925209 (251 participants) and extension NCT02573467 (211). It increased lean mass in some studies but failed the primary 6-minute-walk functional endpoint, illustrating that hypertrophy does not necessarily restore diseased muscle function. (OpenTargets Search: inclusion body myositis, schmidt2018currentclassificationand pages 12-14)
Sirolimus/rapamycin inhibits mTOR, restrains effector T cells, and promotes autophagy. A 44-person phase 2b study missed its primary quadriceps-strength endpoint but showed signals on selected secondary outcomes. Phase 3 NCT04789070 enrolled approximately 140 and was active, not recruiting, in the retrieved registry snapshot. (naddaf2022inclusionbodymyositis pages 6-7, schmidt2018currentclassificationand pages 12-14)
ABC008/ulviprubart is an anti-KLRG1 monoclonal antibody designed to deplete highly differentiated cytotoxic T cells while sparing broader immunity. Phase 1 NCT04659031 enrolled 19; phase 2/3 NCT05721573 enrolled 272 and was listed completed in the retrieved registry snapshot. Peer-reviewed definitive functional efficacy was not available in the retrieved evidence, so it remains investigational. (guglielmi2024sporadicinclusionbody pages 18-19, naddaf2022inclusionbodymyositis pages 6-7)
Other approaches include phenylbutyrate (NCT04421677; phase 1, 10 participants), blood-flow-restricted exercise (NCT02317094; 22), adipose-derived regenerative cells (NCT04975841; 9), intramuscular adipose stromal-vascular-fraction therapy (NCT05032131; planned 32), and follistatin gene transfer. None is established therapy. (guglielmi2024sporadicinclusionbody pages 19-20)

No validated IBM pharmacogenomic algorithm, approved gene therapy, RNA therapy, or genotype-guided treatment exists.

13. Prevention

Primary prevention: unavailable because the initiating cause and modifiable risk factors are unknown. No vaccine, prophylactic medication, dietary strategy, or environmental intervention prevents IBM.

Secondary prevention: no asymptomatic population screening is recommended. Earlier clinical recognition—particularly of asymmetric finger-flexor/quadriceps weakness or otherwise unexplained late-life dysphagia—can reduce diagnostic delay and avoid ineffective immunosuppression.

Tertiary prevention: the practical priority. It includes fall-risk assessment, mobility aids, supervised exercise, home safety modification, swallowing surveillance, aspiration precautions, nutrition/weight monitoring, respiratory assessment, vaccination according to routine age/risk schedules, and treatment of osteoporosis or infection. These measures prevent complications rather than disease onset. (naddaf2022inclusionbodymyositis pages 6-7, schmidt2018currentclassificationand pages 12-14)

Genetic counseling is indicated only when early onset, family history, Paget disease, dementia, congenital contractures, or another syndromic clue suggests a hereditary inclusion-body myopathy.

14. Other species and naturally occurring disease

No well-validated naturally occurring animal disease faithfully reproducing human sporadic IBM was established in the retrieved evidence. Accordingly, no specific companion-animal breed, VBO term, cross-species transmission route, or zoonotic potential should be assigned. IBM is not infectious or zoonotic.

Reports of vacuolar/inclusion-body myopathies in animals should not automatically be treated as orthologous sIBM because they may lack the characteristic human combination of HLA-linked autoimmunity, clonally expanded cytotoxic T cells, selective finger-flexor/quadriceps disease, aging, and proteostatic pathology.

15. Model organisms and experimental systems

The absence of a faithful model is a major translational bottleneck. VCP-mutant mice reproduce portions of hereditary VCP multisystem proteinopathy but only partially model sporadic IBM and cannot establish sIBM drug efficacy. (guglielmi2024sporadicinclusionbody pages 19-20)

Available reductionist systems include patient muscle biopsies, primary myoblasts, fibroblasts, ex-vivo immune cells, and induced stress/protein-aggregation paradigms. IBM primary myoblast studies have shown that the mitochondria-targeting compound MA-5 can increase ATP and reduce mitochondrial reactive oxygen species, but cultured cells do not recreate chronic HLA-restricted immunity, aging stroma, selective muscle distribution, or years-long progression. (guglielmi2024sporadicinclusionbody pages 20-22)

Recent human-biopsy snRNA-seq and spatial transcriptomics are therefore especially valuable because they preserve disease-relevant cell composition and tissue location, although they are cross-sectional and cannot alone establish causal ordering. (wischnewski2024celltypemapping pages 1-2, nelke2023senescentfibroadipogenicprogenitors pages 1-2)

Overall expert assessment

IBM is best represented as an acquired, late-onset, HLA-associated inflammatory-degenerative myopathy without a validated monogenic cause. The strongest current model is a self-reinforcing circuit in which clonally expanded cytotoxic T cells and IFN-γ/MHC-I signaling initiate or amplify myofiber injury, while proteostasis failure, mitochondrial damage, type-2-fiber vulnerability, functional denervation, and senescent fibro-adipogenic progenitors make the process progressively autonomous and resistant to broad immunosuppression. The most important 2023–2024 advance is the cell-type-resolved demonstration that IBM involves not only lymphocytes and myofibers but also dendritic cells and senescent stromal progenitors. Clinically, early diagnosis and rigorous tertiary prevention remain more effective than any current pharmacotherapy; sirolimus and KLRG1-directed therapy represent rational but still investigational attempts to address the immune–degenerative interface. (greenberg2019inclusionbodymyositis pages 10-11, wischnewski2024celltypemapping pages 1-2, nelke2023senescentfibroadipogenicprogenitors pages 1-2)

References

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(OpenTargets Search: inclusion body myositis): Open Targets Query (inclusion body myositis, 14 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(nagy2023inclusionbodymyositis pages 5-6): Sara Nagy, Alaa Khan, Pedro M. Machado, and Henry Houlden. Inclusion body myositis: from genetics to clinical trials. Journal of Neurology, 270:1787-1797, Nov 2023. URL: https://doi.org/10.1007/s00415-022-11459-3, doi:10.1007/s00415-022-11459-3. This article has 32 citations and is from a domain leading peer-reviewed journal.
(naddaf2022inclusionbodymyositis pages 6-7): Elie Naddaf. Inclusion body myositis: update on the diagnostic and therapeutic landscape. Frontiers in Neurology, Sep 2022. URL: https://doi.org/10.3389/fneur.2022.1020113, doi:10.3389/fneur.2022.1020113. This article has 73 citations and is from a peer-reviewed journal.
(nagy2023inclusionbodymyositis pages 2-5): Sara Nagy, Alaa Khan, Pedro M. Machado, and Henry Houlden. Inclusion body myositis: from genetics to clinical trials. Journal of Neurology, 270:1787-1797, Nov 2023. URL: https://doi.org/10.1007/s00415-022-11459-3, doi:10.1007/s00415-022-11459-3. This article has 32 citations and is from a domain leading peer-reviewed journal.
(nelke2022inclusionbodymyositis pages 1-2): Christopher Nelke, Felix Kleefeld, Corinna Preusse, Tobias Ruck, and Werner Stenzel. Inclusion body myositis and associated diseases: an argument for shared immune pathologies. Acta Neuropathologica Communications, Jun 2022. URL: https://doi.org/10.1186/s40478-022-01389-6, doi:10.1186/s40478-022-01389-6. This article has 44 citations and is from a peer-reviewed journal.
(greenberg2019inclusionbodymyositis pages 10-11): Steven A. Greenberg. Inclusion body myositis: clinical features and pathogenesis. Nature Reviews Rheumatology, 15:257-272, Mar 2019. URL: https://doi.org/10.1038/s41584-019-0186-x, doi:10.1038/s41584-019-0186-x. This article has 338 citations and is from a domain leading peer-reviewed journal.
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Artifacts

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OpenScientist Report

Classifications

Comorbidities

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Histopathology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Biochemical Markers

Differential Diagnoses

Clinical Trials

Source YAML

References & Deep Research

Deep Research

1. Disease Information

1.1 Overview

1.2 Key identifiers (all verified from the MONDO:0007827 record via OAK)

1.3 Synonyms (verified synonym: lines from MONDO)

1.4 Information provenance

2. Etiology

2.1 Overall causal model

2.2 Genetic risk factors

2.3 Environmental / acquired risk factors

2.4 Protective factors

2.5 Gene–environment interactions

3. Phenotypes

3.1 Cardinal motor phenotypes

3.2 Bulbar phenotypes

3.3 Laboratory phenotypes

3.4 Electrophysiological phenotypes

3.5 Histopathological phenotypes (biopsy-defined)

3.6 Phenotype characteristics summary

3.7 Quality-of-life impact (per phenotype)

4. Genetic / Molecular Information

4.1 Causal genes

4.2 Susceptibility / risk genes (curate with relationship_type: SUSCEPTIBILITY)

4.3 Pathogenic variants

4.4 Somatic genetic changes

4.5 The IBM / T-LGL leukaemia overlap (a major, under-appreciated finding)

4.6 Modifier genes

4.7 Epigenetics

4.8 Chromosomal abnormalities

5. Environmental Information

6. Mechanism / Pathophysiology

6.1 Proposed causal chain (upstream → downstream)

6.2 Molecular pathways

6.3 Cell types involved (CL terms, OAK-verified)

6.4 Anatomical and subcellular localization

6.5 Molecular profiling

7. Anatomical Structures Affected

Organ level

Selective muscle involvement — the diagnostic signature

Lateralization

Tissue/cell level

Subcellular

8. Temporal Development

Onset

Progression

Patterns

9. Inheritance and Population

9.1 Epidemiology

9.2 Inheritance

9.3 Population demographics

10. Diagnostics

10.1 Clinical diagnostic criteria

10.2 Serological biomarker: anti-cN1A / anti-NT5C1A

10.3 Laboratory tests

10.4 Imaging

10.5 Electrophysiology

10.6 Muscle biopsy (the historical gold standard)

10.7 Swallow assessment

10.8 Genetic testing

10.9 Omics-based diagnostics

10.10 Differential diagnosis

10.11 Screening

11. Outcome / Prognosis

1.3 Synonyms (verified `synonym:` lines from MONDO)

4.2 Susceptibility / risk genes (curate with `relationship_type: SUSCEPTIBILITY`)

Appendix C — Recommended `discussions` entries (knowledge gaps and model mismatches)