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

name: com_Inclusion_Body_Myositis__T_Cell_Large_Granular_Lymphocytic_Leukemia
creation_date: '2026-07-31T00:00:00Z'
curation_status: CURATED
notes: >-
  The inclusion body myositis / T-cell large granular lymphocytic leukaemia
  (T-LGL) overlap is unusual among comorbidities in that it is probably not two
  diseases co-occurring but one clonal cytotoxic T-cell process meeting the
  diagnostic criteria of both. In a prospective screen of 38 IBM patients, 58%
  had blood large granular lymphocyte populations meeting standard diagnostic
  criteria for T-LGL leukaemia, and those populations were clonal in 20 of 20
  tested and stably present on repeat testing a median of 350 days later. The
  same cells invade muscle: LGL invasion was demonstrated in 15 of 15 IBM
  muscle biopsies versus 1 of 28 dermatomyositis or polymyositis biopsies, and
  the extent of CD8+ and CD57+ infiltration in muscle correlated with the size
  of the blood LGL population. This is the empirical basis for the
  `autoimmune_primary` mechanistic hypothesis in the Inclusion_Body_Myositis
  entry, and specifically for its claim that the effector clone is long-lived
  and apoptosis-resistant rather than a conventional activated T-cell response
  - which in turn is the leading explanation for why IBM resists conventional
  immunosuppression.

  Curation caveats. First, direction is left UNKNOWN: the cross-sectional design
  cannot establish whether the clonal expansion precedes the myositis or arises
  from chronic antigenic stimulation within it, and this is exactly the ordering
  question the disorder entry curates as an open CONTROVERSY. Second, the
  association should not be read as IBM causing a haematological malignancy in
  the ordinary sense - the LGL expansion in IBM is generally indolent, and
  recognising it matters clinically mainly to avoid inappropriate
  haematological workup or treatment. Third, the 58% figure comes from a single
  38-patient series at one centre and has not been replicated at scale; the
  broader deep-research literature also reports an approximately 3.9-fold
  increased rate of haematological malignancy in IBM, which is a different and
  much weaker claim than the 58% flow-cytometry overlap.

  Related associations surfaced by the deep research but NOT curated here for
  want of verified primary sources: Sjogren syndrome (~6.2x) and peripheral
  neuropathy (~2.7x). Those warrant their own comorbidity entries once the
  underlying cohort studies are fetched and their statistics quoted directly.
disease_a:
  slug: Inclusion_Body_Myositis
  preferred_term: sporadic inclusion body myositis
  term:
    id: MONDO:0007827
    label: inclusion body myositis
disease_b:
  slug: T_Cell_Large_Granular_Lymphocytic_Leukemia
  preferred_term: T-cell large granular lymphocytic leukaemia
  term:
    id: MONDO:0019469
    label: T-cell large granular lymphocyte leukemia
directionality: UNKNOWN
effect_direction: RISK
literature_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. 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: >-
    The primary quantitative basis for the association: a majority of IBM
    patients meet formal T-LGL leukaemia criteria, and the populations are
    clonal and persistent rather than transient reactive expansions.
- 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 comparison, 2/15 (14%) age-matched patients with dermatomyositis,
    polymyositis, or necrotizing myopathy, and 0/20 (0%) age-matched healthy
    subjects had large granular lymphocyte expansions
  explanation: >-
    Establishes specificity: the expansion is not a generic feature of
    inflammatory myopathy or of age-matched health, which is what makes the
    association informative rather than incidental.
- 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 leukaemic clone to the muscle lesion itself,
    supporting the reading that this is one cellular process presenting in two
    compartments rather than two independent diseases.
- reference: PMID:26920676
  reference_title: Association of inclusion body myositis with T cell large granular
    lymphocytic leukaemia.
  supports: PARTIAL
  evidence_source: HUMAN_CLINICAL
  snippet: >-
    Cross-sectional data suggested more aggressive disease in patients with such
    expansions than without.
  explanation: >-
    Suggests the LGL expansion may mark a more aggressive IBM phenotype, but the
    design is cross-sectional so this is recorded as PARTIAL and no causal or
    prognostic claim is made.
hypotheses:
- description: >-
    Shared clonal cytotoxic T-cell process rather than two independent diseases.
    The leading interpretation is that the LGL population and the
    myofibre-invading cytotoxic T cells are the same clonal, highly
    differentiated, apoptosis-resistant CD8+ effector population, detected in
    blood by flow cytometry and in muscle by immunohistochemistry. On this view
    the "comorbidity" is an artefact of diagnostic boundaries: the clone
    satisfies haematological criteria for T-LGL leukaemia while also producing
    the myositis. The correlation between muscle CD8+/CD57+ infiltration and
    blood LGL burden, and the CD57 positivity of the myofibre-invading cells,
    both support this.
  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: >-
      The extent of CD8+ and CD57+ cells in inclusion body myositis muscle
      correlated with the size of blood large granular lymphocyte populations.
    explanation: >-
      A quantitative link between the blood and muscle compartments, which is
      what distinguishes the shared-clone reading from mere co-occurrence.
  - 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: >-
      Independently characterises the muscle-invading population as terminally
      differentiated and non-proliferative, consistent with a persistent clone
      and with the observed resistance to antiproliferative immunosuppression.