Monomelic Amyotrophy

Acquired MONDO:0011224 Pathograph 8 Show in embeddings browser Motor Neuron Disease

Monomelic amyotrophy (MA; Hirayama disease, juvenile muscular atrophy of the distal upper extremity, juvenile non-progressive amyotrophy of the distal upper limb) is a rare, benign, focal, usually self-limiting lower-motor-neuron disorder that predominantly affects adolescent and young-adult males. The prevailing pathogenic model is a cervical flexion myelopathy: repeated or sustained neck flexion produces forward displacement of the posterior cervical dural sac, compressing and flattening the lower cervical cord (C7-T1) against the vertebral bodies and generating an enlarged crescentic dorsal epidural space. The resulting chronic, repetitive microcirculatory compromise causes ischemic injury to the anterior horn (ventral horn) motor neurons, the structure most vulnerable to ischemia in the cord. Clinically this yields insidious, asymmetric, distal upper-limb (hand and forearm) muscular weakness and wasting with characteristic sparing of the brachioradialis ("oblique amyotrophy"), often with cold paresis and a fine irregular tremor of the fingers. The disorder is largely sporadic, distinguished from progressive motor neuron diseases such as ALS by its spontaneous arrest after a few years of progression. Diagnosis rests on dynamic flexion MRI demonstrating the forward-shifting dura and crescentic epidural component; early cervical-collar therapy that limits neck flexion can halt progression.

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4
Pathophys.
9
Phenotypes
8
Pathograph
2
Medical Actions
3
Differentials
2
References
⚙

Pathophysiology

4
Flexion-Induced Cervical Cord Compression
Sustained or repeated neck flexion causes forward displacement of the posterior cervical dural sac and compressive antero-posterior flattening of the lower cervical cord against the vertebral bodies, with an enlarged crescentic dorsal epidural space. The dynamic anterior shift is confined to the early, progressive stage of disease and resolves in the late non-progressive stage, supporting its pathogenic significance.
spinal cord motor neuron CL:0011001
cervical spinal cord UBERON:0002726 dura mater UBERON:0002363
Downstream
Anterior Horn Motor Neuron Ischemic Injury Mechanical compression of the lower cervical cord during flexion raises intramedullary pressure and compromises the anterior-horn microcirculation, producing ischemic injury to the motor neurons.
Show evidence (2 references)
PMID:10822430 SUPPORT Human Clinical
"A distinctive finding in the disorder was forward displacement of the cervical dural sac and compressive flattening of the lower cervical cord during neck flexion."
Documents the forward dural displacement and cord flattening on neck flexion as the proximal mechanical lesion.
PMID:35136641 SUPPORT Human Clinical
"There was anterior displacement of the thecal sac and spinal cord, and an enlarged, crescent-shaped dorsal epidural space"
Confirms the anterior thecal-sac displacement and crescentic dorsal epidural space seen on flexion MRI.
Anterior Horn Motor Neuron Ischemic Injury
Compression of the lower cervical cord during neck flexion increases intramedullary pressure and disturbs the microcirculation of the anterior (ventral) horn, the spinal structure most vulnerable to ischemia. The resulting chronic, repetitive ischemia produces ischemic necrotic change of the C5-T1 anterior horns (most severe at C7-C8) with loss of lower motor neurons, while the intramedullary and extramedullary vessels themselves remain structurally normal.
spinal cord motor neuron CL:0011001
Response to ischemia GO:0002931 ↑ INCREASED Anterior horn microcirculation GO:0008015 ↓ DECREASED Motor neuron death GO:0051402 ↑ INCREASED
ventral horn of spinal cord UBERON:0002257
Downstream
Asymmetric Distal Lower-Motor-Neuron Denervation Ischemic loss of C7-T1 anterior-horn motor neurons denervates the hand and forearm muscles in their myotomal distribution, producing asymmetric distal lower-motor-neuron weakness and wasting.
Show evidence (3 references)
PMID:18232329 SUPPORT Human Clinical
"The spinal cord showed anteroposterior flattening and ischemic necrotic changes of the anterior horns of the cervical cord at C5-T1, mostly severe at C7 and C8"
Autopsy neuropathology demonstrates ischemic necrotic change of the lower cervical anterior horns, the substrate of the motor neuron loss.
PMID:18232329 SUPPORT Human Clinical
"the compressed cervical cord at the segments induce an increased intramedullary pressure, resulting in microcirculatory disturbance in the anterior horn, the most vulnerable structure to ischemia in the spinal cord"
States the mechanistic link from cord compression to raised intramedullary pressure and anterior-horn microcirculatory disturbance.
PMID:22032508 SUPPORT Other
"causing compression of the cervical cord, and results in atrophic and ischemic changes in the anterior horn"
Review confirms that flexion-induced cord compression produces ischemic and atrophic anterior-horn change.
Asymmetric Distal Lower-Motor-Neuron Denervation
Loss of C7, C8, and T1 anterior-horn motor neurons produces chronic (and at times acute) neurogenic denervation of the muscles in these myotomes, manifest as pure motor focal amyotrophy of the hand and forearm. Wasting is typically unilateral or asymmetric with characteristic sparing of the brachioradialis, giving the appearance of oblique amyotrophy; EMG shows features of acute and/or chronic denervation in the C7-T1 myotomes, sometimes extending to the clinically unaffected contralateral limb.
spinal cord motor neuron CL:0011001
Downstream
Distal upper limb amyotrophy
Distal upper limb muscle weakness
Hand muscle atrophy
Fasciculations
EMG denervation (neuropathic changes)
Show evidence (2 references)
PMID:25766368 SUPPORT Human Clinical
"It is characterized by a pure motor focal amyotrophy in the distribution of C7, C8 and T1 spinal segmental-innervated muscles"
Defines the focal, pure-motor amyotrophy in the C7-T1 myotomal distribution that results from the anterior-horn lesion.
PMID:24063005 SUPPORT Human Clinical
"Electromyography shows features of acute and/or chronic denervation in C7, C8, and T1 myotomes in clinically affected limb and sometimes also in clinically unaffected contralateral limb."
Documents the neurogenic (denervation) EMG pattern in the affected myotomes, including subclinical contralateral involvement.
Self-Limiting (Spontaneous Arrest) Course
After an initially progressive phase the disorder undergoes spontaneous arrest within several years and symptoms stabilize. The dynamic forward dural displacement that drives compression is present in early progressive disease and absent in the late non-progressive stage, which is thought to underlie the benign, ultimately non-progressive course and distinguishes MA from progressive motor neuron diseases such as ALS.
Show evidence (2 references)
PMID:22032508 SUPPORT Other
"it is characterized by progressive muscular weakness and atrophy of distal upper limbs, followed by spontaneous arrest within several years"
States the hallmark spontaneous arrest within several years after an initially progressive phase.
PMID:25766368 SUPPORT Human Clinical
"differs from other motor neuron diseases by virtue of its ultimately non-progressive course"
Contrasts the ultimately non-progressive course with progressive motor neuron diseases.
⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Monomelic Amyotrophy Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
●

Phenotypes

9
Musculoskeletal 1
Skeletal muscle atrophy (asymmetric) Skeletal muscle atrophy HP:0003202
Show evidence (1 reference)
PMID:21799622 SUPPORT Human Clinical
"Neurological examination showed weak and wasted arms, forearms and hand"
Documents the weak, wasted upper-limb musculature characteristic of the disorder.
Nervous System 2
Fasciculations Fasciculations HP:0002380
Show evidence (1 reference)
PMID:24063005 SUPPORT Human Clinical
"Electromyography shows features of acute and/or chronic denervation in C7, C8, and T1 myotomes"
Electrophysiologic denervation in the affected myotomes underlies fasciculations and other lower-motor-neuron signs.
Finger tremor Tremor HP:0001337
Show evidence (1 reference)
PMID:33082767 SUPPORT Human Clinical
"hair loss over the dorsum of the hands, and bilateral minipolymyoclonus"
The Hirayama disease literature review documents bilateral minipolymyoclonus — the fine, irregular finger tremor characteristic of monomelic amyotrophy.
Other 6
Distal upper limb amyotrophy Distal upper limb amyotrophy HP:0007149
Show evidence (1 reference)
PMID:24063005 SUPPORT Human Clinical
"unilateral or bilateral asymmetric atrophy of hand and forearm with sparing of brachioradialis giving the characteristic appearance of oblique amyotrophy"
Describes the asymmetric distal hand/forearm atrophy with brachioradialis sparing (oblique amyotrophy).
Distal upper limb muscle weakness Distal upper limb muscle weakness HP:0008959
Show evidence (2 references)
PMID:29541850 SUPPORT Human Clinical
"Our patient presented with oblique amyotrophy"
Patient presentation with oblique amyotrophy reflects distal upper-limb weakness and wasting.
PMID:21799622 SUPPORT Human Clinical
"presented with one-year history of slowly progressive atrophic weakness of forearms and hands"
Case report documents slowly progressive atrophic weakness of forearms and hands.
Hand muscle atrophy Hand muscle atrophy HP:0009130
Show evidence (1 reference)
PMID:35136641 SUPPORT Human Clinical
"characterised by asymmetrical upper limb weakness and muscle atrophy in the forearm and hand"
Confirms muscle atrophy of the forearm and hand as a core feature.
EMG denervation (neuropathic changes) EMG: neuropathic changes HP:0003445
Show evidence (1 reference)
PMID:24063005 SUPPORT Human Clinical
"Electromyography shows features of acute and/or chronic denervation in C7, C8, and T1 myotomes in clinically affected limb"
EMG denervation in the affected myotomes is the electrophysiologic hallmark.
Cervical myelopathy Cervical myelopathy HP:0002318
Show evidence (1 reference)
PMID:22032508 SUPPORT Other
"Hirayama disease (juvenile muscular atrophy of distal upper extremity) is a cervical myelopathy."
Classifies the disorder as a cervical myelopathy.
Spinal cord compression Spinal cord compression HP:0002176
Show evidence (1 reference)
PMID:25766368 SUPPORT Human Clinical
"forward displacement of the posterior cervical dural sac on neck flexion with resultant cord compression"
Documents flexion-induced compression of the cervical cord.
💊

Medical Actions

2
Cervical Collar Therapy
Action: Therapeutic Procedure NCIT:C49236
A cervical collar that limits neck flexion is the mainstay of conservative management; by preventing the flexion-induced anterior dural shift and cord compression it can halt progression, particularly when applied early.
Show evidence (1 reference)
PMID:29541850 SUPPORT Human Clinical
"He has been successfully treated in a cervical collar."
Documents successful conservative management with a cervical collar.
Surgical Decompression
Action: Surgical Procedure NCIT:C15329
Surgical decompression (anterior or posterior approaches, with or without fusion) is reserved for selected patients, especially those with anterior effacement and severe cervical kyphosis during flexion.
Show evidence (1 reference)
PMID:20515348 SUPPORT Human Clinical
"The anterior decompressive approach may be better for patients showing anterior effacement and severe cervical kyphosis during neck flexion in MR imaging."
Supports surgical decompression for selected patients with anterior effacement and kyphosis.
🔀

Differential Diagnoses

3

Conditions with similar clinical presentations that must be differentiated from Monomelic Amyotrophy:

Amyotrophic Lateral Sclerosis MONDO:0004976
Overlapping Features A progressive degenerative motor neuron disease combining upper and lower motor neuron signs; distinguished from MA by its relentless progression, generalized rather than focal distribution, and absence of flexion-dependent cord compression.
Show evidence (1 reference)
PMID:25766368 SUPPORT Human Clinical
"differs from other motor neuron diseases by virtue of its ultimately non-progressive course"
The ultimately non-progressive course distinguishes MA from progressive motor neuron diseases such as ALS.
Distal Hereditary Motor Neuronopathy MONDO:0015363
Overlapping Features Inherited (often symmetric, length-dependent) lower-motor-neuron disorder; differs from sporadic, focal, flexion-dependent MA by its genetic basis and typically progressive, symmetric distribution.
Show evidence (1 reference)
PMID:24063005 SUPPORT Human Clinical
"HD differs from motor neuron diseases because of its nonprogressive course and pathologic findings of chronic microcirculatory changes in the lower cervical cord"
The nonprogressive course and microcirculatory (rather than genetic-degenerative) pathology distinguish MA from hereditary motor neuronopathies.
Syringomyelia Not Yet Curated MONDO:0017987
Overlapping Features A fluid-filled cavity (syrinx) of the spinal cord that can produce segmental lower-motor-neuron wasting of the hands; distinguished from MA by its cavitary cord lesion and frequent dissociated sensory loss.
Show evidence (1 reference)
PMID:25766368 SUPPORT Human Clinical
"It is characterized by a pure motor focal amyotrophy in the distribution of C7, C8 and T1 spinal segmental-innervated muscles"
The pure-motor focal amyotrophy of MA contrasts with the dissociated sensory loss typical of syringomyelia.
{ }

Source YAML

click to show 
name: Monomelic Amyotrophy
creation_date: "2026-06-26T00:00:00Z"
category: Acquired
description: >
  Monomelic amyotrophy (MA; Hirayama disease, juvenile muscular atrophy of the
  distal upper extremity, juvenile non-progressive amyotrophy of the distal
  upper limb) is a rare, benign, focal, usually self-limiting lower-motor-neuron
  disorder that predominantly affects adolescent and young-adult males. The
  prevailing pathogenic model is a cervical flexion myelopathy: repeated or
  sustained neck flexion produces forward displacement of the posterior cervical
  dural sac, compressing and flattening the lower cervical cord (C7-T1) against
  the vertebral bodies and generating an enlarged crescentic dorsal epidural
  space. The resulting chronic, repetitive microcirculatory compromise causes
  ischemic injury to the anterior horn (ventral horn) motor neurons, the
  structure most vulnerable to ischemia in the cord. Clinically this yields
  insidious, asymmetric, distal upper-limb (hand and forearm) muscular weakness
  and wasting with characteristic sparing of the brachioradialis ("oblique
  amyotrophy"), often with cold paresis and a fine irregular tremor of the
  fingers. The disorder is largely sporadic, distinguished from progressive
  motor neuron diseases such as ALS by its spontaneous arrest after a few years
  of progression. Diagnosis rests on dynamic flexion MRI demonstrating the
  forward-shifting dura and crescentic epidural component; early cervical-collar
  therapy that limits neck flexion can halt progression.
disease_term:
  preferred_term: monomelic amyotrophy
  term:
    id: MONDO:0011224
    label: monomelic amyotrophy
parents:
- Motor Neuron Disease
references:
- reference: PMID:22032508
  title: "Hirayama disease."
- reference: PMID:24063005
  title: "Nosology of juvenile muscular atrophy of distal upper extremity: from monomelic amyotrophy to Hirayama disease--Indian perspective."
pathophysiology:
- name: Flexion-Induced Cervical Cord Compression
  description: >
    Sustained or repeated neck flexion causes forward displacement of the
    posterior cervical dural sac and compressive antero-posterior flattening of
    the lower cervical cord against the vertebral bodies, with an enlarged
    crescentic dorsal epidural space. The dynamic anterior shift is confined to
    the early, progressive stage of disease and resolves in the late
    non-progressive stage, supporting its pathogenic significance.
  cell_types:
  - preferred_term: spinal cord motor neuron
    term:
      id: CL:0011001
      label: spinal cord motor neuron
  locations:
  - preferred_term: cervical spinal cord
    term:
      id: UBERON:0002726
      label: cervical spinal cord
  - preferred_term: dura mater
    term:
      id: UBERON:0002363
      label: dura mater
  evidence:
  - reference: PMID:10822430
    reference_title: "Cervical dural sac and spinal cord in juvenile muscular atrophy of distal upper extremity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A distinctive finding in the disorder was forward displacement of the cervical dural sac and compressive flattening of the lower cervical cord during neck flexion."
    explanation: Documents the forward dural displacement and cord flattening on neck flexion as the proximal mechanical lesion.
  - reference: PMID:35136641
    reference_title: "Hirayama disease: the importance of flexion imaging."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There was anterior displacement of the thecal sac and spinal cord, and an enlarged, crescent-shaped dorsal epidural space"
    explanation: Confirms the anterior thecal-sac displacement and crescentic dorsal epidural space seen on flexion MRI.
  downstream:
  - target: Anterior Horn Motor Neuron Ischemic Injury
    description: >
      Mechanical compression of the lower cervical cord during flexion raises
      intramedullary pressure and compromises the anterior-horn microcirculation,
      producing ischemic injury to the motor neurons.
    causal_link_type: DIRECT
- name: Anterior Horn Motor Neuron Ischemic Injury
  description: >
    Compression of the lower cervical cord during neck flexion increases
    intramedullary pressure and disturbs the microcirculation of the anterior
    (ventral) horn, the spinal structure most vulnerable to ischemia. The
    resulting chronic, repetitive ischemia produces ischemic necrotic change of
    the C5-T1 anterior horns (most severe at C7-C8) with loss of lower motor
    neurons, while the intramedullary and extramedullary vessels themselves
    remain structurally normal.
  cell_types:
  - preferred_term: spinal cord motor neuron
    term:
      id: CL:0011001
      label: spinal cord motor neuron
  locations:
  - preferred_term: ventral horn of spinal cord
    term:
      id: UBERON:0002257
      label: ventral horn of spinal cord
  biological_processes:
  - preferred_term: Response to ischemia
    term:
      id: GO:0002931
      label: response to ischemia
    modifier: INCREASED
  - preferred_term: Anterior horn microcirculation
    term:
      id: GO:0008015
      label: blood circulation
    modifier: DECREASED
  - preferred_term: Motor neuron death
    term:
      id: GO:0051402
      label: neuron apoptotic process
    modifier: INCREASED
  evidence:
  - reference: PMID:18232329
    reference_title: "Juvenile muscular atrophy of unilateral upper extremity (Hirayama disease)--half-century progress and establishment since its discovery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The spinal cord showed anteroposterior flattening and ischemic necrotic changes of the anterior horns of the cervical cord at C5-T1, mostly severe at C7 and C8"
    explanation: Autopsy neuropathology demonstrates ischemic necrotic change of the lower cervical anterior horns, the substrate of the motor neuron loss.
  - reference: PMID:18232329
    reference_title: "Juvenile muscular atrophy of unilateral upper extremity (Hirayama disease)--half-century progress and establishment since its discovery."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the compressed cervical cord at the segments induce an increased intramedullary pressure, resulting in microcirculatory disturbance in the anterior horn, the most vulnerable structure to ischemia in the spinal cord"
    explanation: States the mechanistic link from cord compression to raised intramedullary pressure and anterior-horn microcirculatory disturbance.
  - reference: PMID:22032508
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "causing compression of the cervical cord, and results in atrophic and ischemic changes in the anterior horn"
    explanation: Review confirms that flexion-induced cord compression produces ischemic and atrophic anterior-horn change.
  downstream:
  - target: Asymmetric Distal Lower-Motor-Neuron Denervation
    description: >
      Ischemic loss of C7-T1 anterior-horn motor neurons denervates the
      hand and forearm muscles in their myotomal distribution, producing
      asymmetric distal lower-motor-neuron weakness and wasting.
    causal_link_type: DIRECT
- name: Asymmetric Distal Lower-Motor-Neuron Denervation
  description: >
    Loss of C7, C8, and T1 anterior-horn motor neurons produces chronic (and at
    times acute) neurogenic denervation of the muscles in these myotomes,
    manifest as pure motor focal amyotrophy of the hand and forearm. Wasting is
    typically unilateral or asymmetric with characteristic sparing of the
    brachioradialis, giving the appearance of oblique amyotrophy; EMG shows
    features of acute and/or chronic denervation in the C7-T1 myotomes, sometimes
    extending to the clinically unaffected contralateral limb.
  cell_types:
  - preferred_term: spinal cord motor neuron
    term:
      id: CL:0011001
      label: spinal cord motor neuron
  evidence:
  - reference: PMID:25766368
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is characterized by a pure motor focal amyotrophy in the distribution of C7, C8 and T1 spinal segmental-innervated muscles"
    explanation: Defines the focal, pure-motor amyotrophy in the C7-T1 myotomal distribution that results from the anterior-horn lesion.
  - reference: PMID:24063005
    reference_title: "Nosology of juvenile muscular atrophy of distal upper extremity: from monomelic amyotrophy to Hirayama disease--Indian perspective."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Electromyography shows features of acute and/or chronic denervation in C7, C8, and T1 myotomes in clinically affected limb and sometimes also in clinically unaffected contralateral limb."
    explanation: Documents the neurogenic (denervation) EMG pattern in the affected myotomes, including subclinical contralateral involvement.
  downstream:
  - target: Distal upper limb amyotrophy
  - target: Distal upper limb muscle weakness
  - target: Hand muscle atrophy
  - target: Fasciculations
  - target: "EMG denervation (neuropathic changes)"
- name: Self-Limiting (Spontaneous Arrest) Course
  description: >
    After an initially progressive phase the disorder undergoes spontaneous
    arrest within several years and symptoms stabilize. The dynamic forward
    dural displacement that drives compression is present in early progressive
    disease and absent in the late non-progressive stage, which is thought to
    underlie the benign, ultimately non-progressive course and distinguishes MA
    from progressive motor neuron diseases such as ALS.
  evidence:
  - reference: PMID:22032508
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "it is characterized by progressive muscular weakness and atrophy of distal upper limbs, followed by spontaneous arrest within several years"
    explanation: States the hallmark spontaneous arrest within several years after an initially progressive phase.
  - reference: PMID:25766368
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "differs from other motor neuron diseases by virtue of its ultimately non-progressive course"
    explanation: Contrasts the ultimately non-progressive course with progressive motor neuron diseases.
phenotypes:
- category: Neuromuscular
  name: Distal upper limb amyotrophy
  description: >
    Wasting of the distal upper-limb (hand and forearm) muscles, typically
    asymmetric, with sparing of the brachioradialis producing oblique amyotrophy.
  phenotype_term:
    preferred_term: Distal upper limb amyotrophy
    term:
      id: HP:0007149
      label: Distal upper limb amyotrophy
  evidence:
  - reference: PMID:24063005
    reference_title: "Nosology of juvenile muscular atrophy of distal upper extremity: from monomelic amyotrophy to Hirayama disease--Indian perspective."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "unilateral or bilateral asymmetric atrophy of hand and forearm with sparing of brachioradialis giving the characteristic appearance of oblique amyotrophy"
    explanation: Describes the asymmetric distal hand/forearm atrophy with brachioradialis sparing (oblique amyotrophy).
- category: Neuromuscular
  name: Distal upper limb muscle weakness
  description: Insidious-onset weakness of the distal upper-limb muscles (hand and forearm).
  phenotype_term:
    preferred_term: Distal upper limb muscle weakness
    term:
      id: HP:0008959
      label: Distal upper limb muscle weakness
  evidence:
  - reference: PMID:29541850
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our patient presented with oblique amyotrophy"
    explanation: Patient presentation with oblique amyotrophy reflects distal upper-limb weakness and wasting.
  - reference: PMID:21799622
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "presented with one-year history of slowly progressive atrophic weakness of forearms and hands"
    explanation: Case report documents slowly progressive atrophic weakness of forearms and hands.
- category: Neuromuscular
  name: Hand muscle atrophy
  description: Atrophy of the intrinsic hand muscles innervated by the affected C8-T1 myotomes.
  phenotype_term:
    preferred_term: Hand muscle atrophy
    term:
      id: HP:0009130
      label: Hand muscle atrophy
  evidence:
  - reference: PMID:35136641
    reference_title: "Hirayama disease: the importance of flexion imaging."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characterised by asymmetrical upper limb weakness and muscle atrophy in the forearm and hand"
    explanation: Confirms muscle atrophy of the forearm and hand as a core feature.
- category: Neuromuscular
  name: Skeletal muscle atrophy (asymmetric)
  description: >
    Muscle wasting that is characteristically unilateral or asymmetric across the
    two upper limbs.
  phenotype_term:
    preferred_term: Skeletal muscle atrophy
    term:
      id: HP:0003202
      label: Skeletal muscle atrophy
  evidence:
  - reference: PMID:21799622
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurological examination showed weak and wasted arms, forearms and hand"
    explanation: Documents the weak, wasted upper-limb musculature characteristic of the disorder.
- category: Neuromuscular
  name: Fasciculations
  description: Fasciculations may accompany the denervation of affected myotomes.
  phenotype_term:
    preferred_term: Fasciculations
    term:
      id: HP:0002380
      label: Fasciculations
  evidence:
  - reference: PMID:24063005
    reference_title: "Nosology of juvenile muscular atrophy of distal upper extremity: from monomelic amyotrophy to Hirayama disease--Indian perspective."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Electromyography shows features of acute and/or chronic denervation in C7, C8, and T1 myotomes"
    explanation: Electrophysiologic denervation in the affected myotomes underlies fasciculations and other lower-motor-neuron signs.
- category: Neuromuscular
  name: EMG denervation (neuropathic changes)
  description: >
    EMG shows acute and/or chronic neurogenic denervation changes in the C7, C8,
    and T1 myotomes of the affected limb.
  phenotype_term:
    preferred_term: "EMG: neuropathic changes"
    term:
      id: HP:0003445
      label: "EMG: neuropathic changes"
  evidence:
  - reference: PMID:24063005
    reference_title: "Nosology of juvenile muscular atrophy of distal upper extremity: from monomelic amyotrophy to Hirayama disease--Indian perspective."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Electromyography shows features of acute and/or chronic denervation in C7, C8, and T1 myotomes in clinically affected limb"
    explanation: EMG denervation in the affected myotomes is the electrophysiologic hallmark.
- category: Neurological
  name: Cervical myelopathy
  description: >
    The disorder is a cervical (flexion) myelopathy of the lower cervical cord.
  phenotype_term:
    preferred_term: Cervical myelopathy
    term:
      id: HP:0002318
      label: Cervical myelopathy
  evidence:
  - reference: PMID:22032508
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Hirayama disease (juvenile muscular atrophy of distal upper extremity) is a cervical myelopathy."
    explanation: Classifies the disorder as a cervical myelopathy.
- category: Neurological
  name: Spinal cord compression
  description: >
    Dynamic forward displacement of the posterior dural sac compresses the lower
    cervical cord during neck flexion.
  phenotype_term:
    preferred_term: Spinal cord compression
    term:
      id: HP:0002176
      label: Spinal cord compression
  evidence:
  - reference: PMID:25766368
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "forward displacement of the posterior cervical dural sac on neck flexion with resultant cord compression"
    explanation: Documents flexion-induced compression of the cervical cord.
- category: Neurological
  name: Finger tremor
  description: >
    A fine, irregular tremor of the fingers (bilateral minipolymyoclonus) may
    accompany the weakness in the affected hand.
  phenotype_term:
    preferred_term: Tremor
    term:
      id: HP:0001337
      label: Tremor
  evidence:
  - reference: PMID:33082767
    reference_title: "Monomelic Amyotrophy (Hirayama Disease): A Rare Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "hair loss over the dorsum of the hands, and bilateral minipolymyoclonus"
    explanation: The Hirayama disease literature review documents bilateral minipolymyoclonus — the fine, irregular finger tremor characteristic of monomelic amyotrophy.
treatments:
- name: Cervical Collar Therapy
  description: >
    A cervical collar that limits neck flexion is the mainstay of conservative
    management; by preventing the flexion-induced anterior dural shift and cord
    compression it can halt progression, particularly when applied early.
  treatment_term:
    preferred_term: Therapeutic Procedure
    term:
      id: NCIT:C49236
      label: Therapeutic Procedure
  evidence:
  - reference: PMID:29541850
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "He has been successfully treated in a cervical collar."
    explanation: Documents successful conservative management with a cervical collar.
- name: Surgical Decompression
  description: >
    Surgical decompression (anterior or posterior approaches, with or without
    fusion) is reserved for selected patients, especially those with anterior
    effacement and severe cervical kyphosis during flexion.
  therapeutic_modality: SURGERY
  treatment_term:
    preferred_term: Surgical Procedure
    term:
      id: NCIT:C15329
      label: Surgical Procedure
  evidence:
  - reference: PMID:20515348
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The anterior decompressive approach may be better for patients showing anterior effacement and severe cervical kyphosis during neck flexion in MR imaging."
    explanation: Supports surgical decompression for selected patients with anterior effacement and kyphosis.
differential_diagnoses:
- name: Amyotrophic Lateral Sclerosis
  description: >
    A progressive degenerative motor neuron disease combining upper and lower
    motor neuron signs; distinguished from MA by its relentless progression,
    generalized rather than focal distribution, and absence of flexion-dependent
    cord compression.
  disease_term:
    preferred_term: amyotrophic lateral sclerosis
    term:
      id: MONDO:0004976
      label: amyotrophic lateral sclerosis
  evidence:
  - reference: PMID:25766368
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "differs from other motor neuron diseases by virtue of its ultimately non-progressive course"
    explanation: The ultimately non-progressive course distinguishes MA from progressive motor neuron diseases such as ALS.
- name: Distal Hereditary Motor Neuronopathy
  description: >
    Inherited (often symmetric, length-dependent) lower-motor-neuron disorder;
    differs from sporadic, focal, flexion-dependent MA by its genetic basis and
    typically progressive, symmetric distribution.
  disease_term:
    preferred_term: distal hereditary motor neuropathy
    term:
      id: MONDO:0015363
      label: "neuronopathy, distal hereditary motor, autosomal recessive"
  evidence:
  - reference: PMID:24063005
    reference_title: "Nosology of juvenile muscular atrophy of distal upper extremity: from monomelic amyotrophy to Hirayama disease--Indian perspective."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "HD differs from motor neuron diseases because of its nonprogressive course and pathologic findings of chronic microcirculatory changes in the lower cervical cord"
    explanation: The nonprogressive course and microcirculatory (rather than genetic-degenerative) pathology distinguish MA from hereditary motor neuronopathies.
- name: Syringomyelia
  description: >
    A fluid-filled cavity (syrinx) of the spinal cord that can produce
    segmental lower-motor-neuron wasting of the hands; distinguished from MA by
    its cavitary cord lesion and frequent dissociated sensory loss.
  disease_term:
    preferred_term: syringomyelia
    term:
      id: MONDO:0017987
      label: syringomyelia
  evidence:
  - reference: PMID:25766368
    reference_title: "Hirayama disease."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "It is characterized by a pure motor focal amyotrophy in the distribution of C7, C8 and T1 spinal segmental-innervated muscles"
    explanation: The pure-motor focal amyotrophy of MA contrasts with the dissociated sensory loss typical of syringomyelia.
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References & Deep Research

References

2
PMID:22032508
Hirayama disease.
No top-level findings curated for this source.
PMID:24063005
Nosology of juvenile muscular atrophy of distal upper extremity: from monomelic amyotrophy to Hirayama disease--Indian perspective.
No top-level findings curated for this source.