Hirayama disease (young male asymmetric distal UL LMNL motor weakness)

Question 1

Hirayama disease is a rare, non-progressive, focal lower motor neuron weakness due to flexion-induced cervical cord compression of displaced C5-C7 dura mater, leading to ischaemia and chronic denervation of anterior horn cells.
(Often misdiagnosed as motor neuron disease or cervical myelopathy)

Presents as:
1. Young males (15-25 years old)
2. Asymmetric distal upper limb only LMNL weakness with wasting
3. Without sensory loss.

Question 2

Epidemiology of Hirayama disease
1. Asian (Japan, China, India)
2. Pubertal age 15-25 years old
3. Male predominance (10:1)

Question 3

Pathophysiology of Hirayama disease
1. Possible hormonal and growth related changes to puberty, deficient connective tissue causing forward displacement of dura mater in lower cervical spine (C5-C7)
2. Flexion-induced cervical cord compression of displaced dura mater - repetitive microtrauma
3. Chronic ischaemia and denervation of anterior horn cells
4. Affects C7-T1 anterior horn cells, sparing bulbar and lower limbs

Question 4

Examination findings and signs in Hirayama disease

Answer 4

Inspection
1. YOUNG MALE
2. Asymmetric hand and forearm wasting / smaller than usual
3. Typically affects dominant hand
4. Symptoms worse in cold environment

Examination
5. No fasciculations
6. Probable muscle cramps in early stage
7. Distal lower motor neuron pattern weakness
- Hypotonia, hyporeflexia
- Distal hand and forearm weakness
8. Sparing of brachioradialis (elbow flexion spared)
9. NO sensation loss

Special variants - exceedingly rare
10. Bilateral involvement (O’Brien disease)
11. Upper and lower limb involvement (scapuloperoneal form)

Question 5

Diagnosis and investigations for Hirayama disease

Answer 5

Clinical diagnosis: adolescent male, insidious distal UL LMNL weakness worse with cold, without sensory loss
Progress over 3-5 years then stabilises

Investigations
1. MRI cervical spien with dynamic or flexion view - forward displaced posterior dura, compressive myelopathy
2. Electomyography - normal sensation; denervation in C7-T1 muscles
3. Nerve conduction study - no conduction block, normal velocities

Question 6

Differential diagnosis of asymmetric UL only LMNL weakness without sensory loss

Answer 6

1. Motor neuron disease (ALS, SMA) - mixed UMN and LMN
2. Multifocal motor neuropathy - has conduction block
3. Cervical spondylosis/myelopathy - UMN signs
4. Myotonic dystrophy - usually bilateral
5. Myopathies and myositis - usually bilateral

Question 7

Management of Hirayama disease

Answer 7

1. Multidisciplinary - PT OT, Ortho spine, Neurology
2. Cervical collar - prevents neck flexion and disease progression
3. Cold avoidance to reduce exacerbations
4. Spinal surgery - anterior cervical fusion or dural anchoring