A 15‑25‑year‑old male presents with insidious asymmetric weakness and wasting of the distal hand and forearm, worsened by prolonged neck flexion; what is the diagnosis and recommended evaluation and management?

Hirayama Disease: Diagnosis and Management

Definitive Diagnosis

Hirayama disease is a rare, self-limiting cervical flexion myelopathy affecting predominantly young males (15-25 years) presenting with insidious, asymmetric weakness and wasting of the distal hand and forearm muscles (C7-T1 distribution), characteristically worsened by neck flexion and notably sparing sensory function. 1

Key Clinical Features

• Unilateral or asymmetric bilateral weakness and atrophy of hand and ulnar forearm muscles, with the dominant hand typically affected first 1
• Insidious onset with initial progression over 3-5 years, followed by spontaneous stabilization 1
• Coarse tremors in the fingers during voluntary movements 1
• Cold paralysis (worsening of weakness in cold environments) 1
• Absence of objective sensory loss - this is a critical distinguishing feature 1
• No pyramidal signs in typical cases (though atypical presentations may show positive pyramidal signs) 1

Critical Diagnostic Imaging

Dynamic cervical MRI with neck flexion (30-40 degrees) is the gold standard for diagnosis and must be performed in all clinically suspected cases. 2, 1

Essential MRI Findings (Neutral Position):

• Asymmetric spinal cord flattening and localized lower cervical cord atrophy (C5-C7/cervicothoracic junction) 2, 1
• Loss of attachment between posterior dural sac and subjacent lamina 2, 1
• Straight alignment or kyphosis of cervical spine 1
• Intramedullary high signal intensity in anterior horn cells on T2-weighted imaging 1

Pathognomonic Flexion MRI Findings:

• Forward displacement of posterior cervical dural wall with anterior shift of spinal cord 3, 2
• Prominent enhancing posterior epidural space (mean thickness 5.2 mm on flexion) representing engorged venous plexus 2
• Increased cord compression between posterior vertebral body and posterior dura during flexion 4, 1

Complementary sequences such as 3D-CISS/FIESTA-C may better demonstrate epidural flow voids and should be considered. 2

Electrophysiological Confirmation

Electromyography and nerve conduction studies demonstrate:

• Segmental neurogenic damage of anterior horn cells or anterior roots at lower cervical levels (C7-T1) 1
• Normal sensory nerve conduction - critical for excluding other diagnoses 1
• Chronic denervation changes in affected muscles with preserved sensory responses 1

Differential Diagnosis Exclusions

The following must be systematically excluded:

• Sporadic inclusion body myositis: Occurs after age 50, involves proximal AND distal muscles symmetrically, affects forearm flexors and quadriceps, and shows elevated CK 5
• Amyotrophic lateral sclerosis: Shows both upper and lower motor neuron signs, progressive without plateau, involves bulbar muscles 1
• Cervical spondylotic myelopathy: Symmetric involvement, sensory deficits present, older age group, no dynamic flexion component 1
• Guillain-Barré syndrome: Acute/subacute ascending bilateral weakness, areflexia, sensory involvement, progression over days-weeks not years 6, 7

Management Algorithm

First-Line Conservative Treatment

Cervical collar immobilization to prevent neck flexion is the first-line treatment and should be initiated immediately upon diagnosis. 1

• Strict avoidance of neck flexion during all activities, especially reading, writing, and computer use 1
• Cervical collar worn continuously for 2-3 years minimum 1
• Critical pitfall: Poor brace compliance leads to treatment failure - patient education and regular follow-up are essential 4

Indications for Surgical Intervention

Surgery should be considered when:

• Progressive symptoms despite 1-2 years of adequate conservative treatment with documented collar compliance 3, 4
• Continued neurological deterioration beyond the typical 3-5 year plateau period 1
• Severe disability affecting quality of life with documented dynamic cord compression 3

Surgical Options

Multilevel instrumented anterior cervical discectomy and fusion (ACDF) maintaining slight lordosis is a reasonable option for refractory cases. 3

Alternative surgical approaches include:

• Posterior lateral mass instrumentation without fusion in lordotic alignment at levels of maximal dural shift 4
• Posterior decompression with duraplasty (less commonly performed) 1

Surgical goals: Eliminate dynamic cord compression, maintain cervical lordosis, prevent forward dural displacement during flexion 3, 4

Expected Outcomes

With appropriate treatment (collar or surgery), most patients achieve stabilization within 3-5 years with variable residual weakness but preserved function. 1

Post-surgical improvements documented include:

• Immediate intraoperative motor evoked potential amplitude improvement 3
• Modest reversal of muscle wasting at 1 year postoperatively 3
• Elimination of venous plexus engorgement on follow-up dynamic MRI 3
• Neurological improvement maintained at long-term follow-up 4

Common Pitfalls to Avoid

• Do not delay dynamic flexion MRI - neutral position MRI alone may miss the diagnosis entirely 2, 1
• Do not assume bilateral symptoms exclude Hirayama disease - asymmetric bilateral involvement occurs in up to 30% of cases 1
• Do not pursue muscle biopsy routinely - the diagnosis is clinical and radiological; biopsy shows nonspecific chronic denervation 1
• Do not mistake atypical presentations (proximal weakness, sensory deficits, pyramidal signs) as excluding the diagnosis - these occur in 10-15% of cases 1
• Do not assume self-limitation means no treatment needed - untreated cases may progress to severe disability before plateau 1