Hirayama disease is a rare clinical entity that presents typically as a unilateral, slowly progressive arms weakness, mostly occurring in young men.
We report a case of Hirayama disease in a 20-year-old man presenting with a 4-year history of progressive paresthesia starting in his left arm, progressing to the right arm 1 year later. Four months before the presentation, he experienced bilateral foot paresthesias. Examination revealed weakness of the abductor digiti minimi, hallux extension weakness, and postural tremor bilaterally. He had hypersensitivity to pinprick in both hands with ulnar and median distribution. Sensory examination in the legs was normal. He had a postural tremor in both hands, which worsened on neck flexion. Spinal fluid analysis, including oligoclonal band testing, was normal. Electromyography demonstrated bilateral chronic C7 and C8 radiculopathies. Laboratory tests were normal. Flexion-extension magnetic resonance imaging demonstrated laxity of the dura and ligamentum flavum, with compression of cervical cord, maximal at C5-C6 in neck flexion.
Laxity of the posterior dura during neck flexion has been postulated to lead to asymmetric lower cervical cord atrophy. Involvement of all 4 limbs is rare, and the condition can be mistaken for progressive multiple sclerosis.

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PubMed