Atypical type of Hirayama disease: Onset of proximal upper extremity.

Hirayama disease is a rare, benign motor neuron disease. It has been proposed that the dura mater's posterior wall lacks sufficient elasticity in the lower cervical region and this causes the tense dura part to displace anteriorly upon flexion. The disease is described as involving unilateral upper extremity with a distal-onset. We reported weakness and atrophy of the proximal part of an extremity in a 45-year-old man who is diagnosed with Hirayama disease. Proximal onset is a rare type of Hirayama Disease. Clinicians must be alert of proximal involvement and the diagnosis should be confirmed with electrophysiological and flexion MRI studies.