[A Case of Hirayama Disease Presenting Horn Hand: Spinal Horn Hand].

A 28-year-old man with Hirayama disease presented with a peculiar hand posture called "horn hand" ("main en corne"). The patient noticed that he could not extend his 3rd and 4th fingers when extending the fingers of his right hand 1 year prior to presentation. On neurological examination, the strength of the finger extension is severely weak in the 1st, 3rd and 4th fingers, causing a drop finger posture, but it is only moderately weak in the 2nd and 5th fingers, enabling him to sustain the extension finger posture. The finger posture is like a bull's horns and is named "horn hand". Amyotrophy of the ulnar side of the right forearm, so-called "oblique amyotrophy", and amyotrophy of the right hand are observed. MRI examination reveals atrophy of the lower cervical spinal cord and compression of it in the neck flexion posture. Diagnosis of Hirayama disease (juvenile muscular atrophy of the distal upper extremity) is confirmed. Horn hand has been reported so far in some cases of lead neuropathy, chronic inflammatory demyelinating polyneuropathy, and distal myopathy; a "peripheral" horn hand is characterized by partial and selective lesion of the radial nerve or of the finger extensor muscles. Meanwhile, a "spinal" horn hand in this patient with Hirayama disease represents the partial and selective lesion of the spinal anterior horn neurons.