角状手を呈した平山病の1例—脊髄性角状手（main en corne spinale）

A Case of Hirayama Disease Presenting Horn Hand: Spinal Horn Hand

28歳男性。右手指を伸ばそうとしても，中指と薬指が伸展できず，下垂したままで，いわゆる「角状手（main en corne）」を呈する。右前腕斜め型筋萎縮，右小手筋萎縮，頸髄MRI検査所見（下部頸髄萎縮および頸部前屈位での頸髄圧迫・扁平化）から，平山病（若年性一側上肢筋萎縮症）と診断される。従来，角状手は橈骨神経系・手指伸筋群の部分的選択的障害を示唆する特異的症候として，鉛中毒性ニューロパチー，遠位型ミオパチーなどで報告され，末梢性角状手（main en corne périphérique，peripheral horn hand）と称され得るものであるが，平山病にみられる角状手は，脊髄前角細胞（C7，8髄節）の部分的選択的障害を示唆する特異的症候として，背髄性角状手（main en corne spinale，spinal horn hand）と称され得るものと言える。

Abstract

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.