Juvenile muscular atrophy of distal upper extremity (Hirayama disease): focal cervical ischemic poliomyelopathy.

Hirayama disease is characterized by an initially progressive muscular weakness and atrophy of the distal upper limb(s) in adolescence, occurring predominantly in males, followed by spontaneous arrest within several years. Although the disease could be separated from motor neuron disease, some authors considered the illness to be a variant of degenerative motor neuron disease until the first autopsy case was reported which showed focal ischemic changes in the anterior horn of the lower cervical cord. Since then, many in Japan have recognized the disease as cervical ischemic poliomyelopathy; however, several authors in foreign countries did not or do not appreciate the pathologic findings of the disease, and still consider the illness a degenerative motor neuron disease. The pathology of the disease prompted neuroradiologic investigations, which have revealed dynamic changes of the cervical dural sac and spinal cord induced by neck flexion. The cause of these dynamic changes is unknown. However, as the number of patients is exceedingly large in Japan, there may be an ethnic factor.