This disease is characterized by initially progressive muscular weakness and wasting of the distal upper limb(s) in young people predominantly in men, followed by a spontaneous arrest within several years. This disease has been thought to be separate from motor neuron diseases, yet some authors still consider the illness a variant of motor neuron disease. However, the pathological evidence of ischemic changes in the lower cervical anterior horn should facilitate differentiation of the disorder from degenerative motor neuron disease. Recent radiological investigations proved compressive flattening of the lower cervical cord due to forward displacement of the cervical dural sac and spinal cord induced by neck flexion. These findings suggest that sustained or repeated neck flexion may cause ischemic changes in the cervical anterior horn. Application of a cervical collar to minimize neck flexion prevents progressive muscular weaknessin an early stage of the disease.

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Radiologic abnormalities of the lower cervical dural sac and spinal cord support the hypothesis that this disorder is a type of cervical myelopathy.

Juvenile muscular atrophy of the distal upper extremity (JMADUE, Hirayama disease) was first reported in 1959 as 'juvenile muscular atrophy of unilateral upper extremity'. Since then, similar patients in their teens or 20s have been described, under a variety of names, not only in Japan, but also in other Asian countries, as well as Europe and North America. Biomechanical abnormalities associated with JMADUE have recently been reported through various imaging examinations, proposing its disease mechanism. Since JMADUE differs from motor neuron disease, or spinal muscular atrophy, this disease entity should be more widely recognized, and early detection and effective treatments should be considered. We report an epidemiological study in Japan. Two nationwide questionnaire-based surveys, conducted in Japan from 1996 to 1998, identified 333 cases. The numbers of patients per year, distribution of ages at onset, mode of onset, time lapse between onset and quiescence, neurological signs and symptoms, imaging findings, and the effects of conservative treatments were analyzed. The peak age was 15 to 17 years, with a marked male preponderance, usually a slow onset and progression, and quiescence six or fewer years after onset. There was a predominantly unilateral hand and forearm involvement with 'cold paresis'. The imaging findings are described.

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