Monomelic Amyotrophy (Hirayama Disease)

Excerpt

Monomelic amyotrophy, previously known as Hirayama disease, is a rare, nonfamilial neurologic disorder first described by Hirayama in 1959. Classical findings include unilateral or bilateral muscle atrophy and weakness of the forearms and hands without sensory loss. This condition usually progresses for 1 or 2 years before plateauing, eventually showing an abrupt arrest. Monomelic amyotrophy is caused by chronic ischemic changes to the anterior horn cells of the cervical spine secondary to a limited dural sac laxity. The disorder is predominantly a lower motor neuron pattern of the lesion.

Although often considered a nonprogressive and self-limiting disease, some individuals experience significant disability. Early intervention has been shown to limit the progression of the disease and minimize disability. Other names to describe this entity include benign juvenile brachial spinal muscular atrophy, juvenile asymmetric segmental spinal muscular atrophy, juvenile muscular atrophy of the distal upper extremity, Hirayama disease, and oblique amyotrophy.