monomelic amyotrophy; benign focal amyotrophy; Hirayama syndrome; O'Sullivan-McLeod syndrome

Etiology

• idiopathic
• reports of association with radiation or trauma

Epidemiology

• primarily in males 15-25 years of age
• most frequent in Asia, especially Japan & India
• much less common in North America

Pathology

• motor neuron disease
• slowly progressive variant (O'Sullivan-McLeod syndrome) affects the small muscles of the hand & forearm

Genetics

unconfirmed reports of familial cases

Clinical manifestations

• weakness & wasting in a single limb, generally an arm & hand rather than a foot & leg
• painless
• mild sensory loss (controversial)
• onset is insidious; progression is slow

Diagnostic procedures

• electromyography (EMG) shows denervation in the affected limb

Radiology

• MRI & CT scans may show muscle atrophy

Management

• consult neurologist (neuromuscular disease specialist)
• no cure
• physical therapy:
  • muscle strengthening exercises & training in hand coordination

Prognosis:

• symptoms usually progress slowly for 1-2 years before reaching a plateau, then remain stable for many years
• disability is generally slight
• weakness may uncommonly progresses to the opposite limb

More general terms

• muscle atrophy (amyotrophy)
• motor neuron disease

Patient information

monomelic amyotrophy patient information