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monomelic amyotrophy; benign focal amyotrophy; Hirayama syndrome; O'Sullivan-McLeod syndrome
Etiology:
1) idiopathic
2) reports of association with radiation or trauma
Epidemiology:
1) primarily in males 15-25 years of age
2) most frequent in Asia, especially Japan & India
3) much less common in North America
Pathology:
1) motor neuron disease
2) slowly progressive variant (O'Sullivan-McLeod syndrome) affects the small muscles of the hand & forearm
Genetics: unconfirmed reports of familial cases
Clinical manifestations:
1) weakness & wasting in a single limb, generally an arm & hand rather than a foot & leg
2) painless
3) mild sensory loss (controversial)
4) onset is insidious; progression is slow
Special laboratory:
- electromyography (EMG) shows denervation in the affected limb
Radiology:
- MRI & CT scans may show muscle atrophy
Management:
1) consult neurologist (neuromuscular disease specialist)
2) no cure
3) physical therapy:
- muscle strengthening exercises & training in hand coordination
Prognosis:
1) symptoms usually progress slowly for 1-2 years before reaching a plateau, then remain stable for many years
2) disability is generally slight
3) weakness may uncommonly progresses to the opposite limb
General
muscle atrophy (amyotrophy)
motor neuron disease
References
- NINDS Monomelic Amyotrophy Information Page
https://www.ninds.nih.gov/Disorders/All-Disorders/Monomelic-Amyotrophy-Information-Page