Focal myopathy mimicking posterior interosseous nerve syndrome

A 25-year-old man developed weakness of extension of the right index, middl e, and fourth fingers at the metacarpophalangeal joints, over 2 years. No s ensory deficit was present. Nerve conduction studies, including the right r adial nerve, were within normal limits. Needle electromyographic (EMG) exam ination showed myopathic changes that were limited to the right extensor di gitorum communis and extensor indicis proprius muscles. An intravenous edro phonium chloride test had no effect on weakness and repetitive stimulation showed no significant decremental response. An EMG-guided open biopsy of th e extensor digitorum communis muscle revealed severe myopathic changes. Eva luation for the cause of myopathic involvement was negative. After 13 month s, clinical examination and electrophysiological studies showed no signific ant progression. This case exemplifies the fact that a focal myopathy may m imic an entrapment neuropathy. (C) 2001 John Wiley & Sons, Inc.