Focal myositis presenting with radial nerve palsy.

[focal myositis]

Focal myositis is a rare inflammatory pseudotumor of skeletal muscle which usually has a benign course . We report a 56 -year -old woman with a painful mass in the left arm with a radial nerve palsy . Magnetic resonance imaging (MRI ) of the left arm showed a mass in the triceps muscle that was suggestive of a soft -tissue sarcoma . Electromyography showed a severe radial neuropathy involving both motor and sensory axons . An open biopsy showed focal myositis . Treatment with corticosteroids resulted in complete disappearance of the mass clinically and by MRI , without recurrence for more than 2 years . Radial nerve function also recovered completely . As a treatable cause of focal neuropathy , focal myositis should be included in the differential diagnosis of a muscle mass .