Polymyositis presenting with severe weakness involving only one arm.

A woman presented with severe weakness and wasting involving only one arm. A definite diagnosis was not made until almost six years later when she developed proximal weakness in the legs as well, and a muscle biopsy showed changes of polymyositis. Asymmetry of weakness in polymyositis has been noted previously in the literature, but is rare. In previous reports asymmetry as marked as in the present case has not been noted.