Penicillamine-induced myositis in rheumatoid arthritis.

A patient with rheumatoid arthritis who developed multiple mononeuropathies multiplex was shown to have vasculitis in nerve biopsy, but no evidence of inflammatory muscle disease in muscle biopsy. Treatment with penicillamine caused the rare complication of polymyositis, documented clinically, electrophysiologically, and by light and electron microscopy in a second muscle biopsy. The evidence presented supports the concept that penicillamine may induce polymyositis or aggravate a pre-existing low-grade myositis.