Penicillamine-associated myasthenia gravis.

Electroneuromyographic studies have been reported as abnormal in only 9 of 23 cases of penicillamine-associated myasthenia gravis (MG). We report a patient with rheumatoid arthritis who developed clinical and electrodiagnostic evidence of myasthenia 7 months after beginning penicillamine therapy. Six months after discontinuing penicillamine, it was possible to discontinue anticholinesterase medications. With clinical improvement, electrodiagnostic studies (including single-fiber electrmyography) improved, serum antibody titers to human muscle acetylcholine receptor fell, and lymphocytes became more responsive to the nonspecific mitogen phytohemagglutinin. Evidence suggests that penicillamine-associated myasthenia is a distinct syndrome rather than the chance occurrence of two diseases. This syndrome is clinically and electrophysiologically distinguishable from idiopathic myasthenia only by the high remission rate after penicillamine is discontinued.