Chronic active hepatitis associated with polymyositis. Association with precipitating mitochondrial M-B antibody.

A 20-year-old black female presented with chronic active hepatitis and polymyositis. Interstitial lung disease and transient polyarticular arthritis were also observed, but other features of systemic lupus erythematosus, scleroderma and Sjögren's syndrome were absent. Both myositis and hepatitis responded to prednisone and azathioprine. The patient's serum contained an unusual autoantibody reacting with mitochondrial proteins (M-B) in immunodiffusion.