Acute myocarditis causing fatal ventricular arrhythmia in treated polymyositis.

A patient with definite polymyositis responded clinically to prednisolone in combination with azathioprine, with improvement in muscle strength and normalization of muscle enzyme levels. After 7 weeks' treatment the patient developed chest pain and fatal ventricular arrhythmias. An autopsy showed inflammatory myocarditis, but marked improvement in the skeletal muscle histology. This case illustrates that myocarditis may be a late complication of polymyositis despite immunosuppressive therapy.