Focal myocarditis in familial dystrophia myotonica.

A mother and her two sons with dystrophia myotonica are reported. All three patients had electrocardiographic abnormalities. The mother and one of the sons died. Necropsy revealedfocal myocarditis. It is suggested that myocarditis is a manifestation of the natural history of 'dystrophia myotonica cordis', and that focal myocarditis generally may be a sign of metabolic or degenerative processes in the myocardium.