Myocarditis in mixed connective tissue disease. Association of myocarditis with antibody to nuclear ribonucleoprotein.

A young black woman with clinical and serologic features of mixed connective tissue disease (MCTD) developed myocarditis with congestive heart failure and ventricular ectopic activity. Despite treatment with steroids and cyclophosphamide, progressive myocarditis resulted in death 20 months after cardiomegaly first developed. Necropsy findings in the myocardium included multiple areas of extensive lymphocytic infiltration and patches of fibrosis. Myocarditis has not previously been described in the adult with MCTD but may be an important complication in patients with a high titer of antibody to nuclear ribonucleoprotein.