Myocarditis in mixed connective tissue disease: clinical and pathologic study of three cases and review of the literature.

The clinical course and cardiac pathology of three adults with MCTD who developed myocarditis and that of two other previously reported cases are reviewed. The patients presented with cardiomegaly, congestive heart failure, ventricular arrhythmias, and elevated serum CPK MB fraction. Except for more frequent episodes of serositis and less prevalent neuropsychiatric manifestations and hepatosplenomegaly, no distinguishing features were found in MCTD patients with myocarditis compared with those without myocardial involvement. The concomitant onset of proximal myositis and myocarditis in one patient suggests a common inflammatory pathologic process in the skeletal and cardiac muscles. Circulating antibodies to myocardium and to cardiac conduction tissue were found in nine of 23 (39%) MCTD patients, but the presence of these autoantibodies was not associated with the occurrence of clinical cardiac involvement. The clinical and pathologic features of the five MCTD patients were similar to that of SLE patients with myocarditis. Primary myocardial involvement in MCTD, as in SLE, was associated with a relatively poor prognosis.