Nonspecific myocarditis: a statistical and clinicopathological study of autopsy cases.

Among a total of 634,440 autopsy cases in "The Annuals of Pathological Autopsy Cases in Japan" from 1958 to 1984, 929 cases with nonspecific myocarditis were registered. The average incidence was 0.15%, fluctuating around 3- to 5-year intervals with a remarkable rise observed after 1974. The major complications in cases of myocarditis were pneumonitis, hepatitis or hepatic cirrhosis, pancreatitis, malignancies, lymphatic or thymic involvements. A clinicopathological study of 36 cases of myocarditis and 27 cases of postmyocarditic cardiomegaly indicated a classification of acute, subacute, healing and chronic or recurrent stages as well as dilatation-hypertrophy- and right ventricle-dominant types. Acute myocarditis was characterized by diffuse inflammatory cell infiltration and showed various types of arrhythmias and shock. Subacute myocarditis showed ventricular dilatation, edematous interstitium and severe congestive heart failure. Chronic myocarditis with dilatation and/or hypertrophy and irregular fibrosis included right ventricular involvement, endomyocardial disease, sick sinus syndrome in selected cases, congestive heart failure in most cases, and showed a male predominancy. Postmyocarditic cardiomegaly was similar to chronic myocarditis but showed more hypertrophy, preexcitation waves and prominent negative T waves in electrocardiography and sudden death.