Histopathological findings of acute and convalescent myocarditis obtained by serial endomyocardial biopsy

Serial endomyocardial biopsy findings in 20 cases with acute myocarditis of possible viral origin were analyzed. The histopathological findings were analyzed during the acute (0-10 days after the onset: 8.3±1.9 days; 6 cases), the subacute (11-21 days: 18.2±2.2 days, 6 cases), and the convalescent stages (22-167 days: 54.5±45.4 days: 8 cases). The incidence and severity of various changes of the cardiac myocytes and interstitial changes were analyzed and compared at each stage of the disease. In the acute stage, interstitial cell infiltrations were composed of fibroblasts, macrophages and lymphocytes, taken out in descending order. In the convalescent stage, interstitial cell infiltration showed a marked increase and was replaced by fibrocytes. In the subacute stage, transitional changes between the acute and convalescent stages were observable. A controlled myocardium in 21 cases with myocardial infarction which were compared at various stages revealed that in the acute stage, neutrofiles were most prominent, and in the subacute and convalescent stages, macrophages were most prominent and plasma cells were most often observed. The time course changes of the histopathological findings in acute myocarditis were as follows: In the acute stage, 1) Interstitial cell infiltration which is composed of fibroblasts, macrophages and lymphocytes, 2)fragmentation of the muscle bundles, 3) myocytolytic changes, 4) swelling and scarcity of the cytoplasm and swelling of nuclei, 5) variation in size of the myocytes, 6) disarrangement of the muscle bundles, 7) interstitial edema, 8) increased glycogen deposition in the myocytes, 9) abnormal branching of the myocytes, and 10) interstitial fibrosis were observable. In the convalescent stage, most of the above described findings were still observable except for the myocytolytic change, swelling of myocytes and interstitial edema. In the subacute and convalescent stages, an increase in abnormal branching, an increase in double nuclei in the myocytes, and nuclear degeneration were observable. Further control study comparing the change in the convalescent stage of myocarditis and the myocardial changes in cases with chronic right ventricular overload in 58 cases revealed that in the former, fragmentation of the muscle bundles, abnormal branching, size variation, glycogen deposition, and large mononuclear cell infiltrations were significantly more frequent. It is concluded that serial endomyocardial biopsy is useful in assessing the time-course changes of the myocardium in myocarditis.