Analysis of histopathologic findings in cases with dilated cardiomyopathy with special reference to formulating diagnostic criteria on the possibility of postmyocarditic change.

From our study employing serial endomyocardial biopsy in patients with acute viral or idiopathic myocarditis, we were able to construct histopathologic criteria for acute, subacute and convalescent myocarditis. We realize that it is difficult for the inexperienced observer to make an appropriate diagnosis of myocarditis or postmyocarditic changes in patients with dilated cardiomyopathy (DCM). In order to overcome this problem, each finding was graded and the scores obtained were analyzed statistically and compared with those from hypertrophic cardiomyopathy (HCM) and chronic right ventricular overloading (CRVO). The scores were obtained by summing the gradings for each of the following findings: increase of fibrocytes, increase of fibroblasts in the interstitium, hypertrophy of myocytes, fragmentation of muscle bundles, interstitial fibrosis, disarrangement of muscle bundles, abnormal branching, variation in size, increased glycogen deposition in the sarcoplasm, scarcity of myofibrils, and nuclear degeneration of myocytes and endocardial thickening. Since the increase in number of fibrocytes was considered important, its value was doubled. Scores in each group were as follows: convalescent myocarditis: 17.1 +/- 4.7 (n = 10), DCM: 13.2 +/- 3.3 (n = 47), HCM: 9.7 +/- 2.4 (n = 20), CRVO: 7.0 +/- 3.6 (n = 21). It was found that the scores for cases with myocarditis in the convalescent stage and in DCM were higher than those found for cases with either HCM and CRVO (p less than 0.05). In summary, the high score for postmyocarditis in DCM could suggest that prior myocarditis is an important causative factor of this disease.