Histopathologic aspects of viral myocarditis and its diagnostic criteria

The morphologic criteria in diagnosing myocarditis are detailed. In fulminant cases, apart from the inflammatory infiltrate which often consists of chronic inflammatory cells, necrosis is found, frequently in the form of myocytolysis. Two groups of patients are analyzed. The first consisted of 214 cases who were clinically suspected of suffering from myocarditis. In 50% of these cases, the clinical suspicion was confirmed by morphologic examination of tissue obtained by endomyocardial biopsy. The other group of patients were suspected of having dilated cardiomyopathy and consisted of 1200 patients; in 300 of these patients, myocarditis was diagnosed morphologically by biopsy. Following sequential biopsies monitoring the response to treatment with corticosteroids and immunosuppressive agents, a classification into active, ongoing, resolving (healing), or resolved (healed) forms has been advanced. The different stages depend on the severity of the inflammatory infiltrate, the site of the inflammatory cells, the presence or absence of necrosis of adjacent myocardial fibers, and the degree of fibrosis. It has been emphasized that clear concepts and a uniform approach are essential in diagnosing myocarditis, not only to achieve precise diagnosis, accurately monitoring the response to therapy, but also in helping to establish the pathogenetic pathways for certain forms of cardiomyopathy.