Clinical Diagnosis of Myocarditis

Abstract

The clinical manifestations of myocarditis are highly varied and cannot establish a diagnosis with certainty.1 Clinicians have increasingly relied upon right ventricular endomyocardial biopsy for histologic confirmation of suspected inflammatory heart disease. Mason et al. were among the first to demonstrate evidence of myocardial inflammation using right ventricular endomyocardial biopsies in patients with presumed idiopathic dilated cardiomyopathy.2 Although the endomyocardial biopsy has become "the gold standard", histologic criteria used for establishing the diagnosis of myocarditis have varied considerably. Edwards et al. reported that the presence of more than 5 lymphocyteslhpf was sufficient to diagnose active myocarditis.3 Tazelaar et al., however, cautioned against the use of a focal infiltrate alone in diagnosing myocarditis since isolated lymphocyte aggregations may also be seen in idiopathic dilated cardiomyopathy.4 In order to provide more uniform diagnostic criteria, a panel of cardiac pathologists developed a disease classification known as the "Dallas criteria" that defined myocarditis as a process characterized by an inflammatory infiltrate of the myocardium with necrosis and/or degeneration of adjacent myocytes, not typically seen in ischemic injury.5 The inflammatory infiltrate is typically lymphocytic but may also include eosinophilic, neutrophilic, granulomatous, or mixed cellularity. The amount of inflammation and its distribution may be mild, moderate, or severe and focal, confluent, or diffuse, respectively.5 Some clinicians feel that this definition is too narrow and have proposed a clinicopathologic classification which includes both histologic and clinical features (table I).,6 Despite its clinical appeal, this it has not been widely accepted.