Myocarditis

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Myocarditis is clinically and pathologically defined as “inflammation of the myocardium.” Despite its rather clear-cut definition, the classification, diagnosis, and treatment of myocarditis continue to prompt considerable debate. The more routine use of endomyocardial biopsy has helped to better define the natural history of human myocarditis and to clarify clinicopathological correlations. Clinical presentations of the disease range from nonspecific systemic symptoms (fever, myalgias, palpitations, or exertional dyspnea) to fulminant hemodynamic collapse and sudden death. The extreme diversity of clinical manifestations has made the true incidence of myocarditis difficult to determine. Recent prospective postmortem data have implicated myocarditis in sudden cardiac death of young adults at rates of 8.6% to 12%.1,2 Furthermore, it has been identified as a cause of dilated cardiomyopathy in 9% of cases in a large prospective series.3 Recent molecular techniques have facilitated new insights into inflammatory autoimmune processes that affect the myocardium and ultimately result in acute or chronic dilated cardiomyopathy. Despite the well-established morbidity and mortality associated with myocarditis,4–7 clinical practice guidelines with regard to its evaluation and treatment are lacking.8 The wide variety of etiologies implicated in myocarditis and its heterogeneous clinical presentations5,7,9 have impeded patient identification and consensus on the most appropriate diagnostic criteria. The Dallas pathological criteria, published in 1986, served as the first attempt to develop standardized diagnostic guidelines for the histopathological classification of myocarditis.10 Active myocarditis is characterized by an inflammatory cellular infiltrate with evidence of myocyte necrosis (Figure 1), whereas borderline myocarditis demonstrates an inflammatory cellular infiltrate without evidence of myocyte injury (Figure 2). The inflammatory infiltrate should be further described as lymphocytic, eosinophilic, or granulomatous (Figure 3). The amount of inflammation may be mild, moderate, or severe, and its distribution may be focal, confluent, or diffuse, respectively. A retrospective study of 112 consecutive …