Myocarditis mimicking acute myocardial infarction: role of endomyocardial biopsy in the differential diagnosis

Objective-To test the hypothesis, using endomyocardial biopsies, that unexp lained cases of apparent acute myocardial infarction were caused by myocard itis. Material-Between 1992 and 1998, 12 patients were admitted to the coro nary care unit with severe chest pain, ST segment elevation, increased seru m creatine kinase and MB isoenzyme, and with wall motion abnormalities on e chocardiogram highly suggestive of acute myocardial infarction. These patie nts were further investigated by endomyocardial biopsy, as their coronary a ngiograms were normal. A diagnosis of myocarditis was made according to the Dallas criteria. A panel of antibodies was used for immunohistochemical ch aracterisation of inflammatory cell infiltrate. Polymerase chain reaction ( PCR) was used to detect viral genomes in seven cases. Results-Haematoxylin and eosin staining of the endomyocardial biopsy showed active myocarditis i n six patients and borderline myocarditis in one. Immunohistochemistry was positive for inflammatory cell infiltrates in 11 patients, including all th e seven who were positive on haematoxylin and eosin staining according to t he Dallas criteria. Only one patient had no evidence of inflammation. PCR w as positive in two patients, both for Epstein-Barr virus. Follow up showed complete resolution of echocardiographic abnormalities in all patients exce pt one. Conclusions-Myocarditis can mimic acute myocardial infarction in pa tients with angiographically normal coronary arteries, leading to errors of treatment. In patients with apparent myocardial infarction and a normal co ronary angiogram, endomyocardial biopsy may help in the diagnosis of myocar ditis. The sensitivity of endomyocardial biopsy was enhanced by using immun ohistochemical and molecular biological techniques. (Heart 2000;84:235-250)