Myocarditis may be diagnosed with a moderate degree of certainty when a constellation of clinical features is present: a preceding viral illness, acute onset of symptoms, fever, peri-cardial inflammation, supportive laboratory abnormalities (increased erythrocyte sedimentation rate, leukocytosis, increased concentration of creatine kinase), and electro-cardiographic abnormalities. As previously discussed, however, fewer than 10% of patients present with 2 or more of these supportive clinical features. Further, endomyocardial biopsy, while serving as the most appropriate way to confirm the clinically suspected diagnosis, also has substantial problems as a diagnostic tool. It is invasive, costly, and samples only a tiny portion of the myocardium. Given the focal or multifocal nature of myocarditis, it is not surprising that substantial sampling error exists. Clinicians are increasingly reluctant to recommend routine endomyocardial biopsy, even when myocarditis is clinically strongly suspected.
A noninvasive technique that possesses high sensitivity and specificity has been sought to identify those patients in whom right ventricular biopsy has a high probability of yielding a histologic diagnosis of myocarditis. Creatine kinase or its isoform is not useful as a noninvasive screening method because of low predictive value.27,49 Recently, cardiac troponin T has been shown in a moderate-sized single center study to be useful in establishing the diagnosis. Lauer et al.48 reported an increased serum concentration of troponin T (> 0.1 ng/mL) was associated with a sensitivity for detecting myocarditis (histologically verified by Dallas criteria, by immunohistochemical techniques, or both) of 53%; its specificity was 94%; its positive predictive value, 93%; and the negative predictive value, 56%. Additional confirmatory studies are necessary to verify the utility of this simple serologic method.
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