Indium 111-monoclonal antimyosin antibody imaging in the diagnosis of acute myocarditis.

A definitive diagnosis of myocarditis requires right ventricular biopsy. Despite its specificity, however, right ventricular biopsy may lack sensitivity due to the focal nature of the disease. Because indium 111-monoclonal antimyosin antibody imaging can be used to detect myocardial necrosis, this procedure was performed on 28 patients clinically suspected of having myocarditis, 25 of whom had left ventricular ejection fractions of less than 45%, and the results were compared with those of right ventricular biopsy performed within 48 hr of the scan. Antimyosin scans were positive in nine patients who had evidence of myocarditis on right ventricular biopsy, and negative in 11 who had no evidence of myocarditis by biopsy. The remaining eight had positive antimyosin scans but showed no evidence of myocarditis on right ventricular biopsy. On the basis of a right ventricular biopsy standard, the sensitivity of this method was 100%, the specificity 58%. We conclude that antimyosin antibody imaging is a reliable screening method for the evaluation of patients suspected of having myocarditis, and that a positive antimyosin scan indicates the need for right ventricular biopsy to establish the histologic diagnosis.