DIAGNOSTIC-ACCURACY OF ANTIMYOSIN SCINTIGRAPHY IN SUSPECTED MYOCARDITIS

Background. Radiolabeled antibody specific for cardiac myosin administ ered intravenously has been used to define noninvasively regions of my ocardial necrosis. Inflammatory heart disorders such as myocarditis an d heart transplant rejection demonstrate diffuse and often faint myoca rdial uptake of antimyosin antibody. This study was undertaken to eval uate the reproducibility and diagnostic accuracy of antimyosin antibod y imaging for the detection of patients with suspected myocarditis. Me thods and Results. Fifty antimyosin scans, performed consecutively in patients with suspected myocarditis, were evaluated by one independent observer and two panels of observers. Antimyosin scan interpretations were compared with endomyocardial biopsy results and also with serial changes in left ventricular function. An independent observer (A) and a panel of five observers (A through E) interpreted the antimyosin sc ans as positive or negative on the basis of both planar images and tom ographic reconstructions. Three of the five observers (A through C) ag ain interpreted the scans but based interpretation only on planar imag es. Blinded random sequence evaluation of antimyosin scans based on th e planar and tomographic interpretations revealed moderate agreement b etween the independent observer (A) and the group of observers (A thro ugh E) (kappa = 0.58). There was also moderate agreement between inter pretations based on planar images alone and interpretations based on b oth planar and tomographic images (kappa [A through E]/[A through C] = 0.57; kappa [A through C]/A = 0.48). Comparison of antimyosin scan re sults with histologic evidence of myocarditis in endomyocardial biopsy specimens demonstrated that all scan results obtained from the indivi dual or the panels of observers had a very high sensitivity (91% to 10 0%) and a high negative predictive value (93% to 100%). The specificit y (31% to 44%) and positive predictive value (28% to 33%) were less im pressive. We also compared the scan and biopsy results with the compos ite clinical standard of significant left ventricular functional impro vement. Endomyocardial biopsy demonstrated poor sensitivity (35%) comp ared with antimyosin scans (82% to 94%) but had superior specificity ( endomyocardial biopsy, 79%; antimyosin scan, 25% to 42%). The specific ity of interpretations based on planar and tomographic interpretations (38% to 42%) was better than the planar images alone (25%). If revers ible left ventricular dysfunction is considered clinical evidence of m yocarditis, this study suggests that a negative endomyocardial biopsy significantly misses the presence of the disease. On the other hand, a negative antimyosin scan almost invariably excludes myocarditis. Conc lusions. This study demonstrates a high degree of interobserver reprod ucibility of antimyosin interpretation. Comparison of the scintigraphi c results with histologic and clinical standards indicates a high sens itivity of antimyosin scans for the detection of myocarditis. The anti myosin scan is also not likely to miss clinically or pathologically di agnosed myocarditis, in contrast to the endomyocardial biopsy, which m issed clinically validated myocarditis 65% of time. The combination of high sensitivity and negative predictive value suggests that antimyos in scintigraphy may be an effective screening procedure for obviating biopsies in patients with suspected myocarditis.