Role of noninvasive antimyosin imaging in infants and children with clinically suspected myocarditis.

Abstract

Endomyocardial biopsy is an invasive procedure, often performed on children for the diagnosis of myocarditis, and is not without risk. Therefore, a noninvasive test of adequate diagnostic accuracy is highly desirable. We evaluated the role of antimyosin scintigraphy in infants and children with clinically suspected myocarditis. Forty patients (age range, 2 mo to 14 y) with suspected myocarditis underwent (111)In-antimyosin scintigraphy. All patients were clinically followed for 29 +/- 17 mo; 21 patients underwent serial antimyosin scans (3.8 +/- 1.7 per patient). The antimyosin uptake was assessed by heart-to-lung ratio (HLR). The scan results were compared with endomyocardial biopsy results in 22 patients. Thirty-five of the 40 patients showed abnormal antimyosin findings; 17 patients showed intense myocardial antimyosin uptake (HLR > 2). The HLR was higher in patients presenting within the first 2 mo of illness (2.09 +/- 0.43 vs. 1.74 +/- 0.34, P = 0.01). Of 22 patients with endomyocardial biopsy, 17 demonstrated myocarditis. All 9 patients who had an HLR > 2 and underwent endomyocardial biopsy had histologic evidence of myocarditis. Of the remaining 13 patients with HLR < 2, 8 had biopsy-verified myocarditis (62%). The intensity of antimyosin uptake was the major determinant of survival in children, with a relative risk of 18 (confidence interval, 1.34-242; P = 0.027). High antimyosin uptake (HLR > 2) seen within 2 mo of the onset of symptoms was associated with a higher mortality rate. The survivors with an HLR > 2 and those with an HLR < 2 showed a high likelihood of complete functional recovery. Furthermore, the patients with serial antimyosin scans having persistently positive findings showed a poor clinical outcome. Intense myocardial uptake of antimyosin antibody is a reliable indicator of myocarditis in infants and children. Severe myocardial damage detected in the early phase of disease is associated with a higher mortality rate. The persistence of antimyosin uptake is associated with poor clinical outcomes.