The quality of evidence is downgraded by study limitations (lack of/unclear allocation concealment and blinding), by indirectness (differences between the population of interest and those studied: at least some of the adult study participants may not have had viral myocarditis, as only 10 of 62 had inflammation on cardiac biopsy), and by imprecise results (few patients and outcome events).
A Cochrane review included 2 studies with a total of 145 subjects with a clinical diagnosis of acute myocarditis. The first study compared 2 g/kg intravenous immunoglobulin (IVIG) to an equivalent volume of 0.1% albumin in 62 adult subjects (mean age 43 years) with recent-onset (within 6 months) dilated cardiomyopathy, normal coronary angiography and LVEF ≤ 0.40. All had endomyocardial biopsies, but only 10 had cellular inflammation. The incidence of death or requirement for cardiac transplant or placement of a left ventricular assist device was low in both groups. Event-free survival was not significantly different but favoured the control group (OR 0.52, 95% CI 0.12 to 2.30). Follow-up at 6 (MD 0.00, 95% CI -0.07 to 0.07) and 12 months (MD 0.01, 95% CI -0.06 to 0.08) showed equivalent improvement in LVEF. Functional capacity as assessed by peak oxygen consumption was equivalent in the two groups at 12 months (MD -0.80, 95% CI -4.57 to 2.97). Infusion-related side effects were more common in the treated group, but all appeared to be mild (OR 30.16, 95% CI 1.69 to 539.42).
The second study was a quasi-randomised study conducted in India comparing IVIG 400 mg/kg for 5 consecutive days with no therapy among 83 children (age range from 2 months to 12 years) with suspected viral encephalitis and associated myocarditis with LVEF < 0.40. The incidence of event-free survival was 25/26 (96%) in the treated group and 44/57 (77%) in the control group (OR 7.39, 95% CI 0.91 to 59.86). Follow-up occurred only until hospital discharge, and LVEF was 49.5% in the treated group versus 35.9% in the placebo group (RD 13.6%, 95% CI 5.1 to 22.1%; P value = 0.001).