BACKGROUND: The efficacy of intravenous steroids (IS) for fulminant myocarditis (FMP) remains controversial. We aimed to compare outcomes in FMP patients who received IS [IS(+)] and those who did not [IS(-)]. METHODS AND RESULTS: Data from 344 patients with histologically confirmed FMP requiring catecholamines or mechanical support were extracted from the Japanese Registry of Fulminant Myocarditis. The primary outcome was a composite of 90-day mortality and heart transplantation. Among the patients (median age 54, 40 % female), 195 received IS, 98 died within 90 days, and 16 died or underwent transplantation after 90 days. The IS(+) group had lower left ventricular ejection fraction and lower ratio of lymphocytic myocarditis, higher use of intra-aortic balloon pumping, Venoarterial extracorporeal membrane oxygenation (VA-ECMO), and intravenous immunoglobulin. Crude analysis showed worse 90-day outcomes in the IS(+) group (36.3 % vs. 19.2 %, P = 0.0021)
however, after propensity score matching (PSM), outcomes were similar (26.2 % vs. 24.2 %
P = 0.95). Unadjusted Cox regression indicated worse outcomes with IS (HR 1.95, 95 % CI 1.26-3.04
P = 0.0026), but this was not significant after PSM (HR 1.02, 95 % CI 0.56-1.87
P = 0.95). Among low-risk patients, the IS(-) group showed better outcomes than the IS(+) group post-PSM (P = 0.0031). In the patients with VA-ECMO or ventricular assist devices, early IS (within 2 days of admission) showed comparable prognosis to delayed/no IS, with a trend toward better outcomes post-PSM. CONCLUSIONS: IS effectiveness in FMP patients may vary, showing limited prognostic benefit overall. Careful consideration is warranted in its use for this population.