Prognostic role of systemic immune-inflammation index versus other cardiac markers in acute myocarditis in young adults.

Myocarditis, an inflammatory disease of the myocardium, can range from asymptomatic cases to severe forms such as fulminant myocarditis. The systemic immune-inflammation index (SII) has emerged as a potential biomarker for various inflammatory diseases. This study aimed to determine the effect of SII on the prognosis of young adults with acute myocarditis and compare it with other cardiac markers. We retrospectively analyzed patients aged 18-40 years who were admitted to the emergency department with a diagnosis of acute myocarditis between January 2014 and January 2024. Patients were divided into non-fulminant and fulminant myocarditis groups based on diagnostic criteria. SII, troponin I and N-terminal pro-brain natriuretic peptide (NT-proBNP) levels were significantly higher in the fulminant myocarditis group ( < 0.001 for all). Logistic regression analysis identified SII and NT-proBNP as independent predictors of fulminant myocarditis but not for troponin I ( = 0.064). The optimal cutoff value for SII in diagnosing fulminant myocarditis was 1020, with a sensitivity of 91% and specificity of 83%, outperforming troponin I. Patients with SII ≥1020 had a significantly higher risk of adverse outcomes. The SII enables early detection of adverse outcomes and is an independent predictor of prognosis in young adults with myocarditis.