Distinguishing myocarditis from perimyocardial syndromes in children presenting to the emergency department: a biomarker-based approach

INTRODUCTION: Myocarditis and perimyocardial syndromes share overlapping features but differ in management. Differentiating them in children presenting with chest pain or palpitations remains difficult, particularly in non-fulminant cases. This study evaluated the diagnostic value of inflammatory biomarkers, especially the Systemic Immune-Inflammation Index (SII), in distinguishing perimyocardial syndromes from isolated myocarditis in the pediatric emergency department (PED). METHOD: We retrospectively analyzed patients aged 1-18 years diagnosed with myocarditis, perimyocardial syndromes, or acute pericarditis between 2015 and 2021. Clinical characteristics, laboratory, ECG and echo findings of all patients were recorded. SII was calculated using neutrophil, platelet, and lymphocyte counts obtained within six hours of PED admission. ROC analysis assessed diagnostic performance. RESULTS: 166 eligible subjects were enrolled (74 cases of myocarditis, 63 cases of myopericarditis, 21 cases of perimyocarditis, and 8 cases of acute pericarditis). The median age was 15 (12-17) years, and 76.5% of the patients were male. The median WBC, ANC and SII were respectively 7.44 (IQR 6.22-9.32), 3.93 (IQR 3.38-5.00), and 418 (IQR 286-679) in the myocarditis and significantly lower than the other groups (p < 0.001). In estimation of perimyocardial syndromes, AUC was 0.735 for WBC, 0.805 for ANC, 0.803 for SII (p < 0.001). The optimal cut-off values determined by the Youden Index were 8.24(x109/L) for WBC, 4.85(x109/L) for ANC, and 693 for SII, with corresponding sensitivities of 67.4%, 76.1%, and 73.9%, and specificities of 61.6%, 67.1%, and 75.3%, respectively. CONCLUSIONS: SII and ANC are useful, accessible biomarkers for differentiating perimyocardial syndromes from myocarditis. Their integration into early diagnostic strategies may support efficient triage and decision-making in the PED.