Kawasaki disease vs. MIS-C in a child with congenital coronary artery anomaly: a case report.

Kawasaki disease (KD) and multisystem inflammatory syndrome in children (MIS-C), associated with SARS-CoV-2 infection share overlapping clinical and laboratory features, making differential diagnosis particularly challenging during the COVID-19 pandemic. Accurate distinction is essential due to differences in pathophysiology, management strategies, and cardiovascular outcomes. We report the case of a 7-year-old boy presenting with prolonged fever, mucocutaneous manifestations, arthritis, and elevated inflammatory markers following SARS-CoV-2 exposure. The clinical course demonstrated features compatible with both incomplete Kawasaki disease and MIS-C. Laboratory findings and cardiac biomarkers showed a mixed profile, while echocardiography and coronary imaging revealed the development of coronary artery aneurysms. Notably, a complex congenital coronary artery anomaly was incidentally identified during coronary evaluation. Although such anomalies are not considered independent risk factors for coronary aneurysm formation, their presence may complicate the interpretation of coronary findings in the setting of systemic inflammation. The patient showed a rapid and sustained clinical response to systemic glucocorticoid therapy without intravenous immunoglobulin administration; however, coronary artery aneurysms subsequently developed. This case highlights the diagnostic and therapeutic challenges at the interface of KD and MIS-C and underscores the importance of an integrated, individualized approach that incorporates clinical evolution, laboratory data, and detailed coronary assessment.