Incomplete Kawasaki Disease Presenting With Coronary Artery Aneurysms in a 2.5-Month-Old Infant: A Case Report

Kawasaki disease (KD) is an acute systemic vasculitis of childhood and remains a leading cause of acquired heart disease in children. Diagnosis in infants younger than six months is particularly challenging because presentations are often incomplete and may mimic common infectious conditions, resulting in delayed recognition and an increased risk of coronary artery complications. We report a case of a 2.5-month-old female infant who presented with persistent fever and nonspecific upper respiratory symptoms and was initially treated for a presumed infectious etiology. Despite the absence of classic mucocutaneous features, progressive systemic inflammation with anemia and thrombocytosis, a negative infectious evaluation, and echocardiography demonstrating coronary artery abnormalities within the aneurysm range by Z-score thresholds (maximum Z-scores: left main coronary artery (LMCA) +5.5, left anterior descending artery (LAD) +6.9, right coronary artery (RCA) +6.2, and left circumflex artery (LCx) +3.7) supported the diagnosis of incomplete Kawasaki disease (iKD). The patient received intravenous immunoglobulin (2 g/kg) and aspirin therapy, with rapid defervescence and improvement in inflammatory markers. Follow-up echocardiography approximately six weeks later demonstrated marked interval improvement in coronary artery dimensions, with a reduction in Z-scores. This report highlights the need for a high index of suspicion for iKD in very young infants with persistent fever and systemic inflammation and underscores the importance of early echocardiography to enable timely treatment and reduce potentially preventable coronary complications.