Background: Kawasaki disease (KD) is an acute systemic medium-vessel vasculitis primarily affecting children aged 6 months to 5 years and is the leading cause of acquired heart disease in developed countries. Classic diagnosis relies on prolonged fever and a combination of clinical features, yet incomplete or atypical KD frequently presents without full criteria, especially in infants under 6 months, leading to diagnostic delays and increased risk of coronary artery aneurysms (CAA).Case Presentation: We report a 3-month-old term infant presenting with isolated high-grade fever lasting 9 days, with no classical KD clinical signs. Examination revealed a soft systolic murmur but was otherwise unremarkable. Laboratory evaluation showed normocytic anaemia, marked thrombocytosis (platelets 1,116 ×10^9/L), elevated C-reactive protein (50.4 mg/L), and raised inflammatory markers including fibrinogen, IL-6, D-dimer, and pro-BNP. A comprehensive infectious workup was negative. Given persistent fever beyond 10 days and elevated inflammatory indices, intravenous immunoglobulin (IVIG) (2 g/kg) and moderate-dose aspirin (30 mg/kg/day) were initiated early despite incomplete criteria.Echocardiography confirmed giant coronary aneurysms with left anterior descending artery 4 mm Z-score +12 (Figure 1A) and diffuse coronary dilation. Multidisciplinary management included corticosteroids, clopidogrel, and therapeutic enoxaparin guided by anti-Xa levels. Magnetic resonance angiography (MRA) revealed diffuse aortitis involving the descending thoracic and proximal abdominal aorta (Figure 1B) and vertebral artery inflammation, demonstrating systemic vasculitis beyond coronaries. Genetics testing was also sent and awaiting results.The patient improved clinically and biochemically, with regression of coronary dilatation on serial echocardiograms and normalized inflammatory markers on follow-up. Oral corticosteroids were tapered over three weeks under close cardiology and rheumatology supervision.Discussion: This case highlights the diagnostic challenge of incomplete KD in very young infants, who often lack classical features yet carry a higher risk of severe coronary involvement (1). Early echocardiographic screening is crucial in infants with prolonged unexplained fever to detect CAAs and enable prompt treatment (2). Systemic large-vessel involvement detected via advanced vascular imaging underscores an under-recognized spectrum of KD-related vasculitis warranting comprehensive evaluation in atypical or refractory cases (2, 3).Current AHA guidelines recommend early IVIG therapy with adjunctive corticosteroids for high-risk patients, alongside antiplatelet and anticoagulant therapies in giant aneurysms to mitigate thrombosis risk (4). Multidisciplinary care ensures optimized outcomes.This case underscores several important clinical lessons: first, KD should remain a differential diagnosis in any infant with persistent fever even in the absence of classical signs; second, early echocardiographic evaluation is imperative to identify CAAs and guide timely intervention; third, multidisciplinary collaboration between paediatric hospitalists, cardiology, infectious disease, and rheumatology specialists facilitates comprehensive care, particularly when systemic vascular involvement is suspected; lastly, a personalized treatment regimen incorporating corticosteroids and anticoagulants in addition to IVIG and aspirin may improve outcomes in high-risk infants with giant aneurysms (5).Conclusion: Heightened clinical vigilance, early diagnostic imaging, and a tailored, aggressive therapeutic strategy are essential to reduce morbidity and mortality in infants with incomplete KD.
