Introduction
Kawasaki disease is very rare in infants younger than 3 months, yet this age group carries the highest risk for developing coronary artery abnormalities and diagnosis is particularly challenging.

Case presentation
In October 2025 a 2,5-month-old boy was hospitalized due to increased irritabillity, exudative tonsillitis, a confluent rash, purulent conjunctivitis, right-sided otitis media, mildly elevated CRP (20 mg/L) and leukocyturia. Nasopharyngeal swabs for viruses and blood cultures were negative. Intravenous amoxicillin/clavulanate was started on 2nd day of fever. Abdominal and cardiac ultrasound were normal. On the 3rd day of fever, episodes of sinus tachycardia, cracked lips, swelling and erythema of feet and hands, CRP level 63 mg/L and unremarkable other blood tests, were observed. He was transferred to the Children’s Hospital Ljubljana. Due to strong clinical suspicion of Kawasaki disease, intravenous immunoglobulin (IVIG) 2g/kg and acetylsalicylic acid were administred. Fever, rash, conjuctivitis, and edema resolved within the next day, CRP level declined.
Three days later, fever, mild rash on extremities, necrotic rash on the face, irritabillitiy, erythema of hands/feet reappeared. He received high dose intravenous methylprednisolone for 3 days (20 mg/kg), followed by oral dexamethasone (0.2 mg/kg/d). Fever resolved, but after one week, nonpurulent conjuctivitis with blepharitis, rash on the face, extremities, scrotum and subungual desquamation were present. Laboratory findings revealed CRP 15 mg/L, WBC 24×109/L and thrombocytosis. Echocardiography revealed coronary artery dilatation/aneurysm without thrombosis (LMCA Z score 2,93, LCX Z score 2.50, LAD Z score 1,79, ectatic RCA with highest Z score of 3,05).
Additional IVIG and infliximab were administrated, and corticosteroid therapy with dexamethasone was continued. The patient showed clinical and laboratory improvement. Follow-up echocardiography revealed RCA Z score 3,9 and normal LMCA, LAD, LCX Z score. After another week, RCA Z score decreased to 2,3 and after 4 weeks all Z scores were <2. Altogether, the patient received 3 doses of infliximab, six weeks of dexamethasone, and continues acetylsalicylic acid therapy.

Conclusion
The case report of a young infant with severe Kawasaki disease outlines the importance of timely diagnosis (even before 4-5 days of fever) and early escalating of therapy to prevent long-term cardiac sequelle.