Overcoming diagnostic challenges in an incomplete Kawasaki disease: A case report in an infant

INTRODUCTION

Kawasaki disease (KD) is an acute febrile illness of unknown origin that primarily affects children under 5 years of age and is the leading cause of acquired heart disease in this group. It is a systemic vasculitis, mainly involving medium-sized arteries with a preference for the coronary arteries. Without treatment, 25% of cases may develop coronary artery aneurysms (CAAs).^[1,2]

KD predominantly affects children aged 18–24 months and is more common in Asian populations, especially in Japan. Atypical or incomplete KD is more frequent in infants under 6 months and children over 5 years,^[3] often leading to delayed diagnosis, treatment resistance and increased risk of coronary complications.

Early diagnosis and treatment with intravenous immunoglobulin (IVIG) within 10 days significantly reduces coronary aneurysm risk from 25% to 4%. Here, we present a case of a 3-month-old infant with incomplete KD, illustrating the challenges in early diagnosis and management in very young infants.^[4]

CASE REPORT

A 3-month-old male infant was referred to our outpatient department with a history of high-grade intermittent fever for 1 week. The baby was diagnosed at the referring hospital to have a urinary tract infection and was treated for 7 days with oral antibiotics and 2 days with intravenous (IV) antibiotics. The baby was a healthy term born to a G3P3L2 mother by normal vaginal delivery. He is third by birth order, born out of a non-consanguineous marriage. Birth weight is 3500 g. Antenatal and perinatal history is uneventful.

At admission, the baby was irritable with a temperature of 101°F. Vitals were stable with a heart rate of 131/min, RR: 32/min, mean BP: 50 mmHg and SpO_2: 96 in room air. On examination, he had pharyngitis and perianal rash. Other system examinations were within normal limits. Investigations revealed neutrophilic leucocytosis (total leucocyte count: 23700; neutrophils: 66%; lymphocytes: 22% and monocytes: 3%), pyuria, high erythrocyte sedimentation rate (19 mm/h) and C-reactive protein (CRP) (130 mg/dL) at admission. He was started on IV antibiotics. Blood and urine cultures were sent and were reported as sterile.

Otoscopic examination revealed features suggestive of bilateral acute suppurative otitis media. The baby continued to have a fever in spite of 4 days of IV antibiotics. Cerebral-spinal fluid (CSF) analysis sent on day 5 of admission was suggestive of aseptic meningitis. CSF culture was sterile. The baby developed BCG site induration, rash, erythematous lips, strawberry tongue and non-exudative conjunctivitis on day 10 of hospital admission. Incomplete KD was diagnosed according to the American Heart Association (AHA) criteria.^[3] Transthoracic echocardiography was done, which revealed dilated right coronary arteries with a Z score of 2.3 (normal value <2.0).

The infant was treated with a single dose of IV pooled immunoglobulin 2 g/kg and 4 days of aspirin at 80 mg/kg/day. The baby was discharged after 2 weeks of admission on oral prednisolone 2 mg/kg/day for 1 week and an aspirin anti-platelet dose of 5 mg/kg day. At discharge, the baby was afebrile, active and comfortable. The child has been on regular monthly follow-ups since then and has normal growth and development. Echocardiography done on the last follow-up at 1 year 3 months of age revealed right coronary artery dilatation with a Z score of 2.3 (normal Z score<2), while the left coronary artery was normal. The child is continued on aspirin at the anti-platelet dose of 5 mg/kg day.

DISCUSSION

We present a case of incomplete KD in a young infant. Although many reports exist on KD, literature on incomplete KD – especially in infants – is limited. Diagnosis is often delayed or missed due to overlapping symptoms with common paediatric infectious or rheumatic conditions.^[5] Incomplete KD may initially present with fever and unilateral cervical lymphadenopathy, followed by rash and mucosal changes. These features can be misinterpreted as reactions to antibiotics given for presumed bacterial lymphadenitis. Sterile pyuria may mimic partially treated urinary tract infections, and presentations such as fever, rash and CSF pleocytosis can resemble viral meningitis.

In our case, the AHA criteria for incomplete KD in infants under 6 months were used. The infant had persistent fever for >7 days, anaemia (haemoglobin 10 g/dL), leucocytosis (>15,000/mm³), thrombocytosis (>450,000 on day 7), elevated CRP (130 mg/dL) and coronary artery dilation on echocardiography. According to Chang et al., infants under 6 months have a higher incidence of incomplete KD (35% vs. 12%), coronary involvement (65% vs. 19%) and worse outcomes due to delayed diagnosis.^[6]

Approximately 10% of KD cases occur in infants under 6 months. Diagnosing KD in infants younger than 3 months is especially challenging, with only about 24% meeting at least four of the five classic clinical criteria. Delayed diagnosis increases the risk of CAA, which can develop in 15–25% of untreated cases. To reduce cardiac complications, IVIG should be administered ideally within 10 days, preferably by day 7 of illness.^[7]

CONCLUSION

A high index of suspicion is necessary to diagnose KD, especially in young infants. Early diagnosis and treatment pave the path for successful outcomes and significantly reduce mortality and morbidity. KD should always be part and parcel of differential diagnosis in any prolonged fever >5 days in children younger than 5 years and especially in young infants, in spite of other infective aetiology.