What are the diagnostic criteria and treatment options for Kawasaki disease in children under 5 years old presenting with prolonged fever?

Kawasaki Disease Diagnosis in Children Under 5 Years

Diagnose classic Kawasaki disease when a child presents with fever lasting at least 5 days plus at least 4 of the 5 principal clinical features: bilateral conjunctival injection, oral mucosal changes, polymorphous rash, extremity changes, and cervical lymphadenopathy. 1, 2, 3

Diagnostic Criteria

Classic Kawasaki Disease

The diagnosis requires fever for ≥5 days (day of onset = day 1) plus ≥4 of the following 5 principal features: 1, 2, 3

• Bilateral conjunctival injection: Non-purulent, primarily bulbar with limbal sparing, notably without photophobia or eye pain 1, 3
• Oral mucosal changes: Erythema and cracking of lips, strawberry tongue, and diffuse injection of oral and pharyngeal mucosa 1, 2
• Polymorphous rash: Most commonly diffuse maculopapular eruption, erythroderma, or erythema multiforme-like pattern, typically truncal with groin accentuation 1, 3
• Extremity changes: Acute phase erythema and edema of hands and feet with sharp demarcation at wrists/ankles; convalescent phase periungual desquamation starting 2-3 weeks later 1, 3
• Cervical lymphadenopathy: Usually unilateral, ≥1.5 cm diameter, confined to the anterior cervical triangle (least common principal feature) 1, 2

Fever Characteristics

The fever typically exceeds 39-40°C (102.2-104°F) with a remittent pattern and persists despite antibiotic and antipyretic treatment. 2, 3 Without treatment, fever continues 1-3 weeks on average. 2

Early Diagnosis Exception

Diagnosis can be made with only 4 days of fever when ≥4 principal features are present, particularly with hand/foot swelling. 2 Experienced clinicians may diagnose with 3 days of fever in rare classic presentations. 2

Incomplete (Atypical) Kawasaki Disease

Consider incomplete Kawasaki disease in children with fever ≥5 days AND only 2-3 principal features, or infants with fever ≥7 days without explanation. 2, 3

Evaluation Algorithm for Incomplete Disease

When fever ≥5 days with only 2-3 features present: 3

1. Immediately measure ESR and CRP 2, 3
2. If elevated, obtain: Complete blood count, comprehensive metabolic panel, urinalysis 3
3. Perform echocardiography to assess for coronary artery involvement 2, 3
4. Diagnose incomplete Kawasaki disease if coronary artery disease is detected by 2-dimensional echocardiography or coronary angiography 4, 1

Coronary artery complications occur at least as frequently in incomplete cases as in classic cases. 3

High-Risk Populations Requiring Heightened Suspicion

Infants <6 Months

Infants under 6 months may present with only prolonged fever and irritability, yet have the highest risk of coronary abnormalities. 1, 2, 3 This age group has:

• Fewer clinical manifestations upon admission (average 1.88 vs. 3.54 diagnostic criteria in older children) 5
• Higher incidence of incomplete Kawasaki disease (19.2% vs. 4.2%) 5
• Significantly higher rate of cardiac complications (30.8% vs. 11.7%) 5
• Longer hospitalization periods 5

Children of Asian Descent

Japanese children have incidence rates of 150 per 100,000 versus 10-15 per 100,000 in the United States. 1, 3

Supportive Laboratory Findings

Common laboratory abnormalities include: 2, 3

• Elevated ESR and CRP 2, 3
• Leukocytosis with neutrophil predominance 3
• Thrombocytosis in the second week after fever onset 2
• Low serum sodium and albumin 3
• Elevated liver enzymes 3
• Sterile pyuria 4, 3

Critical Diagnostic Pitfalls to Avoid

Clinical features are typically not all present simultaneously—careful review of prior signs and symptoms over the entire illness course is essential. 3 Common pitfalls include:

• Attributing cervical lymphadenopathy solely to bacterial lymphadenitis 3
• Dismissing strawberry tongue and rash as antibiotic reaction 3
• Failing to consider incomplete Kawasaki disease in infants <6 months with prolonged unexplained fever 5
• Missing the diagnosis in older children and adolescents who often have delayed diagnosis and higher prevalence of coronary artery abnormalities 2

Differential Diagnosis

Consider and exclude: 3

• Scarlet fever 3
• Multisystem Inflammatory Syndrome in Children (MIS-C)—obtain SARS-CoV-2 testing if suspected 3

Treatment Implications

Early treatment with IVIG (2 g/kg as single infusion) plus high-dose aspirin (80-100 mg/kg/day divided into four doses) within 10 days of fever onset significantly reduces coronary artery abnormality risk from approximately 25% to 4-5%. 1, 3

IVIG should be administered as early as possible within the first 10 days of illness onset, as soon as the diagnosis can be established. 1 Fever typically resolves within 36 hours after IVIG completion; persistence indicates IVIG resistance requiring further therapy. 2

Cardiac Evaluation

Baseline echocardiography should be performed at diagnosis to assess for coronary artery dilatation or aneurysm formation. 1 Echocardiography is the diagnostic imaging modality of choice to screen for coronary aneurysms. 1, 6

Patients with aneurysms require life-long and uninterrupted cardiology follow-up. 1