What is the treatment for a child under 5 years old diagnosed with Kawasaki disease?

Treatment of Kawasaki Disease in Children Under 5 Years

All children diagnosed with Kawasaki disease should receive intravenous immunoglobulin (IVIG) 2 g/kg as a single infusion over 10-12 hours combined with high-dose aspirin (80-100 mg/kg/day divided into four doses) as soon as the diagnosis is established, ideally within the first 10 days of fever onset. 1

Initial Treatment Protocol

Standard First-Line Therapy

• IVIG 2 g/kg as a single infusion is the cornerstone of treatment, typically administered over 10-12 hours 1, 2
• High-dose aspirin 80-100 mg/kg/day divided into four doses should be given until the child is afebrile for 48-72 hours 3
• This combination reduces coronary artery aneurysm risk from 15-25% down to approximately 5% for any abnormality and 1% for giant aneurysms 3

Timing Considerations

• Treatment should be initiated as early as possible within the first 10 days of illness once diagnosis is established 1
• Experienced physicians can diagnose and treat before day 5 of fever if typical clinical findings are present 1
• Children presenting after day 10 should still receive IVIG if they have ongoing systemic inflammation (CRP >3.0 mg/dL) with either persistent fever or coronary artery aneurysms (Z score >2.5) 1, 3
• Do not withhold treatment solely based on timing if inflammation persists—the goal is preventing coronary damage 3

Management of Incomplete (Atypical) Kawasaki Disease

High-Risk Populations

• Infants under 6 months are at particularly high risk for incomplete presentations and paradoxically have higher rates of coronary aneurysms if untreated 3, 4
• Children under 1 year and adolescents frequently have delayed diagnosis due to atypical presentations 1

Treatment Approach

• Apply the American Heart Association algorithm for suspected incomplete KD (fever ≥5 days with 2-3 clinical criteria) 1
• Given the low risks of IVIG administration versus high risks of untreated coronary aneurysms, treat suspected incomplete KD when clinical suspicion is high 1
• Supplemental laboratory criteria supporting treatment include: albumin ≤3.0 g/dL, anemia for age, elevated ALT, platelets after day 7 ≥450,000/mm³, WBC ≥15,000/mm³, and urine ≥10 WBC/hpf 1

Management of IVIG-Resistant Disease

Definition and Incidence

• Approximately 10-20% of patients develop persistent or recrudescent fever ≥36 hours after completing initial IVIG infusion 2, 3, 5

Second-Line Treatment Options

• Administer a second dose of IVIG 2 g/kg as a single infusion 3
• Methylprednisolone 20-30 mg/kg IV for 3 days or infliximab 5 mg/kg IV over 2 hours are alternative second-line options with similar efficacy 3
• Some centers use combinations of these approaches for salvage therapy 6

Long-Term Antiplatelet and Anticoagulation Management

Aspirin Dosing Transition

• After fever resolution (48-72 hours afebrile), transition to low-dose aspirin 3-5 mg/kg/day (single daily dose) 3

Risk-Stratified Antithrombotic Therapy

• No coronary abnormalities: Continue low-dose aspirin until 6-8 weeks after disease onset, then discontinue if echocardiogram remains normal 3

• Small coronary aneurysms (<4 mm): Continue low-dose aspirin indefinitely 3

• Moderate aneurysms (4-6 mm): Low-dose aspirin plus a second antiplatelet agent (clopidogrel 1 mg/kg/day, maximum 75 mg/day) 3

• Giant aneurysms (≥8 mm): Low-dose aspirin plus warfarin (target INR 2.0-2.5) or therapeutic low-molecular-weight heparin 3

Critical Monitoring Requirements

Cardiac Surveillance

• Perform echocardiography at diagnosis, 2 weeks, and 6-8 weeks after disease onset at minimum 1
• Patients with giant aneurysms require frequent echocardiography and ECG during the first 3 months, as the highest thrombosis risk occurs within this period, peaking at days 15-45 3

Laboratory Monitoring

• Monitor inflammatory markers (ESR, CRP) to assess treatment response 1
• For patients on warfarin, maintain INR 2.0-2.5 3

Important Caveats and Pitfalls

Immunization Considerations

• Defer measles and varicella immunizations for 11 months after high-dose IVIG administration due to antibody interference 3
• Annual influenza vaccination is mandatory for children on long-term aspirin therapy due to Reye's syndrome risk 3

Drug Interactions

• Never use ibuprofen in children taking aspirin for antiplatelet effects, as it antagonizes irreversible platelet inhibition 3

Diagnostic Pitfalls

• Beware of misdiagnosing KD as antibiotic reaction when rash and mucosal changes follow treatment for presumed bacterial lymphadenitis 1
• Sterile pyuria may be mistaken for partially treated urinary tract infection 1
• Young infants with fever, rash, and CSF pleocytosis may be misdiagnosed with viral meningitis 1
• Consider KD in every child with fever ≥5 days, rash, and nonpurulent conjunctivitis, especially in infants under 1 year where diagnosis is frequently missed 1