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Kawasaki Disease
Kawasaki disease (KD), also called mucocutaneous lymph node syndrome, is an acute, self-limited medium-vessel vasculitis with a predilection for the coronary arteries. It is the leading cause of acquired heart disease in children in the United States.
Epidemiology
- Peak incidence: 6–24 months of age; rare after 14 years
- More common in boys and children of Asian descent (incidence 20–100/100,000 children <5 years in Asia)
- Seasonal clustering in winter and spring suggests an infectious trigger, though no pathogen has been confirmed
- The emergence of a KD-like syndrome (MIS-C) in SARS-CoV-2–infected children has renewed interest in an infectious or immune-trigger hypothesis
Clinical Phases
| Phase | Timing | Features |
|---|---|---|
| Acute (Phase I) | Days 1–12 | Abrupt fever (up to 40°C), conjunctival injection, strawberry tongue, rash on palms/soles spreading to trunk, oral erythema |
| Subacute (Phase II) | Up to day 30 | Desquamation, thrombocytosis, arthritis/arthralgias, carditis — highest risk of sudden death |
| Convalescent (Phase III) | Weeks 6–10 | Most signs resolve; coronary aneurysms detectable in ~25% of untreated cases |
Diagnostic Criteria (CDC)
Fever ≥5 days plus at least 4 of 5 features:
- Polymorphous rash
- Bilateral non-exudative conjunctival injection
- Oral/mucosal changes — injected/fissured lips, strawberry tongue, diffuse pharyngeal erythema
- Cervical lymphadenopathy — ≥1 lymph node >1.5 cm
- Extremity changes — erythema of palms/soles, indurative edema, periungual desquamation
Incomplete (atypical) KD: Fever ≥5 days with only 2–3 features — particularly common in infants <6 months, who are paradoxically at highest risk for coronary complications.
Pathogenesis
Unknown etiology. The leading model: an infectious agent triggers an uncontrolled immunologic response in a genetically susceptible host. Proinflammatory cytokines and activated neutrophils cause endothelial injury; infiltration of the arterial wall by neutrophils, T cells, and macrophages leads to arterial stenosis or — more commonly — aneurysm formation.
Laboratory & Investigations
- CBC: Leukocytosis, thrombocytosis (esp. phase II)
- Inflammatory markers: Elevated CRP, elevated ESR (peaks in phase II, normalizes in phase III)
- LFTs: May be elevated
- Urinalysis: Sterile pyuria possible
- ECG: Abnormal in ~50% — tachycardia, T-wave inversion, ST changes, AV block, rarely ventricular arrhythmia
- Echocardiography: Start from week 2; used to monitor coronary involvement
Cardiovascular Complications
- Coronary artery aneurysms: Develop in up to 25% of untreated patients; ~5% with treatment
- Up to 20% of those with aneurysms eventually develop coronary stenosis
- Sudden death can result from myocardial infarction or aneurysm rupture
- Other: pericarditis, pericardial effusion, myocarditis, valvular dysfunction, cardiac failure
- Peripheral arteries (limb, renal, visceral) may also be involved
- Risk of thrombosis and MI persists even after aneurysm regression — long-term cardiology follow-up into adulthood is required for these patients
Treatment
| Agent | Dose / Notes |
|---|---|
| IVIG | 2 g/kg IV over 10–12 hours — give as soon as diagnosis is made, within 10 days of illness onset. Reduces coronary aneurysm risk ~5-fold |
| Aspirin | 30–100 mg/kg/day (high-dose, anti-inflammatory) until afebrile, then reduce to 3–5 mg/kg/day (antiplatelet) |
| Prednisolone | 2 mg/kg/day if IVIG-resistant (10–20% of cases are refractory) |
| Infliximab (anti-TNF-α) | 5 mg/kg IV — for refractory disease |
| Anakinra (IL-1 receptor antagonist) | 100–200 mg/day SC — for refractory disease |
Note on steroids: Historically avoided because early data suggested increased aneurysm risk. However, current evidence supports corticosteroids as adjunctive therapy in high-risk or IVIG-resistant cases. Antibiotics have no role unless there is a concurrent bacterial infection.
2024 AHA Update: Patients at increased risk for coronary artery aneurysms (age ≤6 months, baseline coronary z-score ≥2.5) require intensification of primary therapy. Direct oral anticoagulants (DOACs) are now an alternative to warfarin or LMWH for patients with giant CAA requiring anticoagulation. (AHA 2024 statement summary)
Differential Diagnosis
| Condition | Distinguishing Features |
|---|---|
| Scarlet fever | Sandpaper rash, +ASO, responds to antibiotics |
| Viral exanthem (measles, EBV) | Exudative conjunctivitis, specific serology |
| Toxic shock syndrome | Hypotension, identifiable focus of infection |
| Staphylococcal scalded skin | Bullous lesions, Nikolsky sign |
| Drug reaction (DRESS/SJS) | Drug exposure history |
| MIS-C | Post-COVID, often older children, prominent GI/shock features |
Prognosis
Most patients recover fully. Mortality is 1–2%. Outcomes are excellent when IVIG + aspirin are given within the first 10 days. Patients with giant coronary aneurysms carry the highest long-term risk of MI and sudden death, and require lifelong cardiology surveillance.
Sources: Rosen's Emergency Medicine, 9e | Braunwald's Heart Disease, 12e | Textbook of Family Medicine, 9e
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