Self-limited medium-vessel vasculitis of young children; principal threat is coronary artery aneurysms; treated with IVIG and aspirin within 10 days of fever onset.
Also known as: mucocutaneous lymph node syndrome, MCLS, Kawasaki syndrome, infantile polyarteritis
Overview
An acute, self-limited febrile vasculitis of medium-sized arteries that predominantly affects children under 5. Cardinal feature is fever ≥5 days with at least four of: bilateral non-exudative conjunctivitis, oral mucosal changes, extremity changes, polymorphous rash, and unilateral cervical lymphadenopathy. Untreated, 20-25% develop coronary artery aneurysms.
Epidemiology
Highest incidence in children of Asian (especially Japanese) descent; ~6,000 US cases/year. 80% of cases in children <5 years. Slight male predominance. Peak in late winter and spring. Etiology unknown, presumed infectious trigger in a genetically predisposed host.
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MIS-C following SARS-CoV-2 has overlapping features but is a distinct entity
Pathophysiology
Postulated infectious trigger initiates an immune cascade in genetically susceptible children, leading to medium-vessel vasculitis with prominent coronary artery involvement. Activated T cells, macrophages, and cytokine surge produce endothelial dysfunction and arterial wall edema, weakening and dilating affected vessels.
Clinical presentation
Symptoms
Fever ≥5 days, often 39-40 °C, unresponsive to antipyretics
Bilateral non-exudative conjunctival injection with limbic sparing
Extremity changes: erythema and edema of palms and soles in week 1; periungual desquamation in week 2-3
Polymorphous rash: morbilliform, scarlatiniform, or erythema multiforme-like; perineal accentuation in infants
Unilateral cervical lymphadenopathy ≥1.5 cm
Irritability disproportionate to exam, especially infants
Signs / physical exam
Tachycardia disproportionate to fever
BCG site reactivation (red, indurated) where BCG given
Hydrops of gallbladder, sterile pyuria, arthritis, aseptic meningitis can occur
Classic findings
Cracked red lips, strawberry tongue, red palms and soles, bilateral conjunctivitis, and a polymorphous rash in a febrile irritable toddler.
Differential diagnosis
Scarlet fever — Strep pharyngitis with sandpaper rash; lacks extremity changes and conjunctivitis
Measles — Three Cs and Koplik spots; cephalocaudal rash
Stevens-Johnson syndrome — Mucosal involvement with sloughing and target lesions, drug exposure
Staphylococcal or streptococcal toxic shock — Hypotension and end-organ failure; toxin-mediated
Multisystem inflammatory syndrome in children (MIS-C) — Recent SARS-CoV-2 exposure, older children, more cardiac dysfunction and shock; overlaps significantly with Kawasaki
Classic Kawasaki: fever ≥5 days plus ≥4 of 5 principal features (conjunctivitis, lip/oral changes, extremity changes, rash, cervical adenopathy). Incomplete Kawasaki: fever ≥5 days with 2-3 features plus supportive labs and/or coronary changes.
Labs
CBC: leukocytosis with left shift in week 1, thrombocytosis (>450,000) classically appears in week 2
ESR and CRP elevated; persistent elevation supports diagnosis
LFTs: mild transaminitis, hypoalbuminemia
Urinalysis: sterile pyuria
BNP/NT-proBNP often elevated
Echocardiogram at diagnosis, 1-2 weeks, and 4-6 weeks — assess coronary artery dimensions (z-scores)
Consider SARS-CoV-2 testing (PCR and antibody) to distinguish from MIS-C in current era
Imaging
Transthoracic echocardiogram is mandatory and serial
ECG to detect arrhythmias and ischemia
Cardiac MRI or coronary CT for follow-up of aneurysms
Diagnostic algorithm
flowchart TD
A[Fever ≥5 days<br/>young child] --> B{≥4 of 5 features?<br/>conj / lips / extremities<br/>rash / cervical node}
B -->|Yes| C[Classic Kawasaki]
B -->|2-3 features| D[Incomplete Kawasaki<br/>check CRP/ESR + echo]
D -->|Supportive| C
C --> E[IVIG 2 g/kg + high-dose ASA<br/>within 10 days]
E --> F{Fever resolves<br/>≤36 h?}
F -->|Yes| G[Low-dose ASA<br/>+ serial echo]
F -->|No| H[IVIG-resistant:<br/>repeat IVIG ± steroids<br/>± infliximab]
G --> I{Coronary aneurysm?}
I -->|Small| J[Continue low-dose ASA]
I -->|Large/giant| K[ASA + anticoagulation<br/>lifelong cardiology follow-up]
Kawasaki disease diagnostic and treatment algorithm.
Treatment
First-line
IVIG + ASA for Kawasaki — IVIG 2 g/kg as a single infusion over 10-12 hours within 10 days of fever onset (and ideally before day 7)
High-dose aspirin 30-50 mg/kg/day in 4 divided doses until afebrile for 48-72 hours, then low-dose aspirin 3-5 mg/kg/day until inflammatory markers and coronary imaging normalize
Continue low-dose aspirin if coronary aneurysms develop; add anticoagulation (warfarin, LMWH) for large or giant aneurysms
IVIG-resistant Kawasaki
Persistent or recurrent fever ≥36 hours after IVIG
Re-treat with second IVIG 2 g/kg
Adjunctive corticosteroids (methylprednisolone pulse or prednisolone taper) for high-risk patients (Kobayashi score)
Infliximab or cyclosporine as third-line
Late presentation (>10 days)
Treat with IVIG if persistent fever, ongoing inflammation, or coronary changes
Aspirin and serial echocardiography
Second-line / adjunct
Live vaccines (MMR, varicella) should be delayed 11 months after IVIG (passive antibody interferes with the live-vaccine immune response); inactivated influenza vaccine is unaffected and need not be deferred
Avoid live MMR/varicella for 11 months after IVIG
Complications
Coronary artery aneurysms (giant aneurysm = z-score >10 or >8 mm) with risk of thrombosis, stenosis, MI, and sudden death
Myocarditis, pericarditis, valvular regurgitation
Arrhythmias
Long-term: premature atherosclerosis, even without persistent aneurysm
Fever ≥5 days with at least four principal features — start IVIG within 10 days to reduce aneurysm rate from 20-25% to ~3-5%.
Periungual desquamation in week 2-3 is a retrospective clue but cannot wait — diagnose and treat early on fever and other features.
Aspirin is one of the few pediatric indications that overrides Reye-syndrome avoidance; benefits outweigh risks here.
Defer live vaccines (MMR, varicella) for 11 months after IVIG.
Incomplete Kawasaki is more common in infants and requires supportive labs plus echo to support diagnosis.
References
AHA 2017 — AHA Scientific Statement: Diagnosis, Treatment, and Long-Term Management of Kawasaki Disease (McCrindle et al., Circulation 2017;135:e927-e999)
AAP Red Book — American Academy of Pediatrics Red Book — Kawasaki Disease
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