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Kawasaki Syndrome

Synonyms: Mucocutaneous Lymph Node Syndrome (MCLS), Infantile Polyarteritis System(s) Involved: Cardiovascular, GI, Hematologic, Musculoskeletal, Nervous, Pulmonary, Renal, Skin ICD-10: M30.3

πŸ”Ž Description

  • Acute, self-limited febrile vasculitis affecting small- and medium-sized arteries, especially coronary arteries
  • Leading cause of acquired heart disease in children in developed countries
  • Can cause coronary artery aneurysms (CAAs), MI, ischemia, or sudden death

πŸ“Š Epidemiology

  • Age: Predominantly 6 months to 5 years (85%); median = 1.5 years
  • Gender: Male > Female (1.5:1)
  • Highest incidence: Asian > African American > Hispanic > White
  • US incidence: 20/100,000 children <5 years
  • Seasonality: Winter–Spring (Jan–Mar); Summer in Asia
  • Outbreaks: Every 2–3 years

🧬 Etiology & Pathophysiology

  • Triggered by infectious agent in genetically predisposed children
  • Necrotizing arteritis β†’ wall destruction, aneurysms
  • Transition to chronic lymphocytic vasculitis β†’ fibrosis, stenosis
  • Key mediators: TNF-Ξ±, IL-1, IL-6, metalloproteinases
  • Genetic susceptibility: SNPs in FcΞ³R2A, CASP3, HLA class II, CD40, TGF-Ξ² pathway
  • Siblings: 10–30Γ— increased risk

⚠️ Risk Factors

  • Male sex
  • Asian or African American ethnicity
  • Sibling or parent with KS

πŸ§ͺ Diagnosis

A. Classic Criteria

  • β‰₯5 days of fever plus β‰₯4 of the following:
    1. Bilateral nonpurulent conjunctivitis
    2. Oral mucosal changes: strawberry tongue, cracked lips
    3. Polymorphous rash
    4. Peripheral extremity changes: edema, erythema, desquamation
    5. Cervical lymphadenopathy >1.5 cm

B. Incomplete (Atypical) KS

  • Fever β‰₯5 days + 2–3 criteria + lab markers of inflammation
  • Common in infants ≀6 months and older children
  • Higher risk of missed diagnosis and CAAs

πŸ‘©β€βš•οΈ Clinical Features

  • Fever: High (β‰₯102Β°F), remittent, unresponsive to antibiotics
  • Conjunctivitis: Bilateral, painless, nonexudative, limbic sparing
  • Oral: Strawberry tongue, red/cracked lips
  • Rash: Polymorphous (morbilliform, maculopapular, etc.)
  • Extremities: Red palms/soles, edema, desquamation
  • Lymphadenopathy: Unilateral, firm, nonfluctuant cervical nodes

🧠 Multisystem Involvement

  • Cardiac: Myocarditis, pericarditis, CAAs, arrhythmias
  • GI: Abdominal pain, vomiting, hydrops of gallbladder
  • Renal: Proteinuria, sterile pyuria
  • Musculoskeletal: Polyarthritis
  • Neuro: Aseptic meningitis, facial palsy

πŸ”¬ Diagnostic Workup

A. Labs

  • CBC: Leukocytosis, thrombocytosis (wk 2–3), normocytic anemia
  • ↑ CRP, ESR, Ξ±1-antitrypsin
  • ↓ Albumin, sodium
  • ↑ AST, ALT, GGT, bilirubin
  • UA: Sterile pyuria
  • CSF: Lymphocytic pleocytosis
  • Nasal swabs: Exclude viral illness (e.g., SARS-CoV-2)

B. Imaging

  • Echo (baseline): CAAs, pericardial effusion, ↓ contractility
  • ECG: PR prolongation, ST/T changes
  • Chest X-ray: Effusion or CHF
  • Cardiac MRI/angiography: Follow-up in CAAs
  • Stress testing: If ischemia suspected

🧾 Differential Diagnosis

  • Infectious: Scarlet fever, EBV, adenovirus, leptospirosis
  • Toxin-mediated: Toxic shock, SSSS
  • Inflammatory: Juvenile idiopathic arthritis, MIS-C
  • Other: Drug reactions (SJS), acrodynia (mercury toxicity)

πŸ’Š Treatment

A. First-line

  • IVIG 2 g/kg IV over 10–12 hr (within 7–10 days of fever onset)
  • Aspirin:
    • High dose: 80–100 mg/kg/day in 4 divided doses
    • Switch to low dose (3–5 mg/kg/day) after afebrile 48–72 hr
    • Continue for 6–8 weeks or longer if coronary abnormalities

B. Refractory Cases

  • Second IVIG dose (2/3 of nonresponders respond)
  • Steroids: Only in high-risk or IVIG-resistant patients
  • Others:
    • Infliximab, cyclosporine, plasmapheresis
    • Clarithromycin may reduce relapse, not fever duration

C. Antithrombotics

  • Long-term ASA, clopidogrel, heparin, LMWH, warfarin for large aneurysms
  • Avoid ibuprofen (antagonizes ASA antiplatelet effect)

D. Vaccination Considerations

  • Avoid live vaccines for 11 months post-IVIG
  • Yearly influenza vaccination for children on long-term ASA

πŸ₯ Referral & Follow-up

  • Pediatric cardiology: All with CAAs
  • Echo schedule: At diagnosis, 6–8 weeks, 6–12 months
  • Monitor for MI risk, arrhythmias, aneurysm regression

🧬 Prognosis

  • Good with early IVIG
  • CAAs in 3–5% treated; up to 25% untreated
  • Giant aneurysms in 1%
  • Rare sudden death in early adulthood
  • Recurrence: <1% (US); ~3% (Japan)

πŸ“Œ Clinical Pearls

  • Always suspect KS in febrile child unresponsive to antibiotics
  • Prompt IVIG and ASA reduce coronary complications
  • Incomplete KS is common in infants and must not be missed
  • Live vaccines contraindicated for 11 months post-IVIG
  • Symptom onset may be staggered β€” examine trends, not isolated features