What is the workup and treatment for Kawasaki disease?

Workup for Kawasaki Disease

All children with suspected Kawasaki disease should undergo immediate echocardiography and laboratory testing to assess for coronary artery involvement and systemic inflammation, with treatment initiated promptly if diagnostic criteria are met. 1, 2

Clinical Diagnosis

Classic (Complete) Kawasaki Disease

• Diagnose based on fever lasting ≥5 days PLUS 4 out of 5 clinical features: 3, 4
  • Bilateral non-purulent conjunctival injection
  • Oral mucosal changes (cracked/erythematous lips, strawberry tongue)
  • Polymorphous rash
  • Extremity changes (erythema, edema, or desquamation of palms/soles)
  • Cervical lymphadenopathy (usually >1.5 cm, often unilateral)

Incomplete (Atypical) Kawasaki Disease

• Suspect in patients with fever ≥5 days and only 2-3 classic clinical features 3, 1
• Infants ≤6 months old require special attention: on day 7 of unexplained fever, perform laboratory testing and echocardiography even without any classic criteria, as this age group has the highest risk of coronary complications 3
• Use the AHA algorithm for incomplete KD: 3
  • If 2-3 clinical criteria present → obtain CRP and ESR
  • If CRP ≥3.0 mg/dL or ESR ≥40 mm/hr → check supplemental laboratory criteria
  • If ≥3 supplemental criteria positive → perform echocardiogram

Essential Laboratory Workup

Initial Laboratory Testing

Obtain the following tests in all suspected cases: 3, 1

• Complete blood count with differential (looking for leukocytosis >15,000/mm³, anemia for age, thrombocytosis after day 7 >450,000/mm³)
• C-reactive protein (CRP ≥3.0 mg/dL supports diagnosis)
• Erythrocyte sedimentation rate (ESR ≥40 mm/hr supports diagnosis)
• Comprehensive metabolic panel (albumin <3.0 g/dL, elevated ALT)
• Urinalysis (sterile pyuria: >10 WBC/high-power field)

Supplemental Laboratory Criteria (for incomplete KD)

At least 3 of the following support treatment: 3

• Albumin ≤3.0 g/dL
• Anemia for age
• Elevated alanine aminotransferase
• Platelets after day 7 ≥450,000/mm³
• White blood cell count ≥15,000/mm³
• Urine ≥10 WBC/high-power field

Cardiac Imaging Workup

Echocardiography (Primary Imaging Modality)

Transthoracic echocardiography is mandatory in all suspected cases 3, 4, 5

Echocardiogram is considered positive if ANY of the following are present: 3

• Z-score of left anterior descending (LAD) or right coronary artery (RCA) ≥2.5
• Coronary arteries meet Japanese Ministry of Health criteria for aneurysms
• ≥3 suggestive features: perivascular brightness, lack of tapering, decreased LV function, mitral regurgitation, pericardial effusion, or z-scores in LAD or RCA of 2.0-2.5

Timing of echocardiography: 2

• Initial echocardiogram at diagnosis
• Repeat at 2 weeks and 6-8 weeks after disease onset for all patients
• More frequent monitoring (weekly or biweekly) for patients with coronary abnormalities during the first 3 months

Electrocardiogram

Obtain baseline ECG at diagnosis to assess for arrhythmias, conduction abnormalities, or signs of myocardial ischemia 3, 2

Key Diagnostic Pitfalls to Avoid

Features That Argue AGAINST Kawasaki Disease

Consider alternative diagnoses if the following are present: 3

• Exudative conjunctivitis (suggests viral or bacterial infection)
• Exudative pharyngitis (suggests streptococcal pharyngitis)
• Discrete intraoral lesions (suggests viral stomatitis)
• Bullous or vesicular rash (suggests viral exanthem)
• Generalized adenopathy (suggests EBV, CMV, or other systemic infection)

High-Risk Populations Requiring Lower Threshold for Workup

• Infants <6 months: highest risk for incomplete presentation and coronary complications; maintain very low threshold for full workup 3, 1
• Infants <1 year: paradoxically have higher rates of coronary aneurysms despite more frequent incomplete presentations 1

Treatment Decision Algorithm

If classic KD criteria met (fever ≥5 days + 4/5 features): treat immediately with IVIG 2 g/kg + high-dose aspirin without waiting for echocardiogram results 1, 2

If incomplete KD suspected (fever ≥5 days + 2-3 features): 3, 1

1. Check CRP and ESR
2. If elevated, check supplemental laboratory criteria
3. Perform echocardiogram
4. Treat if echocardiogram shows coronary abnormalities OR if ≥3 supplemental laboratory criteria are positive
5. Treat patients within 10 days of fever onset AND those beyond day 10 with ongoing clinical and laboratory signs of inflammation (elevated CRP/ESR)

Critical Timing Consideration

Treatment should ideally be initiated within the first 10 days of fever onset to minimize coronary artery complications, but do not withhold treatment beyond day 10 if active inflammation persists 1, 2. Delaying treatment increases the risk of coronary artery abnormalities from 5% (with timely IVIG) to 15-25% (without treatment) 3.