What are the diagnostic criteria and treatment for Kawasaki disease?

Diagnosing Kawasaki Disease

Kawasaki disease is diagnosed clinically when a child has fever lasting at least 5 days plus at least 4 of 5 principal clinical features: bilateral bulbar conjunctival injection without exudate, oral mucosal changes (cracked lips, strawberry tongue), polymorphous rash, extremity changes (erythema of palms/soles or periungual desquamation), and cervical lymphadenopathy (≥1.5 cm, usually unilateral). 1, 2

Classic (Complete) Kawasaki Disease Criteria

The American Heart Association diagnostic framework requires:

• Fever ≥5 days (day of onset = day 1) as the essential criterion 1, 2
• Plus ≥4 of the 5 principal features listed below 1, 2

The Five Principal Clinical Features

• Bilateral conjunctival injection: Nonexudative, primarily bulbar with limbal sparing 2
• Oral mucosal changes: Erythema and cracking of lips, strawberry tongue, diffuse erythema of oral/pharyngeal mucosa 2
• Polymorphous rash: Most commonly diffuse maculopapular eruption 2
• Extremity changes: Erythema of palms and soles in acute phase; periungual desquamation in subacute phase (typically 2-3 weeks after fever onset) 2
• Cervical lymphadenopathy: ≥1.5 cm diameter, usually unilateral, least common of the principal features 2

Early Diagnosis Exception

• Diagnosis can be made with only 4 days of fever when ≥4 principal features are present, particularly with hand/foot swelling 2
• Experienced clinicians may diagnose with 3 days of fever in rare classic presentations 2

Incomplete (Atypical) Kawasaki Disease

Consider incomplete Kawasaki disease when:

• Children with fever ≥5 days AND only 2-3 principal features 1, 2
• Infants with fever ≥7 days without other explanation 1, 2

Evaluation Algorithm for Incomplete KD

When incomplete KD is suspected, proceed systematically:

1. Check inflammatory markers: ESR and CRP 1, 3
2. Assess supplemental laboratory criteria (if ≥3 present, consider treatment): 3
   • Anemia for age
   • Platelet count ≥450,000/mm³ after day 7 of fever
   • Albumin <3.0 g/dL
   • Elevated ALT
   • WBC count ≥15,000/mm³
   • Urine ≥10 WBC/hpf
3. Obtain echocardiogram to evaluate for coronary artery abnormalities 1, 3

Critical point: KD is unlikely if ESR, CRP, and platelet count are all normal after day 7 of illness 3

High-Risk Populations Requiring Extra Vigilance

• Infants <6 months: May present with only prolonged fever and irritability, yet have the highest risk of coronary abnormalities 1, 2
• Older children and adolescents: Often have delayed diagnosis and higher prevalence of coronary artery abnormalities 1, 2

Supportive Laboratory Findings

While no specific diagnostic test exists for Kawasaki disease, typical laboratory abnormalities include: 1, 3

Acute Phase (First Week)

• Leukocytosis: ~50% have WBC >15,000/mm³ with granulocyte predominance 3
• Elevated acute phase reactants: ESR and CRP nearly universally elevated 3
• Normochromic, normocytic anemia: Common 3
• Elevated transaminases: 40-60% have mild-moderate elevations 3
• Hypoalbuminemia: Associated with more severe disease 3
• Sterile pyuria: Present in up to 80% of children 3

Subacute Phase (Second-Third Week)

• Thrombocytosis: Characteristic but typically doesn't occur until second week, peaking in third week (mean ~700,000/mm³) 3

Red Flags

• Leukopenia: Rare; suggests alternative diagnosis 3
• Thrombocytopenia: May indicate disseminated intravascular coagulation and is a risk factor for coronary abnormalities 3

Echocardiography: Essential Diagnostic Tool

• No specific diagnostic test exists for KD; echocardiography is crucial for evaluating suspected incomplete KD 1
• Diagnosis can be made with <4 principal features if coronary artery abnormalities are detected on echocardiography 1
• Transthoracic echocardiography is the screening modality of choice for coronary aneurysms 4

Common Diagnostic Pitfalls to Avoid

• Misinterpreting sterile pyuria as partially treated UTI rather than recognizing it as a KD feature 3
• Missing the diagnosis in infants <6 months who may only have fever and irritability 1, 2
• Delaying diagnosis in older children/adolescents who present atypically 1, 2
• Mistaking CSF pleocytosis for viral meningitis (30% have mononuclear pleocytosis with normal glucose) 3
• Waiting for thrombocytosis to make the diagnosis (it typically doesn't appear until week 2) 3

Differential Diagnosis Considerations

Distinguish from:

• Viral infections: Measles, adenovirus 1
• Bacterial infections: Scarlet fever, staphylococcal scalded skin syndrome 1

Additional Clinical Features Supporting Diagnosis

• Cardiovascular: Gallop rhythm, ECG changes 1
• Gastrointestinal: Diarrhea, abdominal pain (common) 1
• Musculoskeletal: Arthritis/arthralgia in ~one-third of patients during acute phase 2

Treatment Urgency

• Early treatment with IVIG and aspirin within 10 days of fever onset significantly reduces coronary artery abnormality risk from 15-25% to <5% 1, 2, 4
• Fever typically resolves within 36 hours after IVIG completion; persistence indicates IVIG resistance requiring further therapy 2
• Without treatment, fever continues 1-3 weeks on average 2