Atypical Kawasaki Disease: Clinical Presentation
Atypical (incomplete) Kawasaki disease presents with prolonged fever (≥5 days) but fewer than the required 4 out of 5 classic clinical criteria, yet carries the same or higher risk of coronary artery complications as classic Kawasaki disease. 1
Clinical Presentation
Key Features
- Persistent high fever (>102.2°F/39°C) for at least 5 days without other explanation 1
- Presence of only 2-3 of the classic criteria:
- Bilateral non-exudative conjunctival injection
- Oral mucosal changes (cracked lips, strawberry tongue)
- Polymorphous rash (typically truncal)
- Extremity changes (erythema, edema, desquamation)
- Cervical lymphadenopathy (≥1.5 cm, usually unilateral) 1
High-Risk Populations
- Infants <6 months: Often present with fever as the sole clinical finding 2
- Young children: More common in this age group with paradoxically higher rates of coronary artery aneurysms if untreated 1
Laboratory Findings
- Elevated inflammatory markers (ESR often >40 mm/hr, CRP >3 mg/dL) 1
- Leukocytosis (WBC >15,000/mm³) with left shift 1
- Anemia (more pronounced with prolonged inflammation) 1
- Hypoalbuminemia 1
- Elevated liver enzymes 1
- Sterile pyuria (can be mistaken for UTI) 1
- Thrombocytosis (typically after 7 days of illness) 2
Cardiovascular Findings
- Echocardiographic abnormalities may include:
- Coronary artery ectasia or lack of tapering
- Perivascular brightness
- Decreased ventricular function
- Mild valvular regurgitation (typically mitral)
- Pericardial effusion 1
Diagnostic Approach
Algorithm for Suspected Incomplete Kawasaki Disease
- Child with unexplained fever ≥5 days plus 2-3 classic criteria
- Assess laboratory tests: CRP ≥3 mg/dL and/or ESR ≥40 mm/hr
- If elevated inflammatory markers, look for ≥3 supplemental laboratory findings:
- If ≥3 supplemental criteria present: Perform echocardiography
- If echocardiography shows coronary abnormalities: Treat for Kawasaki disease
- If fever persists with ongoing inflammation: Repeat echocardiography 1
Special Considerations for Infants
- For infants ≤6 months with fever ≥7 days without explanation, consider echocardiography even with few or no clinical criteria 2
- Lower threshold for evaluation and treatment due to higher risk of coronary complications 2
Common Pitfalls in Diagnosis
- Misdiagnosis as bacterial lymphadenitis when presenting with fever and unilateral cervical lymph node enlargement 1
- Mistaking rash and mucosal changes for antibiotic reaction 1
- Confusing sterile pyuria for partially treated UTI 1
- Misdiagnosing as viral meningitis in infants with fever, rash, and CSF pleocytosis 1
- Overlooking Kawasaki disease when GI symptoms predominate 2
- Delayed diagnosis in patients with sequential rather than simultaneous appearance of symptoms 3
Differential Diagnosis Exclusions
Conditions with similar features that should be excluded:
- Conditions with exudative conjunctivitis or pharyngitis
- Diseases with discrete intraoral lesions
- Illnesses with bullous or vesicular rash
- Conditions with generalized lymphadenopathy 1, 2
Treatment
- First-line: IVIG 2 g/kg as a single infusion plus high-dose aspirin (80-100 mg/kg/day divided QID) 1, 2, 4
- Treatment should be initiated within 10 days of fever onset when possible 2
- After fever resolution for 48-72 hours, reduce to low-dose aspirin (3-5 mg/kg/day) 2
- For IVIG resistance: Consider second IVIG dose, corticosteroids, or infliximab 2, 4
Prognosis
- Approximately 5% of children develop coronary artery dilation and 1% develop giant aneurysms even with optimal treatment 2
- Atypical Kawasaki disease carries at least the same risk of coronary complications as classic disease 1
- Kawasaki Disease Shock Syndrome represents a severe subtype with higher rates of coronary abnormalities (65%) and mortality (6.8%) 5
Early recognition and prompt treatment of atypical Kawasaki disease are essential to reduce the risk of coronary artery complications and improve outcomes.