Kawasaki Disease: Clinical Overview
Kawasaki disease is an acute systemic vasculitis predominantly affecting children under 5 years of age, representing the leading cause of acquired heart disease in developed countries, with coronary artery aneurysms developing in approximately 25% of untreated patients. 1, 2
Epidemiology
- Incidence: Approximately 25 cases per 100,000 children under 5 years in North America annually 1
- Age distribution: 76% of cases occur in children under 5 years 1
- Gender: Male predominance with ratio of 1.5-1.7:1 1
- Ethnicity: Highest risk in Asian children, particularly those of Japanese ancestry 1
- Seasonality: More common in winter and early spring in North America 1
- Mortality: Case fatality rate <0.1% in Japan; accounts for 5% of acute coronary syndromes in adults under 40 years 1
Pathophysiology
KD is a generalized systemic vasculitis affecting blood vessels throughout the body, though coronary arteries are virtually always involved in fatal cases. 3 The disease process involves:
Vascular inflammation progressing through distinct phases:
- Early stage (7-9 days): Neutrophil infiltration with endothelial swelling and subendothelial edema
- Intermediate stage: Transition to mononuclear cells, lymphocytes (predominantly CD8 T cells), and IgA plasma cells
- Late stage: Destruction of internal elastic lamina, fibroblastic proliferation, and progressive fibrosis over weeks to months 3
Aneurysm formation can occur in extraparenchymal muscular arteries including celiac, mesenteric, femoral, iliac, renal, axillary, and brachial arteries 3
Clinical Diagnosis
Classic KD requires fever lasting at least 5 days plus 4 of 5 principal clinical features (or fever with coronary artery disease detected on echocardiography or angiography with only 4 principal features): 3
The 5 Principal Clinical Features:
- Bilateral bulbar conjunctival injection without exudate
- Oral changes: Erythematous and cracked lips, strawberry tongue, diffuse injection of oral and pharyngeal mucosae
- Extremity changes:
- Acute phase: Erythema of palms and soles, edema of hands and feet
- Subacute phase (weeks 2-3): Periungual desquamation of fingers and toes
- Late finding (1-2 months): Beau's lines (transverse nail grooves)
- Polymorphous exanthem: Most commonly nonspecific diffuse maculopapular eruption; may also present as urticarial or scarlatiniform rash
- Cervical lymphadenopathy: Usually unilateral, ≥1.5 cm diameter 3
Fever Characteristics:
- High spiking and remittent, typically ≥39°C (102°F), often reaching 40°C (104°F)
- Without treatment: persists mean of 11 days, can continue 3-4 weeks
- With appropriate therapy: resolves within 2 days 3
Important Diagnostic Considerations:
Incomplete (atypical) KD occurs when fever lasts ≥5 days with only 2-3 principal features. This presentation is particularly common in infants under 6 months, who paradoxically face the highest risk for developing large or giant coronary artery aneurysms. 4, 5
The diagnosis can be made on day 4 of illness if 4 principal criteria are present, allowing earlier treatment initiation. 3
Differential Diagnosis
Must exclude conditions with similar presentations: 3
- Viral infections (measles, adenovirus, enterovirus, Epstein-Barr virus)
- Scarlet fever
- Staphylococcal scalded skin syndrome
- Toxic shock syndrome
- Bacterial cervical lymphadenitis
- Drug hypersensitivity reactions
- Stevens-Johnson syndrome
- Multisystem inflammatory syndrome in children (MIS-C) associated with SARS-CoV-2 2, 6
Cardiac Complications
Coronary artery aneurysms represent the most serious complication, occurring in approximately 20-25% of untreated patients. 2, 4
High-risk groups for coronary artery aneurysms include:
- Infants younger than 6 months
- Children with early coronary artery dilatation at presentation
- Patients with extreme laboratory abnormalities
- Those not responding to initial intravenous immunoglobulin therapy 2, 7
Giant coronary artery aneurysms, though rare, carry substantial morbidity and mortality risk due to thrombosis, stenosis, and myocardial infarction. 4
Treatment Approach
First-line treatment consists of intravenous immunoglobulin (IVIG) 2 g/kg as a single infusion plus aspirin, which should be initiated promptly upon diagnosis to minimize coronary artery damage. 8, 5, 9
For high-risk patients (infants <6 months, early coronary dilatation, extreme laboratory abnormalities), primary intensification therapy with corticosteroids in addition to IVIG improves outcomes. 2, 7
For IVIG-resistant cases (persistent or recurrent fever ≥36 hours after initial IVIG), treatment options include:
- Second dose of IVIG with or without corticosteroids
- Other adjunctive treatments 5
Long-term Management
Transthoracic echocardiography is the diagnostic imaging modality of choice for screening and monitoring coronary aneurysms. 5 The presence and severity of coronary abnormalities at diagnosis determine the intensity and periodicity of long-term cardiovascular monitoring. 5
Patients with cardiac sequelae require lifelong surveillance, as the standardized mortality ratio remains elevated (SMR 1.86) compared to the general population. 1 Conversely, patients without cardiac sequelae after the acute phase have lower mortality relative to the general population. 1
Prognosis
With current treatment protocols, KD can be controlled without sequelae in more than 95% of cases. 7 The recurrence rate in Japan is approximately 3%, with a 10-fold higher relative risk in siblings of affected children. 1