Define Kawasaki Disease. Describe its aetiology, investigations, management and complications.

Definition

• Kawasaki disease is an acute, self-limiting medium-vessel vasculitis of young children (usually < 5 years), of unknown cause.
• Its importance lies in its predilection for the coronary arteries — it is a leading cause of acquired heart disease in children in developed countries.

Etiology & Pathogenesis

• The cause is unknown; an abnormal immune response to an infectious trigger in a genetically predisposed child is proposed.
• There is a generalised vasculitis of medium-sized arteries, with a special tendency to involve the coronary arteries → aneurysm formation.

Diagnostic Criteria (clinical)

Diagnosis requires fever for ≥ 5 days plus at least 4 of the following 5 features (mnemonic — crash and burn):

Clinical Course (phases)

• Acute (1–2 weeks): high fever and the diagnostic features; the child is very irritable.
• Subacute (2–4 weeks): fever settles; desquamation, thrombocytosis and the peak risk of coronary artery aneurysms.
• Convalescent: clinical recovery; inflammatory markers normalise.

Investigations

• Raised inflammatory markers — high ESR and CRP; neutrophilic leukocytosis.
• Thrombocytosis (a very high platelet count) in the second week (characteristic).
• Anaemia; sterile pyuria; raised transaminases; hyponatraemia.
• Echocardiography — at diagnosis and follow-up, to detect coronary artery aneurysms (the key complication).

Management

• Intravenous immunoglobulin (IVIG) 2 g/kg as a single infusion — given within the first 10 days; it markedly reduces the risk of coronary aneurysms.
• Aspirin — high (anti-inflammatory) dose in the acute phase, then low (anti-platelet) dose until inflammation and platelets normalise.
• IVIG-resistant cases — a second dose of IVIG, corticosteroids, or infliximab.
• Long-term cardiology follow-up (with antiplatelet/anticoagulation) if aneurysms develop.

Complications

• Coronary artery aneurysms — the major complication (→ thrombosis, myocardial infarction, sudden death).
• Myocarditis, pericarditis, arrhythmias; and (rarely) arterial aneurysms elsewhere.

Differential Diagnosis

• Viral exanthems (measles, adenovirus), scarlet fever, and drug reactions (Stevens-Johnson).
• Toxic shock syndrome, juvenile idiopathic arthritis (systemic), and staphylococcal scalded skin syndrome.
• The persistent high fever + coronary risk distinguish Kawasaki and mandate prompt treatment.

Incomplete (atypical) Kawasaki Disease

• Some children — especially infants < 6 months — have prolonged fever with fewer than 4 features.
• Because they are at high risk of coronary aneurysms, the diagnosis is supported by raised inflammatory markers and echocardiographic changes, and they are treated even without the full criteria.

Risk Factors for Coronary Involvement

• Young age (< 1 year); prolonged fever; delayed or no IVIG treatment; and IVIG resistance.
• Persistently high inflammatory markers.

Follow-up & Prognosis

With timely IVIG the great majority recover fully. Children who develop coronary aneurysms need long-term cardiology follow-up with antiplatelet/anticoagulant therapy and surveillance for ischaemia.

Aspirin — Cautions

• High-dose aspirin is used despite the usual paediatric caution (Reye syndrome risk), because the benefit in Kawasaki outweighs the risk.
• Watch for and avoid concurrent varicella/influenza; continue low-dose aspirin until inflammation and platelets normalise (or long-term if aneurysms persist).

Key Learning Points

• Suspect Kawasaki in any child with fever ≥ 5 days and mucocutaneous signs.
• IVIG within 10 days is the single most important step to protect the coronaries; always do an echocardiogram.