Kawasaki Disease

Detailed Overview

The condition presents with prolonged fever and characteristic mucocutaneous findings, including a polymorphous rash, oral mucosal changes, nonpurulent conjunctivitis, and cervical lymphadenopathy. If untreated, 25% of patients develop coronary artery aneurysms (CAAs). Prompt administration of Intravenous Immunoglobulin (IVIG) and Aspirin significantly reduces this risk. The diagnosis is entirely clinical, as no specific diagnostic test exists.

Epidemiology & Demographics

Highest incidence is in children of Asian descent, particularly Japanese, with an incidence of >250 per 100,000 children under 5. In the US, the incidence is about 20 per 100,000. 85% of cases occur in children < 5 years old.

Etiological Mechanism

The exact cause remains unknown. It is hypothesized to be an aberrant immunological response to an unidentified infectious trigger (viral or bacterial) in a genetically susceptible child.

Primary Causes

No specific pathogen has been identified, but seasonal peaks (winter and early spring) and community clustering suggest an infectious trigger.

• Age: Children under 5 years of age are at the highest risk.
• Ethnicity: Significantly higher risk in children of Asian or Pacific Islander descent.
• Genetics: Siblings of affected children have a 10-fold increased risk of developing the disease.

An infectious trigger leads to activation of the innate and adaptive immune systems. Macrophages, T cells, and IgA plasma cells infiltrate the walls of medium-sized arteries, especially the coronaries. The ensuing necrotizing arteritis destroys the internal elastic lamina and media, leading to aneurysm formation. This is followed by a subacute phase of subintimal proliferation, which can cause luminal stenosis or thrombosis.

Characteristic Clinical Presentation

• Prolonged Fever: High-spiking fever (>39°C or 102.2°F), generally unresponsive to antipyretics, lasting at least 5 days.
• Strawberry Tongue: Prominent papillae on a red swollen tongue, often accompanied by cracked, bleeding lips.
• Polymorphous Rash: Maculopapular, scarlatiniform, or erythema multiforme-like rash, typically starting on the trunk and spreading to extremities.

Physical Examination Signs

• Bilateral non-exudative conjunctival injection (often with limbal sparing)
• Erythema and edema of the palms and soles, followed by periungual desquamation
• Unilateral cervical lymphadenopathy (≥ 1.5 cm diameter)

• Coronary Artery Aneurysms: Dilation or ballooning of the coronary arteries, risking thrombosis and myocardial infarction.
• Myocardial Infarction: Caused by thrombosis within a coronary aneurysm.

Diagnostic Criteria & Guidelines

Fever for ≥ 5 days AND at least 4 of the following 5 criteria: 1) Bilateral bulbar conjunctival injection without exudate, 2) Changes in lips and oral cavity (e.g., strawberry tongue), 3) Changes in extremities (e.g., peripheral erythema, edema, or desquamation), 4) Polymorphous rash, 5) Cervical lymphadenopathy (≥ 1.5 cm). Note: Aneurysms on echocardiogram can confirm atypical/incomplete cases.

Differential Diagnosis

• Scarlet Fever
• Toxic Shock Syndrome
• Measles
• Multisystem Inflammatory Syndrome in Children (MIS-C)

Laboratory Tests & Biomarkers

• ESR and CRP: Significantly elevated (CRP often > 30 mg/L)
• Platelet Count: Normal in acute phase, but profound thrombocytosis (often > 1,000,000/microL) in the subacute phase (week 2-3)
• Liver Transaminases: Mild to moderate elevation of ALT and AST in 40% of patients

Imaging Modalities & Findings

• Echocardiogram: Coronary artery dilation (Z-score 2.0 to < 2.5) or aneurysm (Z-score ≥ 2.5), pericardial effusion, or decreased LV function.

• Acute Phase (Days 1-11)
  Fever and mucocutaneous signs; myocarditis may occur.
• Subacute Phase (Days 11-21)
  Resolution of fever and rash, but risk for coronary artery aneurysm and sudden death is highest; thrombocytosis occurs.
• Convalescent Phase (Days 21-60)
  Clinical signs resolve, but ESR and platelets slowly normalize. Aneurysms may begin to remodel or resolve.

Second-Line & Adjunctive Therapy

For IVIG-resistant cases (persistent fever 36h post-IVIG): Second dose of IVIG 2 g/kg, OR Intravenous Methylprednisolone (30 mg/kg for 3 days), OR Infliximab 5 mg/kg IV x 1.

Surgical & Procedural Management

Coronary artery bypass grafting (CABG) using internal mammary arteries for patients with severe ischemic heart disease due to thrombosed aneurysms.

Recommended Lifestyle Changes

• Delay live viral vaccines (MMR, Varicella) for 11 months after IVIG administration.
• Annual influenza vaccination is highly recommended for patients on long-term aspirin.

Patient Counseling & Advice

Warn parents about Reye syndrome risk with aspirin use during viral illnesses (specifically influenza or varicella). Explain the necessity of long-term cardiac follow-up if aneurysms develop.

Follow-Up & Monitoring Schedule

Serial echocardiograms: at the time of diagnosis, 1-2 weeks, and 4-6 weeks after treatment. Further follow-up depends on the maximum Z-score of the coronary arteries.

Preventive Strategies

There is no known way to prevent Kawasaki Disease.

Excellent if treated promptly, with <1% mortality. However, if giant aneurysms (Z-score ≥ 10) form, the lifelong risk of thrombosis, myocardial infarction, and sudden death remains significant.