Kawasaki Disease

Description

Kawasaki disease (KD), also known as mucocutaneous lymph node syndrome, is an acute, self-limited vasculitis of unknown origin, that predominantly affects small- and medium-sized arteries¹. The disease is most commonly seen in children under five years old. KD is the leading cause of acquired heart disease in children in developed countries.

Pathogenesis

The exact pathogenesis of Kawasaki disease remains unknown, although it is believed to result from an aberrant immune response to an infectious trigger in genetically predisposed individuals. The disease affects the endothelial cells, smooth muscle cells, and adventitia of the arterial wall, leading to arterial inflammation and damage.

Subtype

• There are no recognised subtypes of Kawasaki disease.

Epidemiology, Risk Factors & Associations

• Most commonly affects children under the age of 5 (85% of cases).
• More common in boys than in girls (1.5:1).
• Highest incidence in East Asian populations, particularly Japanese and Korean.
• A seasonal peak is seen in winter and spring.

Clinical Features

Three clinical phases are described:

1. Acute Phase
   • Persistent fever (5 or more days).
   • Bilateral non-exudative bulbar conjunctivitis
   • Erythema of lips and oral mucosa, strawberry tongue
   • Erythematous maculopapular rash.
   • Swelling and erythema of the hands and feet.
   • Cervical lymphadenopathy, typically unilateral, firm non-fluctuant nodes
   • Pericarditis, myocarditis, abdominal pain, ascites, and hydrops of the gallbladder may occur at this time
2. Subacute Phase
   • Begins with the resolution of fever and typically lasts for 2 week
   • Coronary artery aneurysms most commonly first develop during the subacute phase
   • Highest risk of sudden cardiac death
3. Convalescent Phase
   • Usually 4–8 weeks after the onset of illness.
   • Most children are asymptomatic during this phase

Complications

• Coronary artery aneurysms or ectasia develop in 15-25% of untreated children.
• Myocarditis, pericarditis with pericardial effusions, dysrhythmia, or sudden death.
• Systemic arterial aneurysms, valvular disease, mild aortic root dilatation and myocardial infarct.

Pathological Features

Histopathology

• Macroscopic: Coronary artery aneurysms can be seen in severe cases.
• Microscopic: There is necrotising arteritis with inflammatory infiltrates.

Serology

• Elevated C-reactive protein and erythrocyte sedimentation rate.

Biochemistry

• Leukocytosis, thrombocytosis.

Radiological Features

General Features

• Characteristically demonstrates coronary artery aneurysms, typically proximal segments of the major coronary arteries. Common sites (highest to lowest frequency):
  • Proximal left anterior descending and proximal right coronary arteries
  • Left main coronary
  • Left circumflex arteries
• Isolated distal coronary artery aneurysms are uncommon.
• Myocardial infarctions can be seen in severe cases due to coronary artery thrombosis.
• Gallbladder hydrops (non-specific finding), due to perivascular inflammatory infiltration

XR

• Non-specific, may show cardiomegaly.

US

• Echocardiography is the primary imaging modality for the diagnosis and follow-up of KD.
• Findings include ectasia, aneurysm formation, lack of normal tapering, and increased perivascular echogenicity
• Luminal diameter of aneurysms are graded:
  • Small < 5 mm (more likely to regress)
  • Medium 5–8 mm
  • Giant > 8 mm (higher likelihood of thrombosis and infarction)

CT

• Non-contrast: Can be used to evaluate coronary calcifications in late disease.
• Contrast-enhanced: Can visualise coronary artery aneurysms and thrombosis.

MRI

• T1WI, T2WI: Can be used to assess myocardial inflammation and oedema in acute KD.
• T1 C+: Can show delayed enhancement in cases of myocardial infarction.

Grading and Staging

• No universally accepted grading or staging system.

Diagnosis

Diagnosis is primarily clinical, based on the presence of fever for at least five days plus at least four of the five principal features.

Differential Diagnosis

• Coronary artery aneurysm from other causes: While Kawasaki disease is a common cause of coronary artery aneurysms in children, other conditions such as connective tissue disorders, congenital abnormalities, or trauma can also lead to aneurysms. The clinical context and age of the patient often aid in distinguishing these possibilities.
• Myocarditis: This condition can result in reduced ventricular function and heart enlargement on imaging, potentially similar to Kawasaki disease. However, myocarditis more commonly causes diffuse myocardial inflammation and may show different patterns on late gadolinium enhancement MRI.
• Infective Endocarditis: It can cause similar signs of inflammation in the heart as seen in Kawasaki disease. However, vegetations on the heart valves are a classic finding in infective endocarditis, typically visualized on echocardiography.
• Other forms of systemic vasculitis: Conditions such as Takayasu arteritis or Polyarteritis nodosa can also cause vessel wall thickening and dilatation on imaging. However, they typically affect different age groups and vessels, and often have different clinical presentations.

Management

• High-dose aspirin and intravenous immunoglobulin (IVIG) are the mainstays of treatment.
• All children suspected of having KD should undergo echocardiographic evaluation at diagnosis and be followed-up after the onset of disease.

References

1. Khanna, G., Sargar, K. and Baszis, K.W., 2015. Pediatric vasculitis: recognizing multisystemic manifestations at body imaging. Radiographics, 35(3), pp.849-865. ↩︎