Kawasaki disease is a diagnosis that paediatricians hold in mind for any young child with a fever lasting more than five days and no clear explanation. The window for effective treatment is narrow: IVIG given within the first ten days of illness dramatically reduces coronary artery complications, but given later or not at all, the risk of coronary aneurysms — which can cause myocardial infarction even in young children — rises sharply.
The disease was first described by Tomisaku Kawasaki in Japan in 1967. It remains more common in children of East Asian ethnicity, though it affects all populations. Its cause is not fully understood — leading theories involve an aberrant immune response to a common infectious trigger in genetically susceptible individuals.
Healthbooq (healthbooq.com) covers important childhood illnesses.
What Kawasaki Disease Is
Kawasaki disease is a systemic vasculitis — inflammation of blood vessels — affecting small and medium-sized vessels throughout the body. The coronary arteries (the blood vessels supplying the heart muscle) are particularly vulnerable. In the acute phase of untreated disease, coronary artery aneurysms develop in approximately 25 per cent of children.
The disease has no confirmed single cause. It is not contagious and does not spread between children. It occurs in seasonal and geographic clusters suggesting an infectious trigger, but no specific pathogen has been consistently identified.
It most commonly affects children under five, with the peak incidence at twelve to eighteen months. Boys are affected slightly more than girls (ratio approximately 1.5:1).
Diagnostic Criteria
The classic diagnostic criteria require fever for five or more days, plus at least four of the following five features:
Rash: a non-specific, non-vesicular (no blisters) rash, usually maculopapular or morbilliform, typically affecting the trunk and extremities. A perineal/genital rash early in the illness is particularly characteristic.
Conjunctival injection: bilateral redness of the whites of the eyes, typically without exudate or crusting (which would suggest bacterial conjunctivitis or viral infection). It is painless.
Changes to the lips and oral cavity: red, cracked, or swollen lips; "strawberry tongue" (red tongue with prominent papillae similar to scarlet fever); diffuse redness of the oral mucosa.
Changes to the extremities: redness and swelling of the palms and soles in the acute phase; subsequently (around ten to twenty days into the illness), characteristic peeling of the skin around the fingertips and toes (periungual peeling).
Cervical lymphadenopathy: usually unilateral, with at least one node greater than 1.5cm. This is the least common criterion, present in around 50 per cent.
The combination of fever with these features in a young child should prompt urgent specialist assessment.
Incomplete Kawasaki Disease
Incomplete Kawasaki disease is defined as fever for five or more days with fewer than four of the classic criteria. It is more common in infants under six months and in older children, and is associated with a higher risk of coronary complications because the diagnosis is often delayed.
A child under six months with unexplained prolonged fever should always be evaluated for incomplete Kawasaki disease with echocardiography and inflammatory markers, even in the absence of classic features.
Investigation
Key laboratory findings: elevated CRP and ESR (acute phase reactants), elevated white cell count with neutrophil predominance, thrombocytosis (elevated platelet count — characteristically rises in the second week), anaemia, elevated ALT. None of these are specific, but the combination informs the clinical picture.
Echocardiography is mandatory at diagnosis to assess coronary artery dimensions and to provide a baseline for follow-up. Abnormal coronary arteries at this stage require closer monitoring and more aggressive treatment.
Treatment
IVIG (intravenous immunoglobulin) as a single high dose (2g/kg over 10 to 12 hours) combined with aspirin is the standard treatment. Aspirin is used initially in anti-inflammatory doses during the febrile phase, then reduced to antiplatelet doses once fever resolves and continued until echocardiography is normal at six to eight weeks.
IVIG given within the first ten days of illness reduces coronary artery abnormalities from approximately 25 per cent to under 5 per cent. In the UK, all suspected cases should be referred to a paediatric cardiologist or paediatric centre with experience managing Kawasaki disease.
Children who do not respond to the initial IVIG course (around 10 to 15 per cent) may require a second dose or additional treatments including infliximab or corticosteroids.
Long-term Follow-up
Children who develop coronary artery aneurysms require long-term cardiology follow-up, ongoing antiplatelet or anticoagulant therapy, and lifestyle guidance regarding physical activity and future cardiovascular risk. Children with normal echocardiograms at six to eight weeks can usually be discharged from cardiology follow-up.
Key Takeaways
Kawasaki disease is a systemic inflammatory vasculitis primarily affecting children under five years, particularly those under two. It is the most common cause of acquired heart disease in children in the UK and other high-income countries. The diagnosis requires fever persisting for five or more days plus at least four of five classic features: rash, red eyes, red lips and strawberry tongue, red swollen hands and feet, and swollen lymph nodes in the neck. Early treatment with intravenous immunoglobulin (IVIG) and aspirin reduces the risk of coronary artery aneurysms from approximately 25 per cent to under 5 per cent. Incomplete Kawasaki disease — where fewer than four criteria are met — is particularly challenging to diagnose and must be considered in any child with prolonged unexplained fever.
