Kawasaki disease is an acute inflammatory vasculitis and is the leading cause of acquired heart disease in children in the developed world.
GPs must always bear the condition in mind when assessing a febrile young child.
The incidence of Kawasaki disease in the UK is about eight per 100,000 and seems to be increasing. Children of north-east Asian origin are most likely to be affected with 80 per cent of cases occurring in children between six months and five years.
The disease is thought to have an infectious trigger. No particular organism has been identified, but this theory is supported by the pronounced seasonality of the disease, with peaks in spring and winter in temperate countries. There is also evidence of a genetic predisposition.
One hypothesis is that Kawasaki disease is caused by an ubiquitous infectious agent that causes clinically apparent disease in genetically susceptible individuals.
Diagnosis and clinical features
There is no diagnostic test for Kawasaki disease and the diagnosis is essentially a clinical one, based on the presence of a fever for five days, and four out of five other clinical criteria.
These are: a bilateral non- exudative conjunctivitis; a polymorphous rash without petechiae or vesicles; changes in lips and mouth (dry cracked lips, strawberry tongue, diffuse redness of oral and pharyngeal mucosa without exudates); changes in the extremities (indurative oedema of hands or feet, erythema of palms or soles, desquamating rash around the nail bed); and cervical lymphadenopathy that is unilateral, painful and >1.5cm in size.
These diagnostic features can appear sequentially, creating a major challenge to diagnosis. A high index of suspicion for Kawasaki disease is required when assessing a febrile child as all the diagnostic criteria may not be met at an initial presentation.
Incomplete Kawasaki disease is also recognised, where coronary artery dilatation occurs in patients who do not fulfil the above diagnostic criteria.
This is more common in children under six months, a group that are at particular risk of delayed diagnosis.
The rash of Kawasaki disease is variable. Most commonly, it is a diffuse maculopapular rash, but may be a generalised erythema (scarletiniform) or an erythema multiforme type of rash.
It often begins in the nappy area and early desquamation may occur in the perineum. The desquamating rash traditionally associated with Kawasaki disease is a less useful diagnostic sign, as it occurs late.
Other clinical features in the extremities occur in the acute phase. Conjunctival injection also occurs early in the illness. Lymphadenopathy is the least frequent clinical sign, occurring in 70 per cent of patients.
A clinical feature unique to Kawasaki disease is acute inflammation at the site of a previous BCG inoculation. As more UK infants are receiving BCG, this is an increasingly useful clinical sign. Children with Kawasaki disease are also typically much more irritable than children with other febrile illnesses.
There is no diagnostic test for Kawasaki disease, but it is associated with many non-specific laboratory findings typical of an acute inflammatory response including a raised WCC, neutrophilia, and a raised ESR and CRP. A sterile pyuria and abnormal LFTs may occur.
The differential diagnosis includes bacterial infection (streptococcal, such as scarlet fever; staphylococcal, such as scalded skin syndrome; and toxic shock syndrome); viral infections (such as Epstein-Barr virus and measles); and Stevens-Johnson syndrome.
Suspected Kawasaki disease needs immediate referral to secondary care and treatment.
Intravenous immunoglobulin (IVIG) within five to 10 days of the onset of fever reduces the risk of cardiovascular complications. Aspirin is also given during the acute illness. In cases refractory to initial IVIG treatment, steroids are recommended.
Although Kawasaki disease is a systemic vasculitis, it has a strong preference for coronary arteries and therefore cardiac complications are the leading cause of long-term morbidity and mortality.
Untreated, approximately 25 per cent of children develop coronary artery aneurysms, but with early treatment, this risk reduces to 5 per cent.
Of those children found to have aneurysms around half regress within five years. Giant aneurysms (>8mm) occur in 1 per cent of patients and carry a poor prognosis. They may heal with stenosis that causes distal myocardial ischaemia, or they can rupture.
Stagnant blood flow in large aneurysms can promote occlusive thrombosis causing MI. Cardiac sequelae are detected by serial echocardiography performed on admission, at two and six weeks.
Children who develop cardiac complications require antiplatelet therapy, restriction of physical activity and long-term cardiac follow-up.
In the longer term, 50 per cent of patients develop an abnormal lipid profile - predominantly a low HDL.
Kawasaki disease may predispose to premature atherosclerosis, but as the disease was only first described in 1967, the patients in the original cohort are still too young for any differences to become apparent.
IVIG can block replication of live viral vaccines and decrease actively acquired immunity, so it is advised that live vaccination be deferred for three months following treatment with immunoglobulin.
- Dr Mistry is a GP north west London