While Kawasaki disease is rare, it is considered to be the commonest cause of acquired heart disease in childhood, killing around 1 per cent of the children affected.
Epidemiological research has shown that Kawasaki disease affects between eight and 33 per 100,000 children under the age of five in the Western world; the incidence is much higher in Japan. However, it is on the increase. Children between six months and five years old are most at risk, particularly those of north-east Asian origin. It occurs more commonly in the spring and winter in temperate regions.
Essentially, Kawasaki disease is a type of vasculitis, which describes an inflammatory condition of the blood vessels. It is thought to be caused by an infectious agent, although the exact cause has yet to be proven. There is evidence that genetics play a role in a person's susceptibility to acquiring Kawasaki disease.
SYMPTOMS
The cardinal feature of Kawasaki disease is fever for four or five days and, in addition, at least four of conjunctivitis, rash, oral disease, disease of the hands or feet and enlarged lymph glands. The conjunctivitis occurs in both eyes and unlike 'common or garden' conjunctivitis, there is no pus.
The rash blanches under pressure and the BCG (Bacille Calmette Guerin) scar, which is the site of the tuberculosis vaccination, tends to become inflamed in children with Kawasaki disease. The lips may crack and the tongue may appear 'strawberry'-like. The back of the throat becomes red but without pus spots. The hands and feet may become swollen and the skin around the fingers can peel, causing a so-called desquamating rash. The glands in the neck enlarge to over 1.5cm in diameter and tend to feel painful.
DIAGNOSIS
There are no specific tests that help doctors to confirm a diagnosis of Kawasaki disease. To complicate matters, there may be variations in the clinical features described above and they do not present at the same time, but rather sequentially over a period of days. Hence, the diagnosis of Kawasaki disease is not necessarily an easy one to make.
Furthermore, Kawasaki disease affecting infants less than six months of age may not have the full repertoire of clinical features and the desquamating rash may occur in the nappy area. Medical literature has described several other symptoms that may occur, including irritability, abdominal pain, cough, inflammation of the eyes, and joint and abdominal pain.
COMPLICATIONS
The blood vessels most likely to be inflamed in Kawasaki disease are those supplying the heart. Without treatment, around a quarter of patients will develop aneurysms of the coronary arteries. An aneurysm in this context describes a dilated blood vessel, which is prone to fatal rupture.
Around half of aneurysms will reduce to normal size over a two to five-year period, whereas the larger ones are more prone to complications.
In addition to rupture, an aneurysm may herald the formation of a narrowing within a coronary artery, known as coronary artery stenosis. Stenoses of a coronary artery can reduce the blood flow to the heart and cause angina or even a heart attack, which is termed medically as myocardial infarction.
Slugging and clotting of blood within the coronary vessels known as thrombosis can also lead to myocardial infarction. Other cardiac complications include inflammation of the heart itself and heart failure. Kawasaki disease can also affect other organs and blood vessels in the body.
TREATMENT
Treatment of Kawasaki disease requires early diagnosis, followed by treatment with aspirin-type drugs and an infusion of antibodies which doctors call immunoglobulins. Aspirin should not normally be given to children under the age of 16 due to the risk of Reye's syndrome, which is a potentially life-threatening condition affecting the brain and liver.
Immunoglobulins given intravenously reduce the risk of aneurysm formation from 25 per cent to 5 per cent. In recent years, the usefulness of aspirin has been questioned in the context of Kawasaki disease. In addition, other treatments have been successfully used, including steroids and more novel drugs, such as infliximab.
Kawasaki disease is rare, not always easy to diagnose and potentially fatal. It is an example of why it is crucial that doctors should always know the cause of a child's fever.
Dr Raj Thakkar BSc(Hons) MBBS MRCGP MRCP(UK) is a full-time GP in Buckinghamshire