KAWASAKI DISEASE
Surjit Singh*
Additional Professor of Pediatric Allergy and Immunology, Advanced Pediatric Centre Post Graduate Institute of Medical Education and Research, Chandigarh.*
KD has replaced acute rheumatic fever as the most common cause of acquired heart disease in children in most developed nations and is believed to be the commonest vasculitic disorder seen in children. KD occurs almost exclusively in young children; 80% of patients being under the age of 5 years. The cause of KD remains unknown; however, clinical features like a febrile exanthem along with conjunctival injection and cervical adenitis strongly suggest an infectious etiology. However, conventional bacterial and viral cultures have so far been unrewarding and serologic investigations have not yielded any definitive clues towards an infectious cause.

Recently, the expression of V-beta T-cell receptor families in peripheral blood T cells in patients with acute KD has been examined; the results are, however, equivocal. The role of staphylococcal and streptococcal superantigens (such as toxic shock syndrome toxin-1), in the etiopathogenesis of KD is currently under scrutiny. This is an especially attractive hypothesis as some of the clinical features of KD (eg. exanthem and peripheral desquamation) are reminiscent of a Toxic shock syndrome.
Diagnosis
In the absence of a specific diagnostic test for Kawasaki disease, clinical criteria have been established to assist the physician in making the diagnosis. It is available in every standard textbook.
Features contributing to Diagnostic confusion in KD
Like many of the other vasculitides, KD is a multisystem disorder and this can make clinical decision making rather difficult. Extreme irritability (out of proportion to the degree of fever) is particularly common in young infants with KD. About one fourth of KD patients have aseptic meningitis. Both arthralgia and arthritis have been described. Mild elevations of serum transaminases occur in many patients in the acute phase. Acute distension of the gallbladder (hydrops) can also occur in KD and contribute to the woes of the attending physician!
Laboratory Findings
Although there are no laboratory tests that are pathognomonic of KD, certain findings may be suggestive. A normal to elevated WBC count with a neutrophilic predominance is typical in the acute phase. Elevations in sedimentation rate and in other acute-phase reactants are almost universally present in the first week of illness and may persist for 4 to 6 weeks. Normocytic anemia is common in patients with acute KD and is more severe in patients with a prolonged febrile stage or who develop coronary disease. The platelet count is generally normal in the first week of illness. Thrombocytosis, often in excess of 10⁶/cu mm., is only seen after the second week of illness is over. This is an acute phase reactant and is rather characteristic of KD, but is usually not there to help the clinician in the crucial period of the first 7-10 days of fever. In our experience, thrombocytosis occurs in almost all patients with KD. Anti-nuclear antibodies and rheumatoid factor are not detectable.

Echocardiography is used for detection of coronary aneurysms and in experienced hands has a sensitivity and specificity of more than 95%. Coronary angiography is almost never required for delineation of the aneurysms
Treatment
Therapy in Acute Stage
Intravenous Immunoglobulin (IVIG) is very effective when given in the first 10 days of illness. It reduces the chances of development of coronary abnormalities from 20-25% to 2-4%. IVIG results in a rapid defervescence of fever and normalization of the acute phase reactants. IVIG also improves myocardial function in KD patients having myocarditis. The role of IVIG has been studied only in the first 10 days of KD. Patients who present in subacute phase and have been afebrile for many days are usually not treated with IVIG, as it is unlikely to prevent coronary disease after the acute inflammatory response has subsided.

Aspirin is administered in patients with KD for its anti-inflammatory and anti-thrombotic effects. During the acute phase of illness, aspirin is administered at 70-80 mg/kg/day given every 6 hours. Somewhat lower aspirin doses (30-50 mg/kg/day) have been used in Japan. Around the 14th day of illness, when fever has resolved, aspirin is reduced to antithrombotic doses of 3 to 5 mg/kg/day as a single daily dose. Corticosteroids are contraindicated in children with KD.

Therapy after the Acute Phase
A repeat echocardiogram, preferably by a pediatric cardiologist, is obtained at 2-3 weeks and again at 6-8 weeks following the onset of illness. Aspirin can be discontinued after the sedimentation rate and platelet counts have normalized (this usually takes 6-8 weeks) and the echocardiograms are reported to be normal. We, however, prefer to continue low dose aspirin for at least six months. If echocardiography is done at 6-8 weeks, shows evidence of coronary dilatation and/or aneurysms, low dose aspirin needs to be continued indefinitely and follow-up investigations (coronary angiography/ dobutamine stress echocardiography) are then mandatory.

Further management of KD patients with aneurysms is dependent on the severity of coronary disease. Patients with a single small aneurysm should receive longterm aspirin and avoid physical sports. Patients with giant/multiple aneurysms should receive more aggressive therapy and are usually put on warfarin. Such patients often need bypass grafting or balloon angioplasty. So far, we have never encountered such a situation.
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