Kawasaki disease is an illness that causes inflammation in the walls of blood vessels throughout the body, particularly affecting the coronary arteries that supply blood to the heart. This condition primarily affects children under the age of five, though it can occur in older children and, rarely, adults. It is considered a form of vasculitis, where the immune system mistakenly injures blood vessels. This inflammation can lead to narrowing or closure of these vessels, potentially resulting in serious heart complications if left untreated.
Primary Diagnostic Criteria
The diagnosis of Kawasaki disease relies primarily on a collection of clinical signs and symptoms rather than a single specific test. A persistent high fever, lasting at least five days, is a defining feature of the illness. This fever often exceeds 102°F (39°C) and may not respond to typical fever-reducing medications.
In addition to the prolonged fever, a diagnosis of “complete” Kawasaki disease usually requires at least four of five other specific clinical signs. These include bilateral conjunctivitis, characterized by redness in both eyes without thick discharge. Children often develop a widespread rash involving the trunk, extremities, and groin area.
Cervical lymphadenopathy, a swollen lymph node in the neck typically measuring at least 1.5 centimeters in diameter and often occurring on one side, is another common finding. Oral changes are also characteristic, including a “strawberry tongue” (a red tongue with prominent bumps), very red and cracked lips, and redness of the mouth and throat lining. Lastly, changes in the hands and feet present as initial swelling and redness, followed by peeling skin around the nails about two to three weeks after the fever begins.
Laboratory and Imaging Tests
While no single test definitively diagnoses Kawasaki disease, various laboratory and imaging studies offer supporting evidence and help assess for potential complications. Blood tests indicate widespread inflammation, a hallmark of the condition. Common findings include elevated C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), both markers of inflammation.
A complete blood cell count may reveal an elevated white blood cell count, particularly with an increase in neutrophils. Platelet counts rise in the second week of illness, often exceeding 450,000/mm³. A low platelet count early in the disease can be a risk factor for coronary artery issues. Other laboratory abnormalities can include mild anemia, low albumin levels, and elevated liver enzymes.
The most important imaging test is an echocardiogram, an ultrasound of the heart. This test visualizes the coronary arteries and detects abnormalities, such as aneurysms (bulging and thinning of artery walls) or dilation, which are serious complications of Kawasaki disease. The echocardiogram is typically conducted upon diagnosis and may be repeated several weeks later to monitor for changes.
Ruling Out Other Illnesses
Because the symptoms of Kawasaki disease can resemble those of many other common childhood illnesses, ruling out these other conditions is an important diagnostic step. This careful approach ensures the correct diagnosis is made, preventing misdiagnosis and delayed treatment. Many infectious diseases, both bacterial and viral, can present with fever, rash, and other similar signs, making differentiation challenging.
Conditions that can mimic Kawasaki disease include scarlet fever, caused by streptococcal bacteria, which also presents with a rash and fever. Measles is another viral infection that shares some overlapping symptoms, such as rash and conjunctivitis. Certain viral infections like adenovirus or enterovirus can also produce similar clinical pictures.
Other conditions considered in the differential diagnosis include juvenile idiopathic arthritis and certain drug hypersensitivity reactions. Doctors carefully evaluate all symptoms and test results to distinguish Kawasaki disease from these mimicking illnesses, noting specific features like non-exudative conjunctivitis (red eyes without discharge) or the characteristic hand and foot changes.
Atypical or Incomplete Kawasaki Disease
In some instances, a child may have incomplete or atypical Kawasaki disease, which presents a diagnostic challenge. This occurs when a child has the characteristic persistent fever for five or more days but does not exhibit four or more additional clinical symptoms. This presentation is more common in younger infants, who are also at a higher risk for developing coronary artery abnormalities.
In these cases, doctors rely more heavily on laboratory test results and the echocardiogram to support the diagnosis. If a child has a prolonged fever and only two or three of the principal clinical features, elevated inflammatory markers such as CRP and ESR can increase suspicion for incomplete Kawasaki disease. An echocardiogram is then performed to check for coronary artery involvement or other heart issues, even if the classic symptoms are not all present. This approach ensures that children with this less classic presentation still receive timely evaluation and treatment to prevent complications.