Kawasaki disease is an illness that causes inflammation in blood vessel walls throughout the body, primarily affecting children under five years old. It is the leading cause of acquired heart disease in children in developed countries, because without treatment, up to 25% of affected children develop dangerous bulging (aneurysms) in the arteries that supply blood to the heart. With prompt treatment, that risk drops to about 5%.
Who Gets Kawasaki Disease
The disease overwhelmingly strikes young children. The median age at diagnosis is about 21 months, and infants under one year old are affected at nearly twice the rate of children between one and four. Boys are roughly 1.5 times more likely to develop it than girls.
Ethnicity plays a significant role in risk. Children of Japanese descent have the highest incidence in the world, followed by Native Hawaiian, other Asian, and Chinese children. The disease occurs in all racial and ethnic groups, but it is diagnosed far more frequently in East Asian populations. It is rare in adults, though not impossible.
What Causes It
No one has identified a single cause. The leading theory is that an unknown trigger, possibly an infection, sets off an exaggerated immune response in genetically susceptible children. During the acute phase, the body’s first-responder immune cells (neutrophils and macrophages) flood into the walls of arteries, particularly the coronary arteries. These cells release enzymes that break down the elastic tissue holding the artery walls together, which is how aneurysms form.
At the same time, a burst of oxidative stress damages the lining of blood vessels. Harmful byproducts of this inflammation injure the cells that line artery walls and promote further swelling, creating a cycle that can weaken arteries if not interrupted by treatment.
Recognizing the Symptoms
Kawasaki disease is diagnosed entirely by its visible signs. There is no blood test or imaging scan that confirms it. The hallmark is a persistent high fever lasting five or more days, though experienced physicians can make the diagnosis as early as three to four days of fever when other signs are clearly present. Along with the fever, at least four of five characteristic features need to appear:
- Changes in the mouth: Red, cracked lips, a bright red “strawberry” tongue, or redness in the back of the throat.
- Red eyes: Both eyes become bloodshot, but without the crusty discharge you’d see with pink eye.
- Rash: A widespread rash on the trunk and limbs that can take several forms, from flat red patches to raised bumps.
- Swollen hands and feet: The palms and soles turn red, and the hands and feet may puff up noticeably. Later, the skin on the fingertips often peels.
- Swollen lymph node: A single enlarged lymph node on one side of the neck, at least 1.5 centimeters across.
These symptoms don’t always appear at the same time, which can make the disease tricky to spot. A child might have a fever and red eyes on day one, then develop the rash two days later. Parents often visit the doctor multiple times before the pattern becomes clear.
Incomplete Kawasaki Disease
Some children, particularly infants, develop fewer than four of the five classic signs. This is called incomplete Kawasaki disease, and it is not a milder form. It carries the same risk of heart damage. Because these children don’t check all the diagnostic boxes, doctors use a combination of blood work and heart ultrasound findings to support the diagnosis. Markers of widespread inflammation in the blood, combined with even a few of the classic symptoms, can be enough to justify treatment.
Incomplete cases are especially common in babies under six months old, who are also the most vulnerable to coronary artery complications. This makes early suspicion critical.
How It Differs From MIS-C
Since 2020, parents often hear about Kawasaki disease alongside Multisystem Inflammatory Syndrome in Children (MIS-C), a condition linked to COVID-19. The two share some overlapping features, like fever and rash, but they differ in important ways.
Kawasaki disease typically affects children under five, while MIS-C tends to appear in older children and teenagers, with an average age around eight. MIS-C requires evidence of a recent COVID-19 infection. It is more likely to cause severe stomach pain, vomiting, diarrhea, and dangerously low blood pressure. While both conditions can affect the heart, Kawasaki disease more commonly causes coronary artery aneurysms, whereas MIS-C is more likely to weaken the heart’s pumping ability directly. Blood tests also look different: Kawasaki disease typically causes a high white blood cell count and elevated platelet levels, while MIS-C often drives those same numbers down.
Treatment in the Hospital
Children diagnosed with Kawasaki disease are admitted to the hospital for treatment. The standard first-line therapy is a high-dose infusion of immunoglobulin, a concentrated solution of antibodies collected from donated blood. This is given through an IV over roughly 24 hours. The infusion works by calming the overactive immune response and dramatically reduces the risk of coronary artery damage.
Alongside the infusion, children receive aspirin to reduce inflammation and help prevent blood clots. Most children respond well, with the fever breaking within 36 hours of starting treatment. About 10 to 20% of children don’t respond to the first infusion and need a second dose or alternative therapies to bring the inflammation under control.
After the fever resolves and blood markers improve, children typically go home on a low dose of aspirin for several weeks. If no coronary artery changes are found on follow-up heart ultrasounds, the aspirin is usually discontinued after six to eight weeks.
What Happens to the Heart
The most serious consequence of Kawasaki disease is damage to the coronary arteries. During the acute illness, the inflammation can weaken artery walls and cause them to balloon outward, forming aneurysms. Small aneurysms often resolve on their own over months to years as the artery wall heals and remodels. Larger aneurysms, however, can persist and create long-term problems.
A persistent aneurysm acts as a site where blood clots can form, potentially blocking blood flow to the heart muscle. The artery wall can also thicken and narrow over time, further restricting flow. These complications can lead to chest pain, heart attacks, or other signs of reduced blood supply to the heart, sometimes appearing years or even decades after the original illness.
Long-Term Outlook
For the majority of children who are treated promptly and never develop coronary artery changes, the long-term outlook is excellent. They go on to live normal, active lives with no lasting heart effects. Follow-up heart ultrasounds in the weeks after diagnosis typically confirm that the coronary arteries are normal, and routine cardiology visits are not needed beyond the initial recovery period.
Children who do develop aneurysms face a different path. According to the American Heart Association, patients with coronary artery aneurysms require lifelong, uninterrupted cardiology follow-up. The frequency and intensity of monitoring depends on the size and location of the aneurysms. Some patients need periodic stress tests or advanced imaging, and certain subsets remain at risk for blood clots, narrowed arteries, and reduced blood flow to the heart over time. These individuals may need blood thinners or other preventive medications well into adulthood.
Because Kawasaki disease was first described in 1967, the first generation of patients is now reaching middle age. Cardiologists are still learning about how childhood coronary damage interacts with the normal cardiovascular aging process, making ongoing follow-up for those with known artery changes especially important.