What is Kawasaki Disease?

Kawasaki disease, also known as mucocutaneous lymph node syndrome, is a rare illness that primarily affects the blood vessels in children. When a child has this condition, the walls of their small to medium-sized blood vessels become swollen and inflamed. This inflammation, meaning swelling and irritation, can happen anywhere in the body, but the biggest concern is when it affects the coronary arteries—the blood vessels that supply oxygen-rich blood to the heart muscle itself.^[1][2]

The condition was first identified in 1967 by a Japanese pediatrician named Dr. Tomisaku Kawasaki. Since then, doctors around the world have learned a great deal about recognizing and treating it, though the exact cause remains unknown. What we do know is that Kawasaki disease triggers a strong immune response that leads to widespread inflammation in the body. This can affect not only blood vessels but also the skin, eyes, mouth, lymph nodes, and other organs.^[4]

While the disease can be scary for families, it is important to know that most children recover fully when treated early. Without treatment, however, Kawasaki disease can cause serious problems with the heart. That is why recognizing the symptoms and getting medical care quickly is so important.^[5]

Epidemiology: How Common is Kawasaki Disease?

Kawasaki disease is considered rare. In the United States and Canada, it occurs in about 10 to 20 out of every 100,000 children under the age of five. In countries like Japan, Korea, and Taiwan, the disease is more common, affecting 50 to 250 out of every 100,000 children in that age group. In 2019 alone, more than 5,000 children under the age of 18 were hospitalized with Kawasaki disease in the United States, with most of them being younger than five years old.^[2][3]

The disease affects children of all backgrounds, but it is significantly more common in those of Asian or Pacific Islander descent. Boys are also more likely to get Kawasaki disease than girls, with a male-to-female ratio of about 1.5 to 1. The condition is rare in infants younger than four months, which suggests that protection from maternal antibodies may play a role.^[4]

Approximately 75 to 80 percent of cases occur in children under five years old, and the average age at diagnosis is around one and a half years. Although Kawasaki disease can affect older children and even adults, it is much less common in those age groups. Interestingly, cases seem to occur more frequently during the winter and early spring months, though the reason for this seasonal pattern is not fully understood.^[4][2]

Despite being rare, Kawasaki disease is the leading cause of acquired heart disease in children in the United States, Japan, and other developed countries. “Acquired” means the heart problem develops after birth, as opposed to being present from birth. This makes recognizing and treating Kawasaki disease even more critical.^[4][2]

Causes and Transmission

The exact cause of Kawasaki disease remains a mystery. Scientists have been studying it for decades, but no single cause has been identified. Many researchers believe that the disease may be triggered by an infection, such as a virus or bacteria, especially since it causes a high fever and swelling of the lymph nodes. More than 40 percent of children diagnosed with Kawasaki disease have tested positive for viral respiratory pathogens, which suggests a possible link.^[4][12]

The theory is that a pathogen, most likely entering through the respiratory tract, triggers an exaggerated immune response in certain children. This response activates immune cells and inflammatory chemicals in the body, such as tumor necrosis factor alpha and interleukins, which are proteins involved in inflammation. These chemicals cause the blood vessels to become inflamed, which leads to the symptoms seen in Kawasaki disease.^[4]

Another important piece of the puzzle is genetics. Researchers have found that siblings of children with Kawasaki disease are 10 to 20 times more likely to develop the condition compared to the general population. Certain genetic markers, such as specific types of immune system proteins, have been associated with a higher risk of the disease. This suggests that some children may be genetically predisposed to developing Kawasaki disease when exposed to a triggering factor.^[4]

One thing that is clear is that Kawasaki disease is not contagious. It does not spread from one child to another through person-to-person contact. Even though a rash is one of the symptoms, it cannot be passed along like chickenpox or the flu.^[2][12]

Risk Factors

Certain factors increase the likelihood that a child will develop Kawasaki disease. The most significant risk factor is age. Children between the ages of six months and five years are at the highest risk, with the majority of cases occurring in children younger than two years old. Infants younger than six months rarely develop the disease, and it is also less common in older children and adults.^[2][4]

Gender also plays a role. Boys are about one and a half times more likely to develop Kawasaki disease than girls. Boys are also more likely to suffer from complications, including heart problems and even death, although these outcomes are rare with proper treatment.^[4]

Ethnicity is another important risk factor. Children of Asian or Pacific Islander descent are significantly more likely to develop Kawasaki disease compared to children of other ethnic backgrounds. In particular, Japanese children have the highest incidence of the disease. Children of African or Black descent also have a higher risk compared to white children.^[4][2]

As mentioned earlier, having a sibling with Kawasaki disease increases a child’s risk substantially. This family connection points to a genetic component, though it does not mean that every sibling will develop the disease. Environmental factors may also play a role, as cases tend to occur more frequently in the late winter and early spring months.^[4]

It is important to remember that even children without any of these risk factors can still develop Kawasaki disease. The condition can affect any child, regardless of their background or family history.^[2]

Symptoms: How Kawasaki Disease Appears

Kawasaki disease is diagnosed based on a set of symptoms that appear over time. The hallmark symptom is a high fever that lasts for at least five days. This fever is usually quite high, often exceeding 102.2 degrees Fahrenheit (39 degrees Celsius), and it does not respond well to typical fever-reducing medicines like acetaminophen or ibuprofen.^[1][3]

In addition to the fever, children with Kawasaki disease must have at least four of the following five symptoms to meet the diagnostic criteria:^[3][1]

• Rash: A non-specific red rash appears on the main part of the body, often on the trunk, and sometimes in the genital area or groin. The rash can look different from child to child—it may be flat and red, bumpy, or resemble other common childhood rashes.
• Red eyes: Both eyes become red or pink, a condition called conjunctivitis. However, unlike typical pink eye caused by bacteria or viruses, there is no thick discharge or pus. The redness often spares the area right around the iris, leaving a clear ring.
• Changes in the mouth and lips: The lips become very red, dry, cracked, and may bleed. The tongue swells and develops a bumpy, red appearance that resembles a strawberry, often called “strawberry tongue.” The inside of the mouth and throat also become red and inflamed, but there are no white patches or pus.
• Swollen hands and feet: The palms of the hands and soles of the feet become swollen, red, and painful. After a week or two, the skin on the fingers, toes, palms, and soles may begin to peel.
• Swollen lymph nodes: At least one lymph node in the neck becomes swollen and tender. This swollen gland is usually on one side of the neck and measures at least 1.5 centimeters in diameter.

Not all of these symptoms appear at the same time. They can develop over several days, which sometimes makes diagnosis challenging. Some children may have additional symptoms that are not part of the official diagnostic criteria but are still common in Kawasaki disease. These can include irritability, abdominal pain, vomiting, diarrhea, joint pain, or painful urination.^[1][2]

In some cases, children may also experience inflammation at the site of a recent vaccination, particularly the BCG vaccine, which is given in some countries to prevent tuberculosis. Additionally, some children may develop inflammation in the gallbladder, which can cause belly pain and vomiting.^[12]

It is important for parents to contact their child’s doctor right away if their child has a fever lasting more than four days, especially if accompanied by any of the other symptoms. Early diagnosis is key to preventing complications.^[1]

Incomplete or Atypical Kawasaki Disease

Some children do not develop all the classic symptoms of Kawasaki disease. This is called “incomplete” or “atypical” Kawasaki disease. A child with incomplete Kawasaki disease has a fever lasting five or more days and only two or three of the main symptoms. Infants and adolescents are particularly likely to present with incomplete disease, and they are also at higher risk for developing heart complications.^[1][16]

Incomplete Kawasaki disease can be especially difficult to diagnose because the symptoms may be subtle or mistaken for other common childhood illnesses. Doctors may need to perform additional tests, such as blood tests or heart imaging, to help confirm the diagnosis. Once diagnosed, the treatment for incomplete Kawasaki disease is the same as for classic Kawasaki disease.^[16]

Prevention: Can Kawasaki Disease Be Prevented?

Unfortunately, there is currently no known way to prevent Kawasaki disease. Because the cause is still not fully understood, there are no vaccines or lifestyle changes that can stop a child from developing the condition. Parents cannot take any specific steps to protect their children from getting Kawasaki disease.^[5]

However, what parents can do is be aware of the symptoms and seek medical care promptly if their child develops a prolonged high fever along with other warning signs. Early recognition and treatment are the best ways to prevent serious complications, particularly damage to the heart and coronary arteries.^[5]

Pathophysiology: What Happens in the Body?

Kawasaki disease causes widespread inflammation in the body, particularly affecting the blood vessels. When a child develops the disease, their immune system goes into overdrive, producing large amounts of inflammatory chemicals. These chemicals cause the inner lining of blood vessels, called the endothelium, to become damaged and swollen.^[4]

As the blood vessels become inflamed, they can weaken and stretch out. In some cases, the walls of the arteries become so weak that they bulge outward, forming an aneurysm. Aneurysms are dangerous because they can burst or lead to the formation of blood clots. If a clot forms and blocks the flow of blood through a coronary artery, it can cause a heart attack, even in a young child.^[2][8]

The inflammation in Kawasaki disease is not limited to the blood vessels. The heart muscle itself can become inflamed, a condition called myocarditis. The membranes surrounding the heart can also become inflamed, leading to pericarditis. The heart valves, which control the flow of blood through the heart, can also be affected, causing them to leak or not close properly.^[2]

Beyond the heart, Kawasaki disease can cause inflammation in many other parts of the body. The brain and spinal cord membranes can become inflamed, leading to a type of meningitis. The liver, pancreas, lungs, and joints can also be affected. This widespread inflammation is what makes Kawasaki disease so serious if left untreated.^[2][4]

Researchers believe that certain immune cells, called oligoclonal IgA plasma cells, play a key role in triggering the inflammation in the coronary arteries. These cells are commonly found in the respiratory tract, which is why many scientists think that a respiratory infection may be the initial trigger for Kawasaki disease.^[4]

The good news is that with early treatment, the inflammation can be controlled, and most children recover without lasting damage. However, without treatment, about one in four children with Kawasaki disease will develop coronary artery aneurysms, which can have long-term consequences for heart health.^[5][8]

Complications of Kawasaki Disease

The most serious complication of Kawasaki disease is damage to the coronary arteries. When these arteries become inflamed, they can develop aneurysms, which are bulges or weak spots in the artery walls. Aneurysms increase the risk of blood clots forming inside the artery. If a clot blocks the flow of blood to the heart muscle, it can cause a heart attack, even in a young child.^[2][8]

In severe cases, an aneurysm can rupture, causing life-threatening internal bleeding. Coronary arteries can also become narrowed due to scarring from the inflammation, which limits the amount of blood that can reach the heart. Over time, this can lead to poor heart function or heart failure, a condition where the heart cannot pump blood effectively.^[2]

Other heart-related complications include problems with the heart valves, which may leak or not close properly. This can affect how well the heart pumps blood through the body. The heart muscle itself can become inflamed, and fluid can build up around the heart, a condition known as pericardial effusion.^[8][2]

Beyond the heart, Kawasaki disease can affect other organs. The liver can become inflamed, leading to hepatitis. The pancreas can also become inflamed, a condition called pancreatitis. The lungs may be affected, and in rare cases, infections can develop in the heart. These complications are less common but can still cause serious problems if not treated.^[2]

With early treatment, the risk of complications is significantly reduced. Most children recover completely within six to eight weeks. However, children who do develop coronary artery problems may require long-term monitoring and treatment to prevent future heart issues.^[5]