Kawasaki disease is not related to the motorcycle and engine company, other than they were both founded or first described in Japan. Kawasaki disease is a vasculitis, or an inflammation of the blood vessels, that primarily affects the coronary arteries but can affect any large- or medium-sized arteries. The immune system attacks the arteries, similar to what we see in many other types of vasculitis, and the endothelial cells get damaged, it exposes underlying collagen and tissue factor found in the tunica media which is the middle layer of the blood vessel. This leads to a few serious problems: First, these exposed materials increase the chance of blood coagulation. When blood coagulates it forms clots that can block blood flow in the coronary arteries leading to ischemia of the heart muscle.
Second, damaged endothelial cells in coronary arteries means weak artery walls, which can lead to coronary aneurysms. These aneurysms form because fibrin is deposited into the blood vessel wall as part of the healing process. Fibrin makes the vessel stiffer, less elastic, and unable to gently stretch with high arterial pressures; instead the arteries develop permanent bulges that we call aneurysms. Aneurysms 8mm or larger are at the highest risk of rupture, which reduces blood flow to the heart, causing ischemia and potentially myocardial infarction, or heart attack.
Third, in some cases the fibrosis doesn’t lead to aneurysms, but instead the fibrosis of the blood vessel walls make the vessel walls thicker, which reduces the lumen diameter and restricts blood flow. So to avoid problems like myocardial infarctions, aneurysms that can be a set up for myocardial infarctions, or scarring of the coronary arteries that causes reduced blood flow - it’s helpful to diagnose Kawasaki disease early on. Kawasaki disease is most commonly seen in infants and children under five years old and is more likely to affect boys. The disease is self-limited which means that the inflammation will resolve after 6 to 8 weeks but if we left it untreated, there is a 20-25% risk of the heart complications we went over. Alright so let’s look at the symptoms of Kawasaki disease. We rarely see any cardiac symptoms in the first few weeks unless the patient has an underlying heart condition already, those typically evolve later.
The classic symptoms include 5 days of high fevers that typically do not resolve with antipyretics. Conjunctivitis with __ sparing (which is red eyes with a margin right around the iris that is still white), Strawberry tongue which is when the top layer of cells on their tongue will slough off giving the tongue a very red, “strawberry” like appearance. Their mouth and throat may look really red, and their lips may become dry and cracked. The palms and soles of their feet might get swollen and develop a rash, and the rash may extend across other parts of their body with well defined borders. Finally they might have enlarged lymph nodes in their neck or cervical lymphadenopathy. There isn’t a specific test to diagnose Kawasaki disease, but there are a number of lab tests that can act as clues. At the beginning of the disease, many patients are anemic and have an increased number of white blood cells with a “shift to the left,” which means there are more immature white blood cells than normal. After a few weeks the patient’s platelet count and coagulability will be high. They’ll also have an increased C-reactive protein and erythrocyte sedimentation rate, as well as increased liver enzymes, which are all good clues to tell us some sort of inflammation is occurring. We also could see inflammatory cells in the cerebrospinal fluid. Microscopic urinalysis will show mononuclear white blood cells in the urine without evidence of bacteria. Phew that’s a lot of tests, but one last test we’d want to do is an echocardiogram to take a look at the coronary artery and heart muscle to see if any of those complications we talked about earlier are happening.
Kawasaki disease is diagnosed based on a combination of patient symptoms and laboratory tests. Four of the five symptoms we talked about earlier including a fever that has lasted for five days or longer are required for Kawasaki disease to be diagnosed. But sometimes patients don’t meet these strict criteria. Vasculitis in the coronary arteries is the definitive judge on whether the disease is or isn’t Kawasaki disease, but you wouldn’t want to wait to find that out. People who don’t perfectly meet all the diagnostic criteria for Kawasaki disease are sometimes classified as incomplete Kawasaki disease. There are guidelines in place to help healthcare providers figure out if they should treat these atypical cases as Kawasaki disease or not, but just know that it’s possible to have cases that don’t meet all the clinical diagnostic requirements.
Now treating Kawasaki disease is also helpful diagnostically, because if the therapy works then it also reassures you that the right diagnosis was made. The main treatment is to give IVIG which is antibody taken from other individuals. It’s thought that this actually helps to calm down the immune system and reduce inflammation. We also give ASA, otherwise known as acetylsalicylic acid or aspirin. Aspirin inhibits platelet cyclooxygenase, which prevents platelets from aggregating together. Now wait a second. Alarm bells! We’re not suppose to give aspirin to kids because they could develop Reye syndrome (which is encephalopathy and serious liver injury, which isn’t really pleasant). For Kawasaki’s disease, we take the risk and monitor the child carefully. We’re done! That’s Kawasaki disease.