What Experts Know About a Rare Inflammatory Syndrome Linked to COVID-19

The syndrome resembles a childhood illness called Kawasaki disease, but research is ongoing about both conditions

A child is tested for COVID-19
Cases of MIS-C are very rare and are mostly popping up in COVID-19 hotspots Paul Biris / Getty Images

As the COVID-19 pandemic spreads, reports of new and unusual symptoms are on the rise. The latest side effects of a novel coronavirus infection range from nerve damage to “COVID toe.” In rare cases, COVID-19 seems to cause severe inflammation in children.

Scientists are racing to better understand what causes the condition, called “multisystem inflammatory syndrome in children,” or MIS-C, Jennifer Couzin-Frankel reports for Science magazine. The children present fevers, stomach pain, rashes and heart problems—or, as 14-year-old Jack McMorrow told the New York TimesPam Belluck, a pain “almost like someone injected you with straight-up fire.”

A lot remains to be discovered about MIS-C. It seems rare among those exposed to the virus behind COVID-19 and has affected both children and young adults, per the Washington Post’s Ariana Eunjung Cha and Chelsea Janes. MIS-C has also been compared to Kawasaki disease, another pediatric inflammatory syndrome.

What is Kawasaki disease?

Like with MIS-C, children with Kawasaki disease (KD) have symptoms like rash and fever. Kids with KD can also show signs like swollen hands and feet, peeling skin, red eyes, “strawberry tongue,” and swollen lymph glands in the neck. KD is a relatively uncommon condition, affecting about 15 to 20 out of 100,000 kids under 5 years old according to the Kawasaki Disease Research Center at the University of California, San Diego, though it can also appear in older kids and teens.

The similarities in symptoms “raise some concern that [MIS-C] is somehow linked to KD, although that exact linkage still has to be figured out,” Adriana Tremoulet, UCSD pediatrician and KD specialist, tells the KD Foundation in a video about the pandemic.

The disease was first described in 1967 by Japanese pediatrician Tomisaku Kawasaki. The cause of KD is not yet known, but the current hypothesis is that kids have a genetic predisposition for the disease. When they encounter something in the environment, called a trigger, the disease appears, per a video by the KD Foundation. Researchers aren’t sure yet what might trigger classic KD, but they have a good idea of what happens in the body when KD takes hold.

As explained in the same video, the coronary arteries, which carry oxygen to the heart, become inflamed when immune cells leave the bloodstream and enter the wall of the blood vessel. When immune cells gather in the wall, they recruit chemicals that cause the arteries to expand.

If the disease is treated quickly, an artery that expands will usually return to normal, but in severe cases the artery could expand further into an aneurysm. An aneurysm prevents blood from flowing normally and can lead a clot and a heart attack. Luckily, an effective treatment for KD exists, and kids with a history of KD just need to follow up with a cardiologist every few years.

Research into KD is ongoing, and previous work at the UCSD lab investigated whether coronaviruses—but not the one that causes COVID-19, since it hadn’t emerged at that time—could trigger KD, and found they could not.

How is MIS-C different from KD?

While MIS-C is triggered by SARS-CoV-2, the virus that causes COVID-19, Kawasaki disease has been recognized for decades longer than the current pandemic and therefore probably has a different trigger. And so far, doctors treating COVID-19 have seen two kinds of Kawasaki-like disease, as Amy McKeever reports for National Geographic. One is viral sepsis, which causes depressed heart function and low blood pressure, and another more closely resembles Kawasaki-like symptoms.

While young children tend to have cases that most closely resemble KD, and it can appear weeks after initial exposure to SARS-CoV-2. But older teens and young adults can have an “overwhelming” response to the virus that involves the heart and other organs, as pediatric infectious diseases doctor Jennifer Lighter tells the Washington Post. For McMorrow, the 14-year-old, symptoms of a 102-degree fever, rash, and sore throat appeared about a month after he cleaned out his locker at school, per the New York Times. He was hospitalized for heart failure.

“He could have definitely died,” said McMorrow’s primary care doctor Gheorghe Ganea to the Times. “When there’s cardiovascular failure, other things can follow. Other organs can fail one after another, and survival becomes very difficult.”

Northwell health pediatric critical care doctor James Schneider emphasized to the Washington Post that the inflammatory syndrome requires hospital care and medications for blood pressure, steroids, and sometimes a ventilator. KD is treated with a high dose of gamma globulin, a protein found in human blood, given through an IV.

Who is at risk of the inflammatory syndrome?

Cases of MIS-C are very rare and are mostly popping up in COVID-19 hotspots like New York City, which as of May 21 had reported 147 cases, per the Washington Post.

“There’s clearly some underlying genetic component” that puts some children at risk, says the director of Columbia University’s Precision Medicine Initiative, Tom Maniatis, to Science magazine. To find out what that genetic component might be, the New York Genome Center, of which Maniatis is CEO, is sequencing the genomes of the affected children, their parents and the virus which with they’re infected.

Not all of those affected by MIS-C have active COVID-19 infections, which are found with the nose swab test. A recent study published in the Lancet found that eight out of ten children with MIS-C in Italy had antibodies to SARS-CoV-2, but new guidelines from the CDC show that antibody test results are far from cut-and-dry. (And immunity to the coronavirus is even more complicated.)

While Kawasaki disease commonly affects children of Asian ancestry, the inflammatory syndrome linked to COVID-19 hasn’t been reported in Asian countries, Science reports. Data from cases of the inflammatory syndrome in London showed that of the 37 cases reported there as of May 7, “a fair number of those children are actually of African and Afro-Caribbean descent,” Tremoulet says in the KD Foundation video. “That definitely needs to be further studied, and we need to understand why that group is having a much higher attack rate than we would expect given the number of African and Afro-Caribbean children in the London area.”

And as the Washington Post points out, while turning 18 years old is the milestone between childhood and adulthood, the distinction is more legal than biological.

“People in their 20s are at their physiological peak in terms of their lung capacity, reproductive system and strength,” Cha and Janes write in the Post. “So in this way, young adults may be more similar to children than to people in their 30s — some of whom may be starting to experience the slow, gradual declines of aging.”

Time and scientific research will tell what’s happening in those affected by the inflammatory syndrome. As Science reports, a project called DIAMONDS is working with children in Europe affected by MIS-C as well as those with COVID-19 to screen their blood for viruses and other pathogens (including SARS-CoV-2) and also study their immune systems. A global research project in adults aims to better understand whether the condition is really unique to children.

To treat those affected by MIS-C, “we need to identify early and we need to intervene early,” says Toronto rheumatologist and immunologist Rae Yeung to Science. “The kids we’re seeing so far, they respond to the treatments we’re giving.”

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