Kawasaki disease & Covid-19: A pediatric specialist explains the links

At the end of April, medical trend reports revealed a chilling trend: Children appear to be increasingly sick with a virus similar to Kawasaki disease, a very rare illness that causes inflammation throughout the body.

This new syndrome might be connected to the Covid-19 pandemic, experts say. It appears to cause a new range of symptoms in children, who usually fall outside the bounds of those who are most severely affected by the novel coronavirus.

In New York, there's estimated to be as many as 100 cases of children presenting this new syndrome, which has been described as "pediatric multisystem inflammatory syndrome" (PIMS). There have also been cases reported in Chicago, Connecticut, Los Angeles, and across Europe.

Symptoms include unrelenting fever, rash, red eyes, swollen hands or feet, dry lips, and abdominal pain. Eventually, those that have died of the illness enter a form of toxic shock, where blood pressure drops and it becomes difficult for oxygenated blood to reach the organs that need it. Three children in New York with this syndrome have died, and two deaths are under investigation.

According to New York Governor Andrew Cuomo, these symptoms present an "entirely different chapter" of the coronavirus pandemic. That's in part because the symptoms don't tend to have the same respiratory symptoms we associated with Covid-19, like shortness of breath or coughing.

Leonard Krilov is a pediatric infectious disease specialist at NYU Langone Health. He tells Inverse that this new condition has more questions than answers, but that it's likely caused by a severe overreaction in the immune system.

"The way I am thinking about it right now is this is a post-infectious inflammatory response triggered, probably, by this virus," Krilov says. "As the body responds it's sort of a balance of how 'too much immunity' or different patterns of immunity, then trigger inflammatory responses."

Not Kawasaki disease – At first reports of this syndrome likened it to Kawasaki disease, a rare condition that affects between nine and 19 children below the age of five, out of every 100,000, according to the CDC.

It's plausible that, in some instances, these patients both have Kawasaki disease and have been exposed to Covid-19. In New York, many of the children thought to have PIMS have tested positive for Covid-19 or its antibodies, even though they don't show the symptoms commonly associated with Covid-19.

As scientists learn more about the syndrome, it's clear that PIMS is probably in a category of its own.

"It is, at best, being described as Kawasaki-like," Krilov says.

One difference is that Kawasaki disease doesn't always involve abdominal pain, though it can happen, notes Krilov. Kawasaki also tends to affect very young children (below the age of 5). This new condition seems to affect older children too; the death of a teenager in New York is being investigated for a possible link to the syndrome.

A case study from The Lancet reported the death of a 14-year-old boy in England who had this condition. A New York City Health Department's bulletin describing the condition notes an age range of between two and 15 but asks healthcare providers to report cases in people under age 21.

PIMS also seems to affect the heart differently than Kawasaki disease does, explains Krilov.

Kawasaki disease causes the inflammation of blood vessels around the heart. PIMS appears to lead to inflammation of the heart muscle itself. This form of inflammation is called myocarditis. Krilov notes, before now, it's typically seen in adolescent patients — not young kids.

"[Myocarditis] may be why a number of those children present with shock. The heart muscle isn't able to pump strongly," Krilov says.

The connection to Covid-19 – Scientists suspect that this condition is linked to Covid-19 for a few reasons, Krilov explains.

While some of these young patients test positive for Covid-19, others don't. Some have had exposure to the virus previously, or test positive for antibodies. This means they may have had the virus weeks earlier, Krilov explains.

To really understand why some children are affected by PIMS during the coronavirus pandemic, and others are not, scientists need to gain a better understanding of how individual immune systems respond to Covid-19 differently.

Immune systems tend to vary with age, so the way the body reacts to Covid-19 could differ for a young child as opposed to an older one. That difference leads to different kinds of symptoms, says Krilov.

"All of this may be playing in," he says, adding "it's really just conjecture at this point."

What does this mean for the pandemic? –  PIMS is still extremely rare, says Krilov. That said, the severity of the illness is enough to give us pause, and prompt a reevaluation of the possible cascading effects of Covid-19.

Before the emergence of PIMS, children were thought to generally be less at risk for developing severe cases of Covid-19. This syndrome presents a new risk that may reshape the conversation around children's health — and around the risks of reopening society. In recent weeks, there's been debate over whether schools should be one of the first parts of public life to open back up.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, addressed this syndrome specifically on Tuesday while discussing concerns over reopening too soon.

"We don't know everything about this virus, and we really better be very careful, particularly when it comes to children, because the more and more we learn, we're seeing things about what this virus can do that we didn't see from the studies in China or in Europe," he said.

For now, it's too early to project what the emergence of this syndrome means in terms of pandemic response. But, like Covid-19, PIMS appeared quickly and our understanding of it is clouded by unanswered questions. The answer to those questions will affect our lives going forward.

"It is starting to beg questions, though I think it's too soon to answer them," says Krilov.