A new and mysterious ailment with similarities to a rare inflammatory disease has been identified in at least one child in Washington and researchers suspect it could have links to the virus that causes COVID-19.

The new illness is called pediatric multisystem inflammatory syndrome. It was first identified in Europe. The New York City health department put out an alert May 4 about the disease and a handful of other states have identified it, too.

“We’re starting to see these cases in other parts of the country, including Seattle,” said Dr. Michael Portman, director of research in the cardiology division at Seattle Children’s hospital and a professor in the Department of Pediatrics at the University of Washington School of Medicine. “We’ve reported to the Department of Health one case that fits the definition. There are other children who have presented with inflammatory-type symptoms.”

Portman said the patients have symptoms that resemble a rare illness called Kawasaki disease.

Symptoms of Kawasaki disease include persistent fever, skin rash, conjunctivitis, swollen hands or feet, swollen lymph nodes and red, swollen lips.

Portman said the newly identified syndrome remains rare and said parents should “not panic,” but added they should not delay seeking care if children have fevers that last four to five days or if they exhibit other unusual symptoms.

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“They should not be reluctant to take their child to see a health care provider, either their own, or the emergency room, because of concerns related to viral exposure,” Portman said.

Portman said there is no blood test for Kawasaki disease. Instead, doctors look for clinical signs of the syndrome. The relationship between the newly identified inflammatory syndrome and Kawasaki disease is not yet clear.

“There’s a lot of confusion. We have this new inflammatory syndrome. We have Kawasaki disease. Do they merge or is one an extension of the other?”

Portman said researchers do not know for sure what causes Kawasaki disease, but they have long suspected that viruses play a role. The prevailing theory is that a protein on a virus — or even multiple, different viruses — causes a delayed reaction in the body and triggers a “hyperactive” immune response.

Children with Kawasaki disease can develop coronary aneurysms, or abnormal widening of their coronary arteries. Portman said an intravenous treatment that infuses patients with antibodies drops the risk of coronary aneurysms from about 25% to between 4 and 7%.

Severe cases can present as Kawasaki disease shock syndrome — where patients present high fevers and can’t maintain blood pressure.

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The patient at Seattle Children’s whose case was reported as pediatric multisystem inflammatory syndrome tested positive for antibodies for SARS-CoV-2, meaning the patient had, at some point, become infected with the virus that causes COVID-19.

Other patients, some who were admitted in the past week at Seattle Children’s, also had these antibodies.

“Some patients have positive serology for COVID. That means they had a prior exposure to COVID and later had an inflammatory response that looks like Kawasaki disease,” Portman said.

Kawasaki disease at Seattle Children’s typically spikes in the spring, he said.

“We won’t know until two to three weeks goes by if we have a massive surge or not in Kawasaki disease,” Portman said, adding that researchers had only just identified the existence of pediatric multisystem inflammatory syndrome.

“This syndrome has only been around for a few weeks at the most starting in Italy and spreading out. There’s a lot we need to learn,” he said.

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Italian researchers Wednesday published a peer-reviewed analysis of cases in 10 children who developed Kawasaki-like symptoms during the COVID-19 pandemic in the medical journal, The Lancet.

Eight of the 10 children tested positive for SARS-CoV-2 antibodies. All 10 survived, but many had more severe symptoms when compared with Kawasaki patients in other years.

“We noticed an increase in the number of children being referred to our hospital with an inflammatory condition similar to Kawasaki disease around the time the SARS-CoV-2 outbreak was taking hold in our region,” said Dr. Lucio Verdoni, one of the study’s authors, in a news release. “Although this complication remains very rare, our study provides further evidence on how the virus may be affecting children.”

The authors noted the study’s sample size was limited, but added it was important to better understand how SARS-CoV-2 affects children, particularly as communities look to relax social distancing.

Researchers in the United Kingdom also have studied a small cluster of young patients with symptoms similar to Kawasaki disease shock syndrome. The cluster prompted a national alert, according to correspondence in The Lancet.