MIS-C is a serious immune-mediated response to COVID-19 infection



One of the take-away messages from a review of multisystem inflammatory syndrome in children (MIS-C) is that clinicians treating this condition “need to be comfortable with uncertainty,” Melissa Hazen, MD, said at a synthesis of multiple published case series and personal experience summarized at the virtual Pediatric Hospital Medicine meeting.

Dr. Melissa Hazen

Dr. Melissa Hazen

She emphasized MIS-C patient care “requires flexibility,” and she advised clinicians managing these patients to open the lines of communication with the many specialists who often are required to deal with complications affecting an array of organ systems.

MIS-C might best be understood as the most serious manifestation of an immune-mediated response to COVID-19 infection that ranges from transient mild symptoms to the life-threatening multiple organ involvement that characterizes this newly recognized threat. Although “most children who encounter this pathogen only develop mild disease,” the spectrum of the disease can move in a subset of patients to a “Kawasaki-like illness” without hemodynamic instability and then to MIS-C “with highly elevated systemic inflammatory markers and multiple organ involvement,” explained Dr. Hazen, an attending physician in the rheumatology program at Boston Children’s Hospital.

A reliable profile of MIS-C is only beginning to emerge from the series of published case series, most of which have only recently reached publication, according to Dr. Hazen. In general, the description of the most common symptoms and their course has been relatively consistent.

In 186 cases of MIS-C collected in a study funded by the Centers for Disease Control and Prevention, 148 (80%) were admitted to intensive care, 90 patients (48%) received vasoactive support, 37 (20%) received mechanical ventilation, and 4 (2%) died.1 The median age was 8 years (range, 3-13 years) in this study. The case definition was fever for at least 24 hours, laboratory evidence of inflammation, multisystem organ involvement, and evidence of COVID-19 infection. In this cohort of 186 children, 92% had gastrointestinal, 80% had cardiovascular, 76% had hematologic, and 70% had respiratory system involvement.

In a different series of 95 cases collected in New York State, 79 (80%) were admitted to intensive care, 61 (62%) received vasoactive support, 10 (10%) received mechanical ventilation, 4 (4%) received extracorporeal membrane oxygenation (ECMO), and 2 (2%) died. 2 Thirty-one percent patients were aged 0-5 years, 42% were 6-12 years, and 26% were 13-20 years of age. In that series, for which the case definition was elevation of two or more inflammatory markers, virologic evidence of COVID-19 infection, 80% had gastrointestinal system involvement, and 53% had evidence of myocarditis.

In both of these series, as well as others published and unpublished, the peak in MIS-C cases has occurred about 3 to 4 weeks after peak COVID-19 activity, according to Diana Lee, MD, a pediatrician at Icahn School of Medicine at Mount Sinai, New York. This pattern, reported by others, was observed in New York State, where 230 cases of MIS-C were collected from the beginning of May until the end of June, which reflected this 3- to 4-week delay in peak incidence.

“This does seem to be a rare syndrome since this [group of] 230 cases is amongst the entire population of children in New York State. So, yes, we should be keeping this in mind in our differential, but we should not forget all the other reasons that children can have a fever,” she said.

Both Dr. Hazen and Dr. Lee cautioned that MIS-C, despite a general consistency among published studies, remains a moving target in regard to how it is being characterized. In a 2-day period in May, the CDC, the World Health Organization, and New York State all issued descriptions of MIS-C, employing compatible but slightly different terminology and diagnostic criteria. Many questions regarding optimal methods of diagnosis, treatment, and follow-up remain unanswered.

Dr. Kevin G. Friedman

Dr. Kevin G. Friedman

Questions regarding the risk to the cardiovascular system, one of the organs most commonly affected in MIS-C, are among the most urgent. It is not now clear how best to monitor cardiovascular involvement, how to intervene, and how to follow patients in the postinfection period, according to Kevin G. Friedman, MD, a pediatrician at Harvard Medical School, Boston, and an attending physician in the department of cardiology at Boston Children’s Hospital.

“The most frequent complication we have seen is ventricular dysfunction, which occurs in about half of these patients,” he reported. “Usually it is in the mild to moderate range, but occasionally patients have an ejection fraction of less than 40%.”

Coronary abnormalities, typically in the form of dilations or small aneurysms, occur in 10%-20% of children with MIS-C, according to Dr. Friedman. Giant aneurysms have been reported.

“Some of these findings can progress including in both the acute phase and, particularly for the coronary aneurysms, in the subacute phase. We recommend echocardiograms and EKGs at diagnosis and at 1-2 weeks to recheck coronary size or sooner if there are clinical indications,” Dr. Friedman advised.

Protocols like these are constantly under review as more information becomes available. There are as yet no guidelines, and practice differs across institutions, according to the investigators summarizing this information.

None of the speakers had any relevant financial disclosures.


1. Feldstein LR et al. Multisystem inflammatory syndrome in U.S. children and adolescents. N Engl J Med. 2020;383:334-46.

2. Dufort EM et al. Multisystem inflammatory syndrome in children in New York State. N Engl J Med 2020;383:347-58.

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