Diagnostic Criteria May Miss Some MIS-C Cases, Experts Say

Diana Phillips

July 02, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

New data from active surveillance of the severe inflammatory condition associated with COVID-19 in previously healthy children provide further insight into the prevalence and course of the rare syndrome, but experts are concerned that current diagnostic criteria may not capture the true scope of the problem.

In separate reports published online June 29 in the New England Journal of Medicine, researchers from the New York State Department of Health and the Centers for Disease Control and Prevention (CDC) describe the epidemiology and clinical features of multisystem inflammatory syndrome in children (MIS-C) on the basis of information derived from targeted surveillance programs in New York State and across the country.

For the New York study, Elizabeth M. Dufort, MD, from the New York Department of Health in Albany, and colleagues analyzed MIS-C surveillance data from 106 hospitals across the state. Of 191 suspected MIS-C cases reported to the Department of Health from March 1 through May 10, 99 met the state's interim case definition of the condition and were included in the analysis.

The incidence rate for MIS-C was two cases per 100,000 individuals younger than 21 years, whereas the incidence rate of confirmed COVID-19 cases in this age group was 322 per 100,000. Most cases occurred approximately 1 month after the state's COVID-19 peak.

"Among our patients, predominantly from the New York Metropolitan Region, 40% were black and 36% were Hispanic. This may be a reflection of the well-documented elevated incidence of SARS CoV-2 infection among black and Hispanic communities," the authors report.

All children presented with fever or chills, and most had tachycardia (97%) and gastrointestinal symptoms (80%). Rash (60%), conjunctival injection (56%), hypotension (32%), and mucosal changes (27%) were reported. Among all of the children, levels of inflammatory markers were elevated, including levels of C-reactive protein (100%), d-dimer (91%), and troponin (71%). More than one third of the patients (36%) were diagnosed with myocarditis, and an additional 16% had clinical myocarditis.

Of the full cohort, 80% of the children required intensive care, 62% received vasopressor support, and two children died.

The high prevalence of cardiac dysfunction or depression, coagulopathy, gastrointestinal symptoms, mild respiratory symptoms, and indications for supplemental oxygen in patients with MIS-C stands in contrast to the clinical picture observed in most acute cases of COVID-19 in hospitalized children, the authors write.

"Although most children have mild or no illness from SARS-CoV-2 infection, MIS-C may follow Covid-19 or asymptomatic SARS-CoV-2 infection. Recognition of the syndrome and early identification of children with MIS-C, including early monitoring of blood pressure and electrocardiographic and echocardiographic evaluation, could inform appropriate supportive care and other potential therapeutic options," they continue.

The incidence of MIS-C among children infected with SARS-CoV-2 is unclear because children with COVID-19 often have mild or no symptoms and because children are not tested as frequently, the authors state. For this reason, "[i]t is crucial to establish surveillance for MIS-C cases, particularly in communities with higher levels of SARS-CoV-2 transmission."

Important Differences From Kawasaki Disease

In a separate study, Leora R. Feldstein, MD, of the CDC, and colleagues report 186 cases of MIS-C collected through targeted surveillance of pediatric health centers in 26 US states from March 15 to May 20, 2020. As with the New York cohort, a disproportionate number of children in this cohort were black (25%) and Hispanic or Latino (31%).

Similar to the New York cohort, 80% of the children in this group required intensive care, 48% received vasoactive support, 20% required invasive mechanical ventilation, and four children died. Skin rashes, gastrointestinal symptoms, cardiovascular and hematologic effects, mucous changes, and elevations of inflammatory biomarkers were also similarly observed.

The researchers note that although many of the features of MIS-C overlap with Kawasaki disease, there are some important differences, particularly with respect to the nature of cardiovascular involvement. "Approximately 5% of children with Kawasaki's disease in the United States present with cardiovascular shock leading to vasopressor or inotropic support, as compared with 50% of the patients in our series," the authors write.

In addition, coronary-artery aneurysms affect approximately one quarter of Kawasaki disease patients within 21 days of disease onset. "In our series, a maximum z score of 2.5 or higher in the left anterior descending or right coronary artery was reported in 8% of the patients overall and in 9% of patients with echocardiograms," they report.

Additional differentiating features include patient age and race/ethnicity. Kawasaki disease occurs most commonly in children younger than 5 years. The median age in the multistate study was 8.3 years, and nearly half of the children in the New York cohort were in the 6- to 12-year age group. Further, Kawasaki disease is disproportionately prevalent in children of Asian descent.

Despite the differences, "until more is known about long-term cardiac sequelae of MIS-C, providers could consider following Kawasaki's disease guidelines for follow-up, which recommend repeat echocardiographic imaging at 1 to 2 weeks."

As was the case in the New York series, treatment in the multistate cohort most commonly included intravenous immunoglobulin and systemic glucocorticoids. Optimal management, however, will require a better understanding of the pathogenesis of MIS-C, Feldstein and colleagues write.

Questions Remain

With the accumulating data on this syndrome, the MIS-C picture seems to be getting incrementally clearer, but there is still much uncertainty, according to Michael Levin, FMedSci, PhD, from the Department of Infectious Disease, Imperial College London, United Kingdom.

"The recognition and description of new diseases often resemble the parable of the blind men and the elephant, with each declaring that the part of the beast they have touched fully defines it," he writes in an accompanying editorial.

"As the coronavirus disease 2019 (Covid-19) pandemic has evolved, case reports have appeared describing children with unusual febrile illnesses that have features of Kawasaki's disease, toxic shock syndrome, acute abdominal conditions, and encephalopathy, along with other reports of children with fever, elevated inflammatory markers, and multisystem involvement. It is now apparent that these reports were describing different clinical presentations of a new childhood inflammatory disorder."

Although a consistent clinical picture is emerging, "[t]he published reports have used a variety of hastily developed case definitions based on the most severe cases, possibly missing less serious cases," Levin writes. In particular, both the CDC and World Health Organization definitions require evidence of SARS-CoV-2 infection or exposure, which might contribute to underrecognition and underreporting, because asymptomatic infections are common, and antibody testing is not universally available.

"There is concern that children meeting current diagnostic criteria for MIS-C are the 'tip of the iceberg,' and a bigger problem may be lurking below the waterline," Levin states. With approximately 1000 cases of the syndrome reported worldwide, "do we now have a clear picture of the new disorder, or, as in the story of the blind men and the elephant, has only part of the beast been described?"

Adrienne Randolph, MD, of Boston Children's Hospital, who is a coauthor of the multistate report, agrees that there is still much to learn about MIS-C before the whole beast can be understood. In an interview with Medscape Medical News, she listed the following key questions that have yet to be answered:

  • Why do some children get MIS-C and not others?

  • What is the long-term outcome of children with MIS-C?

  • How can we differentiate MIS-C from acute COVID-19 infection in children with respiratory failure?

  • Does MIS-C occur in young adults?

Randolph said her team is taking the best path forward toward answering these questions, including conducting a second study to identify risk factors for MIS-C and longer-term follow-up studies with the National Institutes of Health. "We are also getting consent to collect blood samples and look at other tests to help distinguish MIS-C from acute COVID-19 infection," she said. She encouraged heightened awareness among physicians who care for young adults to consider MIS-C in patients aged 21 years and older who present with similar signs and symptoms.

On the basis of the answers to these and additional questions, the case definitions for MIS-C may need refinement to capture the wider spectrum of illness, Levin writes in his editorial. "The challenges of this new condition will now be to understand its pathophysiological mechanisms, to develop diagnostics, and to define the best treatment."

Kleinman has received grants from the Health Services Resources Administration outside the submitted work. Maddux has received grants from the NIH/NICHD and the Francis Family Foundation outside the submitted work. Randolph has received grants from Genentech Inc and personal fees from La Jolla Pharma Inc outside the submitted work and others from the CDC during the conduct of the study.

N Engl J Med. Published online June 29, 2020. Dufort et al, Full text; Feldstein et al, Full text; Editorial

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