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Multisystem inflammatory syndrome in children (MIS-C) caused by SARS-CoV-2 infection was often accompanied by subtle changes in myocardial function that differ from what is seen in classic Kawasaki disease, one center reported.

Various strain parameters on echocardiography showed that left ventricular (LV) systolic and diastolic function were worse in MIS-C compared with Kawasaki disease and healthy controls. Myocardial injury was a common finding, in 17 out of 28 MIS-C patients, and affected patients performed particularly badly on these functional parameters, according to Anirban Banerjee, MD, of Children's Hospital of Philadelphia (CHOP), and colleagues.

Only one out of 28 MIS-C patients had coronary artery dilatation in the acute phase, which resolved over approximately 5 days, the authors reported in their study online in the . On the other hand, four of the 20 kids with classic Kawasaki disease had coronary abnormalities (including two with aneurysms detected).

"The major finding during the acute phase of MIS-C is a myocarditis-like picture, that may remain subtle and sub-clinical, particularly in the preserved EF [ejection fraction] cohort. Even in the presence of normal EF, the latter group showed distinct dysfunction in systolic and diastolic deformation parameters," the researchers wrote.

MIS-C is characterized as a hyperinflammatory syndrome with multi-organ dysfunction.

The observed LV dysfunction in the study may be the result of subclinical myocarditis, which was suspected in 61% of the MIS-C group based on brain natriuretic peptide and troponin elevations, the team explained.

Over brief follow-up, MIS-C patients tended to recover systolic function but have diastolic dysfunction persist; no coronary aneurysms were detected.

"MIS-C is a relatively rare disease affecting only 0.6% in children infected by COVID-19. Although MIS-C shares similarities with KD [Kawasaki disease], it is notably distinct in that the coronary arteries may be often spared and there is a higher frequency of LV dysfunction, myocarditis, and shock," Banerjee and co-authors wrote.

Thus, they said, the results affirm the need for different management of COVID-associated MIS-C vs Kawasaki disease.

For the retrospective study, the team compared the records of three groups of pediatric patients at CHOP:

• 28 MIS-C patients who were admitted from April to June this year and tested positive for COVID-19

• 20 healthy controls with no structural and functional heart defects who had visited the hospital before the COVID-19 pandemic

• 20 consecutive classic Kawasaki disease patients presenting with their first episode (also during the pre-COVID era)

The MIS-C cohort was equally split between boys and girls, and MIS-C patients were significantly older than those with Kawasaki disease (11.4 vs 3.1 years, P<0.01). MIS-C patients were also numerically more likely to be African American compared with the control and Kawasaki disease groups (46% vs 20% vs 20%).

Banerjee's group reported that predictors of myocardial injury in MIS-C included the echocardiographic deformation parameters global longitudinal strain, global circumferential strain, peak left atrial strain, and peak longitudinal strain of right ventricular free wall.

The quality of echocardiography may have been affected by the strict infection control measures during the COVID-19 era, the investigators cautioned. Moreover, the study was limited by the lack of echocardiographic follow-up for 29% of the MIS-C group given that they were followed by other institutions. In addition, no patient underwent endomyocardial biopsy or cardiac magnetic resonance imaging to diagnose myocardial injury.

The study authors noted that MIS-C patients who had Kawasaki-like presentation were treated with IV immunoglobulin, but declined to comment on the effectiveness of this treatment given the small sample.

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