Six-Month Outcomes in the Long-Term Outcomes After the Multisystem Inflammatory Syndrome in Children Study.

Importance: Multisystem inflammatory syndrome in children (MIS-C) is a life-threatening complication of COVID-19 infection. Data on midterm outcomes are limited.

Objective: To characterize the frequency and time course of cardiac dysfunction (left ventricular ejection fraction [LVEF] <55%), coronary artery aneurysms (z score ≥2.5), and noncardiac involvement through 6 months after MIS-C.

Design, setting, and participants: This cohort study enrolled participants between March 2020 and January 2022 with a follow-up period of 2 years. Participants were recruited from 32 North American pediatric hospitals, and all participants met the 2020 Centers for Disease Control and Prevention case definition of MIS-C.

Exposure: MIS-C after COVID-19 infection.

Main outcomes and measures: Outcomes included echocardiography core laboratory (ECL) assessments of LVEF and maximum coronary artery z scores (zMax); data collection on cardiac and noncardiac sequelae during hospitalization and at 2 weeks, 6 weeks, and 6 months after discharge; and age-appropriate Patient-Reported Outcomes Measurement Information Systems (PROMIS) Global Health Instruments at follow-up. Descriptive statistics, linear regression models, and Kaplan-Meier analysis were used.

Results: Of 1204 participants (median [IQR] age, 9.1 [5.6-12.7] years; 724 male [60.1%]), 325 self-identified with non-Hispanic Black race (27.0%) and 324 with Hispanic ethnicity (26.9%). A total of 548 of 1195 participants (45.9%) required vasoactive support, 17 of 1195 (1.4%) required extracorporeal membrane oxygenation, and 3 (0.3%) died during hospitalization. Of participants with echocardiograms reviewed by the ECL (n = 349 due to budget constraints), 131 of 322 (42.3%) had LVEF less than 55% during hospitalization; of those with follow-up, all but 1 normalized by 6 months. Black race (vs other/unknown race), higher C-reactive protein level, and abnormal troponin level were associated with lowest LVEF (estimate [SE], -3.09 [0.98]; R2 = 0.14; P =.002). Fifteen participants had coronary artery z scores of 2.5 or greater at any time point; 1 participant had a large/giant aneurysm. Of the 13 participants with z scores of 2.5 or greater during hospitalization, 12 (92.3%) had normalized by 6 months. Return to greater than 90% of pre-MIS-C health status (energy, sleep, appetite, cognition, and mood) was reported by 711 of 824 participants (86.3%) at 2 weeks, increasing to 548 of 576 (95.1%) at 6 months. Fatigue was the most common symptom reported at 2 weeks (141 of 889 [15.9%]), falling to 3.4% (22 of 638) by 6 months. PROMIS Global Health parent/guardian proxy median T scores for fatigue, global health, and pain interference improved significantly from 2 weeks to 6 months (fatigue, 56.1 vs 48.9; global health, 48.8 vs 51.3; pain interference, 53.0 vs 43.3; P < .001) and by the 6-week visit were at least equivalent to prepandemic population norms.

Conclusions and relevance: Results of this cohort study suggest that although children and young adults with MIS-C can have severe disease during the acute phase, most recovered quickly and had a reassuring midterm prognosis.