During the winter months of 2020/2021 a wave of multisystem inflammatory syndrome in children (MIS-C) emerged in Poland. We present the results of a nationwide register aiming to capture and characterise MIS-C with a focus on severity determinants. The first MIS-C wave in Poland was notably high, hence our analysis involved 274 children. The group was 62.8% boys, with a median age of 8.8 years. Besides one Asian, all were White. Overall, the disease course was not as severe as in previous reports, however. Pediatric intensive care treatment was required for merely 23 (8.4%) of children, who were older and exhibited a distinguished clinical picture at hospital admission. We have also identified sex-dependent differences; teenage boys more often had cardiac involvement (decreased ejection fraction in 25.9% vs. 14.7%) and fulfilled macrophage activation syndrome definition (31.0% vs. 15.2%). Among all boys, those hospitalized in pediatric intensive care unit were significantly older (median 11.2 vs. 9.1 years). Henceforth, while ethnicity and sex may affect MIS-C phenotype, management protocols might be not universally applicable, and should rather be adjusted to the specific population.

Despite the growing literature on multisystem inflammatory syndrome in children (MIS-C), the data in European White population is limited. Our aim was to capture MIS-C emergence in Poland (central Europe) and to describe its characteristics with a focus on severity determinants. Patients who met the MIS-C definition (fever, multiorgan failure, inflammation, and proven SARS-CoV-2 infection or contact) were reported retrospectively and prospectively in an online survey. Study definitions fulfilment was automatically evaluated by a dedicated software. For the assessment of univariate relationships, either directed or divided by sex, age, or disease severity, we used the test for two categorical variables and the Kruskal-Wallis test for categorical-continuous variable pairs. The analysis involved 274 children, 62.8% boys, median age 8.8 years. Besides one Asian, all were European White. Merely 23 (8.4%) required paediatric intensive care treatment (PICU). They were older (11.2 vs. 8.4 years), and at hospital admission had higher respiratory rate (30 v. 20/minute), lower systolic blood pressure (89 vs. 100 mmHg), prolonged capillary refill time (40% vs. 11%), and decreased consciousness (22% vs. 5%). Teenage boys had more common cardiac involvement (fraction 25.9% vs. 14.7% ) and macrophage activation syndrome (31.0% vs. 15.2%) than others. Boys were also more often hospitalised in PICU with age (from median 11.2 years to 9.1). The severity of MIS-C is not as uniform as it seemed, ethnicity and sex may affect MIS-C phenotype. Management might not be universally applicable and should rather be adjusted to the specific population.

Pediatric inflammatory multisystem syndrome (PIMS) is a new entity in children, likely associated with previous coronavirus disease 19 (COVID-19). Most of reports about PIMS come from countries particularly hit by the COVID-19 pandemic. Our aim was to investigate the nature of inflammatory syndromes in Poland (a country with low COVID-19 prevalence) and to perceive the emergence of PIMS in our country. On May 25th, we have launched a nationwide survey of inflammatory syndromes in children for retrospective (since 4th March 2020) and prospective data collection. Up to 28th July, 39 reported children met inclusion criteria. We stratified them according to age (<5 and ≥ 5 years old) and COVID-19 status. The majority of children had clinical and laboratory features of Kawasaki disease, probably non-associated with COVID-19. However, children ≥5 years of age had PIMS characteristics, and 9 children had COVID-19 confirmation. This is the first to our knowledge report of PIMS register from the country with low COVID-19 prevalence, and it proves that PIMS may emerge in any area involved in the COVID-19 pandemic. In a context of limited COVID-19 testing availability, other risk factors of PIMS, e.g. older age should be considered in the differential diagnosis of inflammatory syndromes in children.

Multisystem inflammatory syndrome in children (MIS-C) is an immune-mediated complication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Cardiovascular system is commonly involved. Acute heart failure (AHF) is the most severe complication of MIS-C, leading to cardiogenic shock. The aim of the study was to characterise the course of MIS-C with a focus on cardiovascular involvement, based on echocardiographic (echo) evaluation, in 498 children (median age 8.3 years, 63% boys) hospitalised in 50 cities in Poland. Among them, 456 (91.5%) had cardiovascular system involvement: 190 (48.2%) of patients had (most commonly atrioventricular) valvular insufficiency, 155 (41.0%) had contractility abnormalities and 132 (35.6%) had decreased left ventricular ejection fraction (LVEF < 55%). Most of these abnormalities improved within a few days. Analysis of the results obtained from two echo descriptions (a median of 5 days apart) revealed a >10% increase in LVEF even in children with primarily normal LVEF. Lower levels of lymphocytes, platelets and sodium and higher levels of inflammatory markers on admission were significantly more common among older children with contractility dysfunction, while younger children developed coronary artery abnormality (CAA) more often. The incidence of ventricular dysfunction might be underestimated. The majority of children with AHF improved significantly within a few days. CAAs were relatively rare. Children with impaired contractility as well as other cardiac abnormalities differed significantly from children without such conditions. Due to the exploratory nature of this study, these findings should be confirmed in further studies.

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