EAACI statement on the pathogenesis, immunology, and immune-targeted management of the Multisystem Inflammatory Syndrome in Children (MIS-C) or Pediatric Inflammatory Multisystem Syndrome (PIMS). (preprint)

Multisystem inflammatory syndrome in children (MIS-C) is a rare, but severe complication of coronavirus disease 2019 (COVID-19). It develops approximately four weeks after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and involves hyperinflammation with multisystem injury, commonly progressing to shock. The exact pathomechanism of MIS-C is not known, but immunological dysregulation leading to cytokine storm plays a central role. In response to the emergence of MIS-C, the European Academy of Allergy and Clinical Immunology (EAACI) established a task force (TF) within the Immunology Section in May 2021. With the use of an online Delphi process, TF formulated clinical statements regarding immunological background of MIS-C, diagnosis, treatment, follow-up, and the role of COVID-19 vaccinations. MIS-C case definition is broad, and diagnosis is made based on clinical presentation. The immunological mechanism leading to MIS-C is unclear and depends on activating multiple pathways leading to hyperinflammation. Current management of MIS-C relies on supportive care in combination with immunosuppressive and/or immunomodulatory agents. The most frequently used agents are systemic steroids and intravenous immunoglobulin. Despite good overall short-term outcome, MIS-C patients should be followed-up at regular intervals after discharge, focusing on cardiac disease, organ damage, and inflammatory activity. COVID-19 vaccination is a safe and effective measure to prevent MIS-C. In anticipation of further research, we propose a convenient and clinically practical algorithm for managing MIS-C developed by the Immunology Section of the EAACI.

Analysis of 21 appendices from children with multisystem inflammatory syndrome compared to specimens of acute appendicitis - a new insight into MIS-C pathology (preprint)

Background & Aims: Multisystem inflammatory syndrome in children (MIS-C) is a rare, but severe complication of coronavirus disease 2019, commonly involving the gastrointestinal tract. Some children with MIS-C undergo appendectomy before the final diagnosis. There are several hypotheses explaining pathomechanism of MIS-C, with the central role of the viral antigen persistence in the gut, associated with lymphocyte exhaustion and immune system dysregulation. We aimed to examine appendectomy specimens obtained from MIS-C patients and analyze the pathological features of the disease and the presence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in the appendix. Methods: In this cross-sectional study we included 21 children with MIS-C who underwent appendectomy before the final diagnosis. MIS-C patients were recruited from the Polish national registry of inflammatory syndromes in children. The control group included 21 sex- and age-matched children with acute appendicitis (AA) unrelated to SARS-CoV-2 infection. Histological evaluation involved hematoxylin and eosin staining and immunohistochemical identification of lymphocyte subpopulations, programmed cell death protein 1, and SARS-CoV-2 nucleocapsid antigen. Results: Appendices of MIS-C patients lacked neutrophilic infiltrate of muscularis propria typical for AA (14 vs 95%, p<0.001). The proportion of CD20+ to CD5+ cells was higher in patients with MIS-C (p 0.04), as well as the proportion of CD4+ to CD8+ (p <0.001). We found no proof of SARS-CoV-2 antigen presence, nor lymphocyte exhaustion, in the appendices of MIS-C patients. Conclusions: Our findings describe pathomorphological features of the appendix in MIS-C and argue against the central role of SARS-CoV-2 persistence in the gut and concomitant lymphocyte exhaustion as the major triggers of MIS-C.

Multisystem inflammatory syndrome in European White children – study of 274 cases (preprint)

Background 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. Methods 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. Findings 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). Interpretation 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. Funding PSP: 501-D402-20-0006100

Pediatric Inflammatory Multisystem Syndrome (PIMS) Did Occur in Poland during Months with Low COVID-19 Prevalence. Preliminary Results of a Nationwide Register. (preprint)

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.