Post-COVID-19 multisystem inflammatory syndrome: an evolving concept

INTRODUCTION: A potential association of COVID-19 with inflammatory and autoimmune phenomena opens a new chapter in clinical practice. Among several inflammatory conditions described in the post-COVID-19 context, Kawasaki disease and a new condition named multisystem inflammatory syndrome stand out. AIMS: To review, in a practical and concise way, the concept and diagnostic criteria of multisystem inflammatory syndrome, the overlaps with Kawasaki disease, as well as the immunopathogenesis and treatment of this new and intriguing condition. METHODS: Literature review available in the Pubmed database, with emphasis on systematic reviews with meta-analyses. RESULTS: The multisystem inflammatory syndrome is a post-viral, multiorgan hyperinflammatory disorder. The condition is primarily pediatric, and the first cases were reported in England in May 2020. Diagnostic criteria are still imprecise, and include some Kawasaki disease-like manifestations. However, multisystem inflammatory syndrome differs from Kawasaki disease by usually affecting children above five years of age and of black or hispanic races; in clinical terms, it is distinguished by the high frequency of gastroenteropathy, cardiomyopathy and shock. Differential diagnosis includes bacterial sepsis, macrophage activation syndrome, and systemic forms of rheumatoid arthritis. An overexpression of interferons and other inflammatory cytokines pathogenically characterize the multisystem inflammatory syndrome. The disease is, as a rule, responsive to intensive care, steroids, intravenous immunoglobulin, and immunobiologics. CONCLUSIONS: Multisystem inflammatory syndrome is a new and complex hyperinflammatory condition associated with previous exposure to SARS-CoV-2. It shows interesting interfaces with Kawasaki disease. Despite the recent description, the literature is already quantitatively robust, and some pending issues in immunopathogenesis, diagnostic criteria and therapy should be shortly clarified.