Multisystem inflammatory syndrome in adults (MIS-A) is a systemic inflammatory disease associated with COVID-19 and follows coronary artery aneurysms similar to Kawasaki disease. In many cases, it is improved by treatments such as high-dose steroids or intravenous immunoglobulin (IVIg). However, the role of untreated coronary artery aneurysms leading to future stenosis remains unknown. Untreated MIS-A may potentially lead to the formation of coronary aneurysms. In cases of COVID-19 where young adults present with angina-like symptoms, an evaluation for angina is considered. Herein, we report a case of a 27-year-old female who developed unstable angina with coronary artery aneurysms six months after COVID-19 infection. She required surgery for unstable angina, which resulted in an improvement in chest pain. Coronary artery lesions are considered to be related to MIS-A, and treatment was conducted in accordance with that for Kawasaki disease. Currently, the pathological differences and prognosis between MIS-A and Kawasaki disease remain unclear, but the elucidation of the conditions is warranted in the future.

Multisystem inflammatory syndrome in children (MIS-C) is a relatively new syndrome associated with coronavirus disease 2019 (COVID-19) that is characterized by a severe clinical course compared to pediatric COVID-19. This review aimed to compile the available evidence on the clinical presentation and management of MIS-C in children with COVID-19. During this systematic review, a comprehensive search was performed in the following databases: PubMed, Embase, Medline, Google Scholar, Cochrane, and Scopus, using predetermined search terms, such as Medical Subject Headings (MeSH) and keywords to find relevant studies on the MIS-C. Relevant data were extracted, and the quality of the studies was evaluated using suitable methods. The collected findings were synthesized and discussed in the study. The World Health Organization\'s (WHO) definition of MIS-C was the most favored due to its precision and inclusiveness. MIS-C primarily affected children aged 6-12 years, with male predominance. MIS-C involves a range of systems, including gastrointestinal, cardiovascular, hematologic, mucocutaneous, and respiratory. Radiographic findings revealed cardiovascular abnormalities, solid visceral organ involvement, and bowel abnormalities, reflecting a systemic inflammatory process. Laboratory investigations unveiled elevated inflammatory markers, neutrophil activation, release of extracellular traps in vessels, elevated procalcitonin, hyponatremia, hypoalbuminemia, low hemoglobin, and thrombocytopenia. The inflammatory markers and autoantibody profiles are essential in differentiating MIS-C from COVID-19. The preferred treatment primarily involves immunomodulatory therapies like intravenous immunoglobulin (IVIG), glucocorticoids, and interleukin-6 or 1RA inhibitors or a combination of those. In severe cases, extracorporeal membrane oxygenation (ECMO) and mechanical ventilation are necessary, leading to reduced mortality and quick recovery. This review found that the average hospital stay was seven days, and most discharged children fully recovered within seven days. MIS-C is a life-threatening post-COVID-19 condition and involves multiple systems due to systemic inflammation, with elevated inflammation markers. Recognition of multisystem involvement is crucial, and prompt identification and multidisciplinary treatment are vital for optimal outcomes.