This case report details the clinical course of a 7-year-old patient with an initial presentation of acute appendicitis, who developed symptoms highly concerning multisystem inflammatory syndrome in children (MIS-C) after appendectomy. Despite appropriate management, the patient went on to develop left main coronary artery dilatation. Given the spectrum of clinical presentations and absence of pathognomonic findings or diagnostic tests for MIS-C, it is essential to maintain a high index of suspicion for MIS-C when pediatric patients first present with nonspecific gastrointestinal symptoms and recent exposure to coronavirus disease 2019 (COVID-19). Importantly, this case illustrates that the diagnosis of MIS-C can be missed in three different ways: 1) if the patient has an absence of classic symptoms such as rash, conjunctivitis, edema, or evidence of mucocutaneous involvement on initial presentation; 2) if the patient initially has leukocytosis, instead of leukopenia (which is more prevalent in MIS-C cases), and a normal platelet count early on in the disease course; and 3) if providers confuse MIS-C for other more common postoperative causes of fever, such as atelectasis. Finally, MIS-C should still be considered part of the differential even if abdominal computer tomography (CT) findings are unremarkable for systemic inflammation. Given the potential for a rapid clinical decline in patients with MIS-C, appropriate workup should be completed in a timely manner.
