Expanding the Differential for Alternative Diagnoses in the Workup of Multisystem Inflammatory Syndrome in Children

Background: Multisystem inflammatory syndrome in children (MIS-C) is a rare inflammatory syndrome associated with SARS-CoV-2 infection. Children are increasingly admitted for MIS-C evaluation, but instead found to have alternative diagnoses.

Methods: Retrospective study of all pediatric patients <21 years of age hospitalized between August 1, 2020, and July 31, 2021, with clinical concern for MIS-C at the time of presentation were identified through use of an institutional computerized MIS-C order entry set. Final diagnoses were then collected through primary review of the medical record from the time of initial presentation through 1-month postdischarge.

Results: Of 359 cases identified through the MIS-C order entry set, 126 (35.1%) met criteria for MIS-C, 28 had Kawasaki Disease (KD) (7.8%), and 11 cases met criteria for both MIS-C and KD (3.1%), leaving 194 (54.0%) patients ruled out and categorized as "MIS-C mimickers." Infectious diagnoses were the most common MIS-C mimickers (78.9%). Of the infectious etiologies, bacterial (51.0%) and viral (52.3%) etiologies were seen with similar frequency.

Conclusions: We describe MIS-C mimickers spanning multiple subspecialties, with infectious etiologies predominating, which can aid clinicians in the consideration of diagnostic testing, with the goal of achieving timely and accurate diagnoses.