Comparative study of post- COVID-19 Kawasaki disease and multisystem inflammatory syndrome cases at Alexandria...

Multisystem inflammatory syndrome in children (MIS-C) and Kawasaki disease (KD) share overlapping clinical features, and 25-50% of MIS-C cases may meet KD criteria. Differentiating between both conditions is clinically important for timely and appropriate management. The study aims to compare clinical manifestations, laboratory characteristics, clinical course, and outcomes of children diagnosed with post-COVID-19 MIS-C versus KD, and to develop a discrimination score to aid differentiation.

This retrospective study included 211 children admitted to Alexandria University Children's Hospital pediatric wards or Pediatric ICU from February 2023 to December 2024. Patients were classified as MIS-C/PIMS temporally associated with COVID-19 according to the COVID-19 study case definition, or as post-COVID-19 Kawasaki disease according to the American Heart Association diagnostic criteria for Kawasaki disease. Demographic, clinical, laboratory, and echocardiographic data were collected from medical records. Between-group comparisons were performed, and multivariate logistic regression was used to identify independent predictors and construct an exploratory clinical discrimination score. Diagnostic performance was assessed using ROC analysis.

Of 211 children, 185 (87.7%) had MIS-C and 26 (12.3%) had KD. KD showed significantly higher rates of classic mucocutaneous features including conjunctivitis, stomatitis, lymphadenitis, and extremity edema (all p < .001). MIS-C was associated with significantly higher rates of shock (49.7% vs. 7.7%, p < .001), renal involvement (impairment 42.7% vs. 7.7%, p < .001; proteinuria 40.5% vs. 11.5%, p = .004; hematuria 31.9% vs. 3.8%, p = .002), hepatitis (64.9% vs. 30.8%, p < .001), and neurological involvement including altered level of consciousness (49.7% vs. 7.7%, p < .001). Cardiac involvement differed: myocarditis was more frequent in MIS-C (63.2% vs. 11.5%, p < .001), whereas coronary artery involvement was observed only in KD (15.4% vs. 0%, p < .001) and valvular lesions were more common in KD (80.8% vs. 51.4%, p = .004). A discrimination score demonstrated excellent performance (AUC 0.934; 95% CI 0.876-0.991; p < .001); at a cutoff > 3 points, sensitivity was 94.05% and specificity 84.62%. Mortality occurred in 13 MIS-C patients (7.0%) while all KD patients survived.

In this single-center cohort, the observed differences between MIS-C and Kawasaki disease largely confirm previously reported patterns, with MIS-C showing more frequent shock, renal and neurological involvement, hepatitis, and myocarditis, while Kawasaki disease showed more prominent mucocutaneous and coronary involvement. The proposed discrimination score showed promising exploratory performance in this cohort; however, it requires prospective and external validation before routine clinical application.