76 - INCOMPLETE KAWASAKI DISEASE VERSUS NON-SEVERE MULTISYSTEM INFLAMMATORY SYNDROME IN CHILDREN: DISTINGUISHING FEATURES FROM CONTEMPORANEOUS PATIENTS

Background: There is considerable clinical overlap between Kawasaki disease (KD) and multisystem inflammatory syndrome in children (MIS-C) associated with COVID-19. We sought to determine features and outcomes that distinguish incomplete KD from non-severe MIS-C in a cohort of contemporaneous patients.

Methods: Patients were enrolled through the International KD Registry from 8 countries from January 2020 through October 2023. Of 2146 patients with a site diagnosis of MIS-C, we excluded 211 patients without evidence of prior COVID, and 108 who did not meet CDC criteria. Of the remaining 1827, 769 were defined as non-severe MIS-C (no presentation with shock, no ICU admission). Of 1358 patients with a site diagnosis of KD, we excluded 203 with evidence of prior COVID, and 637 with confirmed complete KD. The remaining patients with incomplete KD included 146 meeting AHA criteria (confirmed) and 372 who did not or did not have sufficient information (unconfirmed). We compared 3 groups including non-severe MIS-C patients, unconfirmed and confirmed incomplete KD regarding presentation, clinical and laboratory features, treatment and cardiac outcomes.

Results: Non-severe MIS-C patients were significantly older (median 7.42 years) versus both unconfirmed and confirmed incomplete KD patients (2.50 and 2.25 years, respectively, p< 0.001). There was no difference in %males, but MIS-C patients had a higher proportion of black ethnicity, and a lower proportion of east Asian and south Asian. MIS-C patients had significantly greater zBMI (mean 0.53, vs. ---0.12 and -0.03 for unconfirmed and confirmed incomplete KD; p< 0.001). KD groups had greater days of fever at presentation, and typical KD criteria were more prevalent with the exception of lymphadenopathy. MIS-C patients were more likely to have other symptoms, particularly gastrointestinal symptoms (eg. abdominal pain 64% vs. 19% in unconfirmed and 25% in confirmed incomplete KD groups; p< 0.001), although were less likely to have irritability. Peak values of white cell counts and platelets were lower for MIS-C patients, particularly in comparison to confirmed incomplete KD patients. MIS-C patients had high peak CRP and ferritin, but not ESR, and higher peak liver transaminases and creatinine. Lower LV ejection fraction was noted for MIS-C, with higher categories of CA involvement for incomplete KD, with CA involvement contributing to confirmation of the diagnosis (Figure).

Conclusions: Clinical (older age, ethnicity, abdominal symptoms), laboratory features (more severe inflammation, greater multi-system involvement), and the pattern of cardiac involvement (greater ventricular dysfunction, less severe CA complications) can differentiate non-severe MIS-C from incomplete KD.