While clinical overlap between Kawasaki disease (KD) and multisystem inflammatory syndrome in children (MIS-C) has been evident, information regarding those presenting with shock has been limited. We sought to determine associations with shock within and between diagnosis groups. The International KD Registry enrolled contemporaneous patients with either KD or MIS-C from 39 sites in 7 countries from 01/2020 to 01/2023. Demographics, clinical features and presentation, management, laboratory values, and outcomes were compared between the diagnosis/shock groups. Shock at presentation was noted for 19 of 672 (2.8%) KD patients and 653 of 1472 (44%; p<0.001) MIS-C patients. Within both groups, patients with shock were significantly more likely to be admitted to the intensive care unit, receive inotropes and to have greater laboratory abnormalities indicative of hyperinflammation and organ dysfunction, including abnormal cardiac biomarkers. Patients with KD and shock had a greater maximum coronary artery Z score (median +2.62) versus KD patients without shock (+1.36; p<0.001) and MIS-C patients with shock (+1.45; versus +1.32 for those without shock; p<0.001). They were also more likely to have large coronary artery aneurysms. In contrast, MIS-C patients with shock had lower left ventricular ejection fraction (mean 51.6%) versus MIS-C patients without shock (56.6%; p<0.001) and KD patients with shock (56.7%; versus 62.8% for those without shock; p=0.04). While patients with KD presenting with shock are clinically similar to patients with MIS-C, especially those with shock, they have more severe coronary artery involvement, while MIS-C patients with shock have lower left ventricular ejection fraction.
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