Macrophage Activation Syndrome in MIS-C.

Background: Multisystem inflammatory syndrome (MIS-C) represents a diagnostic challenge because of its overlap with Kawasaki disease, Kawasaki disease shock syndrome, and toxic shock syndrome. Macrophage activation syndrome (MAS) is a frequently fatal complication of various pediatric inflammatory disorders and has been reported in MIS-C. Early diagnosis and prompt initiation by immune modulating therapies are essential for effectively managing MAS.

Methods: We conducted a retrospective study to determine the frequency, natural history, diagnostic metrics, treatment, and outcome of MAS in MIS-C within a large cohort of patients across 84 Latin American centers in 16 countries. We compared the clinical and laboratory characteristics between patients with and without MAS.

Results: Among 1238 patients with MIS-C, 212 (17.1%) fulfilled MAS criteria. Gastrointestinal and neurologic manifestations were more frequent in cases where MIS-C was complicated by MAS. Patients presenting with MIS-C complicated by MAS had a mortality rate of 12%, which was higher than those without it. Mortality was associated with MAS, seizures, arthritis, and shock. A ferritin or erythrocyte sedimentation rate ratio of >18.7 exhibited a sensitivity of 88.2% and a specificity of 75% in diagnosing MAS in MIS-C.

Conclusions: MAS in MIS-C patients is associated with increased morbidity and mortality rates in the largest MIS-C Latin American cohort. Early recognition and appropriate management are crucial in improving patient outcomes and reducing mortality rates.