Macrophage activation syndrome associated with multi-system inflammatory syndrome in children: a case report and cytokine profile.

Macrophage activation syndrome (MAS) is a potentially life-threatening complication requiring early diagnosis and prompt treatment in rheumatic diseases such as systemic juvenile idiopathic arthritis (sJIA). Recently, multisystem inflammatory syndrome in children (MIS-C) associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was reported to be complicated by MAS. The diagnostic criteria for MAS-associated MIS-C (MIS-C/MAS) remain unknown. We report the case of a 12-year-old boy who presented with fever for 4 days, swollen cervical lymph nodes, conjunctival congestion, red lips, strawberry tongue, irregular erythematous lesions, abdominal pain, and diarrhoea; he had coronavirus disease 2019 (COVID-19) 1 month prior. The patient was diagnosed MIS-C/MAS based on the criteria for sJIA/MAS, treated with intravenous immunoglobulin, glucocorticoids, and cyclosporine without any coronary artery sequelae. Evaluation of the patient's serum cytokine profile revealed that CXCL9 level (14259 pg/mL, reference range <31-83 pg/mL) was significantly elevated, as in sJIA/MAS. Based on cytokine profiles, the diagnostic criteria for MIC-S/MAS may be consistent with those for sJIA/MAS. No previous studies have reported on the cytokine profiles of MIS-C/MAS. Pediatricians should consider that MIS-C may complicate MAS, such as sJIA. Glucocorticoids and cyclosporine may be considered in cases of MIS-C complicated by MAS.