Pediatric-Onset Multiple Sclerosis in Multiple Autoimmune Syndrome: Reporting This Rare Entity in 2 Pediatric Patients

Multiple autoimmune syndrome (MAS) is characterized by the coexistence of 3 or more autoimmune disorders in the same individual and is exceptionally rare in childhood. Pediatric-onset multiple sclerosis (POMS) represents 3% to 5% of all multiple sclerosis (MS) cases and is increasingly recognized within the broader spectrum of immune-mediated diseases. We describe 2 pediatric patients fulfilling MAS criteria in association with POMS-one with type 1 diabetes mellitus and autoimmune thyroiditis, and another with rheumatoid arthritis and autoimmune thyroiditis. Both exhibited HLA-DRB1*15:01 positivity, Epstein-Barr virus IgG seropositivity, and severe vitamin D deficiency, suggesting shared immunogenetic and environmental risk factors. These cases highlight the potential of POMS to manifest as part of a systemic autoimmune diathesis. Early recognition, proactive screening, and multidisciplinary management are essential. Further multicenter studies and registry-based data are needed to clarify the prevalence, mechanisms, and prognostic implications of MAS in pediatric MS.