MOGAD-Like Encephalitic Syndromes Without MOG Antibodies in Children

Background and Objectives Although acute disseminated encephalomyelity (ADEM) can be myelin oligodendrocyte glycoprotein-IgG (MOG-IgG) positive or negative, it is unclear whether other MOG- antibody–associated disease (MOGAD)-like encephalitis syndromes occur without MOG-IgG. We aimed to define the frequency, clinico-radiologic features, outcomes, and antibody asso- ciations of such cases in children. Correspondence Dr. Armangue [email protected] MORE ONLINE Supplementary Material Methods Prospective cohort study of children (<18 years) with encephalitis meeting clinico-radiologic MOGAD criteria, regardless of MOG-IgG status. Serum from all patients and CSF when available were tested by live cell-based assays (CBA-IIF, CBA-FACS) at 2 laboratories. Brain MRIs were centrally reviewed for MOGAD-like patterns (ADEM, cortical encephalitis, isolated/predominant central gray matter). Additional testing included CBAs for MOG-IgA, MOG-IgM, PLP1-IgG, glial fibrillary acidic protein-IgG, and AQP4-IgG, along with rat brain immunohistochemistry. Results Among 160 patients with MOGAD-like encephalitis, 120 were MOG-IgG positive and 40 negative (20 ADEM, 11 cortical encephalitis, 9 isolated/predominant central gray matter encephalitis). Clinical-radiologic features were broadly comparable between groups, including lesion distribution, frequency of associated longitudinally extensive transverse myelitis, lesion resolution, and functional outcomes. Relapses were more frequent in MOG-IgG–positive patients (22, 18% vs 1, 3%; p = 0.017). Immunohistochemistry revealed myelin immunos- taining in 14 (12%) MOG-IgG–positive cases (CBA confirmed cross-reactivity with rodent MOG-epitopes) and 10 (25%) MOG-IgG–negative patients (no cross-reactivity with rodent MOG-epitopes); this included a fulminant case with autopsy showing perivenous de- myelination and C4d complement deposition, suggesting autoantibodies against an unknown myelin antigen. MOG-IgA, MOG-IgM, or PLP1-IgG occurred in 36/111 (32%) MOG- IgG–positive and 7/37 (19%) MOG-IgG–negative cases, without clinical differences between groups