Myelin Oligodendrocyte Glycoprotein Antibody-Associated Disease (MOGAD) in Chile: lessons learned from challenging cases

Anti-Myelin Oligodendrocyte Glycoprotein (MOG) Antibody Associated Disease (MOGAD) is an emerging disorder recognized as a clinical entity distinct from Multiple Sclerosis and Aquaporin-4-positive Neuromyelitis Optica Spectrum Disorders (NMOSD-AQP4+), and its phenotypic spectrum continues to expand. Most information about its clinical course has emerged from retrospective studies, and treatment response both in acute and chronic-relapsing disease is still limited. We aimed to describe the clinical and paraclinical characteristics of monophasic and relapsing, paediatric and adult patients with MOGAD under regular clinical care in Chile, highlighting some challenging cases that are far from being considered benign.Observational, retrospective, and prospective longitudinal multicentre study including patients with positive serum MOG-IgG assessed by cell-based assay.We include 35 patients, 71% women, median age at onset 30 years (range 1-68), 23% had paediatric onset, with a median disease-duration 24 months (range 12-348). In the whole cohort, the most frequent symptoms at onset were isolated optic neuritis (ON) (34%) and myelitis (22%). Encephalitis with seizures or encephalomyelitis was the most common presentation in paediatric-onset patients 75% (n = 6), compared to 11% (n = 3) of the adult-onset patients (p < 0.001). A relapsing course was observed in 34%, these patients were younger (25 vs. 34 years, p = 0.004) and with a longer disease duration (64 vs. 6 months, p = 0.004) compared to monophasic patients. Two patients developed encephalitis with seizures/status epilepticus, with concomitant positive CSF anti-NMDAR-IgG. Chronic immunotherapy was ever prescribed in 77%, the most frequent was rituximab (35%). Relapses under chronic immunotherapy occurred in 5/27 patients (18.5%), two of them under rituximab, one paediatric patient who started combined therapy with monthly IVIG and one adult patient that switched to satralizumab plus mycophenolate. The median EDSS at the last follow-up was 1.5 (range 0-6.0).In Chile, patients with MOGAD exhibit a wide spectrum of clinical presentations at disease onset and during relapses. Close monitoring is needed, particularly in younger patients with short follow-up periods.