Acute optic nerve lesions in first-ever NMOSD-related optic neuritis using conventional brain MRI: A Latin American multicenter study

•Acute optic nerve lesions (P-MRI) were observed frequently using conventional brain MRI•Brain MRI showed unilateral (54.4%) and bilateral (46.6%) lesions•All chiasmatic lesions were associated with unilateral or bilateral lesions.•Typical MRI lesions occurred frequently in the P-MRI subgroup•Poor visual outcome was not independently associated with P-MRI Few studies regarding MRI-defined acute optic nerve lesions (aONL) in patients with first-ever neuromyelitis optica spectrum disorder (NMOSD)-related optic neuritis (ON) have been reported worldwide and none of them was conducted in Latin America (LATAM). Therefore, we aimed to assess the frequency of aONL at disease onset using conventional brain MRI in LATAM. We reviewed the medical records and brain MRIs (≤30 days from ON onset) of patients with ON as first lifetime NMOSD attack. Patients from Argentina (n=48), Ecuador (n=24), Brazil (n=22), Venezuela (n=10) and Mexico (n=8) were included, and further divided into two subgroups according to either presence (P-MRI) or absence (A-MRI) of aONL (T2 hyperintensity and/or contrast enhancement). Clinical, paraclinical, imaging and prognostic data were compared. A total of 112 patients were included and aONL were found in 86 (76.7%) at disease onset. Aquaporin-4 antibodies were detected in 69.6%. Non-Caucasian patients comprised 59.8% of the total cohort. In P-MRI, conventional brain MRI showed isolated or combined unilateral (54.4%, [8.5% of these aONL were associated with chiasmatic lesions]) and bilateral (46.6%, [35.9% of these aONL were associated with chiasmatic lesions]) lesions. Thus, 100% of chiasmatic lesions were associated with unilateral or bilateral lesions. No statistically significant differences were found in age, gender, ethnicity, clinical course, mean follow-up time, disability, and spinal cord MRI findings. However, rituximab use was higher in P-MRI than in A-MRI (p=0.006). More than three quarters of LATAM patients with first-ever NMOSD-related ON have aONL detected by brain MRI. Unilateral lesions were the most common finding. Further studies including different ethnicities are needed to assess the generalizability of our results.