Acute idiopathic optic neuritis: not always benign

Background and purpose Few recent data are available concerning idiopathic optic neuritis ( ON ). We aimed to describe a large cohort of patients with idiopathic ON . We compared this cohort with patients with ON related to myelin oligodendrocyte glycoprotein ( MOG ) or ON related to aquaporin‐4 ( AQP 4) antibodies. Methods This was a monocentric retrospective observational study. Inclusion criteria for idiopathic ON were as follows: age ≥ 16 years, follow‐up of at least 2 years, negative for antibodies against MOG and AQP 4 immunoglobulin G, and no magnetic resonance imaging ( MRI ) lesions suggestive of demyelination (two brain MRI scans, one at baseline and one during follow‐up, and one spinal cord MRI scan). Results Among 23 patients with idiopathic ON (female, 82.6%; median age, 36 years; median follow‐up time, 41.4 months), 56.5% had recurrent ON (median time to a second ON episode, 6 months). The final visual acuity in this group (median, 0; mean, 0.43; range, 0–3) was similar to that in the AQP 4 group ( n = 18; P ‐value after Bonferroni correction = 0.936) but worse than that in the MOG group ( n = 25; P ‐value after Bonferroni correction = 0.019). At the last evaluation, visual acuity levels were ≤0.5 and <0.2, respectively, in 36.8% and 21% of the idiopathic ON group, 58.3% and 26.7% of the AQP 4 group, and 0% and 0% of the MOG group. Conclusion The recovery of visual acuity among patients with idiopathic ON was poor, similar to that observed in the AQP 4 group.