Acute optic neuritis: What are the clues to the aetiological diagnosis in real life?

Background: Previous cross-sectional studies have reported distinct clinical and radiological features among the different acute optic neuritis (ON) aetiologies. Nevertheless, these reports often included the same number of patients in each group, not taking into account the disparity in frequencies of ON aetiologies in a real-life setting and thus, it remains unclear what are the truly useful features for distinguishing the different ON causes. To determine whether clinical evaluation, ophthalmological assessment including the optical coherence tomogra-phy (OCT), CSF analysis, and MRI imaging may help to discriminate the different causes of acute ON in a real-life cohort.Methods: In this prospective monocentric study, adult patients with recent acute ON (<1 month) underwent evaluation at baseline and 1 and 12 months, including, high-and low-contrast visual acuity, visual field assessment and OCT measurements, baseline CSF analysis and MRI.Results: Among 108 patients, 71 (65.7%) had multiple sclerosis (MS), 19 (17.6%) had idiopathic ON, 13 (12.0%) and 5 (4.6%) had myelin oligodendrocyte glycoprotein and aquaporin-4 antibodies, at last follow up respec-tively.At baseline, the distribution of bilateral ON, CSF-restricted oligoclonal bands, optic perineuritis, optic nerve length lesions and positive dissemination in space and dissemination in time criteria on MRI were significantly different between the four groups (p <0.001). No significant difference in visual acuity nor inner retinal layer thickness was found between the different ON aetiologies.Conclusions: In this large prospective study, bilateral visual involvement, CSF and MRI results are the most useful clues in distinguishing the different aetiologies of acute ON, whereas ophthalmological assessments including OCT measurements revealed no significant difference between the aetiologies.