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

•In this prospective monocentric study, among 108 adult 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, respectively.•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 different between the four groups.•No significant difference in visual acuity nor inner retinal layer thickness was found between the different ON aetiologies. 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 tomography (OCT), CSF analysis, and MRI imaging may help to discriminate the different causes of acute ON in a real-life cohort. In this prospective monocentric study, adult patients with recent acute ON (