One-year risk of multiple sclerosis after a first episode of optic neuritis according to modern diagnosis criteria.

Purpose: The last updates to diagnostic criteria for multiple sclerosis (MS) included a diagnostic category of 'possible MS'. However, no recent data is available to assess how much this distinction helps predict MS after isolated optic neuritis (ON). This study aimed to assess the global risk of developing MS one year after a first ON episode, and the specific risk according to the initial diagnosis of isolated ON or ON with possible MS.

Methods: One-year follow-up of a multicentric prospective cohort of adult patients with acute ON.

Results: This study included 55 patients with acute ON of no known etiological diagnosis. Overall, the final diagnosis at one year was MS (23, 42 %), MOGAD (7, 13 %), NMOSD (1, 2 %), CRION (3, 5 %), possible MS (6, 11 %), secondary ON (3, 5 %), and strictly isolated ON (12, 22 %). Three of the 17 (18 %) patients with strictly isolated ON and 2/8 (25 %) with possible MS at baseline progressed to MS. All secondary MS diagnosis were made through radiological monitoring.

Conclusion: One year after the first ON episode, we observed a similar conversion rate to MS for patients with strictly isolated ON and possible MS, with a higher prevalence of MS than found by the ONTT.