In the past decade, the therapeutic arsenal for multiple sclerosis has expanded greatly. Newer more potent disease modifying therapies (DMTs) with varying mechanisms of actions are increasingly used early in the disease course. These newer DMTs include oral therapies (teriflunomide, dimethyl fumarate, fingolimod, siponimod, ozanimod, and cladribine) and infusion therapies (natalizumab, alemtuzumab, and ocrelizumab), and are associated with better control of disease activity and long-term outcomes in patients with MS compared to older injectable therapies (interferon beta and glatiramer acetate). However, they are associated with safety concerns and subsequent monitoring requirements. Adverse events are initially observed in phase 2 and 3 clinical trials, and further long-term data are collected in phase 3 extension studies, case series, and post-marketing reports, which highlight the need to periodically re-evaluate and adjust monitoring strategies to optimize treatment safety in an individualized approach.

Optic neuropathy secondary to Cystic Fibrosis (CF) has been described as a manifestation of chloramphenicol toxicity. Inflammatory optic neuritis and Myelin Oligodendrocyte Glycoprotein (MOG)-related disorders have not been previously described in patients with CF. We report the case of a 19-year-old woman with cystic fibrosis who presented for sub-acute onset decreased visual acuity, dyschromatopsia, and optic disk swelling in both eyes, with near-complete resolution after a course of high-dose corticosteroids. MOG-IgG were positive in the serum. MOG-related optic neuritis can occur in CF and represent a diagnostic and long-term therapeutic challenge. Keywords: Optic neuritis; MOG; cystic fibrosis.