<![CDATA[Background: Optic neuritis in aquaporin-4 immunoglobulin G (AQP4-IgG)-positive neuromyelitis optica spectrum disorder (NMOSD) is severe and frequently corticosteroid-refractory. Plasma exchange is recommended within days of onset, and the evidence that later treatment still helps is thin. Whether an attack first treated a month after onset can still recover fully is unresolved. Objective: To describe the visual and structural recovery that followed therapeutic plasma exchange begun 29 days after onset — far outside the recommended window — in a corticosteroid-refractory aquaporin-4-IgG-positive optic neuritis attack, and to audit the record against the quantified determinants of outcome. Case presentation: A 34-year-old woman with systemic lupus erythematosus, antiphospholipid syndrome and AQP4-IgG seropositivity documented one month earlier presented 24 days after the onset of painful visual loss in the right eye. Best-corrected visual acuity was 3/60 and the Ishihara score 0 of 25. No relative afferent pupillary defect was demonstrable in the affected eye, because the fellow eye, atrophic since an attack 11 years earlier, showed the defect instead. A full Optic Neuritis Treatment Trial course of intravenous methylprednisolone, from day 24 to day 27, produced no measurable change. Plasma exchange was started on day 29; acuity reached 6/60 on day 33 and 6/6 on day 35, and the Ishihara score rose to 5 of 25 by day 40 without any procedure-related adverse event. At day 53 the peripapillary retinal nerve fibre layer measured 91 micrometres in the treated eye against 41 in the fellow eye. Conclusion: Complete recovery of high-contrast acuity followed plasma exchange begun 29 days after onset, far outside the recommended window, while colour vision recovered only partially. A chronically damaged fellow eye can abolish the relative afferent pupillary defect in an acutely inflamed eye, and the attack occurred on azathioprine in a patient already known to be seropositive.]]>
