AQP4 and multiple sclerosis: Because the expected visual prognosis is generally worse in AQP4‐IgG‐positive NMOSD than in other multiple sclerosis and related disorders (Akaishi et al., 2016; Srikajon et al., 2018), active acute treatments with or without adjunctive plasma exchange are required in patients with ON related to AQP4‐IgG.