Aquaporin‐4 Antibody Dynamics and Relapse Risk in Seropositive Neuromyelitis Optica Spectrum Disorder Treated with Immunosuppressants

Objective To investigate aquaporin‐4 antibody (AQP4‐IgG) dynamics and relapse risk in patients with seropositive neuromyelitis optica spectrum disorder treated with immunosuppressants. Methods This observational cohort study with prospectively collected data included 400 neuromyelitis optica spectrum disorder patients seropositive for AQP4‐IgG and treated with immunosuppressants. Serum AQP4‐IgG was detected by fixed cell‐based assay every 6 months. Results After treatment with immunosuppressants, 128 patients became AQP4‐IgG seronegative. The median time to become seronegative for 400 patients was 76.4 months (61.4 months, NA). Among those patients with negative change of AQP4‐IgG, the mean annualized relapse rate significantly decreased after patients became seronegative (0.20 vs 0.77, p < 0.001), and a positive correlation was observed between time to become seronegative and relapse (OR 1.018, 95% CI 1.001–1.035, p < 0.05). Independent risk factors for AQP4‐IgG becoming seronegative were older age at onset, initiation of immunosuppressants at onset, and shorter disease duration before maintenance therapy. Independent risk factors for relapse included younger age (≤46.4 years) at onset, poly‐system involvement in the first attack, and unchanged or increased AQP4‐IgG titer. The relapse risk was not associated with sex, combination with connective tissue disease, seropositivity for systemic autoimmune antibodies, or incomplete recovery from the first attack. Interpretation Patients with younger age at onset, poly‐system involvement in the first attack, and unchanged or increased titer of AQP4‐IgG are most likely to experience relapse under treatment with immunosuppressants. Time to AQP4‐IgG becoming seronegative and change of AQP4‐IgG titer may become the surrogate efficacy biomarkers in clinical trials. ANN NEUROL 2023;93:1069–1081