Neuromyelitis optica and aquaporin‐4 (AQP4) autoantibodies in consecutive optic neuritis patients in Southern Finland

. Purpose: To analyse the frequency of neuromyelitis optica (NMO) among consecutive optic neuritis (ON) patients in Southern Finland and the feasibility of Aquaporin‐4 (AQP4) autoantibody assay in the diagnosis of NMO. Methods: Consecutive patients with symptoms suggestive of acute ON and managed in the Helsinki University Central Hospital were evaluated critically screened for AQP4 autoantibody during a 47.5‐month period. The antibodies were determined using radioimmunoprecipitation method. AQP4 index >15 was considered positive, 10–15 borderline and