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

Abstract

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. 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 <10 normal. Brain magnetic resonance imaging (MRI) was performed for all patients. Of the 300 patients with suspected ON, 191 were eventually diagnosed as ON, and 66 (35%) of them had a previous diagnosis or were diagnosed with multiple sclerosis (MS). Of the 125 patients without MS diagnosis, 62 (50%) had demyelinative lesions in MRI, which is a risk factor for developing MS. Two patients (1.1%; 95% CI 0.3-4.5) fulfilled the criteria of NMO. Positive AQP4 antibodies were found in three patients (1.6% 95% CI 0.3-4.5), one of them had NMO, one had MS and one became diagnosed with MS a month later. Borderline autoantibody levels were found in 10 patients, 7 of whom had MS. NMO is rare among ON patients in the population of Southern Finland. In this small cohort, the sensitivity and positive predictive values of the AQP4 autoantibody index for NMO were low, 1/2 and 1/3 respectively, and do not support initiating routine screening.