title: Neuromyelitis optica and aquaporin-4 (AQP4) autoantibodies in consecutive optic neuritis patients in Southern Finland.
abstract: OBJECTIVE
  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 <10 normal. Brain magnetic resonance imaging (MRI) was performed for all patients.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Ophthalmology, Helsinki University Central Hospital and University of Helsinki, Helsinki, FinlandDepartment of Neurology, Helsinki University Central Hospital and University of Helsinki, Helsinki, FinlandMolecular Neurology Programme, Research Program Unit, Biomedicum, University of Helsinki, Helsinki, FinlandDepartment of Virology and Immunology, HUSLAB, Helsinki University Central Hospital, Helsinki, FinlandDepartment of Bacteriology and Immunology, Haartman Institute, University of Helsinki, Helsinki, Finland.
authors.forename: Mika
authors.initials: M
authors.lastname: Siuko
authors.forename: Pentti J
authors.initials: PJ
authors.lastname: Tienari
authors.forename: Kari-Pekka
authors.initials: KP
authors.lastname: Saastamoinen
authors.forename: Sari
authors.initials: S
authors.lastname: Atula
authors.forename: Aaro
authors.initials: A
authors.lastname: Miettinen
authors.forename: Tero
authors.initials: T
authors.lastname: Kivelä
authors.forename: Kirsi
authors.initials: K
authors.lastname: Setälä
mesh_terms: D000293:Adolescent; D000328:Adult; D051401:Aquaporin 4 / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009471:Neuromyelitis Optica / Q000175:diagnosis* / Q000453:epidemiology / Q000276:immunology; D009902:Optic Neuritis / Q000175:diagnosis* / Q000453:epidemiology / Q000276:immunology; D015531:Radioimmunoprecipitation Assay; D055815:Young Adult
chemical_list: D051401:Aquaporin 4; D001323:Autoantibodies; D001324:Autoantigens
keywords: aquaporin-4 autoantibody; autoimmune optic neuropathy; multiple sclerosis; neuromyelitis optica; optic neuritis