Incidence of neuromyelitis optica spectrum disorder in the Central Denmark Region

Objectives Neuromyelitis optica (NMO)/NMO spectrum disorder (NMOSD) may be misdiagnosed as multiple sclerosis. The aim of this study was to (i) to measure AQP4-IgG in patients who fulfilled the clinical and radiological criteria of NMOSD in the Central Denmark Region and (ii) to estimate the incidence of NMOSD in the region, according to both the 2006 Wingerchuk criteria and the 2015 International Panel for NMO Diagnosis criteria. Materials and methods Medical records of all patients diagnosed with a demyelinating disorder in the region from 1 January 2012 to 31 December 2013 were reviewed. Patients were classified as having (i) "NMO" if the 2006 criteria were met, (ii) "NMOSD with AQP4-IgG" or (iii) "NMOSD without/unknown AQP-IgG" if the new 2015 NMOSD criteria were met. Patients with core symptoms were invited to provide a blood sample for AQP4-IgG analysis with an enzyme-linked immunosorbent assay and a cell-based indirect immunofluorescence assay. Results In 191 patients with core symptoms, one met the 2015 NMOSD with AQP4-IgG criteria. Two patients met the 2006 NMO and 2015 NMOSD without/unknown AQP4-IgG criteria. Among 108 patients providing a blood sample, all were seronegative. The estimated incidence of NMO (2006 criteria) and NMOSD (2015 criteria) was 0.08 and 0.12 per 100 000 person-years, respectively. Conclusion NMO/NMOSD is a rare disease in the Central Denmark Region, with a considerably lower incidence rate than previously estimated in a neighbouring region.