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NMO in a Caucasian population. A population-based study

Background: Epidemiological studies have identified ethnicity-based prevalence differences of NMO which is considered to be rare in Caucasians. However, little is actually known about NMO in Caucasians and NMO may be misdiagnosed. Aims: The aim of the study was to estimate the prevalence of NMO in the Region of Southern Denmark and to perform a clinical characterization of the NMO patients. Patients: Clinical data from patients with multiple sclerosis (MS), optic neuritis (ON), and acute transverse myelitis (ATM) diagnosed January 1, 1998-December 31, 2008 were obtained from the seven departments of Neurology and Ophthalmology in The Region of Southern Denmark. The patient material was cross-checked with information from The National Patient Registry. Additional information was provided from all patients in the region treated with biological therapy (Natalizumab). Study design: Patient files were evaluated and the included patients were invited to participate in the study including a web-based questionnaire, clinical examination and blood sampling. MRI studies in all patients were re-evaluated. Unclear cases were supplemented with MRI or other diagnostic measures. A web-based database with demographic, clinical, imaging, and laboratory data was established. The study included patients with one or more episodes of ON and/or TM and with initial brain MRI that did not meet diagnostic criteria for MS at disease onset. Diagnosis: The diagnosis was established by a neurologist based on the Wingerchuk et al 2006 criteria. Laboratory methods: IgG AQP4 antibodies were measured with a recombinant immunofluorescence assay using HEK293 cells transfected with recombinant human full-length AQP4. Patient sera were screened at a 1:10 dilution. Results: A total of 467 patients were evaluated and 240 were included in the study. At present 71 patients (26 MS, 27 ON and 18 ATM) have been finally investigated for NMO-diagnosis and for 169 the studies are in progress. Of the 71 patients 14 fulfilled the criteria for NMO, of these 9 had definitive NMO, all from the MS group, 5 had the limited form of NMO, 4 from the ATM and 1 from the ON group. A total of 10 patient sera were AQP4 antibody positive. Conclusions: The prevalence of NMO in a sample of 71 patients with MS, ATM and ON is 14/71 = 19.72% (95% CI 11.22-30.87). This preliminary study indicates that NMO is an under diagnosed disease in a predominantly Caucasian (99, 8 %) patient population.

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