title: Multiple sclerosis in the far north--incidence and prevalence in Nordland County, Norway, 1970-2010.
abstract: BACKGROUND
  The risk of multiple sclerosis (MS) increases with increasing latitude. Taking into consideration that Norway has a large latitude range, a south-to-north gradient would be expected. However, previous studies have reported an uneven distribution of the disease in Norway, with a relatively low prevalence in the most northern parts of the country. We describe the incidence and prevalence of MS in a county in the north of Norway over a period of 40 years.
  
  
  METHODS
  All patients with MS living in Nordland County in the period 1970-2010 were identified by reviewing hospital charts. The patients were included if they met the criteria of definitive or probable MS according to Poser [Ann Neurol 13:227-231, 1983] or MS according to McDonalds [Ann Neurol 50:121-127, 2001]. Point prevalence at the beginning of the decades was calculated. The average annual incidence was calculated for 5-year periods.
  
  
  RESULTS
  The total crude prevalence on January 1, 2010 was 182.4 per 100 000. The annual incidence continuously increased from 0.7 per 100 000 in 1970 - 1974 to 10.1 per 100,000 in 2005 - 2009. The time delay from the first symptom to diagnosis was stable from 1975 to 2010. The proportion of primary progressive MS in the prevalence numbers was 38.2% in 1980, and decreases continuously, to 18.6% in 2010. The female to male prevalence ratio has been stable since 1990 at 2.2 to 1.
  
  
  CONCLUSIONS
  The prevalence and the incidence of MS have steadily increased over a 40 year period. Nordland County is a high-risk area for MS.
authors.affiliation: Department of Neurology, Nordland Hospital Trust, Post box 1480, 8092, Bodø, Norway. espen.benjaminsen@nlsh.no.
authors.forename: Espen
authors.initials: E
authors.lastname: Benjaminsen
authors.affiliation: Nordland Hospital Trust, Vesterålen, Norway. johnny.olavsen@trollfjord.no.
authors.forename: Johnny
authors.initials: J
authors.lastname: Olavsen
authors.affiliation: Department of Neurology, Nordland Hospital Trust, Post box 1480, 8092, Bodø, Norway. merethekarlberg@gmail.com.
authors.forename: Merethe
authors.initials: M
authors.lastname: Karlberg
authors.affiliation: Department of Neurology, Nordland Hospital Trust, Post box 1480, 8092, Bodø, Norway. karl.bjornar.alstadhaug@nlsh.no.|Institute of Clinical Medicine, University of Tromsø, Tromsø, Norway. karl.bjornar.alstadhaug@nlsh.no.
authors.forename: Karl B
authors.initials: KB
authors.lastname: Alstadhaug
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003081:Cold Climate; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000453:epidemiology*; D009664:Norway / Q000453:epidemiology; D015995:Prevalence; D012306:Risk; D055815:Young Adult