title: The prevalence of clinically diagnosed ankylosing spondylitis and its clinical manifestations: a nationwide register study.
abstract: BACKGROUND
  Prevalence estimates of ankylosing spondylitis vary considerably, and there are few nationwide estimates. The present study aimed to describe the national prevalence of clinically diagnosed ankylosing spondylitis in Sweden, stratified according to age, sex, geographical, and socio-economic factors, and according to subgroups with ankylosing spondylitis-related clinical manifestations and pharmacological treatment.
  
  
  METHODS
  All individuals diagnosed with ankylosing spondylitis according to the World Health Organization International Classification of Disease codes, between 1967 and 2009, were identified from the National Patient Register. Data regarding disease manifestations, patient demographics, level of education, pharmacological treatment, and geographical region were retrieved from the National Patient Register and other national registers.
  
  
  RESULTS
  A total of 11,030 cases with an ankylosing spondylitis diagnosis (alive, living in Sweden, and 16 to 64 years old in December 2009) were identified in the National Patient Register, giving a point prevalence of 0.18% in 2009. The prevalence was higher in northern Sweden, and lower in those with a higher level of education. Men had a higher prevalence of ankylosing spondylitis (0.23% versus 0.14%, P < 0.001), a higher frequency of anterior uveitis (25.5% versus 20.0%, P < 0.001) and were more likely to receive tumor necrosis factor inhibitors than women (15.6% versus 11.8% in 2009, P < 0.001). Women were more likely than men to have peripheral arthritis (21.7% versus 15.3%, P < 0.001), psoriasis (8.0% versus 6.9%, P = 0.03), and treatment with oral corticosteroids (14.0% versus 10.4% in 2009, P < 0.001).
  
  
  CONCLUSIONS
  This nationwide, register-based study demonstrated a prevalence of clinically diagnosed ankylosing spondylitis of 0.18%. It revealed phenotypical and treatment differences between the sexes, as well as geographical and socio-economic differences in disease prevalence.
authors.affiliation: Rheumatology, Department of Clinical Sciences, Malmö, Lund University, Inga Marie Nilssons gata 32, 205 02, Malmö, Sweden. sofiaexar@hotmail.com.
authors.forename: Sofia
authors.initials: S
authors.lastname: Exarchou
authors.affiliation: Department of Rheumatology and Inflammation Research, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden. ulf.lindstrom@vgregion.se.
authors.forename: Ulf
authors.initials: U
authors.lastname: Lindström
authors.affiliation: Clinical Epidemiology Unit & Rheumatology Unit, Department of Medicine Solna, Karolinska Institute, Stockholm, Sweden. Johan.Askling@ki.se.
authors.forename: Johan
authors.initials: J
authors.lastname: Askling
authors.affiliation: Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institute, Stockholm, Sweden. jonas.eriksson@ki.se.
authors.forename: Jonas K
authors.initials: JK
authors.lastname: Eriksson
authors.affiliation: Department of Rheumatology and Inflammation Research, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden. helena.forsblad@rheuma.gu.se.
authors.forename: Helena
authors.initials: H
authors.lastname: Forsblad-d'Elia
authors.affiliation: Clinical Epidemiology Unit, Department of Medicine Solna, Karolinska Institute, Stockholm, Sweden. Martin.Neovius@ki.se.
authors.forename: Martin
authors.initials: M
authors.lastname: Neovius
authors.affiliation: Rheumatology, Department of Clinical Sciences, Malmö, Lund University, Inga Marie Nilssons gata 32, 205 02, Malmö, Sweden. carl.turesson@med.lu.se.
authors.forename: Carl
authors.initials: C
authors.lastname: Turesson
authors.affiliation: Rheumatology, Department of Clinical Sciences, Malmö, Lund University, Inga Marie Nilssons gata 32, 205 02, Malmö, Sweden. larserik_kristensen@yahoo.com.|The Parker Institute, Department of Rheumatology, Bispebjerg and Frederiksberg Hospital, the Capital Region of Copenhagen, Copenhagen, Denmark. larserik_kristensen@yahoo.com.
authors.forename: Lars Erik
authors.initials: LE
authors.lastname: Kristensen
authors.affiliation: Department of Rheumatology and Inflammation Research, Sahlgrenska Academy at University of Gothenburg, Gothenburg, Sweden. lennart.jacobsson@gu.se.
authors.forename: Lennart T H
authors.initials: LT
authors.lastname: Jacobsson
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000627:therapeutic use*; D061067:Antibodies, Monoclonal, Humanized / Q000627:therapeutic use*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011379:Prognosis; D012042:Registries; D018570:Risk Assessment; D012720:Severity of Illness Index; D017678:Sex Distribution; D013167:Spondylitis, Ankylosing / Q000175:diagnosis* / Q000188:drug therapy / Q000453:epidemiology*; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000894:Anti-Inflammatory Agents, Non-Steroidal; D061067:Antibodies, Monoclonal, Humanized