title: Environmental risk factors for the development of psoriatic arthritis: results from a case-control study.
abstract: OBJECTIVE
  To identify potential risk factors for the onset of inflammatory arthritis (IA) in a large cohort of patients with psoriatic arthritis (PsA) of recent onset.
  
  
  METHODS
  We recruited cases with psoriasis and an onset of IA within the past 5 years. Controls were patients who had psoriasis but no arthritis. We assessed potential factors associated with the development of IA using a detailed postal questionnaire. An unmatched analysis adjusted for age and gender was performed. Exposure was censored in the controls at a "dummy-date" assigned randomly in proportion to the percentage of cases developing IA in any given year.
  
  
  RESULTS
  We studied 98 cases and 163 controls. Exposures showing a positive association before the onset of IA in patients with psoriasis were: rubella vaccination (OR (95% CI) = 12.4 (1.2 to 122)), injury sufficient to require a medical consultation (2.53 (1.1 to 6.0)), recurrent oral ulcers (4.2 (2.0 to 9.0)) and moving house (2.3 (1.2 to 4.4)). Cases were also more likely to have experienced a fractured bone requiring hospital admission (50% vs 9%, p = 0.040).
  
  
  CONCLUSIONS
  We found a number of environmental exposures associated with the onset of IA in subjects with psoriasis. The strongest associations were with trauma thereby adding to the hypothesis of a "deep Koebner phenomenon" in PsA. Our data also suggest that exposure of the immune system to certain infection-related triggers may also be of relevance. Further studies are needed to verify these observations and to examine potential immunological mechanisms that underlie them.
authors.affiliation: Epidemiology Unit, School of Translational Medicine, The University of Manchester, Manchester, UK.
authors.forename: E
authors.initials: E
authors.lastname: Pattison
authors.forename: B J
authors.initials: BJ
authors.lastname: Harrison
authors.forename: C E M
authors.initials: CE
authors.lastname: Griffiths
authors.forename: A J
authors.initials: AJ
authors.lastname: Silman
authors.forename: I N
authors.initials: IN
authors.lastname: Bruce
mesh_terms: D000328:Adult; D017668:Age of Onset; D015535:Arthritis, Psoriatic / Q000209:etiology* / Q000523:psychology; D016918:Arthritis, Reactive / Q000209:etiology / Q000523:psychology; D001424:Bacterial Infections / Q000150:complications; D016022:Case-Control Studies; D005260:Female; D050723:Fractures, Bone / Q000150:complications; D006801:Humans; D007114:Immunization; D008016:Life Change Events; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D019226:Oral Ulcer / Q000150:complications; D011247:Pregnancy; D011565:Psoriasis / Q000150:complications / Q000523:psychology; D012189:Retrospective Studies; D012307:Risk Factors; D012411:Rubella Vaccine / Q000008:administration & dosage