title: Incidence and clinical predictors of psoriatic arthritis in patients with psoriasis: a population-based study.
abstract: OBJECTIVE
  To determine the incidence and disease-specific predictors of clinically recognized psoriatic arthritis (PsA) in patients with psoriasis.
  
  
  METHODS
  We identified an incidence cohort of psoriasis subjects age >/=18 years diagnosed between January 1, 1970 and December 31, 1999 in a population-based setting. Psoriasis diagnoses were validated by confirmatory diagnosis in the medical record. Incident and clinically recognized PsA subjects were classified according to the Classification of Psoriatic Arthritis (CASPAR) criteria. Cox proportional hazards models were used to identify predictors of PsA within the psoriasis cohort.
  
  
  RESULTS
  The psoriasis incidence cohort comprised 1,633 subjects. Of these, 40 were diagnosed with PsA concurrently with psoriasis and were excluded from analysis. The remaining 1,593 psoriasis subjects had a mean age of 43 years and 50% were men. Over 20,936 person-years of followup, 57 subjects were clinically recognized with new-onset PsA, with a cumulative incidence of 1.7% (95% confidence interval [95% CI] 1.0-2.3%), 3.1% (95% CI 2.2-4.1%), and 5.1% (95% CI 3.7-6.6%) at 5, 10, and 20 years following psoriasis incidence, respectively. Psoriasis features associated with higher risk of PsA were scalp lesions (hazard ratio [HR] 3.89, 95% CI 2.18-6.94), nail dystrophy (HR 2.93, 95% CI 1.68-5.12), and intergluteal/perianal lesions (HR 2.35, 95% CI 1.32-4.19). Calendar year was not associated with risk of PsA (P = 0.15), indicating that the likelihood of PsA in psoriasis subjects did not change over time.
  
  
  CONCLUSIONS
  In this population-based study, <10% of patients with psoriasis developed clinically recognized PsA during a 30-year period. Psoriasis features associated with a higher likelihood of PsA were nail dystrophy, scalp lesions, and intergluteal/perianal psoriasis.
authors.affiliation: The Mayo Clinic, College of Medicine, Rochester, Minnesota 55905, USA.
authors.forename: Floranne C
authors.initials: FC
authors.lastname: Wilson
authors.forename: Murat
authors.initials: M
authors.lastname: Icen
authors.forename: Cynthia S
authors.initials: CS
authors.lastname: Crowson
authors.forename: Marian T
authors.initials: MT
authors.lastname: McEvoy
authors.forename: Sherine E
authors.initials: SE
authors.lastname: Gabriel
authors.forename: Hilal Maradit
authors.initials: HM
authors.lastname: Kremers
mesh_terms: D000328:Adult; D015535:Arthritis, Psoriatic / Q000150:complications / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D053208:Kaplan-Meier Estimate; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D008910:Minnesota / Q000453:epidemiology; D009260:Nail Diseases; D016016:Proportional Hazards Models; D011565:Psoriasis / Q000150:complications / Q000453:epidemiology; D012189:Retrospective Studies; D012307:Risk Factors; D012536:Scalp Dermatoses