title: Does the change in season affect disease activity in patients with psoriatic arthritis?
abstract: OBJECTIVE
  To determine whether there is seasonal variation in disease activity of patients with psoriatic arthritis (PsA).
  
  
  METHODS
  The authors identified the first available set of consecutive summer and winter visits for every patient from the prospective cohort of PsA. Comparison between summer and winter visits, and comparison of the repeated summer/winter visits, from 1978 until 2011 for the same identified patients was conducted for demographics, disease activity outcomes, laboratory results and treatment. The authors categorised disease activity into high, moderate and low states, and improvement versus flare/worsening. Descriptive statistics were computed and multivariate analyses using logistic regression and generalised estimating equations were conducted.
  
  
  RESULTS
  The first available summer and winter visit were identified for 253 patients, and 1789 observations were analysed. There was no statistically significant difference in patients' demographics, disease activity outcomes, laboratory results and treatment between summer and winter visits. Bath Ankylosing Spondylitis Disease Activity Index scores were greater for summer visits and patients graded their disease as being worse in winter as compared with summer in the univariate analysis, but this difference did not hold in the multivariate analysis.
  
  
  CONCLUSIONS
  The change in season does not affect PsA patients' characteristics and disease activity outcomes as determined by the physicians and patients.
authors.affiliation: Psoriatic Arthritis Clinic, Centre for Prognostic Studies in the Rheumatic Diseases, Toronto Western Hospital, University of Toronto, Toronto Western Research Institute, Toronto, Canada.
authors.forename: Zahi
authors.initials: Z
authors.lastname: Touma
authors.forename: Arane
authors.initials: A
authors.lastname: Thavaneswaran
authors.forename: Vinod
authors.initials: V
authors.lastname: Chandran
authors.forename: Dafna D
authors.initials: DD
authors.lastname: Gladman
mesh_terms: D000328:Adult; D018771:Arthralgia / Q000175:diagnosis* / Q000503:physiopathology; D015535:Arthritis, Psoriatic / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D004185:Disability Evaluation; D005260:Female; D006304:Health Status; D006801:Humans; D007596:Joints / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D020127:Recovery of Function; D012189:Retrospective Studies; D012621:Seasons; D012720:Severity of Illness Index; D016896:Treatment Outcome