Risk factors for the development of psoriatic arthritis: a population based nested case control study.

OBJECTIVE To identify factors influencing the development of psoriatic arthritis (PsA) in a population-based, inception cohort of psoriasis (PS) patients. METHODS Using the population-based data resources of the Rochester Epidemiology Project. which ensures virtually complete ascertainment of all clinically defined conditions, we previously identified all incident cases of PsA and prevalent cases with PS from 1/1/1982 to 12/21/1991. In this nested case-control study, we assessed potential factors influencing the development of PsA in this cohort using medical record and patient survey information. Each case of PsA was matched with 2 PS controls on age, gender and PS duration/date of onset. Factors influencing the development of PsA were identified, adjusting for the influence of other variables using conditional logistic regression for medical record data and logistic regression for survey data. RESULTS Sixty incident PsA cases were matched with 120 controls with PS. The median age at onset of PS was 31.7 (3.0-78.3) years, and 49% of subjects were male. There were 67% (n = 40) survey responders among cases and 48% (n = 58) among controls. Corticosteroids were used by 10 cases and 6 controls in the 2 years prior to onset of PS through to the development of PsA, and increased the risk of developing PsA (odds ratio 4.33, 95% CI = 1.34-14.02). Pregnancy occurred in 2 cases and 12 controls in the same period, and decreased the risk of developing PsA (odds ratio 0.19, 95% CI = 0.04-0.95). These associations remained significant after adjusting for the influence of gender, age, and duration of psoriasis. CONCLUSION Corticosteroid use and pregnancy, both of which modulate the immune response, may influence the development of PsA in patients with PS.