Risk of osteoarthritis in an incident cohort of people with psoriatic arthritis: a population-based cohort study

Objective. To determine the risk of a diagnosis of osteoarthritis (OA) in patients with psoriatic arthritis (PsA) compared to patients with psoriasis and a general population cohort. Methods. Incident PsA patients aged 18-89 years at diagnosis were identified from the United Kingdom Clinical Practice Research Datalink between 1998 and 2014. All patients with PsA were matched to 2 cohorts of patients, both at a 1:4 ratio. The first cohort included patients with psoriasis (and no PsA) and the second was a general population cohort (with no psoriasis or PsA). The baseline prevalence of OA was calculated for each study cohort. The incidence of OA was calculated, and adjusted relative risks (RRadj) were calculated using conditional Poisson regression. Results. We identified 6783 incident PsA patients. The baseline prevalence of OA ranged from 22.1% (95% CI 21.1-23.1) in the PsA cohort to 12.6% (95% CI 12.2-13.0) and 11.0% (95% CI 10.6-11.3) in the psoriasis and general population cohorts, respectively. The incidence of OA was significantly higher in the PsA cohort compared to the psoriasis and general population cohorts after adjusting for BMI (RRadj 1.68, 95% CI 1.46-1.93, and RRadj 1.86, 95% CI 1.62-2.14, respectively). Conclusion. An increased risk of OA was observed in patients with PsA compared to patients with psoriasis alone and those in the general population. Further work is needed to determine whether this reflects a true increase in OA risk or misdiagnosed PsA, and the extent to which it can be explained by differences in the opportunity for OA diagnosis between cohorts.