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 psoriatic arthritis (PsA) patients compared to patients with psoriasis and a general population cohort.

Methods Incident PsA patients aged 18-89 years at diagnosis were identified from the UK Clinical Practice Research Datalink between 1998 and 2014. All PsA patients were matched to two 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 (RR_adj) were calculated using conditional Poisson regression.

Results We identified 6,783 incident PsA patients. The baseline prevalence of OA ranged from 22.1% (CI₉₅21.1-23.1) in the PsA cohort to 12.6% (CI₉₅12.2-13.0) and 11.0% (CI₉₅10.6- 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 (RR_adj 1.68 CI₉₅1.46-1.93 and RR_adj 1.86 CI₉₅1.62-2.14 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.