Objectives To compare the incidence of psoriatic arthritis (PsA) in patients with psoriasis (PsO) according to different treatments for their skin: topics/no treatment, conventional disease-modifying antirheumatic drugs (DMARDs) (cDMARDs) or biological DMARDs (bDMARDs).

Methods Patients with PsO without PsA followed at a university hospital were included in this retrospective cohort study. Patients were classified according to their treatment in topics (topics, phototherapy or no treatment), cDMARDs (methotrexate and cyclosporine) and bDMARDs (tumour necrosis factor inhibitors (TNFi), interleukin 17 inhibitors (IL-17i) and IL-12-23i ((interleukin (IL) 12/IL-23 inhibitor))) groups. Incident cases of PsA were attributed to one treatment if developed during the administration of that treatment. A Cox proportional hazards model was used to evaluate the adjusted risk of PsA development by treatment group.

Results 1719 patients with PsO contributed a total of 14 721 patient/years (py). 1387 (81%) patients were in the topics, 229 (13%) in cDMARDs and 103 (6%) in the bDMARDs group. During follow-up, 239 patients (14%) developed PsA (231 under topics, six under cDMARDs and two under bDMARDs). Global incidence was 1.6 per 100 py. The risk of developing PsA in patients with PsO treated with bDMARDs was significantly lower (incidence rate ratio (IRR)=0.26; 95% CI 0.03 to 0.94; p=0.0111), compared with topics, but not compared with cDMARDs (IRR=0.35; 95% CI 0.035 to 1.96; p=0.1007). Adjusted Cox proportional hazards regression analysis showed that male sex, nail involvement and higher body max index were associated with increased risk of developing PsA, while biologics use was protective (HR: 0.19; 95% CI 0.05 to 0.81).

Conclusion Treatment with biologics in patients with PsO reduced the risk of PsA development.