Paradoxical onset of psoriatic arthritis during treatment with biologic agents for plaque psoriasis: a combined dermatology and rheumatology clinical study.

To evaluate the incidence of new cases of psoriatic arthritis (PsA) in patients with plaque psoriasis receiving biologic drugs.A retrospective study was performed on 434 psoriatic patients under biologic treatment, attending the Psoriasis Care Centre of Dermatology at the University Federico II of Naples from January 2011 to November 2015. As part of the routine clinical practice, assessment of disease activity was made at baseline, and every 3 months. PsA diagnosis was performed by a rheumatologist through clinical examination, evaluation of the CASPAR criteria, laboratory and radiological assessment.On the basis of the inclusion and exclusion criteria, we reviewed and analysed the clinical data of 327 patients with plaque psoriasis. The biologic drugs adalimumab, etanercept, infliximab and ustekinumab were prescribed to 116 (35.5%), 88 (27.0%), 27 (8.2%), and 96 (29.3%), respectively. We found that 22 out of 327 patients with plaque psoriasis developed PsA during treatment with biologic drugs. In particular, 6 (27.2%) PsA patients were under etanercept therapy, 10 (45.4%) under adalimumab, 4 (18.2%) under ustekinumab and 2 (9.2%) under infliximab.The results of this study show that in several psoriasis patients, biologic therapy may not be sufficient to prevent the onset of articular involvement. In most of the verified PsA cases, arthritis occurred in concomitance with severe cutaneous involvement.