The future of treatment for psoriatic arthritis

Psoriatic arthritis (PsA) is a chronic inflammatory musculoskeletal disease associated with psoriasis, and leads to progressive joint damage and disability. It is estimated that approximately 30% of patients with psoriasis have PsA [1]. PsA is classically described as a seronegative spondylo arthropathy with both peripheral and/ or axial arthritis; however, other significant musculoskeletal manifestations include enthesitis and dactylitis, which can also cause marked functional impairment. Treatment of PsA has advanced significantly in the last two decades, particularly with regard to biologically targeted treatments, such as the TNF inhibitors (TNFi). However, treatment regimens used in PsA have tended to follow those initially applied to rheumatoid arthritis (RA). This may be explained by the fact that peripheral arthritis in PsA has similar clinical characteristics to RA. Furthermore, the incidence and prevalence of RA may be significantly greater than that of PsA, and recruitment for clinical trials is less onerous as a result. While there are commonalities in the immunopathogenesis of both forms of arthritis, there are many genetic, immunologic and phenotypic differences, including gender distribution and extra-articular manifestations. Therefore, the practice of extrapolation and application of results from RA-focused clinical trials to the treatment of patients with PsA is not scientifically robust. To address these deficiencies, an international group of rheumatologists and dermatologists with a special interest in psoriatic disease, the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA), has been established. GRAPPA has been instrumental in directing the psoriatic disease-specific agenda and its work has influenced much of the content of this piece. This article examines current knowledge regarding treatment of PsA and has identified how this content can influence future treatment-specific research questions. The authors have also presented a summary of the evidence surrounding the efficacy of many of the newer psoriatic medications, including those that have been recently licensed for clinical use and those undergoing clinical trial.