INTRODUCTION
Psoriatic arthritis (PsA) is a seronegative spondyloarthropathy
characterized by musculoskeletal signs and symptoms (arthritis, enthesitis, spondylitis) with associated
joint pain and tenderness.1 It affects an estimated 0.3% to 1.0% of the general population,2 and is a common comorbidity in patients with psoriasis, in whom its prevalence is estimated at 30% (ranging from 18% to 42%, depending on geographic region).
3 For psoriasis patients the presence of PsA is associated with increased work-related problems, a substantial disability burden, and potentially reduced survival.4-7 The presence of PsA may also make the selection of treatment for psoriasis patients
more challenging8 and many patients continue to experience significant symptoms and impairment of physical function despite
available treatments.9
Interleukin (IL)-17A, the primary effector cytokine of the Th17 class of T-helper cells, has been implicated in the pathogenesis and chronic inflammation of psoriatic disease, with similar inflammatory
cells affecting both skin and joints.10,11 Th17 levels are increased in the circulation of plaque psoriasis and PsA patients, in the skin of plaque psoriasis patients, and in the synovial fluid of PsA patients.12-15 Other potential cellular sources of IL-17A,