Psoriatic arthritis: from a dermatological perspective.

Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy associated with psoriasis, and included among the seronegative spondyloarthropathies. The presence of cutaneous psoriasis is very important for correct and early diagnosis of PsA, because the cutaneous lesions precede the appearance of joint manifestations. Thus, dermatologists are in a position to detect the condition at its inception. PsA is clinically subdivided into asymmetric oligoarticular arthritis, symmetric polyarthritis, distal interphalanges predominant, arthritis mutilans, and spondylitis types. PsA has several unique characteristics, such as enthesopathy, dactylitis and abnormal bone remodeling. Genetic, environmental, and immunological factors are important in its development. The triggering role of physical stress is seen in the "deep Koebner" phenomenon, which causes inflammation in the synovial membrane and in enthesis, resulting in peripheral arthritis. Cellular infiltrates such as activated T-cells and macrophages are thought to play important roles in the induction of inflammatory and destructive processes in joint tissues, as well as psoriatic skin. New ideas regarding the involvement of the IL-23/Th17 axis have emerged, and the dramatic effects of targeting therapies have highlighted the physiological role of key cytokines in psoriasis. Current views on the pathogenesis of PsA are reviewed from a dermatological perspective.