Psoriatic arthritis update.

Psoriatic arthritis is an inflammatory arthritis occurring in up to 30% of patients with psoriasis. Its clear distinction from rheumatoid arthritis has been described clinically, genetically, and immunohistologically. Updated classification criteria have been recently derived from a large international study. Key pathophysiologic cellular processes are being elucidated, increasing our understanding of potential targets of therapy. Therapies that target cells, such as activated T cells, and proinflammatory cytokines, such as tumor necrosis factor alpha (TNFalpha), are rational to pursue. Outcome measures have been "borrowed" from rheumatoid arthritis and psoriasis studies. A variety of domains are assessed including joints, skin, enthesium, dactylitis, spine, function, quality of life, and imaging assessment of disease activity and damage. The performance qualities of outcome measures in these various domains is being evaluated by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA), and improved measures are being developed and validated specifically for psoriatic arthritis. Traditional therapies for psoriatic arthritis have included nonsteroidal anti-inflammatory agents, oral immunomodulatory drugs, topical creams, and light therapy. These therapies have been helpful in controlling both musculoskeletal and dermatologic aspects of the disease, but they may not be fully effective in all disease domains, may eventually show diminished benefit, and may produce treatment-limiting toxicities. In the past several years, use of biologic agents has generally yielded greater benefit across more domains, yielding significant and enduring benefits for clinical manifestations, function, and quality of life, and especially with the anti-TNF agents, inhibition of structural damage. Adverse effects with these agents can be significant but are usually manageable. Cost is also significant, but cost-effectiveness analysis is demonstrating reasonable trade-off between cost and benefit.