Psoriasis and psoriatic arthritis: clinical features and disease mechanisms.

Psoriasis is a chronic skin disorder affecting approximately 1% to 3% of the world's population. A considerable proportion of patients with psoriasis will develop a form of inflammatory arthritis known as psoriatic arthritis whose prevalence is poorly defined. Significant advances have been made in determining the pathophysiology of both of these diseases, with recent findings strongly implicating T cells and inflammatory cytokines such as tumor necrosis factor alpha in their pathogenesis. There exists an increasing array of therapies to benefit both skin and musculoskeletal manifestations. Newer therapies, such as the biologics, are providing more targeted approaches with potentially fewer systemic toxicities, providing control of disease symptoms and inhibiting progressive joint damage in those with arthritis, as well as improving long-term function and quality of life.