Systematic review of treatments for psoriatic arthritis: an evidence based approach and basis for treatment guidelines.

Psoriatic arthritis (PsA) is a chronic systemic inflammatory disorder characterized by the association of arthritis and psoriasis. In addition to a heterogeneous and variable clinical course, PsA is complex and multifaceted and may include prominent involvement in the peripheral and axial diarthrodial joints, the skin and nails, and in periarticular structures such as entheses. A central mission of the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) is to develop guidelines, based upon the best scientific evidence, for the optimal treatment of patients with PsA. We outline the specific methods and procedures used in this evidence-based, systematic review of treatments for PsA, which we hope will provide a basis for future treatment guidelines.