DEFINITION

PsA is a chronic inflammatory arthritis that affects up to 30% of persons with psoriasis. HLA-B27 is found in 50–70% with axial disease but <20% of pts with only peripheral involvement. Onset of psoriasis usually precedes development of joint disease; approximately 15–20% of pts develop arthritis prior to onset of skin disease. Nail changes occur in most pts with PsA, dactylitis and enthesitis are common in PsA and help to distinguish it from other joint disorders.