Psoriatic arthritis

Psoriatic arthritis (PsA) is a distinctive category of inflammatory arthritis that complicates cutaneous psoriasis. The prevalence of PsA in the general population is estimated to be between 0.3% and 1%, only slightly less common than that of rheumatoid arthritis (RA). PsA is one of the "seronegative spondyloarthropa-thies", along with ankylosing spondylitis (AS), reactive arthritis, and the arthropathy of inflammatory bowel disease. As a seronegative disorder, PsA is not associated with autoantibodies such as rheumatoid factor or antibodies to cyclic citrullinated peptides. A variety of clinical patterns of PsA are recognized: distal joint disease, oligoarthritis, a symmetrical polyarthritis that resembles RA, and spondylitis. Some patients present with combinations of these features: e.g., oligoarthritis plus spondylitis. These clinical patterns are not necessarily stable over time. For example, distal joint disease can evolve into polyarthritis. The most common pattern of joint involvement at presentation is an asymmetric oligoarthritis. This pattern accounts for about 70% of PsA cases.