Psoriatic arthritis is a type of arthritis that often occurs with psoriasis of the skin. Psoriasis is a common, chronic skin condition that causes red patches on the body. About 1 in 20 people with psoriasis will develop arthritis with the skin condition. In most cases, psoriasis comes before the arthritis. The cause of psoriatic arthritis is not known, but genes may play a role. The arthritis may be mild and involve only a few joints, especially those at the end of the fingers or toes. In some people the disease may be severe and affect many joints, including the spine. When the spine is affected, the symptoms are stiffness, burning, and pain, most often in the lower spine and sacrum. People who also have arthritis usually have the skin and nail changes of psoriasis. Often, the skin gets worse at the same time as the arthritis. Polyarticular psoriatic arthritis distinguished from rheumatoid arthritis by presence of dactylitis and absence of anti-cyclic citrullinated peptide antibodies.