Psoriatic arthritis is a spondyloarthritis and a form of joint inflammation that occurs in some people who have psoriasis of the skin or nails.
Psoriatic arthritis is a type of spondyloarthritis (see Spondyloarthritis).
Psoriatic arthritis resembles rheumatoid arthritis but does not produce the antibodies characteristic of rheumatoid arthritis. Psoriatic arthritis occurs in about 5 to 40% of people with psoriasis (a skin condition causing flare-ups of red, scaly rashes and thickened, pitted nails—see see Psoriasis). People with a certain gene (HLA-B27) and those who have affected family members are at increased risk of psoriatic arthritis. The cause of psoriatic arthritis is unknown.
Symptoms and Diagnosis
Inflammation often affects joints closest to the tips of the fingers and toes, although other joints, including the hips, knees, and spine, are often affected as well. Often the joints of the upper extremities are affected more. Back pain may be present. The joints may become swollen and deformed when inflammation is chronic. Psoriatic arthritis affects joints asymmetrically (more on one side of the body than the other), more so than rheumatoid arthritis, and involves fewer joints. The psoriasis rash may appear before or after arthritis develops. Sometimes the rash is not noticed because it is hidden in the scalp, navel, or creases of the skin such as between the back of the buttocks and thigh. The skin and joint symptoms sometimes appear and disappear together.
The diagnosis is made by identifying the characteristic joint inflammation in a person who has arthritis and psoriasis. Doctors also ask people whether they have a family history of psoriasis. There are no tests to confirm the diagnosis, but blood tests for rheumatoid factor are done to exclude rheumatoid arthritis and x-rays are done to show the extent of joint damage.
Prognosis and Treatment
The prognosis for psoriatic arthritis is usually better than that for rheumatoid arthritis because fewer joints are affected. Nonetheless, the joints can be severely damaged.
Treatment is aimed at controlling the skin rash and relieving the joint inflammation. Several drugs that are effective in treating rheumatoid arthritis (see Drugs for Rheumatoid Arthritis) are also used to treat psoriatic arthritis, particularly nonsteroidal anti-inflammatory drugs (NSAIDs), methotrexate, cyclosporine, and tumor necrosis factor (TNF) inhibitors. TNF inhibitors are particularly effective for psoriatic arthritis.
Some people take methoxsalen (psoralen) by mouth and undergo psoralen plus ultraviolet A light treatments (phototherapy). This combination relieves the skin symptoms and most of the joint inflammation but may not help inflammation of the spine.
Last full review/revision May 2013 by Roy D. Altman, MD