Definition of Psoriatic arthritis:

Psoriatic arthritis is an arthritis that is often associated with psoriasis of the skin.

Causes, incidence, and risk factors:

Psoriasis is a common, chronic skin condition that causes red patches on the body. About 1 in 20 individuals with psoriasis will develop arthritis along with the skin condition. In the majority of cases, psoriasis comes before the arthritis.

The arthritis may be generally mild and involve only a few joints. In a few people, the disease may be severe and affect many joints, including the spine. When the spine is affected, the symptoms are very much like those of ankylosing spondylitis.

The cause of psoriatic arthritis is not known, but your genes may play a role. In general, people who have psoriasis have a higher rate of arthritis than the general population.