What is Psoriatic Arthritis?

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Psoriatic arthritis is a joint disease characterized by both psoriasis and a related form of inflammatory arthritis. Psoriasis is a common skin condition. A person with psoriasis typically has patches of raised, red, scaly skin. The affected skin can look different depending on the type of psoriasis the individual has. Arthritis is joint inflammation. Psoriatic arthritis is a particular type of aggressive and potentially destructive, inflammatory arthritis.
Psoriatic arthritis is an autoimmune disease, meaning that the immune system attacks one’s own tissues. Rarely, a person can have psoriatic arthritis without having obvious psoriasis. Usually, the more severe the skin symptoms are, the greater the likelihood a person will have psoriatic arthritis.
Psoriasis affects a small percentage of white people in North America, and is less common in African-American and Native-American people. Psoriatic arthritis affects approximately 15% of people with psoriasis. Many people who have psoriasis may not know that they have psoriatic arthritis.
Males and females are equally likely to have psoriasis. Of patients with psoriatic arthritis, males are more likely to have the form in which the spine is affected (spondylitic form), and females are more likely to have the form in which many joints on both sides of the body are involved (rheumatoid form).
Psoriatic arthritis usually develops in people 35-55 years of age. However, it can develop in people of almost any age.

What causes psoriatic arthritis?
The cause of psoriatic arthritis is currently unknown. A combination of genetic, immune, and environmental factors is likely involved. In patients with psoriatic arthritis who have arthritis of the spine, a blood test gene marker called HLA-B27 is found in about 50%. Several other genes have also been found to be more common in patients with psoriatic arthritis. Certain changes in the immune system may also be important in the development of psoriatic arthritis. For example, the decline in the number of immune cells called helper T cells in people with AIDS (HIV infection) may play a role in the development and progression of psoriasis in these patients. The importance of infectious agents and other environmental factors in the cause of psoriatic arthritis is being investigated by researchers.

What are risk factors for developing psoriatic arthritis?
The major risk factor for developing psoriatic arthritis is having a family member with psoriasis. This relationship has been recognized as so significant that it is used as a helpful part of the health history for the doctor to aid in the diagnosis of psoriatic arthritis. It might be that stressful life situations could affect the immune system, allowing for the expression and/or exacerbation of psoriatic arthritis. However, precisely how these emotional issues are related to psoriatic arthritis has not been established.

What are the different types of psoriatic arthritis?
The type of psoriatic arthritis depends on the distribution of the joints affected. Accordingly, there are five types of psoriatic arthritis: symmetrical polyarthritis (both sides of the body), asymmetric oligoarticular, spondylitis, distal interphalangeal joints, and arthritis mutilans.