Psoriatic arthritis is a chronic inflammatory type of arthritis. It can be progressive and lead to permanent joint damage and disability. Generally, psoriatic arthritis is considered rare, but it is more common among people with psoriasis, affecting between 6 to 10 percent of psoriasis patients. It is even more prevalent among those with severe psoriasis, affecting 20 to 40 percent of that group of patients.
It is important to recognize the risk factors associated with psoriatic arthritis. A risk factor is a characteristic or factor that increases the likelihood a person will develop a specific disease or condition. Risk factors are classified as modifiable or non-modifiable. A modifiable risk factor may present the chance to prevent psoriatic arthritis or control the damage which it can cause.
The identification of risk factors for psoriatic arthritis was late in coming. There were relatively few epidemiological studies that evaluated risk factors for psoriatic disease until around the year 2000. There have also been relatively few studies that investigated risk factors for developing psoriatic arthritis among people who have psoriasis. Researchers have been able to conclude that psoriatic arthritis most likely develops due to a combination of genetic, immunologic, and environmental risk factors.
Approximately 40 percent of patients with psoriasis or psoriatic arthritis have family members who have psoriasis or psoriatic arthritis. Studies have shown that patients with a family history of psoriatic arthritis were 27 to 48 times more likely to develop the disease than those without a family history. Psoriatic arthritis is considered "more highly heritable" than other autoimmune diseases.
Children of parents with psoriasis are three times more likely to develop psoriasis and have a greater risk of developing psoriatic arthritis compared to children of parents without psoriasis. If an identical twin has psoriatic arthritis, the other identical twin is highly likely to also have the disease or to develop it eventually. Many genes that are associated with susceptibility to psoriatic arthritis are also associated with susceptibility to psoriasis. But, not all genes are associated with both diseases.
Various immune system abnormalities contribute to increasing the risk of psoriatic arthritis. Activated T cells are present in the tissue of both the skin and the joints. It is also thought that cytokines, such as TNF-alpha, play a role in the inflammatory process which leads to cartilage destruction and skin inflammation associated with psoriatic arthritis.
There are environmental factors which appear related to the risk of developing psoriatic arthritis. Exposure to certain infections is considered a possible risk factor, especially streptococcal infections. The link has not been proven or confirmed though. Psoriatic arthritis is also more common in people who have been infected with the human immunodeficiency virus (HIV) compared to the general population.
The Koebner phenomenon, which occurs in 52 percent of people with psoriasis according to Kelley's Textbook of Rheumatology, is considered another environmental factor. First described by Dr. Heinrich Koebner (a highly respected dermatologist from the 19th century) in 1876, psoriatic lesions form in previously uninvolved skin following skin trauma. What causes the Koebner phenomenon is still unclear but cytokines, stress proteins, adhesion molecules, and autoantigens may be involved.
Identification of Risk Factors for Psoriatic Arthritis: Scientific Opportunity Meets Clinical Need. Ogdie and Gelfand. JAMA Dermatology. July 2010.
Patient information: Psoriatic arthritis (Beyond the Basics) Gladman and Ritchlin. UpToDate.
Psoriatic Arthritis. M. Elaine Husni. Cleveland Clinic. August 2010.
The Koebner Phenomenon. Clinics in Dermatology. Sagi L. and Trau H. March-April 2011.
Kelley's Textbook of Rheumatology. Ninth edition. Elsevier. Chapter 77. Psoriatic Arthritis. Oliver Fitzgerald.