Some people might hear “psoriasis” and think of the skin disease that causes itchy, scaly rashes and crumbling nails. It's true, psoriasis is an autoimmune disease that primarily affects the skin. But about 30 percent of people with psoriasis also develop a form of inflammatory arthritis called psoriatic arthritis (PsA). Like psoriasis, PsA is an autoimmune disease, meaning it occurs when the body’s immune system mistakenly attacks healthy tissue, in this case the joints and skin. The faulty immune response causes inflammation that triggers joint pain, stiffness and swelling. The inflammation can affect the entire body and may lead to permanent joint and tissue damage if it is not treated early and aggressively.
Most people with psoriatic arthritis have skin symptoms before joint symptoms. However, sometimes the joint pain and stiffness strikes first. In some cases, people get psoriatic arthritis without any skin changes.
The disease may lay dormant in the body until triggered by some outside influence, such as a common throat infection. Another theory suggesting that bacteria on the skin triggers the immune response that leads to joint inflammation has yet to be proven.
Types of Psoriatic Arthritis
There are five types of psoriatic arthritis:
- Symmetric psoriatic arthritis. This makes up about 50 percent of psoriatic arthritis cases. Symmetric means it affects joints on both sides of the body at the same time. This type of arthritis is similar to rheumatoid arthritis.
- Asymmetric psoriatic arthritis: Often mild, this type of PsA appears in 35 percent of people with the condition. It’s called asymmetric because it doesn’t appear in the same joints on both sides of the body.
- Distal psoriatic arthritis: This type causes inflammation and stiffness near the ends of the fingers and toes, along with changes in toenails and fingernails such as pitting, white spots and lifting from the nail bed.
- Spondylitis: Pain and stiffness in the spine and neck are hallmarks of this form of PsA.
- Arthritis mutilans: Although considered the most severe form of PsA, arthritis mutilans affects only 5 percent of people who have the condition. It causes deformities in the small joints at the ends of the fingers and toes, and can destroy them almost completely.
According to the Annals of Rheumatic Disease, between 6 and 42 percent of people who have psoriasis will develop psoriatic arthritis. The disease usually appears between the ages of 30 and 55 in people who have psoriasis, but it can be diagnosed during childhood. Unlike many autoimmune diseases, men and women are equally at risk for developing this condition.