Psoriasis is a skin condition that causes buildup of dead, scaly skin cells called plaques. Psoriasis occurs when a person's immune system malfunctions, causing inflammation that primarily affects the skin. In some people with psoriasis, the inflammation affects joints as well as skin, causing a condition known as psoriatic arthritis, which is characterized by pain, stiffness and decreased range of motion of the joints, along with the skin symptoms.
Symptoms
With psoriasis, dead skin cells build up into rough thick patches (plaques) that resemble scales. Often the itchy and sore plaques occur on the elbows and knees, but they can occur anywhere, including fingernails and toenails and even inside the mouth. According to the National Institute of Arthritis, Musculoskeletal and Skin Diseases, about 30 percent of patients with psoriasis also develop arthritis. Both the skin symptoms and the arthritis pain come and go in episodes called flares, and the arthritis and skin symptoms do not necessarily coincide.
Joint Pain
Psoriatic arthritis occurs in five forms. The pain can be mild and asymmetric (only on one side of your body) or more severe and symmetric (pain on one side mirrors the other). Distal interphalangeal psoriatic arthritis causes pain in the little joints of the fingers, and according to MayoClinic.com, with this type, fingernails will often show signs of psoriasis. Psoriatic arthritis in the spine and lower back is called spondylitis. Fortunately, arthritis mutilans---a destructive form of psoriatic arthritis that deforms the small bones in the hands---is rare, according to MayoClinic.com.
Cause
Arthritis and psoriasis are both caused by inflammation. In psoriasis, the immune system malfunctions by producing too many of the T cells that normally protect a person from infection. The overactive and overabundant T cells trigger other immune changes that cause rapid turnover of skin cells. New skin cells pile up on the skin's surface before they mature, causing the plaques. The downstream effects of T-cell overpopulation can also trigger joint inflammation, causing arthritis.
Risk Factors
The greatest risk factor for psoriatic arthritis is having a family history of psoriasis. If you have a parent or sibling with psoriasis, you are more likely to develop it yourself. If you have psoriasis lesions on your fingernails, you are especially at risk to develop psoriatic arthritis, according to MayoClinic.com. Also according to MayoClinic.com, psoriatic arthritis most commonly affects people between the ages of 30 to 50, before the normal start of osteoarthritis ("old age" arthritis).
Treatment
There is no cure for psoriatic arthritis. Treatment aims to relieve both the skin and joint symptoms and you will probably need different medicines for each aspect. Nonsteroidal anti-inflammatories such as Advil can help with the pain of both conditions. Medications that disrupt the cycle of inflammation---such as corticosteroids, immunosuppressants (like cyclosporine) or TNF-alpha inhibitors (like infliximab, brand name Remicade)---can help both skin and joint symptoms, but they have powerful side effects.
