Psoriatic Arthritis

While many people consider psoriasis a skin disease, its primary cause is a malfunctioning immune system. And it doesn't just affect the skin. Many of its worst effects can come from psoriatic arthritis, a swelling of the joints that develops in some people with psoriasis. Psoriatic arthritis causes symptoms like other types of arthritis -- stiff, painful and swollen joints -- and it can be serious. Untreated, psoriatic arthritis can cause bone loss and deformation of the joints.

Experts don't agree on how common psoriatic arthritis is. The National Psoriasis Foundation estimates that between 10% to 30% of people with psoriasis also have psoriatic arthritis.

While psoriatic arthritis is most common in adults between the ages of 30 and 50, it can develop in anyone, including children. Psoriatic arthritis only affects people who have psoriasis. Even so, diagnosis can be difficult. The symptoms of psoriatic arthritis often appear years after the first signs of psoriasis on the skin. But sometimes the arthritis symptoms develop before you have any lesions.

Because a long time can pass between the appearances of these very different symptoms, psoriatic arthritis can be hard to catch. Bruce E. Strober, MD, PhD, suspects that psoriatic arthritis may be a chronically under-treated condition because people who have it just don't connect the symptoms.

"A lot of people, even a lot of dermatologists, don't link up joint pain with skin disease," says Strober, who is co-director of the Psoriasis and Psoriatic Arthritis Center at New York University. "But if you're not treating the arthritis, you're not addressing one of psoriasis's most debilitating aspects."

What Is Psoriatic Arthritis?

Just like the symptoms of psoriasis, the pain and swelling of psoriatic arthritis are caused by an overactive immune system, which enflames the tissues around the joint. Typically, symptoms will flare-up and recede periodically.

There are five different kinds of psoriatic arthritis.

• Asymmetric arthritis makes up about 70% of all cases of psoriatic arthritis. It often involves one or a few joints, like the knee, hip, or fingers. Although it's frequently mild, it can sometimes be debilitating. The inflamed joints may be red and hands and feet may be swollen.

   

• Symmetric arthritis is the second most common form of psoriatic arthritis. It often causes symptoms in the same joints on both sides of the body. Symptoms are similar to rheumatoid arthritis, and symmetric arthritis can cause permanent damage.

   

   

• Distal interphalangeal predominant (DIP), a less common form of psoriatic arthritis, affects the joints close to the fingernails and toenails. The nails are often affected too.

   

   

• Spondylitis can make movement painful, especially in the neck and back. It can also cause inflammation of the spinal column.

   

   

• Arthritis mutilans is a rare and often debilitating and destructive form of psoriatic arthritis. It often affects the hands and feet -- and sometimes the back and neck -- and it can result in permanent deformity.