Who Gets Psoriatic Arthritis?

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 psoriatic arthritis. Approximately 70 percent of people who develop psoriatic arthritis have previously been diagnosed with psoriasis; another 15 percent develop skin and joint symptoms simultaneously.

What Causes Psoriatic Arthritis?

Like most forms of inflammatory arthritis, psoriatic arthritis has no known single cause. Researchers have found a strong genetic component to both psoriasis and psoriatic arthritis, as 40 percent of people who are diagnosed with these conditions also have family members affected by the disease.

Not everyone who has psoriasis develops psoriatic arthritis. Researchers believe PsA can be triggered by an infection or outside factor, such as extreme stress or injury, that sends the immune system of those already genetically predisposed toward the disease into overdrive.

How Is Psoriatic Arthritis Diagnosed?

Diagnosing psoriatic arthritis can be a difficult and time-consuming process because its symptoms frequently mimic those of other forms of inflammatory arthritis, such as rheumatoid arthritis and even gout. It can also be confused with osteoarthritis, the most common form of arthritis, even though it isn't inflammatory.

“Psoriatic arthritis is like a puzzle,” says Hayes Wilson, MD, chair of the division of rheumatology at Piedmont Hospital in Atlanta. “Many times pain or inflammation will occur in just one or two joints, or the psoriasis might be hidden in the scalp under the hair, so your doctor will need to work with you to put all of the pieces together.”

As part of the diagnostic process, your physician will likely refer you to a rheumatologist, a type of doctor who specializes in arthritis and musculoskeletal diseases. The rheumatologist will perform a physical exam, looking for swelling and inflammation of the joints. He’ll also check for signs of psoriasis on the skin or abnormalities on fingernails and toenails. Keep in mind that psoriasis isn’t always readily visible. It can hide in the scalp, behind your ears, in your belly button and in the groove between your buttocks.

The doctor may order X-rays to detect changes to the bones or joints. Blood can be examined for indicators of inflammation such as C-reactive protein and rheumatoid factor (an autoantibody that may or may not be present in people with rheumatoid arthritis, but is almost never present in people with psoriatic arthritis). Another test measures the sedimentation rate – the distance red blood cells fall in a test tube in one hour. The farther they fall, the greater the inflammation. Your doctor may also test joint fluid to exclude gout or infectious arthritis.

If you’re experiencing symptoms such as those noted above and your doctor doesn’t recommend sending you to a rheumatologist, ask about seeing one. Psoriatic arthritis is an uncommon disease, and many primary care doctors, along with quite a few dermatologists, just aren’t that familiar with it. Getting an accurate diagnosis lets your doctor select an appropriate treatment. Beginning treatment early in the course of the disease can mean improved quality of life for you now and less damage to your joints later on.