Psoriatic arthritis is an inflammatory disease that affects the joints. The presence of inflammatory arthritis with a history of psoriasis makes the psoriatic arthritis diagnosis more likely. Because this form of arthritis can cause deformity and crippling just like rheumatoid arthritis, it is important to have an accurate psoriatic arthritis diagnosis and treat the disease early and effectively.
Psoriatic arthritis usually strikes around age 30 to 50, equally affecting both men and women, but it may also start in childhood. The skin disease precedes the arthritis in nearly 80% of patients. The psoriatic arthritis may precede the psoriasis in up to 15% of patients. Some people may have both at the same time.
The symptoms of psoriatic arthritis can be similar to rheumatoid arthritis, with morning pain and stiffness, along with fatigue. You may have pain and stiffness in the hands, wrists, elbows, shoulders, knees, ankles, feet, and spine.
Arthritis that affects many joints symmetrically is common with psoriatic arthritis. This symmetrical pattern is almost the same as rheumatoid arthritis. At other times, though, it be be asymmetrical, that is not affecting the same joint on both sides of the body. It also tends to affect the last joint ( the DIP that is rarely affected by RA).
With psoriasis you may have thick, inflamed red skin patches (called plaques) covered with white or silvery scales, usually on the elbows, knees, or other areas. In addition, a significant percentage of people with psoriatic arthritis have nail involvement with pitted, discolored, or thickened nails.
Psoriatic arthritis can cause a sausage-like swelling of fingers and toes, which usually occurs when the fingernails are pitted or discolored. In some people with psoriatic arthritis, only one joint is affected yet not the other (one knee only, for example). Sometimes the spine is affected or just the fingers and toes. About 1/3 of patients with psoriatic arthritis have eye problems such as conjunctivitis or pink eye or a more serious eye problem called iritis that is often painful and can lead to loss of vision.
How Is Psoriatic Arthritis Diagnosed?
Your doctor will diagnose psoriatic arthritis based on a physical exam, patient history, family history, and lab tests.
While there is no specific lab test to diagnose psoriatic arthritis, blood tests from some patients may reveal mild anemia and elevated erythrocyte sedimentation rate.
Erythrocyte sedimentation rate (sed rate or ESR) is a test that gives a rough index of inflammation. The sed rate is not specific and can be elevated with many other conditions such as other autoimmune syndromes, infection, tumor, liver disease, or pregnancy.
Your doctor may do other blood tests such as rheumatoid factor or anti-CCP antibody to help exclude the diagnosis of rheumatoid arthritis. Rheumatoid factor is a blood test that is positive in 70% to 80% of those with rheumatoid arthritis. However, this test may be positive in healthy people and negative in people with rheumatoid arthritis, so it is not conclusive.