psoriatic arthritis is a diagnosis made mainly on clinical grounds based on a finding of psoriasis and the typical inflammatory arthritis of the spine and/or other joints. there is no laboratory test to diagnose psoriatic arthritis. blood tests such as sedimentation rate may be elevated and merely reflect presence of inflammation in the joints and other organs of the body. other blood tests such as rheumatoid factor are obtained to exclude rheumatoid arthritis. when one or two large joints (such a knees) are inflamed arthrocentesis can be performed. arthrocentesis is an office procedure whereby a sterile needle is used to withdraw (aspirate) fluid from the inflamed joints. the fluid is then analyzed for infection gout crystals and other inflammatory conditions. x-rays may show changes of cartilage or bone injury indicative of arthritis of the spine sacroiliac joints and/or joints of the hands. typical x-ray findings include bony erosions resulting from arthritis. the blood test for the genetic marker hla-b27 mentioned above is often performed. this marker can be found in over 50% of patients with psoriatic arthritis who have spine inflammation.
how does the doctor diagnose psoriatic arthritis?