Diagnosis of Psoriatic Arthritis
Currently, there is no one definitive test to diagnose psoriatic arthritis (PsA). Diagnosis is made on the basis of the patient's medical history (i.e., a history of psoriasis), physical examination, and diagnostic tests. In patients who have psoriasis, involvement of the fingernails (e.g., development of ridges and pits) may be suggestive of future psoriatic arthritis development.
Laboratory tests that may be performed include erythrocyte sedimentation rate (ESR) and C-reactive protein level. Elevated levels in these tests indicate inflammation in the body. Fluid within the joints (called synovial fluid) also may be tested to detect inflammation. These tests are sometimes used to help differentiate PsA, rheumatoid arthritis (RA), reactive arthritis, and gout, which may cause similar symptoms.
In September 2009, a genetic test for psoriatic arthritis (i.e., PsoriasisDX Genetic Test) was developed and launched. This test, which involves taking a genetic sample from the inside of the cheek, may help physicians identify patients with psoriasis who are at increased risk for developing PsA. Prompt diagnosis and treatment can reduce inflammation and help prevent joint damage associated with psoriatic arthritis.
Imaging tests (e.g., x-rays, MRI scan) of the hands, feet, spine, and sacroiliac joint may be performed. These tests are used primarily to detect bone erosion and new bone formation, which may be present in some types of severe PsA.