Psoriatic Arthritis Diagnosis
Because psoriatic arthritis is similar to other forms of arthritis (such as rheumatoid arthritis), it is important to get a reliable diagnosis. In most cases your doctor or primary care provider will suspect psoriatic arthritis because you have a history of psoriasis. Nevertheless, it is sometimes necessary to rule out other forms of arthritis before treating psoriatic arthritis. It is possible to have psoriatic arthritis along with other forms of arthritis.
There is no definite blood test, MRI scan, x-ray, or other exam that provides an initial psoriatic arthritis diagnosis. If you have lived with psoriasis, and you have changes to the shape and color of your fingernails or toenails, your doctor will likely be comfortable with—and usually correct in—diagnosing psoriatic arthritis.
Ruling Out Other Kinds of Arthritis
If there is a question about your diagnosis, your doctor may perform a blood test to rule out rheumatoid arthritis.
If your joint pain came on quickly, is extremely painful, and is located in your big toe, you may need to rule out gout, another type of arthritis. Your doctor can be fairly certain about a gout diagnosis if the:
- arthritis is only in your first big toe joint or both big toe joints
- arthritis attacks both ankles at the same time
- joint inflammation developed within one day
- a blood test for uric acid comes back with a high reading
- the skin surrounding your inflamed joint is red and extremely painful
- x-rays identify cysts and bumps common in gout
Your doctor can be positive about a gout diagnosis by removing a small amount of liquid, synovial fluid, from your inflamed joint and examining it under a microscope. If the synovial fluid contains uric acid crystals, you have gout.
Definitive Psoriatic Arthritis Diagnosis
If your doctor concludes that you do not have gout or rheumatoid arthritis, he or she will arrive at a psoriatic arthritis diagnosis and begin treating you for it.
Over time your diagnosis will become more certain if:
- arthritis starts to appear in x-rays of your spine
- x-rays of knees, elbows, and other joints begin to display "pencil in cup" markings (a particular bone erosion pattern that occurs in psoriatic arthritis)
Even if you have rheumatoid arthritis or gout, there is still a chance you also have psoriatic arthritis. It may take months or years for your doctor to arrive at a complete diagnosis in these complex situations if multiple types of arthritis are present in your joints.