Diagnosing Psoriatic Arthritis

Arthritis comes in many forms including one called psoriatic arthritis (PsA). Psoriasis is a disease that most people think of as primarily a skin disease because the condition causes a persistent rash in various areas of the body. Psoriatic arthritis is a type of joint disease that occurs in roughly seven percent of people who have psoriasis.

Psoriatic arthritis affects people of all ages, but most get it between the ages of 30 and 50. Usually a patient has psoriasis (the skin rash) for many years before the arthritis develops, and the arthritis comes on slowly. But this is not always the case. No matter what, patients with psoriatic arthritis must manage both the outbreaks of itchy, scaly skin and the pain and stiffness of arthritis.

Psoriatic arthritis (PsA) can be a very aggressive disease. Based on the evidence we have so far, it is believed that early recognition and treatment of this problem yields better results.

Scientists are looking for faster, more reliable ways to tell if someone is developing PsA. Until such tests are available, physicians must rely on screening tools currently available such as the Psoriatic Arthritis Screening and Evaluation (PACE), Toronto Psoriatic Arthritis Screen (ToPAS), and the Psoriasis Epidemiology Screening Tool (PEST).

These screening tools are not enough by themselves because psoriatic arthritis is more than just a skin and joint disease. There is often a wide range of signs and symptoms involving many different body parts. One screening tool can't possibly assess everything equally at the same time.

Physicians must also use other diagnostic tools such as X-rays, ultrasonography, and MRIs. Each one of these tests provides a little different information. For example, X-rays show early signs of bone erosion but do not reveal anything about the condition of tendons, ligaments, or other soft tissues often affected by psoriatic arthritis.

Ultrasonography, the use of sound waves to create a picture of what's going on inside, provides a better look at the whole package: bones, joints, and soft tissues. This diagnostic test is also noninvasive and does not expose the patient to any radiation. Ultrasound also has the ability to show small changes in the nails and early signs of inflammation in tendons and small joints.

MRIs are slowly being replaced by ultrasound studies. MRIs can show bone marrow edema, tenosynovitis, and early joint erosion. Tenosynovitis is the inflammation of the fluid-filled sheath (called the synovium) that surrounds a tendon.

But reliability is a problem with MRIs because what one examiner sees may not be the same as another observer. Changes in the small joints of the hands and feet don't show up well on MRIs like they do with ultrasonography.

One advantage MRIs do have over ultrasonography is the availability of whole body MRI. By scanning the entire body, it is possible to identify areas of inflammation undetected by clinical exam. And whole-body ultrasonography just isn't reasonable.

Until blood studies are able to find biomarkers (biologic evidence of disease) indicating the presence of psoriatic arthritis, physicians will probably have to use a combination of different tests to diagnose the problem. The information these tests provide is important in determining treatment.

Research in the area of psoriatic arthritis is on the brink of making some major discoveries that will improve the diagnosis and management of this disabling disease. Besides serum biomarkers (in the blood), better tools are being developed to assess the progression of this disease.

Likewise, drugs to specifically target the problem called biologic agents will eventually replace current medications that help with symptoms but either have adverse side effects or affect more than just the targeted tissues. Better screening tools would be helpful, too -- or at least knowing which screening tool to use for each clinical setting and/or patient would be a step in the right direction.

This article is the first of two parts bringing us up-to-date on the condition known as psoriatic arthritis (PsA). The second part will cover treatment, including changes in treatment based on imaging findings described here.

Knowing that the management of this condition depends on early detection of bone, joint, and soft tissue pathology helps us understand the need for both improved diagnostic and treatment approaches. The potential for severe progression of disease may be halted (or at least slowed) with a management approach that includes (repeated or serial) diagnostic imaging throughout the course of treatment.

Reference: 

Andreea Coca, MD, and Christopher T. Ritchlin, MD, MPH. Psoriatic Arthritis: A Disease in Full. March 2011. Vol. 28. No. 3. Pp. 95-101.

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