Although psoriatic arthritis (PsA) affects up to one million Americans, obtaining a diagnosis can be difficult. There are no tests to accurately determine its presence, and it can mimic other conditions which can also result in painful inflammation and swelling of the joints. To make a diagnosis, doctors, usually rheumatologists, use a process of elimination which involves a series of tests, clinical observations and information gleaned from patients. The correct diagnosis is crucial because it is the only way to ensure that patients receive appropriate treatment.
Since psoriatic arthritis is similar to other chronic, inflammatory conditions such as gout, osteoarthritis and rheumatoid arthritis, several different tests are used to rule them out. For example, gout occurs when a normal waste product called uric acid causes a build up of crystal deposits in the joints. Rheumatoid arthritis is similarly confused with psoriatic arthritis, but it is almost always associated with the presence of a protein called rheumatoid factor, which is found in patients with rheumatoid arthritis but is usually not present in people with psoriatic arthritis.
To detect inflammation, doctors often use a test that checks the erythrocyte sedimentation rate, or sed rate, in the blood. This is done by measuring the degree of rapidity with which red blood cells sink in a specimen of drawn blood. When the blood cells fall faster, the sed rate is increased and this signals the presence of inflammation. Another test looks for the presence of the C-reactive protein, because it is also a way to measure the degree of inflammation. However, because many conditions involve inflammation, neither test is considered a way to positively identify psoriatic arthritis.
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A more accurate method involves the use of X-rays. X-rays can distinguish the changes in joints that are common only to psoriatic arthritis. These include changes in the distal joints found at the tips of the fingers and toes. Another change that can be seen through the use of X-ray is referred to as the "pencil-in-cup" phenomenon. The term is used to describe how the end of a bone becomes whittled down to a sharp point over time by the disease. However, since most of the changes that show up on X-rays only occur in the later stages of psoriatic arthritis, it is not considered a useful way to diagnose the disease in its earlier stages.
X-rays may also be used to look for signs that are characteristic of the disease, such as increased calcium salt deposits around the ligaments and tendons. A positive test can indicate a condition called enthesopathy, or the inflammation of the tendons, ligaments and the connecting tissues, which is common in psoriatic arthritis.
Doctors also look for particular patterns in the joints that are affected, particularly in the spine, hips, shoulders, hands, and feet. In a case of psoriatic arthritis, it is common for arthritis to affect the joints on both sides of the body symmetrically. It is also common for arthritis to be found predominantly in the spine and sacroiliac joints, which is where the hip girdle attaches to the base of the spine.
About 20 percent of people who suffer from psoriatic arthritis will eventually develop a spinal condition called psoriatic spondylitis. In this situation, inflammation can lead to a complete fusion of the spine or skip areas and only involve the lower back and neck.
Psoriatic arthritis is considered part of a family of chronic, long-term joint diseases called spondyloarthropathies. Although the various spondyloarthropathies have different symptoms and outcomes, there are some similarities that doctors look for. For example, spondyloarthropathies usually involve the attachments between the lower back and the pelvis. All spondyloarthropathies affect areas around the joints, such as at the knee or hip, where the ligaments and tendons attach to bones.
Since psoriatic arthritis takes on so many different forms, the outlook can vary from person to person. For example, if fewer joints are involved, it is more likely that the outlook will be favorable.
The prognosis is least favorable for the 5 percent of psoriatic arthritis patients who experience the crippling form of the disease known as psoriatic arthritis mutilans. Although this is the least common type of psoriatic arthritis, it is the most severe because it eventually results in widespread destruction of the joints in the fingers and toes. Destruction of the joints can cause the bones to fuse, which may leave the digits looking gnarled.
For most psoriatic arthritis patients, however, the outlook is more positive. Some consider psoriatic arthritis a minor annoyance that requires medication only at times when symptoms flare. Others need more therapy to help them manage the disease. In either event, armed with the correct diagnosis and appropriate treatment, patients can control their pain and live their lives with improved function and limited joint damage.