Diagnosing Psoriatic Arthritis

NYU Langone specialists are experienced in diagnosing and managing psoriatic arthritis, which is considered an autoimmune disease. This means that the immune system mistakenly attacks healthy tissues in the body.

In psoriatic arthritis, the immune system attacks the joints, the spine, and the places where tendons attach muscles to bones. Inflammation develops, causing cartilage, which covers the ends of the bones at a joint, to wear down.

When this happens and the space between the bones narrows, the bones eventually rub against one another. This can damage joints, lead to areas of bone loss, and, over time, affect mobility.

Psoriatic arthritis typically occurs in people with a history of psoriasis, a condition in which a person develops thick, scaly patches, or plaques, on the skin. The patches are usually red, but they may be covered with a white or silver layer of skin.

Psoriasis can affect any part of the body and often involves the skin over the knees and elbows.

Millions of Americans have psoriasis, and up to 30 percent of them also develop psoriatic arthritis. The condition typically develops about 7 to 10 years after a person is diagnosed with psoriasis. Arthritis can develop at the same time skin patches emerge; rarely, it occurs before skin patches are visible.

The severity of psoriasis does not necessarily correlate with the severity of psoriatic arthritis. Some people have severe psoriasis and mild arthritis, and others experience mild symptoms of psoriasis but have severe arthritis.

Types of Psoriatic Arthritis

Psoriatic arthritis is classified by type, which affects diagnosis and treatment options.

Symmetric Arthritis

Symmetric arthritis is similar to rheumatoid arthritis, because it affects multiple joints on both sides of the body. It may affect the wrists, hands, feet, and ankles. It’s more common in women.

Asymmetric Oligoarthritis

Up to five joints are affected by asymmetric oligoarthritis. However, the same joints may not be affected on each side of the body.

Spondylitic Arthritis

Spondylitic arthritis affects the spine. It may cause inflammation and stiffness in the neck, lower back, and sacroiliac joints. It can significantly limit mobility.

Distal Interphalangeal Predominant Psoriatic Arthritis

Distal interphalangeal predominant psoriatic arthritis primarily involves the smallest joints at the ends of the fingers and toes.

Arthritis Mutilans

This rare but severe type of psoriatic arthritis also often affects the small joints in the fingers and toes, but any joints may be involved. Arthritis mutilans is rapidly destructive to the joints, leading to significant deformity.

Signs and Symptoms

Psoriatic arthritis can occur at any age, but it usually affects people between the ages of 30 and 50. It affects men and women equally and occurs in people of all ethnic groups. No one knows exactly what causes it, but experts think it may be triggered by a combination of environmental and genetic factors.

Almost half of people with psoriatic arthritis have a family history of skin or joint disease. Having a parent with psoriasis greatly increases your chance of getting psoriasis—and, therefore, psoriatic arthritis.

In the morning, people with psoriatic arthritis may experience stiffness in the joints or spine. Those symptoms usually ease with activity. People may also experience joint pain and swelling.

A person may have tendinitis, or inflammation of the tendons, throughout the body. This inflammation may be especially pronounced in the Achilles tendon, which connects the muscles in the back of your calf to your heel bone.

Dactylitis is when an entire finger or toe swells, so that it’s shaped like a sausage. This may occur in people with psoriatic arthritis.

Other symptoms include constant fatigue due to the toll inflammation takes on the body. Pain in the spine, neck, and back is also common.

Like rheumatoid arthritis, psoriatic arthritis can alternately cause flare-ups—in which symptoms are active for days to months—and remission, which is when symptoms disappear for a period of time.

Some people with psoriatic arthritis may develop Sjogren’s syndrome, another autoimmune disorder. In Sjogren’s syndrome, the immune system attacks and damages the tear ducts of the eye, causing eyes to be dry.

People with psoriatic arthritis are also at risk of developing metabolic syndrome, a group of conditions that occur together and increase your risk of heart disease, diabetes, hypertension, high cholesterol, obesity, and fatty liver disease. If you are diagnosed with psoriatic arthritis and have any of these conditions, your doctor may refer you to a preventive cardiologist or other appropriate specialists for monitoring.

Diagnostic Tests

Diagnosing psoriatic arthritis can be challenging. Unlike with rheumatoid arthritis, there is no marker of psoriatic arthritis that can be detected through a blood test. In addition, psoriatic arthritis can imitate several other forms of arthritis.

Classification Criteria

NYU Langone doctors use a set of diagnostic criteria developed in 2006 to diagnose psoriatic arthritis. The CASPAR classification criteria—the acronym is derived from the phrase “classification criteria for psoriatic arthritis”—have been adopted and used as the standard guide for diagnosis.

The criteria include the following:

  • A person is believed to have “evidence of psoriasis” based on a history of psoriasis or a current diagnosis from a dermatologist or rheumatologist, which is a specialist in conditions that cause painful swelling in joints and muscles. In terms of these classification criteria, a person is also considered to have “evidence of psoriasis” if a first-degree family member, such as a parent, has been diagnosed with the condition, even if he or she has not.
  • A person has pitting, thickening, and irregular contour of a nail or nails.
  • A person has tested negative for rheumatoid factor, an autoantibody that indicates a person has rheumatoid arthritis. This condition has symptoms similar to psoriatic arthritis. This test is important, because some people who have psoriatic arthritis don’t have symptoms of psoriasis.
  • Imaging tests reveal evidence of new bone formation as a result of joint inflammation.

Each criterion is assigned a certain number of points. If, based on the CASPAR criteria, a person has a score of three points and evidence of inflammatory arthritis, spine disease, or enthesitis—which is inflammation in the area where tendons or ligaments connect to bone—then he or she is thought to have psoriatic arthritis.

Other Tests

In addition to using the CASPAR criteria, your doctor may test your blood for evidence of inflammation. This can be detected by measuring markers of inflammation, including C-reactive protein—a protein made by the liver and released into the bloodstream—and by determining the erythrocyte sedimentation rate.

Your doctor also conducts a physical exam to determine how well your joints are moving and how stiff or swollen they may be. He or she may ask you to perform simple physical activities to observe how you move.

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