How is Psoriatic Arthritis Different From Other Types Of Arthritis?

Psoriatic arthritis is caused by the same inflammatory process that causes psoriasis of the skin. Because of joint pain, joint swelling, and a warm feeling to the touch, it may resemble other types of arthritis,particularly rheumatoid arthritis. Between 5% and 30% of  people with psoriasis will get psoriatic arthritis, usually following skin disease by 5 to 10 years. However, it can be the first symptom of psoriasis, in which case it needs to be carefully differentiated from other types of arthritis.

It is important to distinguish psoriatic arthritis from rheumatoid arthritis, osteoarthritis, and other forms of arthritis because the course of the disease and its treatment may differ. A physician may recognize the symptoms of psoriatic arthritis as a clinical diagnosis, but the consultation of a rheumatologist, orthopedist, or other joint specialist is sometimes needed. The most common type of arthritis in most people, including those with psoriasis, is osteoarthritis. Unlike psoriatic arthritis, which is often the worst in the morning, osteoarthritis is usually worse at the end of the day after hours of using the joints.

Depending on the severity of your disease, you may have x-rays taken of the affected joints. These x-rays are helpful to determine how the joints look at diagnosis and to look for changes over time.

There are fairly recently developed criteria now published that are being used to diagnose psoriatic arthritis. One of these systems is the CASPAR criteria. The CASPAR criteria are met when a patient has established inflammatory joint disease and scores at least three points from the following list:

Current psoriasis (scores two points) 

A history of psoriasis (unless current psoriasis was present), a family history of psoriasis (unless cur-rent psoriasis was present or there was a history of psoriasis), dactylitis (swelling of fingers or toes), juxtaarticular new bone formation, rheumatoid factor negativity, and nail dystrophy (each scores one point).

Which joints are affected? 

Joint disease is not necessarily determined by skin dis-ease. That is, a joint directly beneath an affected skin area will not necessarily be involved. Joints that are often involved include the joints of the hands and fingers, the lower back (especially the  sacroiliac joint, where the back meets the hips), and less commonly the knees, hips, or shoulders.

Who gets joint disease? 

Studies suggest that people with nail changes in psoriasis, such as oil spots or onycholysis, are more likely to have joint disease. In different studies in the United States and worldwide, 35% of patients with psoriatic nails had this type of arthritis. People with more severe skin disease are also at increased risk, although the severity of the two conditions may vary considerably in an individual. Therapy for psoriatic arthritis may help improve skin psoriasis as well.

Treatments for active arthritis can be more aggressive than treatments for skin disease, because joint and bone damage, unlike skin changes, are more likely to be permanent. In particular, systemic treatments are usually used for psoriatic arthritis. Some drugs being used or tested to treat both skin and joint psoriasis are methotrexate, sulfasalazine, cyclosporine, infliximab, etanercept, adalimumab, golimumab, and ustekinumab. These systemic treat-ments are usually given by either a rheumatologist or a dermatologist who specializes in psoriasis.

Physicians and medical journals may use the abbrevia-tion PsA or PsoA when referring to psoriatic arthritis, just as they may use Ps or Pso to abbreviate psoriasis.