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Most Common Types of Arthritis

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What Causes Rheumatoid Arthritis?

With rheumatoid arthritis, some of your body's cells recognize one of your own proteins as a foreign intruder. The exact protein involved in rheumatoid arthritis has not yet been discovered. Some experts believe the immune system becomes "confused" after infection with a bacteria or virus and begins attacking the normal joint tissues. Certain immune cells called lymphocytes are stimulated to react to this protein. The reaction causes the release of cytokines, which are chemical messengers that trigger more inflammation and destruction. This battle between the body's chemicals occurs mainly in the joints, but it can spread to other areas of the body.

There are many cytokines, but the most important in terms of causing inflammation are tumor necrosis factor (TNF) and interleukin-1. These cytokines are thought to trigger other parts of the immune system in rheumatoid arthritis. Medicines that block TNF, interleukin-1, and interleukin-6 can improve the symptoms and prevent joint damage in rheumatoid arthritis.

What Is Psoriatic Arthritis?

Psoriatic arthritis is a chronic disease characterized by inflammation of the skin (psoriasis) and joints (arthritis). With psoriasis, there are patchy, raised, red, and white areas of skin inflammation with scaling. Psoriasis usually affects the tips of the elbows and knees, the scalp, the navel, and skin around the genital areas or anus.

About 10% of people with psoriasis also develop an associated inflammation of their joints called psoriatic arthritis. Psoriatic arthritis can cause a sausage-like swelling of fingers and toes and is often associated with fingernails that are pitted or discolored. In some people with psoriatic arthritis, only one joint or a few joints are affected. For example, a person may be affected in only one knee. Sometimes the spine is affected, or just the fingers and toes.

Psoriatic arthritis usually strikes around the age of 30 to 50, affecting both men and women equally. But it can also start in childhood. The skin disease (psoriasis) and the joint disease (arthritis) often appear separately. In fact, the skin disease precedes the arthritis in nearly 80% of patients. The arthritis may precede the psoriasis in up to 15% of patients.

WebMD Medical Reference

Reviewed by David Zelman, MD on September 06, 2014
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