What is reactive arthritis?
Reactive arthritis is an autoimmune condition, named for the fact that it normally occurs as a reaction to an infection somewhere in the body. It is an uncommon but painful form of inflammatory arthritis that affects the heels, toes, fingers, lower back, and joints, such as in the knees or ankles. It is also associated with inflammation of the urethra, the eyes, and sometimes skin and mucous membranes.
The most common infection that triggers reactive arthritis is caused by Chlamydia trachomatis. It can also be caused by other sexually transmitted diseases as well as certain intestinal infections. Common intestinal pathogens include Campylobacter, Shigella, Salmonella, and Yersinia, which can be found in contaminated food.
Not everyone who gets one of these infections will develop reactive arthritis, however. Risk factors for reactive arthritis include sex and genetic predisposition. The disorder is most commonly seen in men between 20 and 50 years of age, although women can also have reactive arthritis. Some people are at increased risk because they are positive for HLA-B27, a specific protein (termed a human leukocyte antigen or HLA) that is found on cell surfaces. The term HLA-B27 is also used to refer to the gene that codes for the HLA-B27 protein. It is estimated that anywhere from 65% to 96% of those with reactive arthritis are positive for HLA-B27, while HLA-B27 is found in only about 6% of the general U.S. population. Although having HLA-B27 is a risk factor for reactive arthritis, it is still possible for people who are HLA-B27 negative to develop reactive arthritis, and it may be that other genetic factors are involved.