Rheumatoid arthritis (RA) is an autoimmune disease in which the immune system mistakenly attacks the joints in the same way it would normally fight viruses or bacteria. In RA, white blood cells attack the synovial membrane that lines the joints, causing inflammation, eroding cartilage and bone, and weakening muscles, tendons, and ligaments. Joints commonly affected by RA include the hands, feet, wrists, elbows, ankles, and knees. With RA, the damage is usually symmetrical. For example, damage tends to occur in both knees, both ankles, or both wrists.
The specific cause of RA is unknown, although it likely involves both hereditary and environmental factors.
It is important to note that while science is good at finding correlations, or apparent relationships, between factors and disease, correlation does not prove that the risk factor causes the disease. Many risk factors for RA have been identified and are being studied, but none have been pinpointed as the cause of RA.
Research has confirmed that people with one or more specific genetic markers are much more likely to be diagnosed with rheumatoid arthritis. The genes that raise the risk for developing RA are not directly passed down from parent to child. However, having a relative diagnosed with RA puts you at higher risk for developing the disease as well. For example, a member of the general population has a 1 percent risk of developing RA. For someone with a sibling who has RA, the risk is 5 percent. If an identical twin has RA, the risk rises to 15 percent.
People with RA also have a higher risk for developing other autoimmune conditions like ankylosing spondylitis, Sjögren's syndrome, and lupus, as well as Lyme disease and anemia.
Women are three times more likely to develop rheumatoid arthritis than men. Researchers theorize that hormones play a role in the development of RA based on changes in disease activity during pregnancy, breastfeeding, and while taking some hormone-based contraceptives. Women who have never given birth have an increased risk for developing RA, while women who have breastfed have a decreased risk.
Studies have shown that past or present smoking significantly raises the risk for developing RA. Risk goes up with the number of cigarettes per day and the number of years of smoking. Risk remains elevated for years after someone stops smoking. Exposure to second-hand smoke and other types of air pollution also raise the risk of developing RA. One study indicated that people whose mothers smoked while pregnant were twice as likely to develop RA as adults.
Research indicates that obesity (defined as a body mass index of 30 or higher) raises the risk for developing RA. Research has also proven that the more overweight someone is, the more severe their RA symptoms tend to be. Scientists attribute these findings to the fact that fat cells continually release inflammatory proteins. Thus, the more fat someone has, the higher the level of inflammation in their body. In addition, extra weight contributes to more stress on damaged joints. Studies also show that some RA medications, including biologics such as Remicade (Infliximab), are up to 50 percent less likely to be effective in obese people.
Several studies have investigated specific infections for links to rheumatoid arthritis. Some scientists believe that one or more common viruses such as the Epstein-Barr virus (the cause of mononucleosis, or “mono”), retroviruses, or parvovirus B19 (the cause of fifth disease, or “slapped cheek disease”) may cause genetic changes in some people, paving the way for the development of RA. Other research theorizes that periodontitis, or gum infections, allow bacteria to enter the bloodstream, triggering immune reactions that contribute to the onset of RA.
Rheumatoid arthritis can go into remission, a period of minimal or no symptoms which can last for months or years. During a flare or exacerbation, current symptoms worsen and new symptoms arise. Some flares (called predictable flares) have known triggers, while other flares (termed unpredictable flares) are not obviously caused by any trigger.
Symptoms of a flare can vary, but they usually involve increased pain, joint swelling, and stiffness. Doctors differ in their definitions of what constitutes a flare. Repeated flares may indicate that medication is not working and needs to be changed. Flare triggers seem to increase inflammation and stimulate autoimmune attacks, bringing new or worse RA symptoms.
Flare triggers differ between people with RA, but common triggers include: