Rheumatoid arthritis is a chronic (long-lasting) inflammatory disease that causes pain, stiffness, warmth, redness and swelling in joints. Over time, the affected joints may become misshapen, misaligned and damaged. Tissue lining the joint can become thick, and may wear away surrounding ligaments, cartilage and bone as it spreads. Rheumatoid arthritis usually occurs in a symmetrical pattern, meaning that if one knee or hand has it, the other usually does, too.
The cause of rheumatoid arthritis is unknown, although it appears to be an autoimmune disease. When the body's immune system does not operate as it should, white blood cells that normally attack bacteria or viruses attack healthy tissue instead — in this case, the synovium, or joint tissue. As the synovial membrane (the thin layer of cells lining the joint) becomes inflamed, enzymes are released. Over time, these enzymes and certain immune cells damage the cartilage, bone, tendons and ligaments near the joint.
Some research suggests that a virus triggers this faulty immune response. However, there is not yet convincing evidence that a virus is the cause of rheumatoid arthritis. At the same time, it appears that some people are more likely to get the disease because of their genetics. Environmental factors may also be important. For example, smoking is a risk factor for rheumatoid arthritis.
Rheumatoid arthritis, the most disabling form of arthritis, generally affects more than one joint at a time. Commonly affected joints include those in the hands, wrists, feet, ankles, elbows, shoulders, hips, knees and neck. Rheumatoid arthritis can result in loose, deformed joints, loss of mobility and diminished strength. It also can cause painless lumps the size of a pea or acorn, called rheumatoid nodules. These develop under the skin, especially around the elbow or beneath the toes.
Generally, the pain of rheumatoid arthritis is described as a dull ache, similar to that of a headache or toothache. Pain is typically worse in the morning. It is not rare to have 30 minutes to an hour or more of morning stiffness. On days when the disease is more active, you may experience fatigue, loss of appetite, low-grade fever, sweats and difficulty sleeping.
Because rheumatoid arthritis is a systemic disease (meaning it can affect the entire body), you also may have inflammation in other areas, including the heart, lungs or eyes. Symptoms vary between people and even in one person over time. People with mild forms of the disease are bothered by pain and stiffness, but they may not experience any joint damage. For other people, damage occurs early, requiring aggressive medical and surgical treatment. People with rheumatoid arthritis may notice worsening and improvement for no apparent reason. Although this disease most often afflicts people between the ages of 20 and 50, it may affect children and the elderly. Of the 2 million people with rheumatoid arthritis in the United States, at least 75 percent are women.