In RA, two processes are occurring in the joints. First, the immune system causes inflammation in the synovial membrane, called synovitis. The synovial membrane is the thin tissue that surrounds all joints. The synovitis is characterized by extra fluid, swelling, and warmth of the joint due to the increased blood flow.
The second process causing the problems in RA results from the ongoing or repetitive synovitis. The blood cells and the swollen membranes of the synovium release chemicals into the synovial fluid (the lubricating fluid of the joint) that can break down or damage the tissues of the joint. This breakdown can cause permanent damage to the cartilage, bones, ligaments, and tendons inside and around the joint. The structural damage usually happens in the first to third year of the disease. The synovitis can come and go, but the structural deterioration progresses and results in permanent damage. As a result, the joint becomes chronically painful and very difficult to move.
RA usually affects many joints on both sides of body (for example, both knees, both ankles, both wrists, and the same joints in both hands may be affected.) Research indicates that almost all the joints that will be affected long term show symptoms of RA in the first year of the disease. This means that each joint may continue to get worse, but you probably won't have many more joints that will develop the symptoms of RA.
Most RA patients also have inflammation in the tendons around the joint. (Tendons connect muscle to bone.) Nodules, or bumps, may form on the tendons, or the tendon sheath (the membrane that surrounds the tendon.)
Most people think of RA as an inflammatory disease of just the joints and related tissue, but it is actually a systemic disease meaning that it affects the whole body. In general, inflammation causes symptoms of swelling, redness, heat, and pain. RA can even show up in organs such as the heart, blood vessels, lungs, and eyes. Sometimes RA occurs in joints and other organs, and sometimes it occurs only in other organs. RA works somewhat differently outside the joints, but the underlying problem is still damage to the tissue and loss of function.
Rheumatoid factor (RF) is an antigen found in about 85 percent of RA patients. Not all patients with RA have RF in their blood. Some patients with RA do not have RF, and people with RF can have forms of arthritis that are not RA. Being RF positive, however, increases your likelihood that your organs will also be affected by RA.
No one knows exactly what causes RA. There are probably different causes in different people. Many doctors and researchers think that a virus or bacteria might cause RA. So far studies have not proven this. Researchers do know, however, that bacteria can cause swelling in the synovial membrane.
Heredity, or your genes, play a part in RA. The disease tends to run in families. If a close relative has RA, you are 16 times more likely to develop the disease yourself.