In rheumatoid arthritis, the synovium becomes inflamed. Like many other rheumatic diseases, rheumatoid arthritis is an autoimmune disease. In an autoimmune disease or condition, a person's immune system, which normally helps protect the body from infection and disease, attacks their own joint tissues for unknown reasons. White blood cells, the agents of the immune system, travel to the synovium and cause inflammation (synovitis), characterized by typical symptoms of rheumatoid arthritis such as warmth, redness, swelling, and pain.
During the inflammation process, the normally thin synovium becomes thick and causess the joint to become swollen and puffy. As rheumatoid arthritis progresses, the inflamed synovium invades and destroys the cartilage and bone within the joint. (illustration) The surrounding muscles, ligaments, and tendons that support and stabilize the joint become weak and unable to work normally. These effects lead to the joint pain and joint damage often seen in rheumatoid arthritis patients.
NIH Publication No. 04-4179