This is one reason early diagnosis and treatment are so important in the management of rheumatoid arthritis. The joint capsule is lined with a type of tissue called synovium, which produces synovial fluid that lubricates and nourishes joint tissues. In rheumatoid arthritis, the synovium becomes inflamed, causing warmth, redness, swelling, and pain. As the disease progresses, abnormal synovial cells invade and erode, or destroy, cartilage and bone within the joint. Surrounding muscles, ligaments, and tendons become weakened.
Some people also experience the effects of rheumatoid arthritis in places other than the joints.
About one-quarter develop rheumatoid nodules. These are bumps under the skin that often form close to the joints. Many people with rheumatoid arthritis develop anemia, or a decrease in the normal number of red blood cells. Other effects, which occur less often, include neck pain and dry eyes and mouth. Very rarely, people may have inflammation of the blood vessels, the lining of the lungs, or the sac enclosing the heart.