Rheumatoid arthritis is a disease that primarily affects the joints, but it may affect the entire body. The joint inflammation characteristic of rheumatoid arthritis may cause joint pain, stiffness, warmth, redness and swelling. Other, more generalized symptoms include fatigue and overall stiffness and aching. Over time, arthritic joints may become misshapen and permanently damaged. However, the disease varies considerably among those affected. Not everyone with rheumatoid arthritis has severe disease with deformed and damaged joints.

Normal joints contain smooth, shiny cartilage with a thin lining called synovium, which is only a few cells thick. The synovium secretes joint fluid (called synovial fluid), which reduces friction in the joint and provides nutrients. In rheumatoid arthritis, the synovium becomes inflamed and then thickens. As it thickens, it forms a tissue called pannus. Pannus is destructive to the joint, attacking both the cartilage and the bone underneath. The inflamed synovium also secretes chemicals into the joint fluid that are thought to damage nearby cartilage, the bones of the joint, as well as the supporting ligaments and tendons. In addition, the altered joint fluid becomes less able to perform its normal functions.

The cause of rheumatoid arthritis and the precise mechanisms underlying bone, cartilage and tendon destruction are not known precisely and are the subject of intense investigation. Research already has led to important improvements in the treatment of this disease. Additional treatments, perhaps even preventive measures, will likely be discovered as a result of ongoing research.

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