Rheumatoid Arthritis is a systemic disease, which means that it affects the whole body. It causes inflammation, or pain, redness, swelling, and warmth, of the synovium. The synovium is a membrane which lines and lubricates the joints. Rheumatoid arthritis can also affect other parts of the body, such as the muscles, skin, eyes, heart and lungs. This condition is an autoimmune disease, which means an individual’s immune system, or defense system, damages his or her own cells or tissues. The focus of treatment for rheumatoid arthritis must be determined on an individual basis. The treatment focus is generally on reducing joint pain, swelling and stiffness, and maintaining as much function of the affected joint or other body part as possible. More information on different types of arthritis is provided in our Section on Arthritis.