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Rheumatoid arthritis (RA) is a chronic disease in which various joints in the body are inflamed, leading to swelling, pain, stiffness, and the possible loss of function. Some experts classify rheumatoid arthritis as type 1 or type 2.

• Type 1, the less common form, lasts a few months at most and leaves no permanent disability.
• Type 2 is chronic and lasts for years, sometimes for life.

Rheumatoid arthritis is an autoimmune disease in which the body's immune system attacks itself. The pattern of joints affected is usually symmetrical, involves the hands and other joints, and is worse in the morning. Rheumatoid arthritis is a systemic (body-wide) disease, involving other body organs, whereas osteoarthritis is limited to the joints. Both forms of arthritis can be crippling.

• The disease process leading to rheumatoid arthritis begins in the synovium, the membrane that surrounds a joint and creates a protective sac.
• This sac is filled with lubricating liquid called the synovial fluid. In addition to cushioning joints, this fluid supplies nutrients and oxygen to cartilage, a slippery tissue that coats the ends of bones.
• Cartilage is composed primarily of collagen, the structural protein in the body, which forms a mesh to give support and flexibility to joints.
• In rheumatoid arthritis, an abnormal immune system produces destructive molecules that cause continuous inflammation of the synovium. Collagen is gradually destroyed, narrowing the joint space and eventually damaging bone.
• If the disease develops into a form called progressive rheumatoid arthritis, destruction to the cartilage accelerates. Fluid and immune system cells accumulate in the synovium to produce a pannus, a growth composed of thickened synovial tissue.
• The pannus produces more enzymes that destroy nearby cartilage, aggravating the area and attracting more inflammatory white cells, thereby perpetuating the process.

This inflammatory process not only affects cartilage and bones but can also harm organs in other parts of the body.

Review Date: 12/21/2006
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

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