Rheumatoid arthritis

Rheumatoid arthritis is a chronic autoimmune disease: the body's defenses turn on the synovium, the thin membrane that lines the joints. It usually starts in the small joints of the hands, wrists and feet and tends to affect both sides of the body at once. Unlike osteoarthritis, which comes from wear on the cartilage, it is driven by inflammation, and it can also involve the lungs, eyes, skin, blood vessels and heart.

Its cause is a mix of inherited risk and outside triggers. Variants of the HLA genes, especially HLA-DRB1, carry the largest genetic risk, and long-term smoking is the best-established environmental factor; women are affected two to three times as often as men. In the joint, immune cells and signaling proteins called cytokines, such as tumor necrosis factor, make the synovium swell and thicken into tissue that eats into cartilage and bone. Patients have pain, swelling and stiffness that is worst in the morning, often in flares separated by calmer spells, along with tiredness.

Diagnosis combines the pattern of joints involved with blood tests for rheumatoid factor and anti-CCP antibodies, markers of inflammation and X-rays or ultrasound. There is no cure, but early treatment with disease-modifying drugs such as methotrexate, or biologic drugs that block cytokines, can prevent much of the joint damage.