Rheumatoid arthritis is characterized by painful, swollen joints that feel warm to the touch and are often stiff. The stiffness and pain are usually worse in the morning. Various blood tests are used to confirm the diagnosis – they look for certain factors in the blood that are characteristic of rheumatoid arthritis.

Inflammation is the cause of the problem, and the part to be affected first is the synovial membrane, although the inflammation later spreads to other parts of the joint. The synovial membrane has an important role to play in the joint, because it produces the fluid that lubricates the joint. The synovium, which surround the joint, is filled with this fluid. In rheumatoid arthritis the synovial membrane is invaded by large numbers of immune cells which cause the inflammation.

The presence of all these immune cells suggests that there is an infection in the membrane, and early theories about rheumatoid arthritis invoked some bacteria or virus. But despite many years of searching, no infectious agent has been found. An alternative theory suggests that the body is mounting an immune reaction against its own proteins – in other words, that rheumatoid arthritis is an autoimmune disease. Some recent discoveries tend to support this idea. A third theory suggests that there is an overgrowth of cells in the synovial membrane which attracts the attention of the immune system – this idea is currently being tested.

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