Inflammatory bowel disease (IBD) refers to two disorders — Crohn's disease and ulcerative colitis — marked by inflammation of the intestinal tract. They are thought to be autoimmune disorders in which the body's immune system mistakenly attacks the intestinal tract, and other parts of the body, although this is unproven.
Some people with inflammatory bowel disease have a type of arthritis that is similar to rheumatoid arthritis in some ways. However, there are some important differences. With the arthritis associated with IBD, inflammation tends to involve only a few, large joints and it tends not to involve both sides of the body equally. For example, it might affect the knee on one side and the ankle on the other. In rheumatoid arthritis, more joints, especially small ones in the hand and wrist are involved and joints on both sides of the body are affected equally. Antibodies commonly found in the blood of people with rheumatoid arthritis are not usually present in the blood of people with IBD arthritis. Unlike rheumatoid arthritis, arthritis associated with IBD may affect the lower spine, especially the sacroiliac joints, and is associated with a certain gene (called HLA-B27).
The bowel problems caused by inflammatory bowel disease usually appear long before the arthritis develops. Occasionally the arthritis appears first and the inflammatory bowel disease is diagnosed months or even years later.