Rheumatoid pannus is inflamed tissue that invades the joints, contributing to joint swelling, pain, and degeneration. It covers the surfaces of a joint’s bone and cartilage and releases chemicals that eat away at those tissues.
Rheumatoid pannus can develop when a joint’s lining becomes inflamed. Most of the joints in the body are surrounded by a thin, delicate lining, called synovium. When RA causes a joint’s synovium to become inflamed, it can thicken and grow out of control, invading areas of the joint where it doesn’t belong.
Other types of inflammatory arthritis, such as psoriatic arthritis and lupus, can also cause pannus. However, rheumatoid pannus is typically more severe and damaging.
A physician may look for indications of pannus during a physical examination, checking for swollen and spongy joints (sometimes called boggy joints). Rheumatoid pannus can develop in any joint. In the early stages of RA, pannus is most likely to develop in small joints, such as those in the hands, wrists, and feet.