Pannus is an abnormal layer of tissue that forms in joints, most often due to rheumatoid arthritis (RA). This extra tissue can cause pain, swelling, and damage to bones, cartilage, and other tissues within the joint.
Understanding Pannus
Pannus is not a single substance but rather a proliferative tissue mass. It's essentially a growth of inflamed synovial tissue, the lining of the joint. In healthy joints, the synovium is thin. However, in RA, the immune system attacks the synovium, causing inflammation and the formation of this abnormal pannus tissue. This pannus tissue then invades and damages the surrounding cartilage and bone.
Location of Pannus
Pannus formation isn't limited to joints affected by rheumatoid arthritis. It can also occur in other locations:
- Eyes: Pannus can develop on the cornea (the clear part of the eye), a condition known as chronic superficial keratitis in dogs.
- Heart Valves: Pannus can form on prosthetic heart valves.
- Cervical Spine: Pannus can form in the cervical spine, even in the absence of rheumatoid arthritis or trauma, potentially following spine surgery.
Composition of Pannus
While the exact composition varies, pannus primarily consists of:
- Inflammatory cells: These cells contribute to the ongoing inflammation and tissue destruction.
- Fibrous tissue: This forms the bulk of the pannus and contributes to its invasive nature. While once thought to be inactive, research suggests it may play a more active role in joint damage than previously believed.
- Blood vessels: These provide the pannus with nutrients and further contribute to inflammation.
The pannus itself is a consequence of the underlying inflammatory process, not a primary cause. Treating the underlying condition, such as rheumatoid arthritis, is key to managing pannus formation and its effects.
