Pannus Rheumatoid Arthritis
Pannus in rheumatoid arthritis is defined as thickened synovial tissue which covers articular cartilage, i.e. the cartilage present in joints. Synovial tissue is the tissue of synovium i.e. the lining of the joints. With the thickening and proliferation of synovium, the joint is filled by the thickened tissue and the tissue thus abnormally proliferated, spreads across the articular cartilage and subsequently causes erosions. There is also a risk of the pannus to penetrate into the bone and bone marrow and harm the surrounding parts such as joint capsule and tendons.
In patients of rheumatoid arthritis, pannus formation is an unavoidable situation in the long run. Pannus triggers destruction of bone and cartilage. Continuous progression of the disease normally coincides with the process of pannus formation. Pannus is generally a membrane of vasuclarised granulated tissue and is formed of mesenchyme and bone marrow derived cells. It is rich in fibroblasts, macrophages and lymphocytes, received from synovial tissue. It overgrows the bearing surface of the arthritic joint and is connected to the breakdown of the articular surface
Pannus formation also triggers macrophges to discharge IL-2, prostaglandins, platelet-derived growth factor, and substance P. All these, in turn, stimulate destruction of cartilage and bone erosion.
Rheumatoid arthritis is an autoimmune, inflammatory, systemic, progressive disease. Though its principal site of occurrence is joints, it may become systemic too, meaning other organs of the body too may be involved.
The ways of joint destruction caused in rheumatoid arthritis vary more than in case of osteoarthritis. Being an autoimmune disease, the rheumatoid arthritis is characterized by impaired immune system which eats up body’s own healthy tissues, the process of which takes place in three phases of inflammation. First is inflammation of synovial lining, second is spread of pannus membrane into the joint and third is release of certain enzymes by the inflamed cells which start digesting cartilage and bone, thereby joint destruction takes place.
Studies, done regarding similarities and differences between the progression of these three processes, and especially, formation of pannus in rheumatoid arthritis and osteoarthritis, show that there is much similarity in the pannus formation of both the conditions. But the osteoarthritis pannus, after invading the cartilage does not give rise to marginal erosions, which happens in rheumatoid arthritis.
MMPs (matrix metalloproteases) are some enzymes belonging to a large proteolytic enzyme group. They degrade the extracellular matrix. In the early stages of RA, MMPs increase in pannus and partake in the invasion of cartilage. They do that by destroying extracellular matrix and by stimulating other proteinases. Some of these stimulated proteinases may either directly degrade the cartilage, thereby causing joint destruction or they may degrade extracellular matrix and thus helps pannus invasion. The proteinases can be released by synovial fibroblast and cells resembling macrophages and are capable to digest the contents of the cartilage matrix and the destruction process takes place mainly in areas near inflamed pannus tissue.
Panuus also occurs in the cornea of the eye from the conjunctiva as a response to inflammation and the condition is called chronic superficial keratitis.
Pannus in rheumatoid arthritis is a quite dangerous condition and if left untreated, may even lead to sudden death and therefore needs immediate attention.