What is Pannus?
Pannus is a term often used in the context of various diseases, particularly those affecting the joints and eyes. In histology, pannus refers to an abnormal layer of fibrovascular or granulation tissue. This tissue can invade and destroy normal tissue, leading to significant complications. Pannus formation is a hallmark of diseases such as
rheumatoid arthritis and
keratitis.
Histological Characteristics of Pannus
Histologically, pannus is characterized by the presence of inflammatory cells, fibroblasts, and newly formed blood vessels. The tissue is often rich in
cytokines and
growth factors, which promote further inflammatory and fibrotic responses. The cells commonly found in pannus include
macrophages,
lymphocytes, and
fibroblasts.
Pannus in Rheumatoid Arthritis
In rheumatoid arthritis, pannus forms within the synovial joints. The synovial membrane becomes thickened and inflamed, producing pannus that invades the articular cartilage and subchondral bone. This process leads to the destruction of the joint and is a key feature in the pathogenesis of rheumatoid arthritis. Histologically, the pannus in rheumatoid arthritis is composed of an aggressive mixture of synoviocytes, inflammatory cells, and fibrovascular tissue.Pannus in the Eye
In the eye, pannus commonly occurs in conditions like chronic conjunctivitis and keratitis. The corneal pannus is characterized by the growth of granulation tissue across the corneal surface, which can impair vision. Histologically, this pannus consists of fibrovascular tissue with a mix of inflammatory cells and neovascularization.Mechanisms of Pannus Formation
The formation of pannus is driven by a combination of inflammatory and fibrotic processes. Cytokines such as
TNF-α and
IL-1 play a crucial role in promoting inflammation and the proliferation of fibroblasts. Growth factors like
VEGF contribute to the development of new blood vessels within the pannus, perpetuating its growth and invasive behavior.
Clinical Implications
The presence of pannus has significant clinical implications. In rheumatoid arthritis, it leads to joint destruction, pain, and loss of function. In ocular conditions, pannus can result in vision impairment or loss. Understanding the histological features and mechanisms underlying pannus formation is essential for developing targeted therapies.Therapeutic Approaches
Treatment strategies for conditions involving pannus often aim to reduce inflammation and inhibit the growth of fibrovascular tissue. In rheumatoid arthritis, medications like
DMARDs and
biologic agents target specific cytokines involved in pannus formation. For ocular pannus, treatments may include anti-inflammatory medications, surgical removal of the pannus, or other interventions to reduce neovascularization.
Conclusion
Pannus represents a significant pathological entity in various diseases, characterized by its invasive and destructive properties. Histologically, it is marked by a combination of inflammatory cells, fibroblasts, and neovascularization. Understanding the mechanisms and clinical implications of pannus is essential for effective treatment and management of the associated conditions.
