What Is Pannus?

Understanding Pannus

This post was written with Consensus AI Academic Search Engine – please read our Disclaimer at the end of this article. Pannus is a term used to describe the proliferation of synovial tissue, which is a significant feature in conditions such as rheumatoid arthritis (RA) and osteoarthritis (OA). It is characterized by invasive granulation tissue that covers the articular surface, leading to joint damage1 3 4. In RA, pannus is an aggressive structure that invades cartilage and bone, causing irreversible joint damage6. It is histologically defined by synovial hypertrophy and a high level of cellular activity that generates and perpetuates inflammation1.

Pannus in Rheumatoid Arthritis

In rheumatoid arthritis, pannus formation is a late-stage manifestation that contributes to the destruction of cartilage and bone. The synovial tissue becomes hyperplastic and infiltrated with immune cells, particularly synoviocytes similar to fibroblasts, which produce cytokines and proteinases that damage bone and cartilage1 6. This process is visible through imaging techniques like MRI and ultrasound, which show tissue widening and hyper-vascularization1.

Pannus in Osteoarthritis

Although traditionally associated with RA, pannus-like tissue has also been observed in osteoarthritis. OA pannus shares some metabolic characteristics with RA pannus, such as the expression of pro-inflammatory cytokines like TNF-alpha and IL-1beta, although at different levels3 4. In OA, pannus is less aggressive and does not typically cause the marginal erosions seen in RA3. Studies in rat models have shown that OA pannus can have both catabolic and reparative features, with the latter becoming more dominant in later stages of the disease4.

Pannus in Other Contexts

Pannus can also refer to a condition affecting the cornea, known as corneal pannus. This condition involves the growth of fibrovascular tissue over the cornea, which can be distinguished from other lesions like ocular surface squamous neoplasia through clinical and imaging techniques5.

Conclusion

Pannus is a critical pathological feature in both rheumatoid arthritis and osteoarthritis, contributing to joint damage through its invasive and inflammatory nature. While it is more destructive in RA, it also plays a role in OA, albeit with different characteristics and outcomes. Understanding pannus is essential for developing targeted treatments to mitigate its effects and improve patient outcomes.

Disclaimer

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