Pannus and rheumatoid arthritis: Historic and pathophysiological evolution

Abstract Pannus refers to synovial tissue proliferation, and has been considered a late, inactive and irreversible manifestation of rheumatoid arthritis (RA), contrary to historical findings. A literature search was performed on terminology about pannus and its historical role in the pathophysiology of RA. Light microscopy studies have shown the destructive impact of pannus tissue with very specific abnormalities, corroborated a year later with electronic microscopy. Some of these findings are the isolation of the immunological cells inside the tissue, especially one cell line with particular capacities, called synoviocytes similar to fibroblasts. This cellular component is the source a large quantity of cytokines and proteinases that perpetuate and cause bone and cartilage damage. Inflammation has been seen in many image techniques, such as magnetic resonance and ultrasound. These show the role of tissue widening and hyper-vascularization in tissue damage, and some reversibility after treatment of RA. With the evidence presented it is possible to conclude that pannus refers to a histological (more than clinical) term for synovial hypertrophy, and includes a large component of cell activity that generates and perpetuates inflammation and thus the disease.