How does rheumatoid arthritis begin in the synovial membranes of joints?

In rheumatoid arthritis, the disease process begins with active inflammation within the synovial membranes of the joints. These membranes, which normally hold the fluid that lubricates the joints, become red and swollen.1

This inflammatory response is driven by an autoimmune mechanism, where the body’s immune system mistakenly attacks its own connective tissues. While the exact trigger remains unknown, evidence suggests that individuals with a genetic susceptibility may experience an immune reaction following exposure to an environmental agent, such as a virus. This activation leads to the production of autoantibodies, such as rheumatoid factor, which initiate the inflammatory cascade.1

As the condition progresses, this inflammation leads to the development of a layer of roughened granulation tissue known as pannus. This tissue eventually protrudes over the cartilage, causing it to erode and be replaced by scarlike tissue, which can lead to permanent joint deformity and loss of function.1