Analyzing synovial tissue samples. What can we learn about early rheumatoid arthritis, the heterogeneity of the disease, and the effects of treatment?

The synovium is the key target of the disease process in rheumatoid arthritis (RA). Examination of synovial tissue samples may provide insight into the events that take place in different phases of the disease and may help to decipher the mechanism of action of antirheumatic treatment. This review describes the features of synovitis in early RA, which clearly represent chronic inflammation. There is marked interindividual variability, suggesting that RA consists of different pathogenetic subsets. Evaluation of serial synovial tissue samples has shown that effective treatment is associated with a reduction in synovial macrophages, independent of the specific mechanism of action of the compound. This suggests that these are key effector cells in the pathogenesis. In addition, it provides a biomarker that can be used in clinical trials.