Comparison of synovial tissues from the knee joints and the small joints of rheumatoid arthritis patients - Implications for pathogenesis and evaluation of treatment

Objective. Serial synovial biopsy samples are increasingly being used for the evaluation of novel therapies for rheumatoid arthritis (RA). Most studies have used tissues from knee biopsies, but technical improvements have made serial small joint arthroscopy feasible as well. Theoretically, there could be differences in the features of synovial inflammation between various joints as a result of mechanical factors, differences in innervation, and other factors. We therefore undertook this study to compare the cell infiltrate in paired synovial biopsy samples from inflamed knee joints and paired inflamed small joints of patients with RA. Methods. Nine RA patients with both an inflamed knee joint and an inflamed small joint (wrist or metacarpophalangeal joint) underwent an arthroscopic synovial biopsy of both joints on the same day. Multiple biopsy specimens were collected and stained for macrophages, T cells, plasma cells, fibroblast-like synoviocytes, and interleukin-6 (IL-6) by immunohistochemistry. Sections were evaluated by digital image analysis. Results. There were no significant differences in mean cell numbers for all markers investigated in samples from the knee joint compared with samples from the small joints. We detected statistically significant correlations for the numbers of sublining macrophages, T cells, and plasma cells, as well as for IL-6 expression, between the knee joint and the small joints. However, there was no significant correlation between different joints for the numbers of intimal macrophages or fibroblast-like synoviocytes. Conclusion. The results of this study show that the inflammation in one inflamed joint is generally representative of that in other inflamed joints. Therefore, it is possible to use serial samples from the same joint, selecting either large or small joints, for the evaluation of antirheumatic therapies.