Synovial membrane and fluid morphologic alterations in early rheumatoid arthritis: microvascular injury and virus-like particles.

Eight patients have been studied during the first 6 weeks of rheumatoid synovitis. All of them exhibited microvascular injury, which was manifested by gaps between endothelial cells, vascular occlusion, erythrocyte extravasation, or endothelial cell injury. In four patients, a variety of virus-like particles were found associated with the endothelium or perivascular cells. In two cases, particles were seen in electron-dense deposits in vessel walls. Lymphocytes and PMN infiltrated the synovial membranes, but plasma cells were uncommon. Evidence of phagocytosis was prominent in synovial lining cells and other large mononuclear cells, but not in PMN. These observations are consistent with injury to synovium and, specifically, synovial vessels as an early stage in RA synovitis. The virus-like particles require further investigation, because nonviral cell components remain very difficult to distinguish in electron microscopy tissue sections.