Synovial Histopathology in Early Rheumatoid Arthritis

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Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by a progressive destruction of joints. Previous studies identified capillary damage, edema, vascular congestion, and cellular infiltrates as earlier pathological changes in the rheumatoid synovium of disease of less than 6 weeks duration. However, it is possible that even 6 weeks is too late to identify some important early changes, since recent studies have suggested that the debut of RA already represents a chronic phase of the disease. In this report, we show the histological features of the synovium in early RA. Synovial tissues were obtained by arthroscopic synovectomy from three patients who had had episodes of monoarthritis for one or two years prior to the development of typical RA, satisfying the American Rheumatism Association 1987 criteria. As controls, four patients with osteoarthritis in the knee joints and, two patients with systemic lupus erythematosus and aseptic necrosis of the knee joints were additionally studied. The common histologic findings of the synovium of the early RA patients on the light microscopy revealed very mild proliferation of lining cells with capillary congestion and mild mononuclear cell infiltration. However, similar changes were also detected in the control patients. Of note, a proportion of the biopsied synovium showed only angioneogenesis without either lining cell proliferation or mononuclear cell infiltration, which was not detected in the control patients. The results thus suggest that angioneogenesis may precede any other features, such as lining cell proliferation and cellular infiltration in early RA. Moreover, it is most likely that angioneogenesis might be the feature that is most proximal to the etiology in early RA.