Objective: To investigate the immunologic features of synovitis in patients with polymyalgia rheumatica (PMR) and to assess the modifications induced by corticosteroids. Methods. Arthroscopic biopsies of shoulder synovium were obtained from 12 patients with untreated PMR and from 7 patients with PMR that had been treated. Immunohistochemistry was performed on frozen sections utilizing a panel of monoclonal antibodies and computerized image analysis. Results. Synovitis was present in 10 of 12 (83%) untreated patients and in only 2 of 7 (29%) treated patients. The synovitis was characterized by vascular proliferation and leukocyte infiltration. Infiltrating cells consisted predominantly of macrophages and T Lymphocytes. Almost all T lymphocytes were CD45RO positive. A few neutrophils, but no B cells, natural killer cells, or γ/δ T cells were found. Intense expression of HLA class II antigens (DR moreso than DP moreso than DQ) was found in the lining layer cells as well as in macrophages and lymphocytes. DR, but not DP or DQ, was expressed by the endothelium of a few vessels. ClassII antigen expression correlated with the number of macrophages and lymphocytes. Macrophage infiltration of arteriole walls was observed in 1 untreated patient without giant cell arteritis (GCA). In untreated patients, there was a positive correlation between the percentage of infiltrating T cells and the duration of disease. Steroid therapy was associated with a significant reduction in the number of blood vessels and of HLA class II expression. One treated patient who no longer had symptoms of PMR still had active synovitis: a relapse occurred 4 months after the biopsy. Conclusion. Our findings support the hypothesis that synovitis is a major cause of the musculoskeletal symptoms of PMR. There are immunologic similarities with the vascular inflammation observed in GCA. Corticosteroids act on both the vascular and cellular components of synovitis.
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