Acute monosynovitis or oligoarthritis in patients with quiescent rheumatoid arthritis: some possible causes

Joint manifestations in patients with rheumatoid arthritis (RA) are usually caused by the rheumatoid disease or, less often, by secondary osteoarthritis or an infection. Effusions related to crystal deposits have been reported but are uncommon. We report on seven patients with quiescent RA who presented with incompletely explained, acute, mostly monoarticular, joint or bursal exacerbations that may have been caused by apatite or lipid crystals or by reactions to tissue and cell debris. In one of these patients, the joint symptoms were related to the development of pigmented villonodular synovitis. Whether or not our hypothesized mechanisms are correct, it is important to be aware that exacerbations in a single or a few sites out of proportion to the rest of the RA need not be because of activity of the RA or infection. This awareness can prevent inappropriate aggressive treatment of the rheumatoid disease or extensive antibiotic therapy. In our cases, careful analysis of the synovial fluid was helpful in ascertaining that active RA was less likely and in identifying some possible causes of the effusions.