Erosive arthritis in monoclonal gammopathy of uncertain significance: report of four cases.

We report 4 case histories in which an erosive arthritis was associated with the presence of a monoclonal gammopathy of uncertain significance. In all 4 cases, the appearance of paraprotein was noted either before or during the development of the arthritis. Two patients had a rather atypical oligoarthritis, while the others had a rheumatoid-like, symmetric polyarthritis. A synovial amyloid deposit was present in 2 patients, while mild mixed mononuclear infiltrates were the main pathologic finding in the others. In 2 patients, immunohistochemical investigation demonstrated deposits of immunoglobulin-derived material of the same isotype as the monoclonal component in the synovial tissue.