Non-IgM monoclonal gammopathy in patients with Sjögren's syndrome.

Two Japanese patients with Sjögren's syndrome with non-immunoglobulin M(IgM) class monoclonal gammopathy are described. The monoclonal IgA lambda detected in the serum and saliva was confirmed to possess rheumatoid factor activity in the first patient with a hypergammaglobulinemic purpura and hyperviscosity syndrome. Idiotype specificity was present on the surface membrane of peripheral blood lymphocytes as well as in the cytoplasm of infiltrating cells in the salivary glands. Common idiotypic specificity was found in four of 60 other patients who had rheumatoid factors. In the serum and saliva of the other patient, a monoclonal immunoglobulin G, kappa type (IgG kappa), was detected. Kappa type IgG was found in most of the infiltrating cells in the salivary glands and also in the saline extract from a resected submandibular gland. Our findings indicate that non-IgM class monoclonal gammopathy is also one of the complications of Sjögren's syndrome.