Monoclonal gammopathies in patients with Sjögren's syndrome

We studied 18 sera of Sjögren's syndrome (SS) with monoclonal gammopathy. Monoclonality was established by typical immunoelectrophoretic findings in all patients and confirmed by idiotypic (Id) studies in 12 patients. Four of the monoclonal gammopathies were of the IgG class, 8 were of the IgA class and 4 were of the IgM class, and 2 patients had 2 M proteins (IgMK/IgGK and IgAK/IgGK). The monoclonal rheumatoid factor (RF) was found in 6 patients (4 IgA and 2 IgM). A review of the literature revealed additional 19 monoclonal gammopathies (2 IgG, 9 IgA, 7 IgM and one Bence Jones protein) in Japanese SS patients. In non-Japanese SS patients, 27 monoclonal gammopathies (4 IgG, 2 IgA, 20 IgM and once Bence Jones protein) were reported. Both Japanese and non-Japanese patients showed a higher incidence of monoclonal gammopathies in primary than in secondary SS. The non-IgM class monoclonal gammopathies were predominant in Japanese SS patients, whereas monoclonal gammopathies were mostly confined to the IgM class in non-Japanese SS patients. These results indicate that monoclonal gammopathy is another significant complication of SS.