Monoclonal gammopathy in systemic lupus erythematosus.

We studied the prevalence, type and associated features of monoclonal gammopathy in patients with systemic lupus erythematosus (SLE). Patients included in the University of Toronto Lupus Database with an abnormal band on serum electropheresis were identified. Monoclonal gammopathy patients were matched with two controls each from the same database by age at SLE diagnosis, sex and disease duration. Of 1083 patients followed at the Lupus Clinic 59 (5.4%) were identified with monoclonal gammopathy. The gammopathies included 32 with IgG, 14 IgM and 12 IgA, one undefined. Nine (15.3%) malignancies were detected in monoclonal gammopathy and 12 (10.1%) in the controls during the entire course of their disease (P = 0.13). None had multiple myeloma. There was no difference between patients with monoclonal gammopathy and their controls with respect to disease activity, damage, or dose of steroids. The mean ESR and gammaglobulin levels in the monoclonal gammopathy patients were higher than the controls at last visit. We conclude that monoclonal gammopathy is more frequent in SLE patients than in the general population and has a benign course in patients with SLE. There were no differences in disease manifestations, treatment approaches, or malignancies between SLE patients with and those without monoclonal gammopathy.