Systemic lupus erythematosus with paraproteinemia.

Nine patients (2.2%) in a group of 415 who were followed in a longitudinal prospective study of systemic lupus erythematosus (SLE) were found to have various monoclonal (M) proteins in their blood (IgG [6 patients], IgA [2 patients], IgM [1 patient]). No other findings compatible with plasmacytic dyscrasia were found. Bence Jones proteinuria was absent. Bone marrow aspirates and skeletal radiographs did not reveal any associated features of malignancy. Four of the 9 patients were under the age of 50. From the point of view of the M components, 3 groups emerged: transient (2 patients), persistently stable (6 patients), and increasing serum concentrations (1 patient). Using current measures of disease status, no correlation was apparent between the presence, type, and concentration of the M protein and the clinical and laboratory variables of lupus activity. Thus, M proteins were found in 2% of our SLE patients, but their relationship to the polyclonal B cell activation seen in this disorder, or perhaps to therapeutic modalities used in its treatment, remains to be elucidated.