Glomerular lesions in monoclonal gammopathies and mixed essential cryoglobulinemias IgG-IgM

Histologic studies of renal tissue were performed in 21 cases of IgG or IgA benign monoclonal gammopathy, in 19 cases of IgM monoclonal gammopathy, and in 11 cases of mixed idiopathic IgG-IgM cryoglobulinemias. Except for myeloma, glomerular lesions were very frequent. Amyloidosis was found in one patient with myeloma, in two with benign IgG gammopathy, and in three with Waldenström macroglobulinemia. Intraglomerular deposits were found in 13 patients. In 7 of these patients (6 with Waldenström macroglobulinemia, 1 with benign IgA monoclonal gammopathy), the deposits were isolated without cellular proliferation. In the other 6 patients (one with benign IgG monoclonal gammopathy, five with IgG-IgM cryoglobulinemias) the deposits were associated with severe endocapillary proliferation. Immunohistologic study showed the presence of immunoglobulins in these deposits. The immunoglobulin(s) present in the glomerular deposits was (were) similar to the serum monoclonal immunoglobulin or immunoglobulins of the cryoglobulin. Crystals were found in the glomerular endothelial cells in one case of benign IgG gammopathy. The significance of these lesions is briefly discussed.