Monoclonal IgG cryoglobulinemia with secondary development of glomerulonephritis and nephrotic syndrome.

A 45-year-old man developed in 1965 skin lesions on cold exposure and was found to have cryoglobulinemia due to an M-component of IgG class. Glomerular damage was first noted in 1970, and progressed to renal impairment and nephrotic syndrome during the next two years. Reduced serum levels of complement components C3 and C4 were found, indicating in vivo complement activation. Renal biopsy revealed proliferative glomerulonephritis and deposition of IgG and C3 along the glomerular basement membrane. Electron microscopical examination revealed a striking deposition of a 'fibrillar' or microcrystalline material in the glomerular basement membrane. This material had an ultrastructure similar to that found in the cryoprecipitate from serum. There were no tubular changes of myeloma type, neither were there any monoclonal light chains detected in the urine. So far, there are no other signs of myeloma or lymphoma. Immunosuppressive treatment with prednisone and cyclophosphamide resulted in a decrease in the serum M-component as well as a decrease in protein leakage through the glomeruli and a return to normal of glomerular filtration rate. The finding of monoclonal cryoglobulinemia, demonstrable at room temperature, in a patient developing proliferative glomerulonephritis with complement activation is unusual. It is probably that the M-component is causally related to the glomerular lesions.