• cryoglobulinemia;
  • membranoproliferative glomerulonephritis;
  • nephrotic syndrome

An 81-year-old man was admitted to our hospital because of leg edema. Serological studies for anti-neutrophil cytoplasmic antibody (ANCA), anti-double stranded DNA antibodies, and antibodies to hepatitis C and B were negative. Severe hypocomplementemia was present and a cryoglobulin was detected with serum immunoelectrophoresis being positive for the immunoglobulin (Ig)M κ type. The cryoglobulin was characterized by immunoelectrophoresis which showed that the protein was composed of polyclonal IgG and κ-type monoclonal IgM. A diagnosis of essential type II cryoglobulinemia was made and the patient underwent a renal biopsy. The renal biopsy revealed endocapillary and mesangial cell proliferation with increased matrix. The resultant lobular appearance of the glomerulus and double contours of the basement membrane were indicative of membranoproliferative glomerulonephritis (MPGN). Immunofluorescence studies demonstrated granular staining in the capillary wall for IgG, IgA, IgM and C4 with little C3 deposition but no C1q. He was finally diagnosed with MPGN due to mixed cryoglobulinemia type II. MPGN with essential cryoglobulinemia type II without evidence of hepatitis C virus infection, like that found in the present case, is very rare.