Monoclonal Membranous Glomerulopathy in a Patient with Positive Serology for Lupus Nephritis

Abstract Introduction/Objective Monoclonal membranous glomerulopathy (M-MGN) is a rare entity; only two reports are available in the literature. Monoclonal membranous glomerulopathy has been called either monoclonal immunoglobulin deposition disease associated with membranous features in a 3-patient small series report or membranous glomerulopathy with light chain restriction in another larger series with 28 cases. We report M-MGN in a patient with positive serology lupus. Methods/Case Report The patient was a 74-year-old man with hypertension and nephrotic range proteinuria (protein/creatinine ratio at 8.5). His serum creatinine remained normal at 0.6 mg/dL. The patient was positive for double-stranded DNA and ANA at low titer, but had reduced complement C3 and C4. Immunofixation was negative for monoclonal protein. The light microscopy of the renal biopsy revealed thickened loops of glomeruli with mild interstitial nephritis. Immunofluorescent studies showed a positive linear/granular pattern of IgG and lambda but negative kappa staining along the glomerular loops. Electron microscopy revealed smooth contoured stage 2 subepithelial deposits. An outside consultation confirmed our diagnosis and found IgG2 restriction in glomeruli. Electrophoresis revealed no monoclonal protein in the serum. Results (if a Case Study enter NA) NA Conclusion Our patient demonstrated M-MGN with mild interstitial nephritis; the latter may be related to his lupus status. As 30% of patients with M-MGN have either monoclonal serology or B-cell lymphoproliferative disorders, with most having a restricted IgG subtyping, a close follow-up and even chemotherapy for a B-cell clone should be considered.