A Case of Membranous-Like Glomerulopathy with Masked IgG-kappa Deposits (MGMID) in an Otherwise Healthy Young Man without Autoimmune Disease

Introduction: MGMID is characterized histologically by immunoglobulin deposits that are absent on routine frozen immunofluorescence (IF) but show strong staining for IgG and Kappa when IF is performed on formalin-fixed, paraffin embedded tissue. MGMID is largely seen in young patients with a female predominance and is associated with nonspecific autoimmune serologies and monotypic immunoglobulin deposition without underlying hematologic malignancy. Case Description: A 27 y/o man with no known past medical history was evaluated for subnephrotic proteinuria found on routine labs. He takes no medications and denies any symptoms. Labs were notable for normal serum creatinine, absence of hematuria, and unrevealing serological workup. Renal biopsy revealed a membranous glomerulopathy pattern with IF showing weak IgM & C3 staining in glomeruli, however IF was performed on a paraffin embedded sample which revealed IgG, Kappa, C3, and C1q staining in glomerular capillary walls, consistent with MGMID pattern. Discussion: This case of MGMID is unique as the patient is male and lacks features commonly seen in other MGMID patients including hematuria and positive autoimmune serologies. It is vital to consider MGMID when examining cases of glomerular disease with membranous pattern and particularly when only weak C3 staining is detected on IF.