A middle-aged woman presented with worsening renal function, hematuria, and nephrotic range proteinuria. Investigations were significant for an IgG kappa monoclonal protein. Serological studies were negative for hepatitis C antibody, ANA, and antibodies to myeloperoxidase (MPO) and proteinase 3 (PR3). Immunofluorescence microscopy (IF) studies demonstrated smudgy staining of the capillary loops and mesangium with IgG (3+), C3 (3+), and kappa (3+) and lambda light chains ( 3+). IgG subclass studies demonstrated strong staining with IgG4 and IgG1. No extraglomerular deposits were noted.
Mariam (Priya) Alexander, M.D.
Senior Associate Consultant, Division of Anatomic Pathology
Assistant Professor of Laboratory Medicine and Pathology,
Mayo Clinic College of Medicine