Crystalline inclusions in the glomerular podocytes in a patient with benign monoclonal gammopathy and focal segmental glomerulosclerosis.

We report a case of a 40-year-old woman with benign monoclonal gammopathy who developed focal segmental glomerulosclerosis associated with widespread deposition of large crystalline inclusions in the glomerular podocytes. Electron microscopy showed that the crystalline structures were electron dense and needle shaped or polygonal. At a higher magnification, they were seen to be surrounded by unit membranes and to feature a longitudinal filamentous substructure. These inclusions showed positive immunohistochemical staining for kappa light chain. Clinically, the patient had shown nephrotic syndrome on the first medical examination, and later revealed chronic renal failure and monoclonal gammopathy of the immunoglobulin G kappa type, but no evidence of multiple myeloma or other lymphoproliferative diseases. This patient seems to have had a rare form of glomerular involvement associated with benign monoclonal gammopathy.