Monoclonal gammopathy of renal significance; experience of a tertiary care hospital in India

Introduction: Monoclonal gammopathy of renal significance (MGRS) disorders are indolent B-cell or plasma cell lymphoproliferative neoplasms which do not meet the hematological criteria for malignancy, however they cause renal dysfunction as a result of production of nephrotoxic monoclonal immunoglobulin (MIg). Objectives: To study the clinical presentation, laboratory features, light microscopy and immunofluorescence (IF) characteristics of all cases of MGRS diagnosed at our hospital over a period of five years. Patients and Methods: A record of all renal biopsies performed at our hospital between 2014-2019 was accessed from the database. Out of 1356 kidney biopsies, 68 had evidence of MIg deposition on immunofluorescence. Only six cases met the criteria of MGRS. Histopathological and immunofluorescence characteristics were studied to classify the lesions as per International Kidney and Monoclonal Gammopathy (IKMG) Research Group classification. Results: All six cases presented with deranged renal function. Four had sub-nephrotic and one had nephrotic range proteinuria. MIg was identified in only one case on serum protein electrophoresis and free light chain assay. Using a conjunction of histomorphology of renal lesions, special stains and immunofluorescence all six cases of MGRS were categorized as per IKMG classification into monoclonal immunoglobulin deposition disease (two cases), AL amyloidosis, light chain cast nephropathy, proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) and light chain proximal tubulopathy (LCPT). Conclusion: MGRS presents as renal failure and proteinuria. MIg may not be detected on protein electrophoresis due to low-secretion in serum. A kidney biopsy is essential to study the morphology of renal lesions and identify MIg deposition.