Light and heavy chain deposition revealed by repeat renal biopsy after inconclusive initial biopsy

Monoclonal gammopathy is a premalignant condition associated with an abnormal circulating immunoglobulin indicative of an expanded B cell clone. Apart from monitoring, no other intensive management is prescribed in these cases. Periodic bone marrow biopsies when free light chain imbalances are detected are used to spot incidental cases of multiple myeloma. New reports have suggested the existence of a monoclonal gammopathy of renal significance where a circulating antibody and normal bone marrow biopsy results may be associated with proteinuric renal disease due to monoclonal immunoglobulin deposition. We report a case of a 65-year-old male with an immunoglobulin G kappa monoclonal gammopathy of undetermined significance, chronic kidney disease, proteinuria, and an initial inconclusive renal biopsy. His chronic kidney disease worsened with persistence of 0.5 g of proteinuria. Given the finding of ongoing Bence Jones proteinuria, a repeat renal biopsy was done revealing monoclonal immunoglobulin G kappa deposition disease. Bone marrow biopsy showed 20% plasma cells that could be consistent with smoldering myeloma. The patient’s renal disease has stabilized after starting treatment for the monoclonal gammopathy of renal significance. This case illustrates the importance of renal biopsy in making the diagnosis of monoclonal immune deposition disease and monoclonal gammopathy of renal significance.