Progression of Monoclonal Gammopathy with Undetermined Significance to Multiple Myeloma Diagnosed by Kidney Biopsy: A Case Report

Monoclonal gammopathy with undetermined significance (MGUS) carries a risk of progression to multiple myeloma, and progression is usually diagnosed with changes in M-protein or bone marrow biopsy. We report a case of 62-year-old female patient showing MGUS progression to multiple myeloma without significant changes in M-protein but diagnosed by kidney biopsy. During the follow-ups, azotemia and tubular proteinuria were aggravated without elevation of M-protein. Kidney biopsy showed intratubular and glomerular inclusions associated with plasma cell dysplasia. The progression of MGUS to multiple myeloma was diagnosed by this kidney biopsy. The patient's renal function and tubular proteinuria were markedly improved after chemotherapy.