IgM monoclonal gammopathy accompanied by nodular glomerulosclerosis, urine-concentrating defect, and hyporeninemic hypoaldosteronism.

A 54-year-old male had monoclonal IgM-kappa light chains in the serum and free monoclonal kappa light chains in the urine. Renal biopsy revealed nodular glomerulosclerosis associated with the accumulation of kappa light chains. Isolated microscopic hematuria was present for over 1 year. He also showed a defect in urine concentration for which the light chains deposited along the basement membrane in the inner medullary tubules were judged to be responsible. When the glomerular filtration rate fell to 30 ml/min, the syndrome of mild renal failure, decreased potassium excretion, and hyporeninemic hypoaldosteronism developed, suggesting that kappa light chain nephropathy is a cause of this syndrome. Chemotherapy appeared to have some beneficial effects in maintaining renal function.