Proliferative glomerulonephritis with monoclonal immunoglobulin light chain deposits: a rare entity mimicking immune-complex glomerulonephritis.

A 39-year-old man developed proteinuria, hematuria, and renal insufficiency. A renal biopsy revealed the presence of mesangial proliferative glomerulonephritis with monoclonal λ-light chain deposits without evidence of immunoglobulin G (IgG), immunoglobulin A (IgA) or immunoglobulin M (IgM) deposits. Electron microscopy revealed granular electron-dense deposits resembling immune-complex deposits. No monoclonal proteins were detected in the serum or urine. The patient was treated with an angiotensin II receptor antagonist, and his condition was almost stable during the 1-year follow-up. This case shares common pathological characteristics with the newly described entity referred to as "proliferative glomerulonephritis with monoclonal IgG deposits" in which, glomerular deposits are composed entirely of monoclonal IgG. Therefore, we term the unusual form of glomerulonephritis observed in the present case "proliferative glomerulonephritis with monoclonal immunoglobulin light chain deposits."