Renal involvement in non-malignant IgM gammopathy.

Renal involvement is observed frequently in association with malignant gammopathies, mainly those related to light chain deposition [1]. Nevertheless, light chain deposition renal disease has also been described in non-malignant monoclonal gammopathy, namely in IgG or IgA plasma cell dyscrasia [2,3]. Renal involvement in IgM monoclonal disorders is traditionally described in patients with malignant disease (Waldenström’s macroglobulinaemia) that includes the deposition of monoclonal IgM and light chains on mesangium and glomerular capillary wall [4–6]. IgM monoclonal gammopathy without malignant criteria can be found in asymptomatic patients or associated with polyneuropathic disease, but renal involvement has rarely been described in this clinical setting [7,8]. We report the case of a patient with non-malignant IgM/k gammopathy, who developed nephrotic proteinuria and progressive renal failure in association with renal deposition of IgM and k light chains.