RESUMEN
BACKGROUND: Morbidity associated with monoclonal gammopathy of renal significance is high due to the severe renal lesions and the associated systemic alterations. Accordingly, early diagnosis is fundamental, as is stopping the clonal production of immunoglobulins using specific chemotherapy. CASE PRESENTATION: A 75-year-old man with chronic renal disease of unknown origin since 2010 experienced rapid worsening of renal function over a period of 6 mos. Bone marrow biopsy showed monoclonal gammopathy of undetermined significance. Kidney biopsy showed the presence of C3 glomerulonephritis, with exclusive deposits of C3 visible on immunofluorescence and a membranoproliferative pattern on light microscopy. Skin biopsy showed endothelial deposition of complement. Given both the renal and cutaneous involvement the patient was considered to have monoclonal gammopathy of renal significance. We considered an underlying pathogenic mechanism for the renal alteration secondary to activation of the alternative complement pathway by the anomalous immunoglobulin. Despite treatment with plasmapheresis, bortezomib and steroids, advanced chronic kidney disease developed. CONCLUSIONS: The possible underlying cause of the monoclonal gammopathy of renal significance suggests that monoclonal gammopathy should be considered in adult patients with membranoproliferative glomerulonephritis.