C3 glomerulonephritis in multiple myeloma

BACKGROUND C3 glomerulonephritis (C3 GN) is a recently defined entity characterized by predominant C3 deposition in glomeruli due to abnormal activation of the alternative pathway of complement system. C3 GN has been reported to be associated with several systemic diseases. However, the association between C3 GN and multiple myeloma (MM) has not been well established. METHODS We herein describe a case presenting with C3 GN on top of MM. RESULTS A 64-year-old Chinese female presented with gross hematuria, renal dysfunction, anemia, and weight loss. Results of serum immunofixation assay and bone marrow biopsy confirmed the diagnosis of IgG-λ-type MM. In addition, renal biopsy demonstrated histological findings characteristic of C3 GN, including mesangial and endocapillary proliferation under light microscope, electron-dense deposits under electron microscope, and diffuse granular deposition of C3 with no immunoglobulin under immunofluorescence microscope. These histological findings, combined with low serum C3 level, suggested the occurrence of C3 GN in the context of MM. CONCLUSION This case study provides additional evidence to the literature in terms of the association between C3 GN and MM. We hypothesize that C3 GN may present as a new variant of nephropathy in MM and the mechanism behind this association merits further study.