Monoclonal gammopathy of renal significance: A novel combination of C3 glomerulopathy and light-chain proximal tubulopathy

Introduction: According to the recent International Kidney and Monoclonal Gammopathy Research Group Consensus report, the spectrum of monoclonal gammopathies of renal significance merges more than 12 conditions; and combinations of various patterns of monoclonal gammopathies of renal significance–associated kidney damage have already been described. We present a case of a previously unreported combination of C3 glomerulopathy and light-chain proximal tubulopathy. Case description: A 53-year-old Caucasian man presented with general weakness. Three years prior, a check-up revealed proteinuria and microhematuria, later accompanied by arterial hypertension, elevated serum creatinine, and a low serum C3 levels. On admission, his creatinine was 1.5 mg/dL; his protein excretion was 1900 mg/24 h with microhematuria at 150 hpf. His serum C3 was 79 mg/dL with a normal C4 level. Serum protein electrophoresis revealed an M-spike, immunochemistry confirmed monoclonal immunoglobulin G kappa secretion of 920 mg/dL, and traces of Bence–Jones protein kappa in his urine. A kidney biopsy showed mesangial hypercellularity with diffuse fine granular C3 mesangial expression and tubular atrophy with diffuse coarse granular kappa light-chain tubular epithelial cytoplasmic expression. Computed tomography did not reveal any destructive lesions. A bone marrow smear showed 5% plasma cells, and bone marrow cell flow cytometry demonstrated 87.4% of plasma cells with an aberrant phenotype. The patient was diagnosed with an monoclonal gammopathy of renal significance and administered bortezomib–cyclophosphamide–dexamethasone. After four courses, his monoclonal immunoglobulin G kappa secretion halved, but his serum creatinine and proteinuria remained almost unchanged. Chemotherapy was switched to lenalidomide–dexamethasone, and after five courses his immunoglobulin G kappa secretion decreased to traces, Bence–Jones protein was not observed and his urinalysis, serum creatinine, and C3 levels were detected as normal. Conclusion: The combination of kidney damage patterns, one of which was directly and the other indirectly associated with monoclonal gammopathy, complements the monoclonal gammopathies of renal significance spectrum. Chemotherapy led to a very good partial response and kidney function recovery.