Monoclonal Gammopathy-Associated C3 Glomerulonephritis Secondary to Follicular Lymphoma: A Case Report

Introduction: C3 glomerulopathy (C3G) is defined by dominant complement component C3 deposition on kidney biopsy. Monoclonal immunoglobulin-associated C3G (MIg-C3G) is a unique subtype, and lymphoma-associated C3G is rare. Case Description: A 38-year-old male with a history of hepatitis B virus infection and follicular lymphoma presented with proteinuria, acute kidney injury, and a left neck mass. Renal biopsy revealed C3 glomerulonephritis (C3GN) with lymphoma cell infiltration in the interstitium. Kidney immunohistochemistry showed positive lymphoma (CD19 and CD20) and its subtype follicular lymphoma biomarkers (CD10 and Bcl2). Serum electrophoresis revealed a monoclonal IgM kappa M-spike. Positive autoantibodies to complement C3 convertase and complement factor H indicated complement dysregulation. Treatment with CD20 and CD79b monoclonal antibodies, Zebutinib, and Lenalidomide resolved proteinuria and restored renal function to normal. Discussion: This case underscores the rarity of follicular lymphoma-associated C3G, with only one previous report in the literature. The patient's diagnosis at a relatively young age without evidence of multiple myeloma or other forms of monoclonal gammopathy of renal significance (MGRS) emphasizes the need for a broad differential diagnosis in glomerulopathies with monoclonal immunoglobulins.The presence of lymphoma cells in the kidney interstitium represents a previously unreported occurrence in patients diagnosed with MIg-C3GN.The patient treated with lymphoma-directed therapy, resolving proteinuria and normalizing renal function, indicating effective B-cell clone treatment.Kidney histology and immunohistochemistry for general lymphoma and its subtype follicular lymphoma markers.(A) Light microscopy showed a mesangial proliferative pattern of injury with multifocal numerous lymphoma cells infiltration in the interstitium.(B) Immunofluorescence staining showed bright C3 staining along capillary walls and within mesangial areas.(C) Electron Microscopy showed electron-dense deposits in mesangial and endothelial regions (red arrows).(D) CD19.(E) CD 20.(F) CD 10.(G) Bcl2.