IgG4-related nephropathy with monoclonal gammopathy: two cases and literature review

Qian Dong^1*Xuanli Tang²Jiang Liu¹Pengjie Xu¹

• ¹The Affiliated Lihuili Hospital of Ningbo University, Ningbo, China
• ²Hangzhou Hospital of Traditional Chinese Medicine, Hangzhou, Zhejiang Province, China

Backgroud: IgG4-related disease (IgG4-RD) is a newly classified but poorly understood immue-medicated systemic disease. Monoclonal gammopathy is a type of disease characterized by the abnormal increase of monoclonal immunoglobulin in blood or urine due to clonal proliferation of plasma cells. IgG4-related nephropathy combined with monoclonal immunoglobulinemia is very rare in clinical practice and the underlying mechanisms are not well understood. Case presentation: This article reports two rare cases of IgG4-related kidney disease combined with monoclonal gammopathy. Case 1 was a 69-year-old male presented with renal insufficiency and mild proteinuria, along with significant elevations of IgG, IgG4, EOS, and IgE, and severe reductions in complement C3 and C4. Serum free light chains κ and λ levels were elevated, monoclonal immunoglobulin IgG-λ was detected, and lymphadenopathy was observed. Renal biopsy revealed multi-focal and flaky storiform fibrosis.In the renal interstitium, IgG4-positive cells >10/HPF, IgG4/IgG >40%. Interstitial inflammatory cells k were scattered weakly positive, and λ was diffuse strong positive. Bone marrow aspiration did not show obvious plasmablast or abnormal plasma cell clones, but eosinophils were significantly elevated. Case 2 was a 71-year-old male presented with renal insufficiency and massive proteinuria, along with elevated IgG and IgG4 levels. Serum free light chain κ and λ were elevated, and monoclonal IgM-k was identified. PLA2R testing was negative. Renal biopsy revealed secondary membranous nephropathy(SMN)without evidence of monoclonal renal injury. Bone marrow aspiration showed evident eosinophils, mature plasma cells accounted for 3.5% and no express light chain restriction. Conclusions: Case 1 was diagnosed with IgG4-TIN combined with MGRS, which showed significant renal and hematological improvement after corticosteroid therapy. Case 2 was diagnosed secondary membranous nephropathy combined with MGUS, but IgG4-MN cannot be ruled out.His renal function improved with corticosteroids and RTX treatment, M-protein persisted.