Membranous nephropathy as a late manifestation of unrecognized IgG4-related disease — a case report and literature review

Introduction: IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder characterized by tissue lymphocyte infiltration and IgG4-secreting plasma cells, accompanied by elevated serum IgG4 levels. It typically affects the pancreas, orbits, retroperitoneum, and kidneys, usually as IgG4-related tubulointerstitial nephritis (TIN). Case report: A 64-year-old woman with hypertension, type 2 diabetes, chronic pancreatitis, bilateral cataracts, and right submandibular salivary gland excision was admitted due to nephrotic proteinuria and deteriorated kidney function, with an estimated glomerular filtration rate (eGFR) of 43 ml/min/1.73 m 2 . Laboratory tests confirmed nephrotic syndrome and revealed monoclonal gammopathy. Kidney biopsy showed membranous nephropathy (MN) negative for anti-PLA2R antibodies. Bone marrow biopsy excluded multiple myeloma. Her serum IgG4 concentration was markedly elevated, and in the context of her clinical history the findings were consistent with IgG4-R. Treatment with steroids and mycophenolate mofetil (MMF) was initiated, resulting in a favorable clinical response with improvement in proteinuria and stabilization of renal function. Conclusions: This case highlights the importance of considering IgG4-RD in patients presenting with anti-PLA2R-negative membranous nephropathy and systemic features suggestive of multi-organ involvement. Prompt diagnosis and immunosup-pressive therapy can lead to significant clinical improvement.