The coexistence of membranous glomerulonephritis and its cause in the same biopsy: The two faces of IgG4-related kidney disease

IgG4-related disease (IgG4-RD) is a systemic immune-mediated disease characterized by fibroinflammatory tumor-like masses that show the peculiar morphological features of storiform fibrosis, lymphoplasmacytic infiltrates rich in IgG4 positive plasma cells and obliterans phlebitis. The disease affects virtually any organ or apparatus and is often associated with increased serum IgG4 levels. Many previously described conditions (e.g. autoimmune pancreatitis, Mikulicz’s syndrome, Küttner’s tumor, and Riedel’s thyroiditis) are now classified to be part of IgG4-RD with the characteristic clinic, serologic and pathologic features. The kidney represents an important target-organ of the disease, mainly as tubulointerstitial nephritis (TIN). Nevertheless, some cases of glomerular disease, especially membranous glomerulonephritis (MNG), have been described in IgG4-related TIN. We report a case of IgG4-related kidney disease in which the two pathological patterns, TIN and MNG, were observed simultaneously in the same biopsy.