[Case of MPO-ANCA-associated vasculitis with membranous nephropathy]

We experienced a rare case of membranous glomerulopathy(MN) with myeloperoxidase antineutrophil cytoplasmic antibody (MPO-ANCA)-associated glomerulonephritis. A 79-year-old woman was admitted to our hospital because of pyrexia, microscopic hematuria, massive proteinuria and positive MPO-ANCA on June, 2007. We diagnosed her as MPO-ANCA-associated vasculitis accompanied by nephrotic syndrome. Intravenous methylprednisolone sodium succinate (500 mg/day for three days)therapy and oral prednisolone (40 mg/day) improved her fever, hematuria, serum CRP and MPO-ANCA titer. Renal biopsy was performed and light microscopic examination of a renal biopsy specimen containing 21 glomeruli revealed global sclerosis in 3 and thickened basement membrane in 18 of the glomeruli. Fibrocellular crescents were found in 2 and segmental necrosis in 1. Immunofluorescence microscopy showed granular staining with IgG and C3 along the capillary walls. Electron microscopic examination disclosed subepithelial dense deposits in the thickened glomerular basement membrane. To investigate the pathogenesis of MN, IgG subclass was examined by means of immunofluorescence microscopy. IgG1 and IgG4 were deposited on the glomerular capillary walls, which suggested secondary MN. However, this patient refused to take any medicines and had no disease such as infection or cancer which cause secondary MN. MPO staining was performed to investigate the relation of MPO-anti-MPO antibody immune complex in the pathogenesis of MN. The results showed only a few MPO-positive cells in the glomeruli and MPO stains on the glomerular capillary walls near the MPO-positive cells. These findings suggested that the patient had MPO-ANCA-associated glomerulonephritis superimposed on idiopathic MN. In the case of nephrotic syndrome with MPO-ANCA, we should consider the coexistence of other types of glomerulonephritis, especially MN.