A case of MPO-ANCA-positive granulomatosis with polyangiitis followed by rapidly progressive glomerulonephritis mediated by anti-GBM antibody

Abstract

A 65-year-old man developed rapid deterioration in renal function, demonstrating an elevated serum creatinine level of up to 9.2 mg/dL, after previously being treated for lung involvement due to granulomatosis with polyangiitis (GPA) with positive findings of myeloperoxidase-antineutrophil cytoplasmic antibodies (MPO-ANCA) for two months. Renal pathology revealed necrotizing crescentic glomerulonephritis with giant cells, and immunofluorescence microscopy showed characteristic linear deposition of IgG along the glomerular basement membrane (GBM). According to the positive findings of anti-GBM antibodies of over 350 U/dL, the patient was diagnosed with rapidly progressive glomerulonephritis (RPGN) mediated by anti-GBM antibodies. At the onset of the development of the lung lesions, the patient was negative for proteinase 3-antineutrophil cytoplasmic antibodies (PR3-ANCA), and had slightly elevated titers of MPO-ANCA. However, only the latter increased significantly at the onset of development of the rapid deterioration in renal function. The patient’s renal function was not restored when treated with a combination of plasmapheresis and a high dose of intravenous methylprednisolone, and the patient ultimately required maintenance dialysis. We report this as a case of GPA followed by anti-GBM disease. This case highlights the importance of making a pathological diagnosis of small vessel vasculitis and considering its pathogenesis.