Fibrillary glomerulonephritis presenting as rapidly progressive glomerulonephritis

Fibrillary glomerulonephritis (GN) is an uncommon cause of rapidly progressive kidney failure. We report a case of rapidly progressive kidney failure with kidney biopsy showing crescentic GN on light microscopy and immunofluorescence showing linear/globular glomerular basement membrane (GBM) staining for immunoglobulin G and C3, consistent with anti-GBM disease. However, electron microscopy showed fibrillary deposits in the GBM, suggesting a diagnosis of fibrillary GN. As exemplified by this case, it is important to consider fibrillary GN in the differential diagnosis of crescentic GN with linear immunoglobulin G deposits within the GBM. Electron microscopy is crucial to make this diagnosis.