Fibrillary and immunotactoid glomerulonephritis (FGN & IGN) are uncommon glomerular diseases, diagnosed by electron microscopic identification of fibril deposits which are negative by the Congo red stain. Micro-fibrils are similar to normal structures in glomerular basement membrane and matrix and they can be missed by EM. Pathogenesis of these glomerulopathies is unclear but they are not believed to be associated with monoclonal gammopathies as in AL amyloidosis. Immunofluorescense (IF) on FGN indicates the fibrils typically are positive for IgG and both immunoglobulin light chains while IGN fibrils are light chain monoclonal. We did immunogold labeling on four cases of FIGN in to improve the diagnosis of these diseases and investigate fibril protein composition.
Renal biopsies from four patients consisted of one IGN and 3 FGN. Tests included frozen section IF (IgG, IgA, IgM, C3), paraffin section histology (Congo Red) and conventional EM (osmium fixation and epoxy embedding).