fibrillary glomerulonephritis ( fgn ) is an uncommon glomerular disease seen in 1% of native kidney biopsies resulting from glomerular accumulation of non - amyloid fibrillary deposits . the most common mode of presentation is nephrotic range proteinuria , microscopic haematuria and renal insufficiency . morphologically , fgn exhibits a spectrum of glomerular involvement , the most common pattern being membranoproliferative glomerulonephritis ( mpgn ) . the presentation with rapidly progressive renal failure ( rprf ) and associated crescentic glomerulonephritis is uncommon [ 13 ] . when faced with such a clinical situation in conjunction with immunofluorescence finding on renal biopsy of linear or pseudolinear immunoglobulin staining ( igg staining ) of glomerular capillary wall , the possibility of anti - glomerular basement membrane ( anti - gbm ) glomerulonephritis is often considered . we report a case wherein above clinical scenario was eventually determined to be related to fgn based on electron microscopic findings . a 59-year - old man was referred with 6 days history of nausea , headache , severe hypertension ( bp 200/100 mmhg ) and biochemical evidence of advanced renal failure ( serum creatinine concentration of 1150 mol / l , serum urea concentration of 26.2 a 24-h urinary protein excretion was 5.4 g and midstream urine contained numerous red cells ( 500  10/l ) , white cells ( 150  10/l ) but no casts . there was no evidence of pre - existing renal dysfunction , a serum creatinine concentration done a year ago was normal . he was known to have diet controlled type 2 diabetes mellitus with no documented clinical or laboratory evidence of micro or macro vascular complications . laboratory test results for antinuclear antibodies , anti - dna antibody and antineutrophillic cytoplasmic antibodies were negative . serologic tests results for human immunodeficiency virus , hepatitis b and c infection were negative . the test for circulating anti - gbm antibodies that was available after a week since the commencement of treatment was also negative . segments away from crescents showed endocapillary proliferation with necrosis in the form of nuclear pyknosis , karyorrhexix and focal deposition of fibrinoid material . there was moderate interstitial infiltrates comprising of lymphocytes , plasma cells , neutrophils along with tubular injury with epithelial sloughing . ( a ) lm : cellular crescents ( arrow ) and fibrinoid necrosis of glomerular tuft ( original magnification 200 ) . ( b ) if : linear igg staining along capillary walls ( original magnification 200 ) . ( c ) em : non - branching fibrils mesangium and capillary wall ( original magnification 36 000 ) . immunofluorescence microscopy showed intense 4 + linear deposits of igg with moderate 2 + confluent deposits of c3 along segmental mesangial and capillary loops ( figure 1b ) . in view of a diffuse proliferative and crescentic glomerulonephritis with linear igg , a diagnosis of anti - gbm glomerulonephritis was made and was treated with combination of methylprednisolone , plasmaphaeresis and cyclophosphamide and haemodialysis . these were composed of non - branching fibrils measuring 16 nm in diameter on average ( figure 1c ) . computed tomographic examination of chest , abdomen and pelvis done to screen for lymphoproliferative disorders was normal . in the above vignette , the patient had rapidly progressive glomerulonephritis ( rpgn ) clinically and crescentic glomerulonephritis pathologically . rpgn is a disease of the kidney characterized clinically by a rapid decrease in the glomerular filtration rate of at least 50% over a short period , from a few days to 3 months . rpgn comprises three major categories : ( i ) anti - gbm antibody disease ( 3% of cases ) , ( ii ) immune complex disease ( 45% of cases ) and ( iii ) pauci - immune disease form of glomerulonephritis , with the highest frequency ( 50% of cases ) . fgn is a non - amyloid glomerulopathy characterized by extracellular deposition of randomly arranged , elongated non - branching fibrils within the mesangium and capillary walls of renal glomeruli . the diameters of the fibrils are approximately twice those of the amyloid fibrils with an average of 20 nm ( range 1230 nm ) [ 4 , 5 ] . largest single centre series of fgn reported occurrence of diverse morphological patterns on light microscopy , including diffuse proliferative glomerulonephritis ( dpgn ) , mpgn , mesangial proliferative / sclerosing ( mes ) , membranous glomerulonephritis ( mgn ) and diffuse sclerosing ( ds ) . however , crescentic variety of glomerular injury is relatively uncommon and occurs in 2025% of cases [ 4 , 5 ] . immunofluorescence shows polyclonal igg and c3 staining predominantly in mesangium and granular or pseudo linear pattern along the glomerular basement membrane . the renal disease is commonly manifested clinically as nephrotic syndrome or combinations of proteinuria , haematuria , hypertension and renal insufficiency . most patients present with significant renal insufficiency and have a poor outcome despite immunosuppressive therapy , and outcome correlates with histologic subtype mean time to end - stage renal disease being : ds 7 months , dpgn 20 months , mpgn 44 months compared to mes 80 months and mgn 87 months . the presentation with rprf and dialysis dependency is rather unusual with two such anecdotes of idiopathic fgn being reported in the literature so far [ 6 , 7 ] . these two cases along with our patient share all the histological features that would allow one to make a reasonable assumption of anti - gbm - mediated glomerulonephritis , with potential to expose patients to yet unproven and often unsatisfactory immunosuppressive treatment . the majority of cases of fgn are idiopathic , although association with systemic diseases such as cryoglobulinaemia , lupus , hepatitis c virus infection and rarely dysproteinaemia have been reported . our patient never demonstrated any clinical or serological evidence of systemic disease and his continued survival > 5 years following diagnosis makes underlying lymphoproliferative disorders unlikely . this case therefore highlights the crucial role of em in the differential diagnosis of the anti - gbm antibody negative , crescentic and necrotizing glomerulonephritis with linear immunoglobulin g staining of glomerular capillary wall . since its first description in 1977 by rosenmann and eliakim , fgn has been anecdotally reported as an unusual cause of rpgn , the definitive diagnosis of which requires em .
we report an unusual case of fibrillary glomerulonephritis ( fgn ) presenting as rapidly progressive renal failure and extensive crescent formation along with linear staining of capillary walls of the glomeruli on immunofluorescence , mimicking anti - glomerular basement membrane ( anti - gbm ) antibody - mediated disease . 
 laboratory results for circulating anti - gbm antibodies were negative . 
 the subsequent electron microscopic findings were that of presence of electron - dense deposits in the glomerular mesangium and capillary walls , comprising of non - branching fibrils with an average diameter of 16 nm consistent with a diagnosis of fgn . 
 this case illustrates the crucial role of electron microscopy in differential diagnosis of crescentic glomerulonephritis .