Fibrillary glomerulonephritis (FGN) is a rare primary glomerular disease (0.5-1% of renal biopsies). It is defined by the ultrastructural finding of randomly arranged, straight fibrils measuring 10-to-30 nm in thickness at electronic microscopy (EM), which is the gold standard for diagnosis. On the contrary, light microscopic patterns are not specific, including mesangioproliferative/sclerosing GN, membranous or membrano-proliferative patterns. By definition, mesangial and/or capillary wall immunoglobulin IgG deposits are Congo-red negative. On immunofluorescence, deposits are composed mostly of polyclonal IgG4. FGN is associated with poor renal prognosis because one-half of patients progress to end-stage renal disease within few years after diagnosis. The therapeutic strategy in FGN remains to be defined (Guillermo A Herrera – 2010 , Nasr SH – 2011  (full text), Javaugue V – 2013 ). We report about all FGN cases followed at our institution.
All consecutive patients with a biopsy-proven FGN performed at our Unit between first January 2008 and 31th December 2012 were included.
In 145/450 biopsies, electronic microscopy was performed. In four patients FGN was diagnosed (see Table). The mean age was 56±11 years. An underlying disease was found in three patients: mixed connective tissue disease, Coxackie-related endocarditis, MGUS. Clinical presentation included nephrotic proteinuria (100%), acute renal failure (25%), haematuria (75%), and hypertension (50%). The LM histological pattern was different. On immunofluorescence, polyclonal IgG and complement were evident. Two patients received steroids alone, two in association with mycophenolate-mofetil (N.1) or cyclophosphamide/azatioprine (N.4). At 6-month follow-up, patient 1 was dialysis-dependent; patient 2 and 3 preserved normal renal function with significant proteinuria reduction to 1 and 2 g/day at 6-month and one-year follow-up, respectively. Patient 4 recovered renal function and proteinuria disappeared at 4-year follow-up.
Renal diseases with organized deposits can be divided into 2 categories: 1. Congo-red positive diseases, including all amyloidosis types; 2. Congo-red negative diseases, such as FGN, immunotactoid GN and cryoglobulinemic GN. The correct diagnosis has a crucial impact on patient management and treatment options. Electron microscopy plays a key role in resolving diagnostic dilemmas. FGN etiopathogenesis is still undefinied. In the first case reports FGN was considered as idiopathic. In most recent case series an underlying disease such as malignancy, infection, dysproteinaemia and autoimmune diseases has been described. This finding has changed our therapeutic approaches, which are now addressed to control both FGN and associated diseases. In our experience, immunosuppressive regimens induced remission in 3/4 patients. Recently, the use of biologicals in FGN, such as anti-CD20 monoclonal antibodies, has improved the response and clinical course of the disease.