Fibrillary Glomerulonephritis

Abstract

Fibrillary glomerulonephritis (FGN) is a rare disorder characterized by Congo-red negative fibrillary deposits in the glomeruli. The incidence of FGN in native renal biopsies is only 0.8–1.5%. The pathological hallmark of FGN is fibrillary deposits in the mesangium and glomerular basement membrane. These fibrils are straight, non-branching and randomly oriented. In the majority of patients, FGN presents with nephrotic syndrome. Renal insufficiency is present in two-thirds of patients with a mean serum creatinine of 2.1 mg/dL. Approximately one-half of FGN patients progress to end-stage renal disease (ESRD). Renal biopsy establishes the diagnosis of FGN. Light microscopy findings include amorphous acellular deposits in the glomeruli. In the mesangium these deposits have a smudged texture and form a pseudolinear or confluent granular pattern along the basement membrane. Immunofluorescent studies of the biopsy tissue in FGN show staining for polyclonal Immunoglobulin G (IgG) and complement with a tendency towards higher IgG and C3. Electron microscopy reveals extensive infiltration of the glomerular basement membrane with spike formation. Standard therapeutic treatments for FGN have not been well defined. The clinical outcome of patients with FGN is not encouraging. In a recent study, 44% of patients with FGN progressed to ESRD. The average time to progress to ESRD was 2–4 years. Immuno-suppressant therapies that include corticosteroids, cyclophosphamide and cyclosporine, and most recently rituximab, have not demonstrated uniform clinical success.