Other primary glomerular diseases

Abstract

Fibrillary glomerulonephritis (FGN) and immunotactoid glomerulopathy (ITG) are both glomerular diseases characterized histologically by a diffuse increase in mesangial matrix due to deposits having a fibrillary structure by electron microscopy, which are negative for Congo-red stains but positive for immunoglobulin deposition. Most patients present with proteinuria, often in a nephrotic range, microhematuria, and hypertension. Almost half of patients have a reduced renal function at presentation. Although FGN and ITG have quite similar light microscopical and clinical features the current opinion is that they represent two separate diseases. FGN is an idiopathic (primary) condition characterized by polyclonal immune deposits with restricted gamma isotypes. Most patients present with significant renal insufficiency and have a poor outcome despite immunosuppressive therapy. By contrast, ITG very often contains monoclonal IgG deposits and has a significant association with underlying monoclonal paraproteinemia and hypocomplementemia. ITG is more properly classified as a mono-clonal immunoglobulin deposition disease (MIDD). Differentiation of FGN from the much more rare entity ITG appears justified on immunopathologic, ultrastructural, and clinical grounds (Fogo et al., 1993; Bridoux et al., 2002; Rosenstock et al., 2003). Both will be discussed together, although only FGN should be regarded as a primary glomerular disease, as defined in this monograph.