Fibrillary glomerulonephritis and immunotactoid glomerulopathy

The features of GPs with Congo red-negative, noncryoglobulinaemic deposits have been surveyed. These disorders are rare and clinically heterogeneous and their pathogenesis is unclear. There is controversy concerning the nomenclature of Congo-red negative glomerular fibrilloses. A practical and reproducible approach is to classify these GPs on the basis of the substructure and arrangement of the deposits assessed at conventional electron microscopic magnifications. Accordingly, FGN and ITG can be identified. FGN is characterized by randomly arranged microfibrils (diameter: 12-30nm) composed of subclass-restricted polyclonal IgG and a low incidence of underlying systemic disease. In contrast, ITG is characterized by parallel bundles of microtubules (diameter: 10-90 nm) composed mainly of monoclonal IgG and a high incidence of associated lymphoproliferative disease or monoclonal gammopathy. The finding of Congo red-negative organized deposits on renal biopsy should prompt a careful search and follow-up for monoclonal gammopathy, cryoglobulins and haemopoietic malignancy.