[Extracapillary glomerulonephritis].

Extracapillary glomerulonephritis is characterized by cell proliferation within the urinary space of 50% of the glomeruli, where it covers more than 50% of the filtration chamber, associated with acute or rapidly progressive renal failure. It is a model of curable human renal failure. Extracapillary cell proliferation is an elementary lesion which may complicate any glomerulopathy and many systemic diseases, or appear to be primary. Its clinical manifestations may be extremely marked in some systemic diseases, but they may be minimal and delay a diagnosis which rests entirely on renal biopsy. An early renal biopsy commands the prognosis which depends on the finding of young cellular crescents that respond to treatment before fibrous transformation sets in. Experiments in animals and man suggest that cell proliferation results from rupture of the capillary walls and from the production of polymerized fibrin in the urinary space. This is followed by a cascade of reactions, with increased synthesis of local mediators issued from resident and invasive glomerular cells. These data constitute the basis of modern therapies, such as emboli of methylprednisolone, plasma exchange and immunodepressive drugs, aimed not only at a possible aetiological treatment but also at the cell proliferation itself. The use of such treatments, whose risks must be carefully weighted, has transformed the prognosis of extracapillary glomerulonephritis, since almost 50% of the cases the kidneys survive at 5 years.