Crescentic GN may be caused by a number of different diseases, some restricted to the kidney and others systemic. RPGN may be associated with a number of diseases, as follows: • Anti-GBM antibody–mediated crescentic GN (Goodpasture disease) is characterized by linear deposits of IgG and, in many cases, C3 in the GBM. In some patients, the anti-GBM antibodies also bind to pulmonary alveolar capillary basement membranes to produce the clinical picture of pulmonary hemorrhages associated with renal failure. These patients are said to have Goodpasture syndrome. Anti-GBM antibodies are present in the serum and are helpful in diagnosis. It is important to recognize anti-GBM antibody–mediated crescentic GN, because affected individuals benefit from plasmapheresis, which removes pathogenic antibodies from the circulation.
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Immune complex–mediated crescentic GN may complicate any of the immune complex nephritides, including post-streptococcal GN, systemic lupus erythematosus, IgA nephropathy, and Henoch-Schönlein purpura. In other cases, immune complexes are demonstrated but the underlying cause is undetermined. This type of RPGN frequently shows cellular proliferation and influx of leukocytes within the glomerular tuft, in addition to crescent formation. A consistent finding is the characteristic granular pattern of staining of the GBM and/or mesangium for immunoglobulin and/or complement on immunofluorescence studies. This disorder usually does not respond to plasmapheresis.
Pauci-immune type crescentic GN is defined by the lack of anti-GBM antibodies or significant immune complex deposition. Anti-neutrophil cytoplasmic antibodies (ANCA) typically are found in the serum, which, as discussed in Chapter 10, have a pathogenic role in some vasculitides. In some instances, therefore, crescentic GN is a component of a systemic vasculitis such as microscopic polyangiitis or granulomatosis with polyangiitis. In many cases, however, pauci-immune crescentic GN is limited to the kidney.
MORPHOLOGYThelightmicroscopicchangesaresimilaralthoughnotidenticalinvariousformsofcrescenticglomerulonephritis.Theglomerulishowcellularproliferationoutsidethecapillaryloops,sometimesinassociationwithsegmentalcapillarynecrosis,breaksinGBM,anddepositionoffibrininBowman’sspace.Thesedistinctiveproliferativelesionsoutsidethecapillaryloopsarecalledcrescents owingtotheirshapeastheyfillBowman’sspace.Crescentsareformedbothbyproliferationofepithelialcellsandbymigrationofmonocytes/macrophagesintoBowman’s space(Fig.