rapidly progressive glomerulonephritis

RPGN is classified into three immunopathologic types based on immunofluorescence findings: Type I (anti-GBM disease, e.g., Goodpasture syndrome - linear IgG deposition along GBM, antibodies against type IV collagen alpha-3 chain); Type II (immune complex-mediated, e.g., post-infectious GN, lupus nephritis, IgA nephropathy/Henoch-Schönlein purpura - granular immune complex deposition); Type III (pauci-immune, e.g., ANCA-associated vasculitides like granulomatosis with polyangiitis, microscopic polyangiitis, eosinophilic granulomatosis with polyangiitis - little to no immune deposits, associated with c-ANCA/PR3 or p-ANCA/MPO). Pathophysiology involves severe glomerular injury causing rupture of the glomerular basement membrane, allowing fibrin and inflammatory cells (macrophages, T cells) to enter Bowman's space, forming characteristic crescents composed of proliferating parietal epithelial cells, macrophages, and fibrin. This crescent formation compresses and destroys the glomerulus, leading to rapid loss of function. Clinical presentation includes hematuria (often with dysmorphic RBCs), RBC casts, subnephrotic proteinuria, hypertension, edema, and rapidly rising creatinine over days to weeks. Diagnosis requires renal biopsy showing crescents, with immunofluorescence and serologic testing (anti-GBM antibodies, ANCA, complement levels, ANA) to determine the underlying cause. Treatment is aggressive and includes high-dose corticosteroids, cyclophosphamide, and plasmapheresis (especially for anti-GBM disease and severe ANCA-associated vasculitis) to remove pathogenic antibodies. Prognosis depends on the extent of crescent formation and timeliness of treatment; delayed treatment often leads to end-stage renal disease requiring dialysis or transplantation.