Rapidly Progressive Glomerulonephritis (RPGN)

Rapidly progressive glomerulonephritis is a time-critical syndrome of inflammatory glomerular injury, not a single disease. Histologically, at least 50% of glomeruli show crescents. Clinically, the estimated GFR falls by at least 30% within 3 months of symptom onset. A crescent forms when severe capillary-wall injury allows fibrin and inflammatory mediators into Bowman’s space. Parietal epithelial cells proliferate and macrophages accumulate there, compressing the glomerular tuft. Filtration falls quickly, which explains the rising creatinine and declining urine output. Damage to the filtration barrier also allows erythrocytes and protein to enter the urine. The three major causes have different immune signatures: - Anti-GBM disease: Immunofluorescence shows a smooth, linear IgG pattern along the glomerular basement membrane. The same type of basement-membrane injury can affect pulmonary alveoli, producing a pulmonary–renal syndrome with pulmonary haemorrhage. - ANCA-associated vasculitis: Immunofluorescence shows few or no immune deposits, described as pauci-immune disease. Examples include granulomatosis with polyangiitis, microscopic polyangiitis, and eosinophilic granulomatosis with polyangiitis. - Immune-complex glomerulonephritis: Immunofluorescence shows a granular pattern. Lupus nephritis, IgA nephropathy, post-infectious glomerulonephritis, and other immune-complex disorders may produce this pattern. These...