Membranoproliferative GN typically shows which of the following on light microscopy?

• A. Crescents
• B. Thickened capillary loops
• C. Subepithelial humps
• D. Linear IgG along GBM

Answer: (C)

Membranoproliferative GN is driven by immune complex–mediated injury that causes proliferation in the glomerulus and duplication of the glomerular basement membrane. On light microscopy this shows thickened capillary walls with a double-contour, or tram-track, appearance from GBM reduplication. That thickened capillary loops finding best captures the LM hallmark of MPGN. The other options point to different patterns: crescents suggest rapidly progressive GN; subepithelial humps are an EM feature classic for postinfectious GN; linear IgG along the GBM is typical of anti-GBM disease.