Subepithelial 'humps' on electron microscopy are characteristic of which condition?

• A. Anti-GBM disease
• B. Minimal change disease
• C. Diabetic nephropathy
• D. Immune complex–mediated glomerulonephritis

Answer: (D)

Subepithelial humps reflect immune complexes deposited on the epithelial side of the glomerular basement membrane, a hallmark of immune complex–mediated glomerulonephritis. This pattern is classic for post-infectious GN such as post-streptococcal GN, where circulating antigen–antibody complexes form and trap in the glomerulus, producing discrete electron-dense deposits that appear as humps on electron microscopy. Clinically, this pattern often accompanies nephritic features and low complement, with granular staining for IgG/IgM and C3 on immunofluorescence along the GBM and mesangium.

Other conditions don’t fit this EM finding: anti-GBM disease shows linear IgG along the GBM with crescent formation and lacks subepithelial humps; minimal change disease has normal glomerular structure on EM except for podocyte foot process effacement and no immune deposits; diabetic nephropathy shows GBM thickening and mesangial expansion rather than discrete subepithelial humps.