## Distinguishing Membranous Nephropathy from Minimal Change Disease ### Key Pathological Features **Key Point:** The 'spike-and-dome' appearance — subepithelial immune deposits with intervening basement membrane projections — is pathognomonic for membranous nephropathy and is absent in minimal change disease. ### Comparative Table | Feature | Membranous Nephropathy | Minimal Change Disease | | --- | --- | --- | | **Light Microscopy** | Thickened GBM, no cellular proliferation | Normal or near-normal | | **Immunofluorescence** | IgG, IgM, C3 deposits along GBM | Negative (no deposits) | | **Electron Microscopy** | Subepithelial deposits (spike-and-dome) | Foot process effacement only | | **Serum Complement** | Normal (except secondary forms) | Normal | | **Proteinuria** | Non-selective (heavy, mixed) | Selective (albumin-predominant) | | **Steroid Response** | Poor (30–40% remission) | Excellent (>90% remission) | ### Why This Feature Discriminates **High-Yield:** Electron microscopy is the gold standard for differentiating these two nephrotic syndromes. The subepithelial deposits in membranous nephropathy are visible only on EM; light microscopy and immunofluorescence alone cannot distinguish them reliably. **Clinical Pearl:** Membranous nephropathy accounts for ~30–40% of adult nephrotic syndrome in developed countries, while minimal change disease is the most common cause in children. Both present with nephrotic-range proteinuria, but their EM findings diverge completely. ### Pathophysiology Membranous nephropathy involves: 1. Immune complex deposition (often anti-PLA2R antibodies in primary disease) 2. Complement activation (C5b-9 membrane attack complex) 3. Podocyte injury and proteinuria Minimal change disease involves: 1. Podocyte foot process effacement (reversible) 2. Loss of charge selectivity of the filtration barrier 3. No immune complex deposition [cite:Robbins 10e Ch 20]
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