A 32-year-old Indian woman presents with gradual onset ankle swelling and facial puffiness for 3 weeks. She reports heavy proteinuria in routine urine examination. On examination, blood pressure is 128/82 mmHg, and 3+ pitting edema is noted over both ankles. Serum albumin is 2.1 g/dL (normal 3.5–5.5), total cholesterol 380 mg/dL, and serum creatinine 0.9 mg/dL. Urinalysis shows 24-hour proteinuria of 8.5 g/day with oval fat bodies. Renal biopsy shows thickening of the glomerular basement membrane with a characteristic "spike and dome" appearance on electron microscopy. What is the most likely diagnosis?

Explanation

## Diagnosis: Membranous Nephropathy ### Clinical Presentation **Key Point:** Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults, particularly in the 40–60 age group, but can present in younger patients. This patient presents with: - Nephrotic syndrome (proteinuria >3.5 g/day, hypoalbuminemia, edema, hyperlipidemia) - Preserved renal function (creatinine 0.9 mg/dL) - Oval fat bodies in urine (lipiduria) ### Pathological Hallmark **High-Yield:** The "spike and dome" appearance on electron microscopy is pathognomonic for membranous nephropathy. This represents: 1. Thickening of the glomerular basement membrane (GBM) 2. Subepithelial immune complex deposits 3. Projections of GBM material between deposits (the "spikes") 4. The "dome" is the electron-dense immune complex deposit ### Light Microscopy Features - Thickened GBM (PAS-positive) - Capillary wall thickening without hypercellularity - Minimal or absent mesangial proliferation - Subepithelial "humps" may be visible on silver stain ### Immunofluorescence Pattern **Clinical Pearl:** Granular IgG and C3 deposits along the capillary wall in a fine, diffuse pattern ("membranous pattern"). ### Electron Microscopy Findings | Feature | Membranous | MPGN | FSGS | MCD | |---------|-----------|------|------|-----| | GBM Thickness | Markedly increased | Normal/slightly thick | Normal | Normal | | Deposits | Subepithelial (spikes) | Subendothelial/intramembranous | None | None | | Mesangial involvement | Minimal | Prominent | Focal | Absent | | Foot process fusion | Diffuse | Diffuse | Segmental | Diffuse | ### Etiology in This Case - In India, secondary causes (hepatitis B, malaria, TB) must be excluded - Primary membranous nephropathy is associated with anti-PLA2R antibodies in ~70% of cases - Secondary causes include malignancy, SLE, infections, and drugs ### Natural History **Mnemonic:** "One-third rule" — approximately one-third of patients achieve complete remission, one-third have persistent proteinuria with stable renal function, and one-third progress to ESRD over 5–10 years. ### Management Approach 1. Exclude secondary causes (hepatitis B/C serology, ANA, complement levels) 2. Assess risk: proteinuria >8 g/day, male sex, older age, elevated creatinine = poor prognosis 3. Supportive therapy: ACE-I/ARB, diuretics, statins 4. Immunosuppression for high-risk or progressive disease: corticosteroids + cyclophosphamide or calcineurin inhibitors [cite:Robbins 10e Ch 20]