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📘 About
- Membranous Glomerulonephritis (MGN) accounts for ~25% of all glomerulonephritis cases in adults.
- Defined by diffuse thickening of the glomerular basement membrane (GBM) due to immune complex deposition.
- Classically presents with nephrotic syndrome (proteinuria, hypoalbuminaemia, oedema, hyperlipidaemia).
🧬 Aetiology & Pathogenesis
- Immune-complex disease: Immune complexes accumulate on the subepithelial side of the GBM, between podocytes and the GBM.
- Mechanisms:
- In situ immune complex formation (e.g. antibodies to phospholipase A2 receptor on podocytes).
- Deposition of circulating immune complexes (less common).
- Triggers may be intrinsic (renal antigens) or exogenous (infection, drugs, tumour antigens).
📝 Causes
- Primary (Idiopathic): ~80% of cases, no obvious secondary trigger.
- Secondary MGN: Due to systemic disease, infection, drugs, or malignancy:
- 🦠 Infections: Hepatitis B, syphilis, malaria, leprosy, schistosomiasis.
- 💊 Medications: Gold, NSAIDs, penicillamine, captopril, mercury.
- 🧬 Systemic diseases: SLE, diabetes, sarcoidosis.
- 🎗️ Malignancy: Lung, colon, breast, prostate, ovary, melanoma, lymphoma, leukaemia.
👩⚕️ Clinical Presentation
- Typically affects adults >30 years.
- Nephrotic syndrome:
- Proteinuria >3.5 g/day
- Hypoalbuminaemia → oedema
- Hyperlipidaemia
- ⬆️ Risk of venous thrombosis (renal vein, DVT, PE) due to urinary loss of antithrombin III.
- May be asymptomatic proteinuria detected on routine urinalysis.
🔬 Investigations
- Urine dipstick: Proteinuria ± microscopic haematuria.
- 24-hour urine protein quantification.
- Bloods: Serum creatinine, albumin, U&Es, lipids.
- Renal biopsy (diagnostic): Granular subepithelial IgG and C3 deposits on immunofluorescence; GBM thickening on light microscopy.
- Screen for secondary causes:
- CXR for lung malignancy.
- Colonoscopy for colorectal cancer.
- Mammography in women.
- Serology for HBV, HCV, syphilis.
💊 Management
- General:
- Treat underlying cause (infection, malignancy, drug withdrawal).
- Salt restriction + diuretics for oedema.
- Statins for hyperlipidaemia.
- Anticoagulation (warfarin/LMWH) if nephrotic with thrombosis risk.
- Immunosuppression:
- Consider steroids + cyclophosphamide or ciclosporin if persistent proteinuria or renal decline.
- Some patients remit spontaneously → “watchful waiting” acceptable initially.
📉 Prognosis & Prognostic Factors
- 1/3 remit spontaneously, 1/3 develop chronic proteinuria, 1/3 progress to ESRF.
- Better prognosis: Mild proteinuria, normal renal function at presentation.
- Worse prognosis: Severe proteinuria, older age, impaired renal function at baseline.
📖 References
