✅ Model Answer:
• Diagnosis: Primary membranous nephropathy (anti-PLA2R positive).
• Evidence: Nephrotic-range proteinuria (P/C 3.5), hypoalbuminemia (2.2), edema, normal C3/C4, positive anti-PLA2R antibody.
• Next step: Start ACE inhibitor/ARB for proteinuria. If persistent nephrotic syndrome after 6 months of conservative therapy, consider immunosuppression (steroids + cyclophosphamide or rituximab). Renal biopsy may be performed for confirmation (subepithelial immune deposits). Monitor for complications (thrombosis, infection).

✅ Model Answer:
• Definition: An autoimmune glomerular disease characterized by subepithelial immune complex deposition.
• Target antigen: In primary MN, the target antigen is the M-type phospholipase A2 receptor (PLA2R) on podocytes – antibodies (IgG4) bind to PLA2R → complement activation → podocyte injury → proteinuria.
• Pathology: Diffuse thickening of the glomerular basement membrane (GBM) with subepithelial immune deposits ("spikes" on silver stain).
• Secondary causes: Lupus, hepatitis B/C, malignancy, drugs (NSAIDs, penicillamine).
• Prevalence: Rare in children (most common cause of nephrotic syndrome in adults, but can occur in children).

✅ Model Answer:
• Classic features:
- Nephrotic syndrome: Edema, proteinuria (P/C >2.0), hypoalbuminemia, hyperlipidemia.
- Normal complement (C3, C4 – unlike MPGN or lupus).
- Hypertension: May be present (less common in early disease).
- Hematuria: Usually absent or microscopic.
- Thromboembolism: Increased risk (renal vein thrombosis, DVT, PE) – due to loss of antithrombin III.
- Slow progression: May have a relapsing-remitting course.
- Anti-PLA2R antibody: Positive in 70-80% of primary MN.

✅ Model Answer:
• Urine P/C ratio: Nephrotic-range (>2.0).
• Serum albumin: Low (<2.5 g/dL).
• Serum complement (C3, C4): Normal (differentiates from MPGN and lupus).
• Anti-PLA2R antibody: Positive in primary MN (highly specific).
• Serum creatinine/eGFR: Assess renal function.
• Hepatitis B/C, HIV serology: To rule out secondary causes.
• ANA, dsDNA: To rule out lupus.
• Renal biopsy: Gold standard – shows subepithelial immune deposits, GBM thickening, and "spikes" on silver stain. Immunofluorescence: IgG (predominantly IgG4) and C3 along the GBM.
• Thrombophilia workup: If thrombosis is suspected (renal vein thrombosis).

✅ Model Answer:
• Conservative therapy:
- ACE inhibitor/ARB: First-line to reduce proteinuria and BP.
- Sodium restriction, fluid restriction.
- Diuretics: For edema.
- Statins: For hyperlipidemia (if elevated).
- Anticoagulation: Prophylactic for high-risk patients (albumin <2.0 g/dL, severe proteinuria).
• Immunosuppressive therapy (if persistent nephrotic syndrome after 6 months):
- Steroids + cyclophosphamide (Ponticelli regimen): Alternating steroids and cyclophosphamide for 6 months.
- Rituximab: Anti-CD20 monoclonal antibody – increasingly used as first-line therapy in children (steroid-sparing).
- Calcineurin inhibitors (cyclosporine, tacrolimus): Alternative.
• Monitoring: Anti-PLA2R titers (to monitor response), BP, proteinuria, creatinine.
• Treat secondary causes: If identified (e.g., hepatitis C, lupus).

✅ Model Answer:
• Thromboembolism: Renal vein thrombosis (most common), DVT, PE (due to loss of antithrombin III).
• Nephrotic syndrome complications: Infections (pneumococcal peritonitis), AKI, hyperlipidemia.
• Progressive CKD: 30-40% progress to ESKD over 10-15 years without treatment.
• Hypertension.
• Steroid toxicity: If long-term steroids are used.
• Malignancy: Secondary membranous nephropathy is associated with malignancy in adults (rare in children).
• Recurrence: Can recur after kidney transplantation.

✅ Model Answer:
• Prognosis:
- Variable: 30-40% achieve spontaneous remission; 30-40% have persistent proteinuria; 20-30% progress to ESKD.
- Children: Better prognosis than adults (higher remission rates).
- Anti-PLA2R positive: Associated with higher remission rates with immunosuppression.
- Rituximab: Improves outcomes and reduces steroid exposure.
- Life expectancy: Good with treatment.
• Long-term follow-up:
- Monitor anti-PLA2R titers, proteinuria, BP, creatinine.
- Monitor for thrombosis.
- Vaccinations: Pneumococcal, varicella (when off immunosuppression).
- Screen for secondary causes.

✅ Model Answer:
• Anti-PLA2R antibody: Autoantibody against the M-type phospholipase A2 receptor on podocytes.
• Role:
- Diagnostic: Positive in 70-80% of primary membranous nephropathy (highly specific).
- Prognostic: Higher titers are associated with more severe proteinuria and lower remission rates.
- Monitoring: Used to monitor disease activity and response to treatment (decreasing titers correlate with remission).
- Recurrence: Can predict recurrence after kidney transplantation.
• Interpretation:
- Positive anti-PLA2R + normal C3/C4 + nephrotic syndrome = primary membranous nephropathy.
- Negative anti-PLA2R: May still have primary MN (other antigens like THSD7A) or secondary MN.
• Clinical use: Reduces the need for renal biopsy in some cases; used to guide therapy.