A 28-year-old Indian male with known hepatitis B surface antigen (HBsAg) positivity presents with nephrotic syndrome: 24-hour urine protein 6.5 g, serum albumin 2.4 g/dL, and ankle edema. Serum creatinine is 1.1 mg/dL. Urinalysis shows 4+ proteinuria with no RBCs or casts. Complement C3 and C4 are normal. Kidney biopsy light microscopy shows capillary wall thickening without proliferation. Immunofluorescence reveals IgG, IgM, and C3 in a granular pattern along the capillary walls. Electron microscopy shows subepithelial electron-dense deposits. What is the most likely diagnosis?

Question

Accepted Answer

C. Hepatitis B-associated membranous nephropathy. ## Diagnosis: Hepatitis B-Associated Membranous Nephropathy

### Clinical Context
**High-Yield:** Hepatitis B virus (HBV) is a well-established cause of **secondary membranous nephropathy**, particularly in endemic regions (Southeast Asia, Africa, India). HBsAg-positive patients with nephrotic syndrome and membranous pattern on biopsy should be presumed to have HBV-associated disease until proven otherwise.

### Pathological Features

| Finding | This Case | Interpretation |
|---------|-----------|----------------|
| **Light microscopy** | Capillary wall thickening, no proliferation | Membranous pattern (Stage 1–2) |
| **Immunofluorescence** | IgG, IgM, C3 granular | Immune complex deposition; IgM suggests HBV (hepatitis B core antigen, HBcAg) |
| **Electron microscopy** | Subepithelial electron-dense deposits | Pathognomonic for membranous nephropathy |
| **Serum complement** | Normal C3, C4 | Excludes MPGN; consistent with in situ immune complex formation |

### Mechanism of HBV-Associated Membranous Nephropathy
**Key Point:** HBV immune complexes (HBsAg, HBcAg, anti-HBc) deposit in the glomerular basement membrane, triggering in situ complement activation and proteinuria. Unlike MPGN, systemic complement is not consumed, so C3/C4 remain normal.

### Clinical Features of HBV-Associated GN

| Type | Prevalence | Complement | EM Deposits | Clinical Presentation |
|------|-----------|-----------|-------------|----------------------|
| **Membranous** | 50–60% | Normal | Subepithelial | Nephrotic syndrome |
| **MPGN** | 30–40% | Low C3 | Subendothelial | Nephrotic + hematuria |
| **FSGS** | 5–10% | Normal | Foot process effacement | Variable |

**Clinical Pearl:** HBV-associated membranous nephropathy is more common in **children and young adults** from endemic areas. The presence of IgM on immunofluorescence (reflecting HBcAg) is a clue to HBV etiology.

### Management Implications
**High-Yield:** Treatment of HBV-associated membranous nephropathy includes:
1. **Antiviral therapy** (tenofovir, entecavir) — can induce remission of proteinuria
2. **ACE inhibitors/ARBs** — reduce proteinuria and slow progression
3. **Immunosuppression** — reserved for steroid-resistant cases (avoid in HBV reactivation risk)

**Warning:** Immunosuppressive therapy without concurrent antiviral coverage risks HBV reactivation and fulminant hepatitis.

### Why Not MPGN?
**Key Point:** MPGN would show **low C3 and C4** (complement consumption), **subendothelial deposits** (not subepithelial), and often **hypercellularity** on light microscopy. This patient has normal complement and a pure membranous pattern.

Answer

A. IgA nephropathy secondary to chronic liver disease

Answer

B. Hepatitis B-associated focal segmental glomerulosclerosis

Answer

D. Hepatitis B-associated membranoproliferative glomerulonephritis

Explanation

Diagnosis: Hepatitis B-Associated Membranous Nephropathy

Clinical Context

Pathological Features

Mechanism of HBV-Associated Membranous Nephropathy

Clinical Features of HBV-Associated GN

Management Implications

Why Not MPGN?

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Finding	This Case	Interpretation
Light microscopy	Capillary wall thickening, no proliferation	Membranous pattern (Stage 1–2)
Immunofluorescence	IgG, IgM, C3 granular	Immune complex deposition; IgM suggests HBV (hepatitis B core antigen, HBcAg)
Electron microscopy	Subepithelial electron-dense deposits	Pathognomonic for membranous nephropathy
Serum complement	Normal C3, C4	Excludes MPGN; consistent with in situ immune complex formation

Type	Prevalence	Complement	EM Deposits	Clinical Presentation
Membranous	50–60%	Normal	Subepithelial	Nephrotic syndrome
MPGN	30–40%	Low C3	Subendothelial	Nephrotic + hematuria
FSGS	5–10%	Normal	Foot process effacement	Variable