A 28-year-old Indian man with systemic lupus erythematosus presents with nephrotic syndrome and hematuria. Kidney biopsy shows diffuse proliferative glomerulonephritis with subendothelial immune deposits and wire-loop lesions. Which feature best distinguishes lupus nephritis (Class IV) from membranoproliferative glomerulonephritis (MPGN)?

Question

Accepted Answer

C. Presence of wire-loop lesions and subendothelial deposits with full-house immunofluorescence pattern. ## Distinguishing Lupus Nephritis (Class IV) from MPGN

### Key Discriminating Features

**Key Point:** The 'full-house' immunofluorescence pattern (IgG, IgA, IgM, C1q, and C3 all positive) combined with wire-loop lesions and subendothelial deposits is pathognomonic for lupus nephritis and distinguishes it from MPGN.

### Wire-Loop Lesions

Wire-loop lesions are:
- Thickened capillary walls with subendothelial immune complex deposits
- Visible on light microscopy as wire-like thickening of capillary loops
- Pathognomonic for lupus nephritis
- Absent in MPGN (which shows intramembranous or subendothelial deposits without this appearance)

### Comparison Table: Lupus Nephritis (Class IV) vs. MPGN

| Feature | Lupus Nephritis (Class IV) | MPGN |
| --- | --- | --- |
| **Light Microscopy** | Diffuse proliferative, wire-loop lesions, hyaline thrombi | Proliferative, double contour (tram-track) |
| **Immunofluorescence** | Full-house (IgG, IgA, IgM, C1q, C3) | C3-dominant, IgM variable |
| **Electron Microscopy** | Subendothelial deposits (humps) | Intramembranous or subendothelial |
| **Serum Complement** | Low C3, C4 (consumed) | Low C3 (MPGN Type II) or normal (Type I) |
| **Systemic Features** | Malar rash, photosensitivity, ANA+, anti-dsDNA+ | None (primary MPGN) |
| **Hematuria Pattern** | Dysmorphic RBCs, RBC casts (nephritic) | Dysmorphic RBCs, RBC casts (nephritic) |
| **Clinical Presentation** | Nephrotic + nephritic (mixed) | Nephrotic or nephritic |

### Full-House Immunofluorescence

**High-Yield:** The 'full-house' pattern is virtually diagnostic of lupus nephritis:
- **IgG** — positive (most prominent)
- **IgA** — positive (distinguishes from other diseases)
- **IgM** — positive
- **C1q** — positive (complement activation via classical pathway)
- **C3** — positive (often with C1q, unlike post-infectious GN)

MPGN typically shows:
- **C3-dominant** pattern (C3 > immunoglobulin)
- IgM may be present but not the full spectrum
- C1q usually absent

### Pathophysiology

**Lupus Nephritis:**
1. Circulating immune complexes (anti-dsDNA, anti-nucleosome) deposit in glomeruli
2. Subendothelial location → wire-loop lesions
3. Classical complement pathway activation (C1q, C4 consumption)
4. Proliferative inflammation

**MPGN:**
1. Immune complex deposition (post-infectious, cryoglobulins, membranoproliferative pattern)
2. Alternative or classical pathway activation
3. Intramembranous or subendothelial deposits without wire-loops

**Mnemonic:** **FULL-HOUSE** = Fluorescence pattern with all Immunoglobulins and Complement components positive, Lupus-specific, Unique to SLE, Subendothelial deposits, Helps distinguish from MPGN, Outcome varies by class, Urgent treatment needed, Serology confirms (anti-dsDNA)

**Clinical Pearl:** Wire-loop lesions are so characteristic of lupus that their presence should immediately raise suspicion for SLE even if serology is initially negative. They represent acute immune complex-mediated injury and indicate active lupus nephritis.

[cite:Robbins 10e Ch 20]

Answer

A. Hematuria with dysmorphic red blood cells and red cell casts

Answer

B. Selective proteinuria with normal serum complement C3 levels

Answer

D. Crescent formation with rapid progression to renal failure

Explanation

Distinguishing Lupus Nephritis (Class IV) from MPGN

Key Discriminating Features

Wire-Loop Lesions

Comparison Table: Lupus Nephritis (Class IV) vs. MPGN

Full-House Immunofluorescence

Pathophysiology

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Feature	Lupus Nephritis (Class IV)	MPGN
Light Microscopy	Diffuse proliferative, wire-loop lesions, hyaline thrombi	Proliferative, double contour (tram-track)
Immunofluorescence	Full-house (IgG, IgA, IgM, C1q, C3)	C3-dominant, IgM variable
Electron Microscopy	Subendothelial deposits (humps)	Intramembranous or subendothelial
Serum Complement	Low C3, C4 (consumed)	Low C3 (MPGN Type II) or normal (Type I)
Systemic Features	Malar rash, photosensitivity, ANA+, anti-dsDNA+	None (primary MPGN)
Hematuria Pattern	Dysmorphic RBCs, RBC casts (nephritic)	Dysmorphic RBCs, RBC casts (nephritic)
Clinical Presentation	Nephrotic + nephritic (mixed)	Nephrotic or nephritic