A 35-year-old woman with a 5-year history of systemic lupus erythematosus (SLE) presents with nephrotic-range proteinuria and hematuria. Renal biopsy shows wire-loop lesions and subendothelial immune complex deposits. Which feature most reliably distinguishes lupus nephritis (Class IV) from membranoproliferative glomerulonephritis (MPGN) due to hepatitis C?

Question

Accepted Answer

A. Wire-loop lesions and subendothelial deposits on electron microscopy. ## Distinguishing Lupus Nephritis from Hepatitis C–Associated MPGN

### Morphologic Hallmarks

**Key Point:** Wire-loop lesions (thickened capillary walls with subendothelial immune complex deposition) are characteristic of lupus nephritis and are NOT seen in hepatitis C–associated MPGN.

### Comparison Table

| Feature | Lupus Nephritis (Class IV) | HCV-Associated MPGN |
|---------|---------------------------|---------------------|
| **Wire-loop lesions** | Present (pathognomonic) | Absent |
| **Subendothelial deposits** | Prominent (EM) | Mesangial/intramembranous |
| **Cryoglobulins** | Absent or low | Present (Type II mixed) |
| **ANA/anti-dsDNA** | Positive (diagnostic) | Negative |
| **Complement pattern** | C3 + C4 low | C3 dominant |
| **Associated systemic features** | Malar rash, arthritis, serositis | Liver disease, vasculitis |

### Why This Matters

**High-Yield:** Wire-loop lesions are virtually diagnostic of lupus nephritis and are a distinguishing morphologic feature absent in other forms of MPGN, including hepatitis C–associated disease.

**Clinical Pearl:** The combination of wire-loop lesions + subendothelial deposits + positive ANA/anti-dsDNA antibodies makes lupus nephritis diagnosis certain, whereas hepatitis C–associated MPGN is driven by cryoglobulin immune complexes.

### Why Other Options Are Incorrect

- **Option 0 (Cryoglobulins):** Cryoglobulins are characteristic of hepatitis C–associated MPGN, NOT lupus nephritis. This finding points toward HCV, not SLE.
- **Option 2 (Nephrotic proteinuria):** Both lupus nephritis and HCV-associated MPGN can present with nephrotic-range proteinuria; this is not discriminatory.
- **Option 3 (Hematuria + RBC casts):** Both conditions present with active urinary sediment; hematuria and casts are not specific to lupus nephritis.

Answer

B. Presence of cryoglobulins in serum

Answer

C. Hematuria with red blood cell casts

Answer

D. Nephrotic-range proteinuria

Explanation

Distinguishing Lupus Nephritis from Hepatitis C–Associated MPGN

Morphologic Hallmarks

Comparison Table

Why This Matters

Why Other Options Are Incorrect

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Feature	Lupus Nephritis (Class IV)	HCV-Associated MPGN
Wire-loop lesions	Present (pathognomonic)	Absent
Subendothelial deposits	Prominent (EM)	Mesangial/intramembranous
Cryoglobulins	Absent or low	Present (Type II mixed)
ANA/anti-dsDNA	Positive (diagnostic)	Negative
Complement pattern	C3 + C4 low	C3 dominant
Associated systemic features	Malar rash, arthritis, serositis	Liver disease, vasculitis