## 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.
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