A 32-year-old Indian woman with biopsy-proven SLE presents with persistent proteinuria (2.5 g/day) and rising creatinine. Which finding best distinguishes lupus nephritis (Class IV) from lupus membranous nephropathy (Class V)?

Explanation

## Lupus Nephritis: Class IV vs Class V ### Pathological Distinction **Key Point:** Class IV (proliferative) lupus nephritis is defined by **subendothelial immune deposits with endocapillary or extracapillary glomerular proliferation**, whereas Class V (membranous) is characterized by **subepithelial 'spike and dome' deposits without proliferation**. ### Comparative Pathology | Feature | Class IV (Proliferative) | Class V (Membranous) | |---------|--------------------------|----------------------| | **Light microscopy** | Endocapillary/extracapillary proliferation, wire-loop lesions | Capillary wall thickening, no proliferation | | **Immunofluorescence** | Subendothelial IgG, C3, C1q deposits | Subepithelial IgG, C3 deposits | | **Electron microscopy** | Subendothelial electron-dense deposits | Subepithelial 'spike and dome' deposits | | **Clinical presentation** | Hematuria, RBC casts, active urinary sediment | Proteinuria (often nephrotic), bland sediment | | **Prognosis** | Higher risk of ESRD if untreated | Better prognosis; may remit spontaneously | ### Mnemonic **High-Yield:** **SPIKES = Subepithelial Proliferation In Class V (membranous) — KEep Subendothelial for Class IV** Alternatively: **Class IV = 4 letters in "Four" = Proliferation (4 types of proliferation); Class V = 5 letters in "Five" = Membranous (5th type)** ### Clinical Pearl **Clinical Pearl:** Class IV lupus nephritis is the most common and aggressive form, requiring aggressive immunosuppression (induction with cyclophosphamide or mycophenolate + corticosteroids). Class V may present with nephrotic syndrome but often responds to conservative management or less intensive therapy. The distinction is made on renal biopsy, not serum markers alone [cite:Robbins 10e Ch 20]. ### Why Electron Microscopy is Diagnostic Light microscopy and immunofluorescence show overlapping features, but **electron microscopy definitively shows the location of deposits**: subendothelial (Class IV) vs. subepithelial (Class V). This is the gold standard for classification.