A 34-year-old woman with known SLE presents with new haematuria, proteinuria 3.5 g/day, and serum creatinine 180 µmol/L. Renal biopsy shows diffuse glomerulonephritis with 'full house' immunofluorescence (IgG, IgM, IgA, C3, C1q). The ISN/RPS 2018 classification for this pattern is:

• A Class II: Mesangial proliferative lupus nephritis
• B Class IV: Diffuse lupus nephritis ✓
• C Class III: Focal lupus nephritis
• D Class V: Membranous lupus nephritis

Explanation

Class IV (diffuse) lupus nephritis involves >50% of glomeruli with endocapillary or extracapillary proliferation. The combination of nephrotic-range proteinuria, haematuria, rising creatinine, and diffuse glomerulonephritis with 'full house' immunofluorescence (deposition of IgG, IgM, IgA, C3, C1q) is the hallmark of Class IV LN. Class III involves <50% glomeruli. Class V shows subepithelial deposits (membranous pattern) without proliferation. Class II shows mesangial deposits only. Treatment of Class III/IV includes high-dose steroids plus mycophenolate mofetil (Euro-Lupus protocol with low-dose cyclophosphamide is an alternative).

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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