A 35-year-old woman with SLE has worsening proteinuria (3.2 g/day), hematuria, and creatinine of 1.8 mg/dL. Renal biopsy shows mesangial and subendothelial deposits with wire-loop lesions on light microscopy and global subendothelial deposits on electron microscopy. What is the WHO/ISN-RPS class of lupus nephritis?

• A Class II (mesangial proliferative)
• B Class III (focal proliferative)
• C Class V (membranous)
• D Class IV (diffuse proliferative) ✓

Explanation

Wire-loop lesions on light microscopy and global subendothelial deposits on electron microscopy are hallmarks of Class IV (diffuse proliferative) lupus nephritis, which involves >50% of glomeruli. This is the most severe form associated with nephritic syndrome and renal insufficiency. Class III involves <50% of glomeruli (focal). Class V shows membranous pattern with subepithelial deposits. Class IV requires induction with mycophenolate mofetil or cyclophosphamide plus high-dose corticosteroids.

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

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