A 28-year-old woman from Delhi presents with a 6-week history of polyarthritis affecting the small joints of both hands, morning stiffness lasting 2 hours, and a malar rash that worsens in sunlight. She reports photosensitivity, oral ulcers, and recent hair loss. Laboratory investigations show: ANA 1:640 (homogeneous), anti-dsDNA antibody positive, anti-Smith antibody positive, C3 60 mg/dL (normal 80–160), C4 12 mg/dL (normal 15–45), ESR 78 mm/hr, and urinalysis shows 2+ proteinuria with RBC casts. Which of the following is the most appropriate next step in management?

Explanation

## Clinical Diagnosis **Key Point:** This patient meets ACR/EULAR 2019 criteria for SLE with: - Malar rash (photosensitive) - Polyarthritis (small joints) - Oral ulcers - Hair loss (non-scarring alopecia) - ANA positive with anti-dsDNA and anti-Smith antibodies (highly specific) - Complement consumption (low C3, C4) - Proteinuria with RBC casts (lupus nephritis) ## Lupus Nephritis Classification & Management | Class | Histology | Prognosis | Initial Treatment | |-------|-----------|-----------|-------------------| | I | Minimal mesangial | Excellent | Observation ± hydroxychloroquine | | II | Mesangial proliferation | Good | Hydroxychloroquine ± low-dose prednisolone | | III | Focal proliferative | Intermediate | Prednisolone + cyclophosphamide or mycophenolate | | IV | Diffuse proliferative | Poor | High-dose prednisolone + cyclophosphamide | | V | Membranous | Variable | Prednisolone ± immunosuppression | | VI | Sclerotic | Poor | Supportive care | **Clinical Pearl:** The presence of RBC casts with proteinuria indicates active proliferative lupus nephritis (Class III or IV). This patient requires: 1. **Renal biopsy** to determine class and guide therapy intensity 2. **Induction therapy** with prednisolone (1 mg/kg/day) while awaiting biopsy results 3. **Cyclophosphamide or mycophenolate** if Class III/IV confirmed **High-Yield:** Prednisolone 1 mg/kg/day is the standard induction dose for active lupus nephritis. Renal biopsy is mandatory to classify nephritis and predict response to therapy. IV methylprednisolone is reserved for severe, rapidly progressive disease with crescentic GN or pulmonary hemorrhage — not indicated here as the patient is hemodynamically stable. **Mnemonic:** RENAL BIOPSY FIRST — **R**enal casts present, **E**vidence of proliferation, **N**eed to classify, **A**void blind therapy, **L**ower mortality with targeted treatment. ## Why This Answer Prednisolone 1 mg/kg/day is guideline-standard for lupus nephritis induction. Renal biopsy is essential to: - Confirm lupus nephritis class - Assess chronicity (sclerosis, atrophy) vs. activity - Guide intensity of immunosuppression - Predict long-term renal outcomes [cite:Harrison 21e Ch 280]