In a patient with systemic lupus erythematosus (SLE) who develops renal involvement, how should lupus nephritis be diagnosed and what are the recommended induction and maintenance treatment regimens?

Diagnosis and Treatment of Lupus Nephritis

For patients with SLE and suspected renal involvement, obtain a kidney biopsy to confirm lupus nephritis and guide treatment, then initiate induction therapy with glucocorticoids plus mycophenolic acid analogs (MPAA), low-dose intravenous cyclophosphamide, or MPAA with a calcineurin inhibitor, with strong consideration for adding belimumab to any of these regimens. 1, 2

Diagnosis

When to Suspect Lupus Nephritis

• Monitor for proteinuria routinely in all SLE patients 3
• Suspect LN with: proteinuria, hematuria, cellular casts, rising creatinine, or active urinary sediment
• Approximately 50-60% of SLE patients develop LN, often within the first decade of disease 4, 5

Kidney Biopsy is Essential

Kidney biopsy remains the diagnostic gold standard and is indispensable for management 6, 3. The biopsy determines:

• ISN/RPS classification (Classes I-VI)
• Activity and chronicity indices
• Presence of concurrent pathology (e.g., thrombotic microangiopathy)
• Treatment selection and prognosis

Common pitfall: Do not rely solely on serologic markers or proteinuria levels to guide treatment decisions without histologic confirmation 6.

Induction Treatment for Proliferative LN (Class III/IV)

First-Line Regimens (All Grade 1B)

The 2024 KDIGO guideline provides four equally recommended options 1, 2:

Glucocorticoid backbone for all regimens:

• Methylprednisolone IV 0.25-0.5 g/day for 1-3 days (based on severity)
• Then prednisone oral 0.35-1.0 mg/kg/day (max 80 mg/day)
• Taper over months to maintenance dose

Plus ONE of the following:

1. MPAA monotherapy

   • Mycophenolate mofetil 1.0-1.5 g twice daily, OR
   • Mycophenolic acid sodium 0.72-1.08 g twice daily

2. Low-dose IV cyclophosphamide

   • 500 mg every 2 weeks × 6 doses

3. Belimumab + MPAA or cyclophosphamide

   • Belimumab IV 10 mg/kg every 2 weeks × 3 doses, then every 4 weeks
   • Combined with MPAA (doses above) OR IV cyclophosphamide 500 mg every 2 weeks × 6

4. MPAA + Calcineurin inhibitor (CNI)

   • Voclosporin 23.7 mg twice daily + MPAA (if eGFR >45 ml/min/1.73m²)
   • Tacrolimus + MPAA (alternative when voclosporin unavailable)
   • Caution: CNIs carry nephrotoxicity risk with significantly impaired kidney function 2

When to Add Belimumab from Onset

Consider belimumab addition at disease onset for moderate-to-severe proliferative nephritis 6, defined as:

• NIH activity index >5 PLUS ≥1 of:
  • NIH chronicity index >2
  • Proteinuria >3 g/24h
  • Serum creatinine increase >20%

When to Consider Voclosporin

Voclosporin + MPAA is particularly useful when rapid proteinuria reduction is critical 6:

• Heavy proteinuria well above nephrotic range
• Need to avoid nephrotic syndrome complications (thrombosis, infection, edema)
• Can be used up to 3 years, though long-term use beyond 1 year requires careful monitoring 6

Treatment of Pure Membranous LN (Class V)

Stratify by Proteinuria Level

Low-level proteinuria:

• RAS blockade and blood pressure control
• Hydroxychloroquine
• Immunosuppression guided by extrarenal SLE manifestations 1

Nephrotic-range proteinuria:

• RAS blockade and blood pressure control
• Combined immunosuppression: glucocorticoid + one agent (MPAA, cyclophosphamide, or CNI)
• Hydroxychloroquine
• Rationale: Unlike primary membranous nephropathy, heavy proteinuria in Class V LN rarely remits spontaneously and carries high risk of thrombosis and infection 1

Maintenance Treatment

First-Line Options

After achieving response (typically 6-12 months), transition to maintenance therapy 1:

Preferred agents:

• MPAA (mycophenolate mofetil or mycophenolic acid sodium) - continue for ≥3 years
• Azathioprine - alternative to MPAA

Alternative agents when MPAA/azathioprine cannot be used:

• CNIs (voclosporin, tacrolimus, cyclosporine)
• Mizoribine
• Leflunomide (contraindicated in pregnancy; discontinue 2 years before conception) 1

Triple immunosuppression option:

• Patients on glucocorticoids + tacrolimus + low-dose MPAA can continue this regimen for up to 24 months 1

Belimumab continuation:

• Can be continued up to 2.5 years based on trial data 2

Monitoring Treatment Response

Response Definitions (6-12 months) 1

Complete response:

• Proteinuria <0.5 g/g (50 mg/mmol) on PCR
• Stable or improved kidney function (±10-15% of baseline)
• No rescue therapy needed

Partial response:

• ≥50% reduction in proteinuria AND <3 g/g (300 mg/mmol)
• Stable or improved kidney function (±10-15% of baseline)

No response:

• Failure to achieve partial or complete response within 6-12 months

Managing Inadequate Response 1

Algorithmic approach when response is unsatisfactory:

1. Verify medication adherence
2. Check drug levels (mycophenolic acid levels if on MPAA; review cyclophosphamide infusion records)
3. Repeat biopsy if concerned about chronicity or alternative diagnosis (e.g., TMA)
4. Switch to alternative recommended regimen for persistent active disease
5. For refractory disease, consider:
   • Addition of rituximab or other biologics
   • Extended IV cyclophosphamide course
   • Clinical trial enrollment

Timing consideration: If inadequate response by 3 months on standard therapy, consider adding belimumab 6.

Treatment of Relapse

After achieving complete or partial remission, treat relapses with the same initial therapy that achieved the original response, or switch to an alternative recommended regimen 1.

Special Considerations

Lupus Nephritis with Thrombotic Microangiopathy

Test immediately for: 1

• ADAMTS13 activity and antibodies
• Antiphospholipid antibodies
• Start plasma exchange + glucocorticoids while awaiting results (adults)

Management depends on etiology:

• Low ADAMTS13 (<10%): SLE-associated TTP → plasma exchange + glucocorticoid + rituximab ± caplacizumab
• Positive antiphospholipid antibodies: anticoagulation ± plasma exchange
• Complement-mediated TMA: consider eculizumab

Adjunctive Therapy for All Patients

• Hydroxychloroquine for all SLE patients at 5 mg/kg real body weight/day 4
• RAS blockade for blood pressure control and proteinuria reduction 1
• Minimize glucocorticoids to ≤5 mg/day prednisone equivalent for maintenance, withdraw when possible 4

Treatment Goals

Target complete renal response 7. The median time to reduce proteinuria to <0.5 mg/mg was 3.6 months with voclosporin in trials 1, establishing expectations for response kinetics.

Critical distinction: The 2024 guidelines represent a paradigm shift toward earlier triple therapy and more aggressive initial treatment, moving away from sequential induction-maintenance approaches toward sustained multitarget regimens 8, 3.