Lupus Nephritis

Detailed Overview

LN affects up to 50% of patients with SLE. It presents clinically with proteinuria, hematuria, hypertension, and impaired renal function. The International Society of Nephrology/Renal Pathology Society (ISN/RPS) categorizes LN into six histological classes, with Class III (focal) and Class IV (diffuse) being the most severe and proliferative, requiring aggressive immunosuppressive therapy to prevent irreversible kidney failure.

Epidemiology & Demographics

Occurs in 40-50% of SLE patients, more frequently and severely in African American, Hispanic, and Asian populations. Affects women of childbearing age much more frequently than men.

Etiological Mechanism

An autoimmune process secondary to Systemic Lupus Erythematosus. Genetic susceptibility, environmental triggers (UV light, infections), and hormonal factors contribute to autoantibody production.

Primary Causes

Production of anti-double-stranded DNA (anti-dsDNA) antibodies and other nuclear autoantibodies that form immune complexes.

• Non-White Ethnicity: African American and Hispanic SLE patients have a higher incidence and faster progression to ESKD.
• High anti-dsDNA Titers: High levels of these specific autoantibodies strongly correlate with active renal disease.
• Low Complement Levels: Hypocomplementemia (low C3 and C4) is a strong predictor of active lupus nephritis.

Circulating autoantibodies (primarily IgG anti-dsDNA) bind to intra-glomerular antigens or form circulating immune complexes that deposit in the mesangium, subendothelial, or subepithelial spaces of the glomerulus. These complexes activate the classical complement pathway, generating C3a and C5a, which attract neutrophils and macrophages. The ensuing intense inflammatory response causes endothelial damage, cellular proliferation, capillary necrosis, and eventually glomerulosclerosis and interstitial fibrosis.

Characteristic Clinical Presentation

• Peripheral Edema: Swelling in the legs and periorbital area due to hypoalbuminemia from severe proteinuria.
• Foamy Urine: Visible froth in the urine bowl indicating high protein content.
• Fatigue and Malaise: Non-specific symptoms relating to uremia or systemic SLE flare.

Physical Examination Signs

• Hypertension (often new-onset or acutely worsening)
• Pitting edema in the lower extremities
• Other SLE signs: Malar rash, joint tenderness, oral ulcers

• End-Stage Kidney Disease (ESKD): Progressive loss of kidney function requiring dialysis or transplantation in 10-20% of patients within 10 years.
• Thrombosis: Increased risk of DVT/PE due to nephrotic syndrome and loss of antithrombin III, often compounded by antiphospholipid antibodies.

Diagnostic Criteria & Guidelines

Renal biopsy is the gold standard and absolute requirement to diagnose the class of LN. Clinically suspected when an SLE patient has persistent proteinuria (>0.5 g/24hr), cellular casts, or an unexplained drop in GFR.

Differential Diagnosis

• IgA Nephropathy
• ANCA-associated Vasculitis
• Membranous Nephropathy (idiopathic)
• Preeclampsia (in pregnant SLE patients)

Laboratory Tests & Biomarkers

• Urinalysis: Proteinuria, dysmorphic RBCs, and RBC casts (active nephritic sediment)
• Anti-dsDNA / Complement (C3, C4): Elevated anti-dsDNA; Low C3 and C4 indicating complement consumption
• Urine Protein-to-Creatinine Ratio (UPCR): > 0.5 g/g, often in the nephrotic range (> 3.5 g/g)

Imaging Modalities & Findings

• Renal Ultrasound: Used to rule out obstruction and assess kidney size (echogenic, shrunken kidneys suggest chronic stage VI disease).

• Class I & II
  Minimal mesangial / Mesangial proliferative. Low-grade proteinuria, normal renal function. Rarely requires specific therapy.
• Class III & IV
  Focal / Diffuse proliferative. Active inflammation, heavy proteinuria, active urine sediment. Requires aggressive immunosuppression.
• Class V
  Membranous. Nephrotic-range proteinuria, often normal GFR initially.
• Class VI
  Advanced sclerosing. >90% global glomerulosclerosis. Represents end-stage damage.

Second-Line & Adjunctive Therapy

Add-on therapy: Belimumab 10 mg/kg IV monthly, or Voclosporin 23.7 mg PO BID. For refractory disease: Rituximab 1000 mg IV on days 1 and 15.

Surgical & Procedural Management

Renal transplantation for patients who reach Class VI / ESKD (after SLE has been clinically inactive for 6 months).

Recommended Lifestyle Changes

• Strict sodium restriction (< 2g/day) to help control hypertension and edema.
• Sun protection (SPF 50+, protective clothing) to prevent UV-induced SLE flares.
• Avoid NSAIDs to protect remaining GFR.

Patient Counseling & Advice

Stress strict adherence to immunosuppressants to prevent kidney failure. Explain the high risk of infections due to therapy. Women of childbearing age need counseling on teratogenic drugs (MMF, Cyclophosphamide) and the need for effective contraception.

Follow-Up & Monitoring Schedule

Monthly check of BP, UPCR, urinalysis, serum creatinine, eGFR, anti-dsDNA, and C3/C4 levels until remission, then every 3 months.

Preventive Strategies

Adherence to background Hydroxychloroquine dramatically reduces the incidence of lupus nephritis in SLE patients.

With aggressive therapy, 50-80% achieve partial or complete remission. However, flares are common (up to 30%). 10-20% progress to ESKD requiring dialysis.