Systemic Lupus Erythematosus (SLE) - Complete Overview

Definition & Epidemiology

• Sex: Female:Male = ~9:1 (reproductive age)
• Peak onset: Ages 15-45; can occur at any age
• Ethnicity: More common and severe in Black, Hispanic, and Asian populations
• Prevalence: ~50-100 per 100,000 in developed countries

Etiology & Risk Factors

Genetic Factors

• Strong genetic component: monozygotic twin concordance ~24% vs 2% in dizygotic twins

• 150 susceptibility loci identified via GWAS

• Key pathways:
  • MHC (HLA-DR2, HLA-DR3) - antigen presentation
  • Type I interferon axis: ~half of susceptibility loci affect IFN production or signaling (TLR7, STAT4, IRF5, IRF7, IRF8)
  • Complement deficiencies (C1q, C2, C4) - impaired immune complex clearance
  • Nucleic acid clearance genes (DNASE1, DNASE1L3, TREX1)
  • B cell (BANK1, BACH2) and T cell (OX40L) activation genes

Environmental Triggers

• UV radiation (triggers keratinocyte apoptosis, exposing nuclear antigens)
• EBV infection (molecular mimicry with Sm/nuclear antigens)
• Hormones: Estrogens promote disease (explains female predominance and flares with pregnancy/OCP)
• Smoking, silica dust, certain drugs

Drug-Induced Lupus

Pathogenesis

1. Apoptotic cell overload / defective clearance - NETs (neutrophil extracellular traps) release chromatin into circulation
2. Type I Interferon overproduction - Plasmacytoid dendritic cells (pDCs) sense self-nucleic acids via TLR7/9 → massive IFN-α/β production (the "IFN signature" seen in >75% of patients)
3. Autoreactive B cells - Produce anti-dsDNA, anti-Sm, anti-Ro/SSA, anti-La/SSB antibodies
4. T cell dysregulation - Reduced Tregs, overactive Th17 cells; self-reactive T cells help B cells differentiate into autoantibody-secreting plasma cells
5. Immune complex deposition - Circulating anti-DNA antibody + DNA complexes deposit in glomeruli, skin, joints, choroid plexus → activate complement → inflammation and tissue damage
6. Complement consumption - Low C3, C4 during active disease

Clinical Features

Frequency of Manifestations

System-by-System Breakdown

• Fatigue (most common symptom), fever, weight loss, malaise, lymphadenopathy

• Acute: Malar (butterfly) rash, maculopapular rash, bullous lupus
• Subacute (SCLE): Photosensitive annular or papulosquamous lesions; associated with anti-Ro/SSA
• Chronic: Discoid lupus (scarring, follicular plugging), panniculitis, chilblain lupus
• Other: Photosensitivity, oral/nasal ulcers, non-scarring alopecia, periungual telangiectases

• Symmetric polyarthritis - non-erosive (unlike RA)
• Jaccoud's arthropathy - reversible deformities from periarticular laxity
• Avascular necrosis (especially femoral head; worsened by steroids)
• Myalgias, inflammatory myopathy

• Lupus nephritis is a major cause of morbidity
• Classified by ISN/RPS (WHO) histologic classes:
  • Class I: Minimal mesangial
  • Class II: Mesangial proliferative
  • Class III: Focal proliferative (<50% glomeruli)
  • Class IV: Diffuse proliferative (≥50% glomeruli) - most severe; "wire-loop" lesions on EM
  • Class V: Membranous - presents as nephrotic syndrome
  • Class VI: Advanced sclerosing
• Urinalysis shows hematuria, proteinuria, RBC casts (class III/IV)

• Cognitive dysfunction (most common), headache, depression, psychosis
• Seizures, stroke/TIA, transverse myelitis, aseptic meningitis
• Mononeuropathy, polyneuropathy

• Pleuritis (30%), pericarditis (25%)
• Libman-Sacks endocarditis (verrucous, non-infective; associated with antiphospholipid antibodies)
• Premature atherosclerosis - major cause of late mortality
• Diffuse alveolar hemorrhage (rare but life-threatening)
• Pulmonary hypertension, shrinking lung syndrome

• Autoimmune hemolytic anemia (Coombs positive)
• Leukopenia, lymphopenia
• Thrombocytopenia (ITP-like)
• Antiphospholipid syndrome (APS) - in ~30-40%: venous/arterial thrombosis, recurrent pregnancy loss

• Sicca syndrome, episcleritis, retinal vasculitis ("cytoid bodies" on fundoscopy)

Classification Criteria

2019 EULAR/ACR Classification Criteria (most current)

• Entry criterion: ANA ≥1:80 by IIF (required)
• Then weighted clinical and immunological domains are scored
• Score ≥10 = classified as SLE
• Domains include: constitutional, hematologic, neuropsychiatric, mucocutaneous, serosal, musculoskeletal, renal, antiphospholipid antibodies, complement proteins, SLE-specific antibodies

2012 SLICC Criteria

• Requires ≥4 of 11 clinical + ≥1 immunologic criterion, OR biopsy-proven lupus nephritis + positive ANA or anti-dsDNA
• Higher sensitivity but lower specificity than EULAR/ACR 2019

Laboratory / Investigations

Autoantibodies

Complement

• Low C3, C4 (consumed by immune complexes) = active disease marker

Other Labs

• CBC: anemia, leukopenia (<4000/μL), lymphopenia (<1000/μL), thrombocytopenia (<100,000/μL)
• Urinalysis + sediment: hematuria, proteinuria, RBC/WBC casts
• BUN, creatinine, spot urine protein:creatinine ratio
• Coombs test (positive in AIHA)
• Direct Coombs, ESR, CRP (often normal in SLE flares)

Treatment

All Patients - Background Therapy

• Hydroxychloroquine (HCQ, 200-400 mg/day): Cornerstone of SLE management. Reduces flares, organ damage, thrombosis, improves survival. Should be prescribed to ALL patients unless contraindicated. Annual ophthalmologic screening required (risk of retinopathy at cumulative doses).
• Sun protection: High-SPF sunscreen, protective clothing
• Vitamin D supplementation
• NSAIDs: For joint and serositis symptoms (short-term)

Mild-Moderate Disease (skin, joints, fatigue)

• Hydroxychloroquine ± NSAIDs
• Low-dose glucocorticoids (prednisone ≤7.5 mg/day)
• Methotrexate (15-25 mg/week) - for cutaneous and articular disease
• Belimumab (anti-BLyS/BAFF monoclonal antibody) - approved for moderate-to-severe SLE; reduces flares and organ damage
• Anifrolumab (anti-type I IFN receptor monoclonal antibody) - approved 2021 for moderate-to-severe SLE; particularly effective for skin and joint disease

Severe/Organ-Threatening Disease

• High-dose glucocorticoids (IV methylprednisolone pulses for acute flares)
• Mycophenolate mofetil (MMF) - first-line for lupus nephritis (induction and maintenance)
• Azathioprine - maintenance therapy; preferred agent in pregnancy
• Cyclophosphamide (IV pulses, Euro-Lupus low-dose regimen preferred) - for severe nephritis (class III/IV), CNS lupus, severe vasculitis
• Voclosporin (23.7 mg BID) + MMF + glucocorticoids - FDA-approved 2021 for active lupus nephritis
• Belimumab + MMF + glucocorticoids - FDA-approved 2020 for lupus nephritis
• Tacrolimus / Cyclosporine - calcineurin inhibitors for nephritis, especially proteinuria
• Rituximab (anti-CD20) - not approved but widely used for refractory nephritis, hemolytic anemia, severe thrombocytopenia

Emerging Therapies (Harrison's 22E, 2025)

• Obinutuzumab (next-gen anti-CD20) - phase III trials
• SGLT2 inhibitors - under study for nephroprotection in lupus nephritis
• CAR-T cell therapy - remarkable early results in very severe refractory SLE (case series)

Adjunctive

• ACE inhibitor / ARB - for lupus nephritis with proteinuria
• Warfarin (not DOACs) - for APS with thrombosis
• Colchicine - for pleuritis/pericarditis
• Gonadotropin-releasing hormone agonist before cyclophosphamide - to preserve fertility

Type 1 vs Type 2 SLE (new conceptual framework)

Pregnancy in SLE

• Pregnancy is possible but high-risk; ideally planned during remission (≥6 months)
• Risks: preeclampsia, preterm birth, IUGR, flares
• Neonatal lupus: Maternal anti-Ro/SSA IgG crosses placenta → neonatal skin rash, thrombocytopenia, hepatitis, complete congenital heart block (permanent, may require pacemaker)
• HCQ and low-dose prednisone can be continued; azathioprine preferred for IS in pregnancy
• Avoid: MMF, methotrexate, cyclophosphamide, belimumab in pregnancy
• Antiphospholipid antibodies → heparin (LMWH) + low-dose aspirin during pregnancy

Prognosis & Mortality

• 10-year survival now >90% with modern treatment
• Early mortality (<5 years): disease activity (nephritis, CNS, hemorrhage), infections
• Late mortality (>5 years): premature atherosclerosis and cardiovascular disease (3-10x increased risk), infections, malignancy
• Damage accrual (measured by SLICC damage index) is the strongest predictor of poor outcomes

Recent Evidence Update (PubMed, 2024-2026)

A 2024 systematic review informing the 2023 EULAR SLE management update (Ann Rheum Dis, PMID 38777375) confirms HCQ as backbone therapy, supports treat-to-target strategies, endorses voclosporin and belimumab for lupus nephritis, and highlights the role of anifrolumab for non-renal SLE.

Pregnancy outcomes research (PMID 39153486, Lancet Rheumatol 2024) identifies anti-dsDNA positivity, active nephritis at conception, and antiphospholipid antibodies as the strongest predictors of adverse pregnancy outcomes.