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Internal MedicineRheumatologySystemic Lupus Erythematosus (SLE)

Systemic Lupus Erythematosus (SLE)

Must-Not-Miss / Red Flags

  • Lupus nephritis: proteinuria >500 mg/24h or cellular casts → renal biopsy
  • Neuropsychiatric lupus: seizures, psychosis, aseptic meningitis
  • Catastrophic antiphospholipid syndrome: multi‑organ thrombosis – 50% mortality
Patient Explanation
“You have a condition where your immune system attacks your own body, causing inflammation in different parts. We have many treatments to control it and keep you well.”
Board Fact
“The presence of anti‑dsDNA antibodies and low complement levels (C3, C4) correlate with disease activity, especially in lupus nephritis.”
ICD-10
M32.9

Definition & Core Concept

Systemic lupus erythematosus (SLE) is a chronic, multisystem autoimmune disease characterized by the production of antinuclear antibodies (ANA), immune complex deposition, and inflammation affecting skin, joints, kidneys, and other organs.

Epidemiology & Risk Factors

  • Prevalence: 20‑150 per 100,000; female‑to‑male ratio 9:1
  • Peak onset 15‑44 years
  • More severe in African American, Hispanic, and Asian populations

Pathophysiology (Rule of 3)

  1. Genetic predisposition + environmental trigger (UV light, infection, drugs) → loss of self‑tolerance
  2. Autoantibody production (ANA, anti‑dsDNA, anti‑Sm) → immune complex formation
  3. Immune complex deposition in tissues (glomeruli, skin, joints) → complement activation → inflammation and tissue damage

Clinical Presentation

  • Constitutional: fever, fatigue, weight loss
  • Musculoskeletal: arthralgia, non‑erosive arthritis
  • Mucocutaneous: malar rash (butterfly), discoid lesions, photosensitivity, oral ulcers
  • Renal: proteinuria, hematuria, hypertension
  • Hematologic: anemia, leukopenia, thrombocytopenia
  • Serositis: pleuritis, pericarditis

Diagnostic Workup

ANA: sensitive but not specific (positive in >95% of SLE). Anti‑dsDNA and anti‑Sm: highly specific. Complement C3/C4: low in active disease. Urinalysis: proteinuria, cellular casts. Renal biopsy: if urine abnormalities to classify lupus nephritis.

Management Protocol

  1. Mild (skin/joint): Hydroxychloroquine 200‑400 mg daily (all patients unless contraindicated), NSAIDs, low‑dose corticosteroids
  2. Moderate: Azathioprine, Mycophenolate mofetil, or Methotrexate as steroid‑sparing agents
  3. Severe (nephritis, CNS): High‑dose corticosteroids (Methylprednisolone 500‑1,000 mg IV ×3 days) + Cyclophosphamide or Mycophenolate; consider Rituximab or Belimumab
  4. Sun protection: broad‑spectrum sunscreen SPF ≥50

Complications & Prognosis

  • End‑stage renal disease from lupus nephritis
  • Cardiovascular disease (accelerated atherosclerosis)
  • Avascular necrosis of the hip from chronic steroids
  • Infections (leading cause of death)

ICU Criteria

ICU admission if: diffuse alveolar hemorrhage, catastrophic antiphospholipid syndrome, or severe neuropsychiatric lupus.

Clinical Vignette

A 25‑year‑old African American woman presents with malar rash, oral ulcers, and inflammatory polyarthritis for 2 months. Labs: ANA 1:640, anti‑dsDNA positive, C3 low. Urinalysis shows 3+ protein and RBC casts. Renal biopsy shows Class IV lupus nephritis.

Pearls & Pitfalls

  • Hydroxychloroquine reduces flares and mortality – it should be prescribed to every SLE patient unless contraindicated (retinal toxicity screen annually).
  • Pregnancy in SLE should be planned when disease is quiescent for ≥6 months due to high risk of flare and fetal loss.

Discharge & Follow-Up

Rheumatology visits every 3‑6 months. Labs (CBC, C3/C4, anti‑dsDNA, urinalysis) to monitor activity. Annual ophthalmology exam for hydroxychloroquine retinopathy.

Literature & Guidelines

EULAR 2024 Recommendations for SLE Management. PMID: 38703200.

Personal Clinical Notes