SLE: High-Yield Pathology for NEET PG
Systemic Lupus Erythematosus (SLE) is the quintessential Type III hypersensitivity disorder. It is a multisystem autoimmune disease characterized by the production of autoantibodies against nuclear antigens, leading to widespread immune complex deposition.
1. Diagnostic Autoantibody Profile
For exam purposes, you must distinguish between high sensitivity (screening) and high specificity (diagnostic):
| Antibody | Clinical Correlation |
|---|---|
| ANA (Antinuclear) | Best screening test (High sensitivity). |
| Anti-dsDNA | Highly specific; levels correlate with disease activity and lupus nephritis. |
| Anti-Smith (Sm) | Most specific marker for SLE. |
| Anti-Histone | Diagnostic for Drug-Induced Lupus (e.g., Hydralazine, Procainamide, Isoniazid). |
2. High-Yield Clinical Features
- Skin: Malar “butterfly” rash (spares nasolabial folds); discoid rash (scarring).
- Renal: Lupus Nephritis is the major cause of morbidity. The most common pattern is Diffuse Proliferative Glomerulonephritis (Class IV).
- Serositis: Pleuritis, pericarditis.
- Hematologic: Anemia of chronic disease, leukopenia, thrombocytopenia (type II hypersensitivity).
- Libman-Sacks Endocarditis: Sterile vegetations on both sides of the mitral/tricuspid valves.
3. Pathological “Exam Must-Knows.”
Crucial Concept: SLE-associated Anti-phospholipid Syndrome (APS) is characterized by venous/arterial thrombosis and recurrent spontaneous abortions. It presents with a falsely positive VDRL/RPR (syphilis test) because the test uses cardiolipin as an antigen, which cross-reacts with anti-phospholipid antibodies.
- Lupus Nephritis Class IV (Diffuse Proliferative): Exhibits “wire-loop” capillary appearance on light microscopy and granular IgG/C3 deposits on immunofluorescence.
- Mnemonic for Drug-Induced Lupus: “SHIMP” – Sulfonamides, Hydralazine, Isoniazid, Methyldopa, Procainamide.
- Immune Complexes: These deposit in basement membranes of various organs, triggering local complement activation, neutrophil recruitment, and subsequent tissue destruction.