A 32-year-old Indian woman with a 3-year history of systemic lupus erythematosus develops acute pleuritic chest pain and dyspnea. Chest X-ray shows a small left-sided pleural effusion. Which is the most common pulmonary manifestation of SLE?

Explanation

## Most Common Pulmonary Manifestation of SLE **Key Point:** Pleural effusion is the most common pulmonary manifestation of SLE, occurring in 20–60% of SLE patients during the disease course. It is often the presenting feature of pulmonary involvement and is generally reversible with treatment. ## SLE Pulmonary Manifestations — Frequency and Features | Manifestation | Frequency | Characteristics | Prognosis | |---|---|---|---| | Pleural effusion | 20–60% | Most common; exudative; LE cells present; reversible | Excellent | | Acute lupus pneumonitis | 1–12% | Fever, cough, dyspnea, infiltrates; acute onset | Good with steroids | | Pulmonary hemorrhage | <5% | Hemoptysis, diffuse alveolar infiltrates; life-threatening | Poor; requires urgent treatment | | Shrinking lung syndrome | <1% | Restrictive pattern, diaphragmatic dysfunction; rare | Chronic, progressive | | Pulmonary hypertension | 5–14% | Elevated PA pressure; may be isolated or with ILD | Variable; often progressive | | Interstitial lung disease | 3–13% | Fibrosis, restrictive pattern; late manifestation | Progressive | **High-Yield:** Characteristics of SLE pleural effusion: - Exudative (LDH >200 IU/L, protein >3 g/dL) - LE cells often present in pleural fluid (pathognomonic but rarely tested) - ANA and anti-dsDNA may be positive in pleural fluid - Usually small to moderate volume - Often bilateral but asymmetric - Responds well to NSAIDs or low-dose corticosteroids **Clinical Pearl:** The presence of LE cells or ANA in pleural fluid is highly specific for lupus pleuritis and helps distinguish SLE-related effusion from other causes (infection, malignancy, heart failure). **Mnemonic:** **PLEA** = **Pleural Effusion is the most common pulmonary manifestation of SLE** — occurs in up to 60% of patients. ## Why Pleural Effusion is Most Common 1. **Immune complex deposition** in pleura triggers inflammation 2. **Complement activation** (low C3, C4) drives pleural inflammation 3. **Antinuclear antibodies** and anti-dsDNA cross-react with pleural tissue 4. **Reversibility** — responds to immunosuppression, allowing patients to survive and be counted in prevalence studies 5. Acute pneumonitis and pulmonary hemorrhage are rarer because they are more severe and may be fatal if untreated ## Distinguishing SLE Pleural Effusion from Other Causes **SLE pleural effusion:** - Exudative; low complement (C3, C4) - LE cells or ANA in fluid - Negative bacterial/viral cultures - Associated with other SLE features (rash, arthritis, ANA+) **Parapneumonic effusion:** - Associated with pneumonia - Bacterial culture positive - No LE cells **Malignant effusion:** - Cytology positive for malignancy - No LE cells - No ANA in fluid [cite:Harrison 21e Ch 319]