Pleural Effusion Can Be Both Restrictive and Obstructive
The answer is A. Pleural effusion, which causes restrictive physiology by limiting lung expansion and can also cause obstructive physiology when associated with endobronchial obstruction or trapped lung.
Restrictive Mechanism of Pleural Effusion
Pleural effusion primarily causes restrictive lung disease through multiple mechanisms:
- Reduced lung volume occurs as fluid accumulates in the pleural space, physically preventing full lung expansion during inspiration 1
- Decreased chest wall compliance results from the mechanical effects of fluid accumulation, contributing to dyspnea 2
- Depression of the diaphragm further limits inspiratory capacity 1
- The pathophysiology involves disruption of normal pleural fluid formation and drainage mechanisms 3
Obstructive Component in Specific Scenarios
Pleural effusion can demonstrate obstructive features in several clinical contexts:
- Endobronchial obstruction should be suspected when the lung fails to expand completely after pleural space drainage 4
- Trapped lung creates a fixed mediastinum, evidenced by absence of contralateral mediastinal shift despite large effusion volume 4
- Initial pleural fluid pressure <10 cm H₂O at thoracentesis suggests trapped lung, indicating obstructive pathophysiology 4
- Bronchoscopy may be needed to diagnose and potentially treat endobronchial obstruction when lung re-expansion fails 4
Clinical Implications for Diagnosis
The dual restrictive-obstructive nature has important diagnostic considerations:
- CT scanning can help differentiate between pleural effusion and identify endobronchial obstruction 4
- Before attempting pleurodesis in malignant effusions, complete lung expansion should be demonstrated to exclude trapped lung 4
- In lung cancer patients, adenocarcinoma spreads to the parietal pleura along existing pleural adhesions, potentially causing both restrictive fluid accumulation and obstructive airway involvement 5
Why Other Options Are Incorrect
- Pneumonia (B) causes primarily restrictive changes from consolidation, not obstructive physiology
- ARDS (C) is a restrictive process from alveolar damage and decreased compliance, without obstructive features
- Bronchial Asthma (D) is purely obstructive, characterized by reversible airway narrowing without restrictive components