Causes of Secondary Spontaneous Pneumothorax
Secondary spontaneous pneumothorax occurs in patients with clinically apparent underlying lung disease, most commonly chronic obstructive pulmonary disease (COPD), followed by tuberculosis, cystic fibrosis, HIV-associated Pneumocystis pneumonia, and interstitial lung disease. 1, 2
Definition and Distinction from Primary Pneumothorax
Secondary spontaneous pneumothorax (SSP) is defined as air in the pleural space occurring without antecedent trauma or iatrogenic cause, but in the presence of clinically apparent underlying lung disease. 1 This distinguishes it from primary spontaneous pneumothorax, which occurs in patients without clinically apparent lung abnormalities or underlying conditions known to promote pneumothorax (such as HIV disease). 1
Major Underlying Lung Diseases
Most Common Causes
Chronic Obstructive Pulmonary Disease (COPD): This is the predominant underlying condition, accounting for approximately 46% of SSP cases in recent series and representing the most common etiology in guideline assumptions. 1, 2, 3, 4
Pulmonary Tuberculosis: Historically one of the most important causes, tuberculosis remains a significant underlying disease, particularly in endemic regions, accounting for approximately 31% of cases in some series. 5, 2
Emphysema/Massive Bullous Disease: Severe emphysematous changes and massive bullous disease account for approximately 26% of SSP cases. 5, 4
Other Important Causes
HIV/AIDS with Pneumocystis Pneumonia: HIV disease, especially when associated with Pneumocystis carinii pneumonia (PCP), represents a significant and potentially life-threatening cause of SSP. 1, 2
Cystic Fibrosis: This condition is associated with more severe and potentially life-threatening presentations of SSP. 2, 3
Interstitial Lung Disease: Various forms of ILD, including interstitial pneumonia, account for approximately 13% of SSP cases and represent an independent risk factor for postoperative complications. 3, 4, 6
Clinical Characteristics and Risk Factors
The average age of patients with SSP is significantly higher than primary pneumothorax (mean 66.8 years), and smoking remains a critical risk factor with a 12% lifetime risk in male smokers versus 0.1% in non-smokers. 2, 5
Key Clinical Features
Symptom Severity: Clinical symptoms associated with SSP are generally more severe than those with primary pneumothorax, with dyspnea being the most common presenting symptom. 2, 5
Hypoxemia: The average arterial oxygen tension at onset of SSP is significantly lower (61.1 ± 12.1 mm Hg) compared to primary spontaneous pneumothorax. 5
Radiographic Findings: Adhesions on chest radiography are present in approximately 38% of cases and represent a significant risk factor for recurrence (odds ratio 4.90), while mediastinal shift is present in 40% and predicts extended hospitalization (odds ratio 6.05). 4
Pathophysiology
Despite the presence of underlying lung disease, subpleural blebs and bullae play a role in the pathogenesis of SSP, being found in up to 90% of cases at thoracoscopy or thoracotomy and in up to 80% of cases on CT scanning. 1, 2 The aetiology of these bullous changes in diseased lungs relates to the underlying parenchymal destruction from the primary lung disease. 1
Important Clinical Pitfalls
No relationship exists between physical activity and the onset of pneumothorax, contrary to common assumptions. 1, 2
Recurrence rates are high (approximately 41% in recent series), making SSP a challenging condition requiring aggressive management. 4
Prolonged air leakage before surgical intervention (>5 days) is an independent risk factor for postoperative complications, suggesting earlier surgical intervention may be beneficial in appropriate candidates. 6