What causes bronchiectasis?

Causes of Bronchiectasis

Bronchiectasis is primarily caused by recurrent bacterial colonization and infection leading to progressive airway injury, resulting in permanent dilation of bronchi with destruction of elastic and muscular components of their walls. 1

Pathophysiological Mechanism

Bronchiectasis develops through a cycle of:

1. Initial airway injury (from various causes)
2. Inflammation mediated by neutrophils, T lymphocytes, and monocyte-derived cytokines
3. Destruction of elastic and muscular components of bronchial walls by inflammatory mediators, elastase, and collagenase
4. Expansion of airway diameter due to contractile force of surrounding lung tissue exerting traction 1

Distribution Patterns and Causes

Focal Bronchiectasis

• Bronchial obstruction:
  • Foreign body
  • Tumor
  • Broncholithiasis
  • Compression by peribronchial lymph nodes 1
• Previous pneumonia (less common with increased antibiotic use) 1

Diffuse Bronchiectasis

• Cystic Fibrosis (CF): Most common identifiable cause in the US and Europe 2
• Reduced host immunity:
  • Congenital and acquired hypogammaglobulinemia (especially IgG and IgG subclasses)
  • HIV infection
  • Primary ciliary dyskinesia (PCD) 1, 2
• Allergic/inflammatory conditions:
  • Allergic bronchopulmonary aspergillosis (ABPA)
  • Rheumatoid arthritis
  • Inflammatory bowel disease 1
• Infections:
  • Chronic Mycobacterium avium complex (MAC) infection
  • Tuberculosis
  • Severe childhood infections (pertussis, measles) 1, 3
• Aspiration or toxic inhalation 1
• Congenital disorders:
  • Alpha-1 antitrypsin deficiency
  • Tracheobronchomegaly (Mounier-Kuhn syndrome)
  • Cartilage deficiency (Williams-Campbell syndrome)
  • Young syndrome
  • Pulmonary sequestration
  • Marfan syndrome
  • Yellow nail syndrome 1

Epidemiology and Risk Factors

• Prevalence increases substantially with age (7 per 100,000 in individuals 18-34 years vs 812 per 100,000 in those ≥75 years)
• More common in women than men (180 vs 95 per 100,000) 3
• Associated conditions include:
  • Gastroesophageal reflux disease (47%)
  • Asthma (29%)
  • Chronic obstructive pulmonary disease (20%) 3
• Up to 38% of cases are idiopathic 3

Key Diagnostic Considerations

• High-resolution CT (HRCT) is the diagnostic procedure of choice with >90% sensitivity and specificity 1, 2
• Key HRCT findings include:
  • Enlarged internal bronchial diameter (signet ring sign)
  • Failure of airways to taper while progressing to lung periphery
  • Air-fluid levels in dilated airways
  • Identification of airways in extreme lung periphery 1

Clinical Implications

• A systematic search for underlying causes is essential as it may lead to specific treatments that can slow or halt disease progression
• In a study of 150 adults with bronchiectasis, causative factors were identified in 47% of cases, with important therapeutic or prognostic significance in 15% 1
• Early diagnosis and treatment may prevent irreversible loss of lung function 4

Common Pitfalls to Avoid

1. Failure to investigate for underlying causes: Always perform a diagnostic evaluation for underlying disorders, as identification may lead to targeted treatments that slow or halt disease progression 1

2. Missing CF diagnosis in adults: Consider CF in any young adult with bronchiectasis, even without obvious GI symptoms 2

3. Inadequate imaging: Standard chest X-rays have limited sensitivity; HRCT is required for definitive diagnosis 2

4. Confusing chronic bronchitis with bronchiectasis: Chronic productive cough is more common in chronic bronchitis, asthma, upper airway cough syndrome, and GERD than in bronchiectasis 1