What is bronchiectasis and what are its common causes?

What is Bronchiectasis?

Bronchiectasis is a chronic inflammatory lung disease defined by permanent, irreversible dilation of the bronchi visible on chest CT scan, accompanied by clinical symptoms of chronic cough, sputum production, and recurrent respiratory infections 1.

Radiologic and Clinical Definition

The diagnosis requires both components:

• Radiologic: Permanent bronchial dilation on chest computed tomography (CT) scan - this is the gold standard imaging modality 1
• Clinical: Characteristic symptoms including chronic cough, sputum production, and recurrent respiratory infections 1

The "Vicious Vortex" Pathophysiology

The disease operates through four interrelated components that drive progressive lung damage 1:

1. Airway inflammation
2. Impaired mucociliary clearance
3. Chronic airway infection
4. Structural lung damage

These components create a self-perpetuating cycle where damaged epithelium impairs mucus removal, facilitating bacterial colonization, which drives further inflammation and structural damage 2.

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Common Causes of Bronchiectasis

The Etiologic Landscape

Bronchiectasis results from a wide variety of underlying conditions including infectious, autoimmune, allergic, genetic, and inflammatory disorders, but approximately 40% of cases have no identified cause (idiopathic) 1.

Major Etiologic Categories 1, 3:

Infectious causes:

• Post-infectious (most common identified cause globally)
• Post-tuberculous bronchiectasis (particularly prevalent in socially disadvantaged regions) 4
• Non-tuberculous mycobacterial (NTM) infection
• Severe or recurrent pneumonia
• Chronic pulmonary aspiration 5

Immunologic causes:

• Primary immunodeficiencies (e.g., combined variable immune deficiency) 2
• Allergic bronchopulmonary aspergillosis (ABPA) 1

Genetic/Congenital causes:

• Primary ciliary dyskinesia (PCD) 1
• Cystic fibrosis (managed separately with distinct guidelines) 1
• Congenital cartilage development disorders 6

Autoimmune/Inflammatory causes:

• Rheumatoid arthritis 7
• Other autoimmune diseases 2

Obstructive airway diseases:

• COPD-associated bronchiectasis (increasingly recognized) 4
• Severe asthma-associated bronchiectasis (progressively increasing prevalence) 4

Geographic Heterogeneity

Important caveat: There is considerable geographic variation in etiology 4:

• Socially disadvantaged regions or areas with poor healthcare access: Post-infectious and post-tuberculous forms clearly predominate
• Developed regions: Greater proportion of idiopathic cases, COPD-associated, and immune-mediated forms

Clinical Implications

The importance of identifying underlying etiology cannot be overstated - standardized testing to identify the cause is essential because targeted treatment of treatable etiologies (such as immune deficiency, ABPA, or NTM infection) is associated with better patient prognosis 3, 8, 4.

Disease Impact

Bronchiectasis carries significant morbidity and mortality 3, 7:

• Decreased health-related quality of life
• Increased mortality risk
• Chronic bacterial colonization (most commonly Pseudomonas aeruginosa and Haemophilus influenzae) 3
• Recurrent exacerbations that drive disease progression
• Risk of massive hemoptysis in severe cases 6