Bronchiectasis¶

Chapter 301 | Part 7: Disorders of the Respiratory System · Part 7 – Respiratory Disorders · Chapter 301

Key Clinical Points¶

Bronchiectasis is defined as irreversible airway dilation (cylindrical/tubular, varicose, or cystic) occurring in a focal or diffuse manner.
The 'vicious cycle hypothesis' describes how susceptibility to infection and poor mucociliary clearance lead to microbial colonization, inflammation, and subsequent airway wall damage.
Chest CT is the imaging modality of choice; key findings include 'tram tracks', 'signet-ring sign' (airway diameter ≥ 1.5 times adjacent vessel), lack of tapering, and 'tree-in-bud' patterns.
Diagnosis requires radiologic criteria (e.g., airway-to-artery ratio ≥ 1.5, lack of tapering) combined with a clinical syndrome (cough, sputum, exacerbations).
Focal bronchiectasis requires bronchoscopy to exclude airway obstruction by mass or foreign body.
Nontuberculous mycobacteria (NTM), specifically the MAC complex, is common; management requires macrolide susceptibility testing and ruling out colonization before starting chronic therapy.
Long-term macrolide therapy (azithromycin/erythromycin) reduces exacerbations and mucus production but carries risks of QT prolongation and NTM resistance.
Dornase (DNase) is indicated for CF-related bronchiectasis only; it is not used in non-CF cases due to lack of efficacy and potential harm.
Management of massive hemoptysis requires a sequence: intubation → identification of bleeding source → bronchial artery embolization.
Lung function in non-CF bronchiectasis declines at 50–55 mL/year (similar to COPD), compared to 20–30 mL/year in healthy controls.

DEFINITION & OVERVIEW¶

• Definition: Irreversible airway dilation that involves the lung in either a focal or a diffuse manner. • Morphological Classifications: ◦ Cylindrical or tubular (most common form) ◦ Varicose ◦ Cystic • Pattern Classification: ◦ Focal: Localized area; may result from obstruction of the airway—either extrinsic (e.g., compression by lymphadenopathy or tumor mass) or intrinsic (e.g., airway tumor, aspirated foreign body, scarred/stenotic airway, or bronchial atresia).

EPIDEMIOLOGY¶

• General Trends: ◦ Prevalence in the United States is increasing. ◦ Incidence increases with age. ◦ More common among women than men. • Specific Etiology Distributions: ◦ Cystic Fibrosis (CF): Often develops significant clinical bronchiectasis in late adolescence or early adulthood. ◦ NTM (MAC): Classically affects non-smoking women >50 years of age. • Comorbidities: Frequently co-diagnosed with chronic obstructive pulmonary disease (COPD) or asthma. • Geographic Variations: ◦ TB-prevalent areas: More frequently occurs as a sequela of granulomatous infection. ◦ Developing nations: High incidence of non-CF bronchiectasis with unknown mechanisms; potentially linked to malnutrition and immune dysfunction. ◦ Focal cases: May arise from extrinsic compression by enlarged granulomatous nodes or broncholithiasis (erosion of a calcified lymph node through the airway wall).

ETIOLOGY & PATHOPHYSIOLOGY¶

• Pathogenesis: ◦ Vicious cycle hypothesis: Susceptibility to infection + poor mucociliary clearance → microbial colonization → inflammation → airway wall damage. • Mechanism of Damage: ◦ Small-airway inflammation: Release of proteases, reactive oxygen species, and pro-inflammatory cytokines leads to destruction of larger airway walls (loss of elastin, smooth muscle, cartilage). ◦ Antiproteases: Alpha-1 antitrypsin deficiency leads to failure to neutralize neutrophil elastase, resulting in bronchiectasis and emphysema. • Noninfectious Mechanisms: ◦ Immune-mediated reactions (e.g., Sjögren's syndrome, rheumatoid arthritis, inflammatory bowel disease). ◦ Environmental allergen sensitization. • Traction Bronchiectasis: Result of parenchymal distortion from lung fibrosis (e.g., postradiation fibrosis or idiopathic pulmonary fibrosis). • Anatomical Distribution & Specific Causes: ◦ Upper lung fields: CF; postradiation fibrosis. ◦ Lower lung fields: Chronic recurrent aspiration (e.g., esophageal motility disorders); end-stage fibrotic disease; immunodeficiency-associated infections. ◦ Midlung fields: NTM (specifically MAC). ◦ Central airways: Allergic bronchopulmonary aspergillosis (ABPA). ◦ Central airway/Cartilage deficiency: Tracheobronchomegaly (Mounier-Kuhn syndrome); Williams-Campbell syndrome. • Idiopathic: Found in 25–50% of patients referred for bronchiectasis.

CLINICAL FEATURES¶

• Presentation: ◦ Persistent productive cough with thick, tenacious sputum. • Physical Findings: ◦ Crackles and wheezing; potential for clubbing of digits. • Pulmonary Function Tests (PFTs): ◦ Mild to moderate airflow obstruction (similar to COPD). • Acute Exacerbations: ◦ Characterized by increased volume and purulence of sputum. ◦ Note: Fever and new infiltrates may not be present during exacerbation. • Focal Bronchiectasis Evaluation: ◦ Requires bronchoscopy to rule out obstruction by mass or foreign body.

DIFFERENTIAL DIAGNOSIS¶

• Radiographic Features: ◦ 'Tram tracks' (parallel dilated airways). ◦ 'Signet-ring sign' (airway diameter ≥ 1.5 times adjacent vessel). ◦ Lack of airway tapering. ◦ 'Tree-in-bud' pattern. • Etiological Categories: ◦ Obstruction: Foreign body, tumor mass. ◦ Infection: Bacterial, NTM. ◦ Immunodeficiency: Hypogammulhemia, HIV, post-transplant bronchiolitis obliterans. ◦ Genetic: Cystic fibrosis, Kartagener's syndrome, α1 antitrypsin deficiency. ◦ Autoimmune/Rheumatologic: Rheumatoid arthritis, Sjögren's syndrome, inflammatory bowel disease. ◦ Immune-mediated: Allergic bronchopulmonary aspergillosis (ABPA). ◦ Mechanical: Recurrent aspiration. ◦ Miscellaneous: Yellow nail syndrome, traction from fibrosis.

DIAGNOSTIC APPROACH¶

Imaging: • Chest X-ray and/or CT (CT is the preferred modality). • Criteria for diagnosis: Radiologic evidence of at least one of the following:
Inner- or outer-airway-artery diameter ratio ≥ 1.5.
Lack of airway tapering.
Visibility of airways in the periphery.
Bronchoscopy: • Required for focal bronchiectasis to rule out obstruction by mass or foreign body.
Sputum Analysis: • Gram stain, cultures (acid-fast bacilli, fungi). • If no pathogen identified → consider bronchoscopy with bronchoalveolar lavage (BAL).
Laboratory Tests: • CBC with differential; Immunoglobulins; HIV testing. • Sweat chloride (for CF); α1 antitrypsin levels. • Nasal/respiratory tract brush/biopsy (for cilia syndrome). • Serologic testing for rheumatoid factor; swallowing function/neuromuscular strength tests.
Clinical Criteria: • Diagnosis requires at least two of the following:
Cough most days of the week.
Sputum production most days of the week.
History of exacerbations.
NTM Specific Diagnostic Steps: • Perform macrolide susceptibility testing. • Rule out colonization before initiating chronic therapy.

MANAGEMENT & TREATMENT¶

Antibiotic Treatment: • Standard treatment based on identified pathogens. • NTM specific: Requires macrolide susceptibility testing; rule out colonization before starting chronic therapy.
Bronchial Hygiene: • Routine management of mucus production and clearance.
Mucolytics: • Dornase (DNase): Recommended for CF-related bronchiectasis only. • Note: Not used in non-CF cases due to lack of efficacy and potential harm.
Macrolide Therapy: • Agents: Azithromycin or Erythromycin. • Benefits: Reduces exacerbations and mucus production. • Risks: Macrolide-resistant NTM; QT prolongation.
Emergency Management (Hemoptysis): • Massive hemoptysis → Intubation → Identification of bleeding source → Bronchial artery embolization.

PROGNOSIS & COMPLICATIONS¶

• Lung Function Decline: ◦ Non-CF bronchiectasis: FEV1 declines 50–55 mL/year (similar to COPD). ◦ Healthy controls: FEV1 declines 20–30 mL/year. • Microbial Resistance: ◦ Risk of developing macrolide-resistant NTM with long-term therapy. • Hemoptysis: ◦ Potential for severe complications requiring intervention (e.g., embolization).

SPECIAL CONSIDERATIONS¶

• Immunodeficiency: ◦ Includes hypogammaglobulinemia and HIV infection. • Smoking: ◦ Relevant in the context of α1 antitrypsin deficiency and COPD overlap. • HIV: ◦ Specific consideration for those with underlying immunodeficiency.

KEY PEARLS & CLINICAL TRAPS¶

• Imaging Gold Standard: CT is the preferred modality to identify 'signet-ring' signs and lack of tapering. • Clinical Rule of Thumb: Diagnosis requires a combination of radiologic criteria (1/3) and clinical symptoms (2/3). • NTM Management: Always perform macrolide susceptibility testing before initiating long-term therapy to avoid resistance. • Mucolytic Restriction: Do not use Dornase (DNase) in non-CF patients. • Anatomical Mapping: Use location of bronchiectasis to narrow differential (e.g., Midlung → NTM; Lower → Aspiration/Fibrosis; Central → ABPA). • Hemoptysis Protocol: Massive hemoptysis is a medical emergency requiring immediate intubation and source identification.

TABLE 301-1: Major Etiologies of Bronchiectasis and Proposed Workup¶

• Focal: ◦ Obstruction (e.g., aspirated foreign body, tumor mass) ◦ Infection (e.g., bacterial, nontuberculous mycobacterial) ◦ Immunodeficiency (e.g., hypogammaglobulinemia, HIV infection, bronchiolitis obliterans after lung transplantation) ◦ Genetic causes (e.g., cystic fibrosis, Kartagener's syndrome, α1 antitrypsin deficiency) ◦ Autoimmune or rheumatologic causes (e.g., rheumatoid arthritis, Sjögren's syndrome, inflammatory bowel disease); immune-mediated disease (e.g., allergic bronchopulmonary aspergillosis) ◦ Recurrent aspiration ◦ Miscellaneous (e.g., yellow nail syndrome, traction bronchiectasis from postradiation fibrosis or idiopathic pulmonary fibrosis) ◦ Idiopathic • Workup for Focal: Chest imaging (chest x-ray and/or chest CT); bronchoscopy.

Reference Tables¶

TABLE 301-1 Major Etiologies of Bronchiectasis and Proposed Workup¶

Harrison's 22e, p.2242

PATTERN OF LUNG INVOLVEMENT	ETIOLOGY BY CATEGORY (EXAMPLES)	WORKUP
Focal	Obstruction (e.g., aspirated foreign body, tumor mass)	Chest imaging (chest x-ray and/or chest CT) a; bronchoscopy
	Infection (e.g., bacterial, nontuberculous mycobacterial)
	Immunodeficiency (e.g., hypogammaglobulinemia, HIV infection, bronchiolitis obliterans after lung transplantation)
	Genetic causes (e.g., cystic fibrosis, Kartagener’s syndrome, α antitrypsin 1 deficiency)
	Autoimmune or rheumatologic causes (e.g., rheumatoid arthritis, Sjögren’s syndrome, inflammatory bowel disease); immune-mediated disease (e.g., allergic bronchopulmonary aspergillosis)
	Recurrent aspiration
	Miscellaneous (e.g., yellow nail syndrome, traction bronchiectasis from postradiation fibrosis or idiopathic pulmonary fibrosis)
	Idiopathic