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Bronchiectasis and Bronchiolitis for ABIM

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Bronchiectasis and Bronchiolitis for the American Board of Internal Medicine Exam
Bronchiectasis
Pathophysiology
  • Chronic Inflammation and Infection:
    • Bronchiectasis involves permanent dilation of the bronchi due to chronic inflammation and recurrent infections. Damage to the bronchial walls leads to mucus stasis, promoting bacterial colonization and further lung injury.
    • Inflammatory mediators (e.g., neutrophils, proteases) contribute to the destruction of elastin and collagen, causing irreversible airway dilation and fibrosis.
  • Mucociliary Clearance Dysfunction:
    • Impaired clearance of mucus and debris results from the structural damage to the airways. This leads to pooling of secretions, increasing the risk of recurrent infections and perpetuating inflammation.
Bronchiectasis pathophysiology
  • Etiologies:
    • Infections: Prior severe lung infections, such as tuberculosis, pertussis, or pneumonia, are common causes.
    • Cystic Fibrosis: A genetic condition causing defective chloride channels, leading to thickened mucus and impaired mucociliary function.
    • Primary Ciliary Dyskinesia: Impaired ciliary function leads to poor mucus clearance and recurrent infections.
    • Immunodeficiencies: Conditions like common variable immunodeficiency (CVID) result in increased susceptibility to infections, contributing to bronchiectasis.
    • Obstruction: Airway obstructions (e.g., foreign body, tumors) can lead to localized bronchiectasis.
Clinical Features
  • Chronic Productive Cough:
    • Persistent cough with daily production of large volumes of purulent sputum is characteristic of bronchiectasis.
  • Recurrent Respiratory Infections:
    • Frequent bacterial infections, often with Pseudomonas aeruginosa or Haemophilus influenzae, are common.
  • Hemoptysis:
    • Blood-streaked sputum or frank hemoptysis may occur due to erosion of the bronchial vessels.
  • Dyspnea and Wheezing:
    • These symptoms often worsen with exacerbations, and may be present at baseline in more severe cases.
  • Clubbing:
    • Digital clubbing is sometimes observed in advanced cases of bronchiectasis, indicating chronic hypoxia.
Diagnosis
  • High-Resolution CT Scan (HRCT):
    • The gold standard for diagnosis, showing dilated bronchi with thickened walls ("tram track" or "signet ring" appearance).
  • Pulmonary Function Tests (PFTs):
    • PFTs typically show an obstructive pattern with decreased FEV1/FVC and possible reversibility after bronchodilator administration.
  • Sputum Culture:
    • Used to identify pathogens, particularly Pseudomonas aeruginosa or atypical mycobacteria, to guide antibiotic therapy.
Management
  • Airway Clearance Techniques:
    • Chest physiotherapy, postural drainage, and devices like oscillatory positive expiratory pressure (PEP) are used to clear secretions.
  • Antibiotics:
    • Acute Exacerbations: Empiric antibiotics targeting common pathogens are prescribed based on sputum culture results.
    • Chronic Suppressive Therapy: Long-term macrolides (e.g., azithromycin) may reduce exacerbation frequency in severe cases.
  • Bronchodilators and Corticosteroids:
    • Bronchodilators (SABAs or LABAs) and inhaled corticosteroids (ICS) can help reduce bronchospasm in patients with concurrent airflow obstruction.
  • Surgical Intervention:
    • In patients with localized disease or recurrent hemoptysis unresponsive to medical therapy, surgical resection of the affected lung segment may be considered.
Bronchiolitis
Pathophysiology
  • Small Airway Inflammation:
    • Bronchiolitis refers to inflammation and narrowing of the bronchioles (small airways), often due to viral infections or exposure to toxic inhalants.
  • Types:
    • Acute Infectious Bronchiolitis: Primarily seen in children, usually caused by respiratory syncytial virus (RSV), influenza, or adenovirus. In adults, it is less common but may occur in immunocompromised patients or as a result of viral infections.
    • Bronchiolitis Obliterans (Constrictive Bronchiolitis): A more severe, non-reversible form, often associated with toxic inhalants, autoimmune diseases, or post-lung transplantation.
  • Etiologies:
    • Viral Infections: RSV is the leading cause of bronchiolitis in children, while influenza and adenovirus are common in adults.
    • Toxic Fumes: Inhalation of chemical irritants (e.g., ammonia, chlorine) or smoke can lead to bronchiolar damage.
    • Transplantation: Bronchiolitis obliterans is a major cause of chronic lung allograft rejection in lung transplant recipients.
    • Autoimmune Diseases: Conditions like rheumatoid arthritis can cause bronchiolar inflammation and fibrosis.
Clinical Features
  • Cough:
    • A persistent, nonproductive cough is common, often worsening with exertion.
  • Dyspnea:
    • Progressive shortness of breath, especially with exertion, is the predominant symptom.
  • Wheezing:
    • Wheezing may occur due to the narrowed airways, particularly in acute viral bronchiolitis.
  • Fever:
    • Fever is common in infectious bronchiolitis but may be absent in non-infectious forms (e.g., bronchiolitis obliterans).
Diagnosis
  • High-Resolution CT (HRCT):
    • HRCT is the diagnostic test of choice, showing mosaic attenuation, air trapping, and tree-in-bud opacities in acute bronchiolitis. In bronchiolitis obliterans, it may show areas of hyperlucency due to air trapping.
  • Pulmonary Function Tests (PFTs):
    • PFTs often show an obstructive pattern with decreased FEV1 and a normal or mildly reduced FVC. Air trapping may be indicated by an increased residual volume (RV).
  • Viral Testing:
    • Nasopharyngeal swabs can identify viral pathogens (e.g., RSV, influenza) in infectious bronchiolitis.
Management
  • Supportive Care:
    • For viral bronchiolitis, supportive care includes hydration, antipyretics, and oxygen supplementation as needed.
  • Bronchodilators:
    • SABAs (e.g., albuterol) may provide symptom relief, though their efficacy in bronchiolitis is variable.
  • Corticosteroids:
    • Systemic corticosteroids may be used in cases of bronchiolitis obliterans or when inflammation is suspected, although their role in acute infectious bronchiolitis is limited.
  • Antibiotics:
    • Not indicated for viral bronchiolitis but may be required if a secondary bacterial infection is suspected.
  • Immunomodulatory Therapy:
    • In cases of bronchiolitis obliterans associated with autoimmune diseases, immunosuppressive agents (e.g., methotrexate, azathioprine) may be used.
  • Lung Transplantation:
    • For severe cases of bronchiolitis obliterans unresponsive to medical management, lung transplantation may be the only definitive treatment.
Key Points
  • Bronchiectasis is characterized by permanent dilation of the bronchi due to chronic infection and inflammation. Patients present with a chronic productive cough, recurrent infections, and possibly hemoptysis. Diagnosis is confirmed with HRCT, and management focuses on airway clearance, antibiotics, and bronchodilators.
  • Bronchiolitis involves inflammation of the small airways and can be infectious (typically viral in children) or non-infectious (e.g., bronchiolitis obliterans). Diagnosis relies on HRCT and PFTs, and treatment is largely supportive for viral bronchiolitis, with immunosuppressive therapy used for bronchiolitis obliterans.

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