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Bronchiectasis and Bronchiolitis for USMLE Step 3

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Bronchiectasis and Bronchiolitis for the USMLE Step 3 Exam
Bronchiectasis
Pathophysiology
  • Chronic Inflammation and Infection:
    • Bronchiectasis is a result of chronic inflammation and recurrent infections that lead to permanent dilation of the bronchi. The bronchial walls become damaged, weakening mucociliary clearance and leading to mucus stasis, which further predisposes the airways to infections.
Bronchiectasis pathophysiology
  • Etiologies:
    • Infectious Causes: Severe or recurrent infections, such as tuberculosis, pneumonia, and pertussis, damage the airways.
    • Cystic Fibrosis (CF): A genetic disorder causing thick mucus that obstructs airways and promotes bacterial colonization.
    • Immunodeficiency: Conditions like common variable immunodeficiency (CVID) increase the risk of frequent respiratory infections.
    • Obstruction: Tumors or foreign bodies can lead to localized bronchiectasis by blocking airflow.
Clinical Features
  • Chronic Cough with Sputum:
    • Persistent cough with production of large volumes of thick, purulent sputum is a hallmark of bronchiectasis.
  • Recurrent Respiratory Infections:
    • Frequent exacerbations are common, with pathogens such as Pseudomonas aeruginosa often involved.
  • Hemoptysis:
    • Blood-tinged sputum or significant hemoptysis may occur due to erosion of bronchial blood vessels.
  • Dyspnea and Wheezing:
    • Shortness of breath and wheezing are frequent, especially during infections or exacerbations.
Diagnosis
  • High-Resolution CT (HRCT):
    • The diagnostic standard, showing dilated bronchi with thickened walls (“tram track” and “signet ring” signs).
  • Pulmonary Function Tests (PFTs):
    • Reveal an obstructive pattern (decreased FEV1/FVC ratio) and may show partial reversibility with bronchodilators.
  • Sputum Culture:
    • Identifies pathogens to guide antibiotic therapy, particularly in chronic cases.
Management
  • Airway Clearance:
    • Chest physiotherapy, postural drainage, and oscillatory positive expiratory pressure (PEP) devices help clear mucus from the lungs.
  • Antibiotics:
    • Targeted antibiotics are used during exacerbations. Chronic suppressive antibiotics (e.g., macrolides) may be considered in patients with frequent exacerbations.
  • Bronchodilators:
    • Short-acting beta-agonists (SABAs) or long-acting bronchodilators are used for patients with concomitant airflow obstruction.
  • Surgery:
    • Reserved for localized disease or recurrent hemoptysis unresponsive to medical therapy.
Bronchiolitis
Pathophysiology
  • Small Airway Inflammation:
    • Bronchiolitis involves inflammation of the bronchioles, leading to swelling and mucus production, which narrows the small airways and obstructs airflow.
  • Types:
    • Acute Viral Bronchiolitis: Common in infants and young children, usually caused by respiratory syncytial virus (RSV), influenza, or adenovirus.
    • Bronchiolitis Obliterans: A chronic, non-reversible condition causing fibrosis and narrowing of bronchioles, often following lung transplantation or exposure to toxic inhalants.
Clinical Features
  • Cough and Dyspnea:
    • A persistent, nonproductive cough and progressive shortness of breath are the most common symptoms.
  • Wheezing and Crackles:
    • Wheezing, fine crackles, or rhonchi may be heard on auscultation, especially in viral bronchiolitis.
  • Fever:
    • Typically seen in acute infectious bronchiolitis.
Diagnosis
  • High-Resolution CT (HRCT):
    • HRCT shows air trapping, mosaic attenuation, and tree-in-bud patterns, especially in bronchiolitis obliterans.
  • Pulmonary Function Tests (PFTs):
    • Show an obstructive pattern with decreased FEV1 and increased residual volume (RV), indicating air trapping.
  • Viral Testing:
    • Nasopharyngeal swabs help identify viral pathogens (e.g., RSV, influenza) in cases of infectious bronchiolitis.
Management
  • Supportive Care:
    • Acute viral bronchiolitis is managed with hydration, oxygen supplementation, and antipyretics. Hospitalization may be necessary in severe cases.
  • Bronchodilators:
    • May provide symptomatic relief, though their efficacy in acute bronchiolitis is limited.
  • Corticosteroids:
    • Systemic corticosteroids are useful in bronchiolitis obliterans but have limited benefit in acute viral bronchiolitis.
  • Immunosuppressive Therapy:
    • In bronchiolitis obliterans, immunosuppressants (e.g., corticosteroids, azathioprine) may help reduce inflammation.
Key Points
  • Bronchiectasis is characterized by irreversible dilation of the bronchi due to chronic inflammation and infection. Diagnosis is confirmed with HRCT, and management includes airway clearance, antibiotics, and bronchodilators.
  • Bronchiolitis involves inflammation of the bronchioles, commonly caused by viral infections in children or chronic conditions like bronchiolitis obliterans in adults. Diagnosis is confirmed with HRCT and PFTs, and treatment is supportive for viral cases, with immunosuppression used for chronic forms like bronchiolitis obliterans.

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