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Bronchiectasis and Bronchiolitis for USMLE Step 2

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Bronchiectasis and Bronchiolitis for the USMLE Step 2 Exam
Bronchiectasis
Pathophysiology
  • Chronic Infection and Inflammation:
    • Bronchiectasis is a permanent dilation of the bronchi caused by chronic infection and inflammation. Repeated cycles of inflammation lead to bronchial wall destruction, impaired mucociliary clearance, and airway dilation.
  • Mucus Stasis and Bacterial Colonization:
    • The damaged airways trap mucus, allowing bacteria to colonize and propagate chronic infections. This perpetuates inflammation and further airway damage.
Bronchiectasis pathophysiology
  • Etiologies:
    • Infectious Causes: Severe or recurrent infections such as pneumonia, tuberculosis, and whooping cough.
    • Cystic Fibrosis (CF): Causes thick, sticky mucus that blocks airways and fosters infections.
    • Immunodeficiency: Conditions like common variable immunodeficiency (CVID) lead to recurrent infections.
    • Primary Ciliary Dyskinesia: Impaired ciliary movement results in poor mucus clearance, leading to bronchiectasis.
Clinical Features
  • Chronic Cough with Sputum:
    • Persistent, productive cough with large volumes of thick, purulent sputum.
  • Recurrent Respiratory Infections:
    • Patients frequently suffer from exacerbations with infections, especially with pathogens like Pseudomonas aeruginosa.
  • Hemoptysis:
    • Mild or severe blood-streaked sputum, often during exacerbations.
  • Dyspnea and Wheezing:
    • Shortness of breath and wheezing, especially during or after infections.
Diagnosis
  • High-Resolution CT (HRCT):
    • The gold standard for diagnosis, revealing bronchial dilation with thickened walls (signet ring sign).
  • Pulmonary Function Tests (PFTs):
    • Show an obstructive pattern with reduced FEV1/FVC ratio, reflecting airway narrowing.
  • Sputum Culture:
    • Identifies pathogens responsible for chronic infections, guiding antibiotic therapy.
Management
  • Airway Clearance:
    • Chest physiotherapy, postural drainage, and devices like positive expiratory pressure (PEP) help mobilize and clear mucus.
  • Antibiotics:
    • For acute exacerbations, antibiotics targeting specific pathogens are used, with chronic suppressive antibiotics in severe cases (e.g., macrolides).
  • Bronchodilators:
    • Short-acting beta-agonists (SABAs) or long-acting bronchodilators for patients with coexisting airway obstruction.
  • Surgery:
    • Rarely, localized resection may be considered for severe, unresponsive cases.
Bronchiolitis
Pathophysiology
  • Small Airway Inflammation:
    • Bronchiolitis refers to inflammation of the bronchioles, often triggered by viral infections or toxic exposures. This inflammation leads to mucus production and small airway narrowing.
  • Types:
    • Acute Viral Bronchiolitis: Common in children, especially caused by respiratory syncytial virus (RSV), influenza, and adenovirus.
    • Bronchiolitis Obliterans: Chronic and irreversible inflammation causing bronchiolar fibrosis and obstruction, often seen after lung transplantation or exposure to toxins.
Clinical Features
  • Cough:
    • A persistent dry cough is common, often accompanied by progressive dyspnea.
  • Dyspnea:
    • Shortness of breath, worsening with exertion, is a typical symptom.
  • Wheezing and Crackles:
    • Wheezing and fine crackles may be heard on auscultation, especially in viral bronchiolitis.
  • Fever:
    • Fever may accompany infectious bronchiolitis.
Diagnosis
  • High-Resolution CT (HRCT):
    • Shows air trapping, mosaic attenuation, and tree-in-bud patterns, particularly in bronchiolitis obliterans.
  • Pulmonary Function Tests (PFTs):
    • An obstructive pattern with decreased FEV1 and increased residual volume (RV) due to air trapping.
  • Viral Testing:
    • Nasopharyngeal swabs can identify viral causes like RSV or influenza in infectious bronchiolitis.
Management
  • Supportive Care:
    • Hydration, oxygen, and antipyretics for acute viral bronchiolitis. Hospitalization may be required in severe cases.
  • Bronchodilators:
    • May be used for symptom relief, though their efficacy in viral bronchiolitis is variable.
  • Corticosteroids:
    • Systemic corticosteroids may be used in bronchiolitis obliterans but are not typically recommended for acute viral bronchiolitis.
  • Immunosuppressive Therapy:
    • Bronchiolitis obliterans may require treatment with immunosuppressive agents (e.g., corticosteroids, methotrexate).
Key Points
  • Bronchiectasis is a chronic condition characterized by the irreversible dilation of bronchi, with recurrent infections and sputum production. Diagnosis is made with HRCT, and management includes airway clearance, antibiotics, and bronchodilators.
  • Bronchiolitis involves inflammation of the bronchioles, often due to viral infections in children (e.g., RSV) or toxic exposures in adults. Management of acute viral bronchiolitis is supportive, while bronchiolitis obliterans may require immunosuppression. HRCT and PFTs are key diagnostic tools.

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