Bronchiectasis and Bronchiolitis for USMLE Step 1
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Bronchiectasis and Bronchiolitis for the USMLE Step 1 Exam
Bronchiectasis
Pathophysiology
- Chronic Infection and Inflammation:
- Bronchiectasis results from chronic or recurrent lung infections, causing permanent dilation of the bronchi. Inflammation and immune responses damage the bronchial walls, impairing mucus clearance and increasing infection risk.
- Impaired Mucociliary Clearance:
- Structural damage in bronchiectasis leads to poor mucus clearance. The buildup of thick secretions predisposes patients to recurrent infections, perpetuating a cycle of infection and inflammation.
- Causes:
- Infectious: Recurrent or severe lung infections (e.g., tuberculosis, pneumonia) are major causes.
- Cystic Fibrosis: Inherited disorder leading to thick mucus production and chronic lung infections.
- Immunodeficiency: Disorders like common variable immunodeficiency increase susceptibility to infections.
- Obstruction: Airway obstruction from tumors or foreign bodies may cause localized bronchiectasis.
Clinical Features
- Chronic Cough with Sputum:
- Patients present with persistent cough and daily production of large amounts of purulent sputum.
- Recurrent Infections:
- Repeated respiratory infections, commonly involving Pseudomonas or Haemophilus species.
- Hemoptysis:
- Coughing up blood, either streaked or more substantial, may occur due to inflamed bronchial vessels.
- Dyspnea and Wheezing:
- Shortness of breath and wheezing are common, particularly during exacerbations.
Diagnosis
- High-Resolution CT (HRCT):
- HRCT is the diagnostic standard, showing dilated airways with thickened bronchial walls (“tram tracks” or “signet ring” sign).
- Pulmonary Function Tests (PFTs):
- Show an obstructive pattern (decreased FEV1/FVC), often reversible with bronchodilators.
Management
- Airway Clearance:
- Chest physiotherapy and postural drainage help clear mucus.
- Antibiotics:
- Target bacterial pathogens, particularly in exacerbations. Chronic suppressive antibiotics (e.g., macrolides) may be used in severe cases.
- Bronchodilators:
- Short-acting beta-agonists (SABAs) can alleviate airflow obstruction.
Bronchiolitis
Pathophysiology
- Small Airway Inflammation:
- Bronchiolitis is inflammation of the bronchioles, the smallest airways. It often follows viral infections or exposure to toxic fumes, leading to swelling and mucus buildup, obstructing airflow.
- Types:
- Acute Viral Bronchiolitis: Primarily affects children, caused by respiratory syncytial virus (RSV) or other viruses.
- Bronchiolitis Obliterans: A severe form causing fibrosis and narrowing of the bronchioles, often following lung transplantation, toxic exposure, or autoimmune diseases.
Clinical Features
- Cough and Dyspnea:
- Nonproductive cough and progressive shortness of breath are common symptoms.
- Wheezing:
- Wheezing may occur due to airway narrowing, especially in viral bronchiolitis.
- Fever:
- Often present in infectious bronchiolitis.
Diagnosis
- High-Resolution CT (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, indicating air trapping.
- Viral Testing:
- Nasal swabs can identify RSV, influenza, or other viral pathogens in cases of infectious bronchiolitis.
Management
- Supportive Care:
- In viral bronchiolitis, treatment is supportive, including hydration, oxygen, and antipyretics.
- Bronchodilators:
- SABAs (e.g., albuterol) may provide symptom relief, though evidence for their benefit in bronchiolitis is limited.
- Corticosteroids:
- May be used in bronchiolitis obliterans, but their role in acute viral bronchiolitis is controversial.
- Immunosuppressive Therapy:
- For bronchiolitis obliterans associated with autoimmune diseases or post-transplantation, agents like corticosteroids or methotrexate may be required.
Key Points
- Bronchiectasis is characterized by permanent dilation of the bronchi, leading to chronic cough with sputum, recurrent infections, and possibly hemoptysis. Diagnosis is confirmed with HRCT, and management includes airway clearance and antibiotics.
- Bronchiolitis involves inflammation of the bronchioles, most often due to viral infections or toxic exposure. Management is supportive in viral cases, while bronchiolitis obliterans may require immunosuppressive therapy. HRCT and PFTs are key diagnostic tools.