Bronchiectasis: A High-Yield USMLE Review

Bronchiectasis is permanent, abnormal dilation of the bronchi resulting from chronic infection and inflammation. It is an obstructive lung disease, but crucially it is not a diagnosis in itself \an it is a consequence \an so the most important exam skill is identifying and treating the underlying cause. It shows up frequently on the USMLE both as a cause of recurrent infection and as a downstream complication of immunodeficiency, cystic fibrosis, and ciliary disorders.

Presentation

• Chronic cough with daily, copious sputum production
• Recurrent "pneumonias" and recurrent respiratory infections
• Spirometry showing an obstructive pattern
• History suggesting an underlying cause: childhood infection, immunodeficiency, or genetic disease

Diagnosis

• HRCT chest showing bilateral bronchial dilation with the "signet ring sign" (dilated airway larger than its accompanying vessel)
• Spirometry demonstrating obstruction
• Sweat chloride test or genetic testing to evaluate for cystic fibrosis
• Quantitative immunoglobulins (IgG, IgA, IgM) to evaluate for immunodeficiency such as CVID
• Aspergillus testing (IgE, IgG, skin testing) for ABPA
• Sputum cultures including mycobacterial cultures
• Nasal nitric oxide or ciliary biopsy when primary ciliary dyskinesia is suspected

Management

• Find and treat the underlying cause \an this is the most important next step once bronchiectasis is identified
• Airway clearance techniques
• Suppressive antibiotics for recurrent exacerbations
• In acute exacerbations with Pseudomonas risk (structural lung disease/bronchiectasis), cover with an antipseudomonal regimen

High-yield

• Bronchiectasis is not a diagnosis \an it is a consequence; always search for the cause
• CT buzzword: "signet ring sign" and bronchial dilation
• Cystic fibrosis is the most common cause in developed countries
• Kartagener syndrome = primary ciliary dyskinesia: bronchiectasis + sinusitis + situs inversus
• ABPA causes bronchiectasis in patients with asthma or CF
• Structural lung disease/bronchiectasis is a key risk factor for Pseudomonas infection
• Untreated humoral immunodeficiency (e.g., CVID) leads to recurrent pneumonias that scar airways and cause bronchiectasis

Pitfalls

• Stopping at the label "bronchiectasis" without pursuing the underlying etiology, which changes management and may explain systemic disease
• Assuming all obstruction with wheeze/cough is asthma or COPD \an confirm with objective testing and CT
• Confusing traction bronchiectasis (a passive consequence of surrounding fibrosis, as seen in UIP) with the primary airway disease of true bronchiectasis
• Missing an underlying immunodeficiency such as CVID in a patient with recurrent sinopulmonary infections