Mastering Medical
USMLE Step 1 · Respiratory

Non-cystic fibrosis bronchiectasis vs Cystic fibrosis

How to tell Non-cystic fibrosis bronchiectasis and Cystic fibrosis apart when a board question makes them look alike.

Fastest separator

Bronchiectasis is the airway damage pattern; cystic fibrosis is a multisystem CFTR cause of bronchiectasis.

Side by side

Non-cystic fibrosis bronchiectasisCystic fibrosis
Key clue

Permanent bronchial dilation with chronic daily purulent sputum, recurrent infections, hemoptysis, and CT airway widening from many possible non-CF causes.

CFTR disease with bronchiectasis plus recurrent sinus/lung infections, pancreatic insufficiency, failure to thrive, high sweat chloride, meconium ileus history, or male infertility.

Mechanism

Repeated infection, impaired clearance, obstruction, or inflammation injures airway walls and creates a cycle of mucus pooling and infection.

Defective chloride transport thickens secretions across lungs, pancreas, intestine, sweat glands, and reproductive tract.

Labs and tests

Dilated bronchi on CT with chronic purulent sputum establishes bronchiectasis; normal sweat chloride and absent multisystem clues support non-CF bronchiectasis.

High sweat chloride, CFTR variants, Pseudomonas colonization, pancreatic enzyme need, meconium ileus, or congenital absence of vas deferens points CF.

The trap

Do not diagnose CF from bronchiectasis alone; require the genetic/sweat chloride or multisystem exocrine pattern.

Watch it explained

In the rapid reviewObstructive Lung Disease for USMLE Step 1: Asthma, COPD & Emphysema Made Easy
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The repair move

For bronchiectasis questions, first identify airway dilation, then ask whether CF explains the whole body pattern.

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Core

An adult has years of recurrent bacterial pneumonia, chronic daily purulent sputum, episodic hemoptysis, and CT showing permanently dilated bronchi. Sweat chloride is normal. Which diagnosis best fits?

Show answer and explanation

Answer: A. Non-cystic fibrosis bronchiectasis. Bronchiectasis is permanent airway dilation from recurrent infection, obstruction, impaired clearance, or inflammatory injury; it can occur without CF.

Why the other choices are tempting

  • B. CF causes bronchiectasis but also has CFTR-related multisystem clues such as high sweat chloride, pancreatic insufficiency, and male infertility.
  • C. Asthma is reversible bronchospasm rather than fixed airway dilation.
  • D. Acute bronchitis is short-term airway infection without permanent dilation.
  • E. PE causes acute dyspnea/pleuritic pain, not chronic purulent sputum and dilated bronchi.

Flashcards

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What is the fastest separator for Non-cystic fibrosis bronchiectasis vs Cystic fibrosis?

Bronchiectasis is the airway damage pattern; cystic fibrosis is a multisystem CFTR cause of bronchiectasis.

What clue should make you choose Non-cystic fibrosis bronchiectasis?

Permanent bronchial dilation with chronic daily purulent sputum, recurrent infections, hemoptysis, and CT airway widening from many possible non-CF causes.

Quick answers

What is the fastest way to tell Non-cystic fibrosis bronchiectasis from Cystic fibrosis?

Bronchiectasis is the airway damage pattern; cystic fibrosis is a multisystem CFTR cause of bronchiectasis.

What is the key clue for Non-cystic fibrosis bronchiectasis?

Permanent bronchial dilation with chronic daily purulent sputum, recurrent infections, hemoptysis, and CT airway widening from many possible non-CF causes.

What is the key clue for Cystic fibrosis?

CFTR disease with bronchiectasis plus recurrent sinus/lung infections, pancreatic insufficiency, failure to thrive, high sweat chloride, meconium ileus history, or male infertility.

What is the common trap with Non-cystic fibrosis bronchiectasis vs Cystic fibrosis?

Do not diagnose CF from bronchiectasis alone; require the genetic/sweat chloride or multisystem exocrine pattern.