Clinical scenario: recurrent chest infections| large bulky stools | elevated sweat chloride
A 5-year-old boy is referred for evaluation of recurrent chest infections and poor growth. His parents report that he has had frequent episodes of cough with thick sputum since infancy. He also passes large, bulky, foul-smelling stools that are difficult to flush. On examination, he is underweight with scattered crackles on chest auscultation.
Investigations show:
- Sweat chloride concentration: 85 mmol/L (elevated)
- Chest X-ray: hyperinflation with bronchial wall thickening
- Serum albumin: normal
Which of the following is the most likely mechanism responsible for his gastrointestinal symptoms?
A. Autoimmune destruction of pancreatic acinar cells
B. Reduced chloride transport causing thick pancreatic secretions
C. Defective intestinal lactase activity
D. Increased bile acid synthesis
E. Impaired intestinal lymphatic drainage
Correct answer & Explanation:
Correct answer: B. Reduced chloride transport causing thick pancreatic secretions
Explanation:
Cystic fibrosis is caused by mutations in the CFTR gene, which encodes a chloride channel. Defective chloride and bicarbonate transport results in dehydrated, thick secretions.
In the pancreas:
- Thick secretions obstruct pancreatic ducts
- Cause pancreatic enzyme deficiency
- Lead to malabsorption of fat and fat-soluble vitamins
- Cause steatorrhea (bulky, greasy, foul-smelling stools)
- Result in poor weight gain
Why other options are incorrect:
- A. Autoimmune destruction: Occurs in type 1 diabetes, not CF pancreatic disease.
- C. Lactase deficiency: Causes lactose intolerance but not recurrent chest infections or steatorrhea.
- D. Increased bile acids: Not the mechanism of malabsorption in CF.
- E. Lymphatic obstruction: Causes protein-losing enteropathy, not typical CF features.
Exam pearl:
A child with:
- Recurrent chest infections
- Chronic wet cough
- Failure to thrive
- Steatorrhea
- Salty-tasting skin
→ Think of cystic fibrosis.
