Cystic Fibrosis Presenting as Nasal Polyps
A 7 year old boy is referred with 8 months of nasal obstruction and loss of smell. Nasal endoscopy shows bilateral pale glistening polyps filling both middle meati. He has had 3 episodes of pneumonia in 2 years, passes bulky greasy foul smelling stools, and his weight has fallen from the 25th to the 3rd centile. There is mild digital clubbing. Which is the most helpful investigation?
- A.Sweat chloride testCorrect
- B.Plain radiograph of the sinuses
- C.CT of the paranasal sinuses
- D.Histological biopsy of the polyp
Explanation
Nasal polyps are distinctly uncommon in childhood, and bilateral polyps in a child must be assumed to indicate cystic fibrosis until proven otherwise, since cystic fibrosis is by far the commonest cause in this age group and polyps occur in 10 to 30 percent of affected children. The additional features here of recurrent pneumonia, steatorrhea from pancreatic exocrine insufficiency, weight faltering with relative preservation of height, and clubbing make the diagnosis highly likely. The quantitative pilocarpine iontophoresis sweat chloride test is the standard diagnostic test: a value of 60 mmol/L or more on 2 separate occasions confirms cystic fibrosis, 30 to 59 mmol/L is intermediate and requires genetic testing, and less than 30 mmol/L makes the diagnosis unlikely. Cystic fibrosis is autosomal recessive, caused by mutations in the CFTR gene on chromosome 7, and defective chloride transport produces viscid secretions that obstruct airways, pancreatic ducts and vas deferens. Sinus imaging with plain films or CT will show opacified sinuses and polyposis but only describes the anatomy, giving no clue to the underlying systemic disease, and CT adds radiation to a child's orbits and thyroid. Biopsy of a benign inflammatory polyp is unnecessary in a child unless a unilateral mass raises concern for an angiofibroma, encephalocele or malignancy. Unilateral polyps in a child should also raise suspicion for antrochoanal polyp or a nasal mass rather than cystic fibrosis. Primary ciliary dyskinesia and allergic fungal sinusitis are other, less common causes of pediatric polyps.
Why each option
- A.
- Correct. Bilateral nasal polyps in a child, especially with steatorrhea and recurrent chest infection, demand a sweat chloride test because cystic fibrosis is the commonest cause.
- B.
- Plain sinus radiographs are insensitive and only demonstrate opacification without identifying the underlying systemic disease.
- C.
- CT delineates sinus anatomy for surgical planning but does not diagnose the cause and delivers unnecessary radiation.
- D.
- Biopsy of a typical benign bilateral inflammatory polyp adds nothing; it is reserved for unilateral masses suspicious for a tumour or encephalocele.
Reference: Nelson Textbook of Pediatrics, 22nd ed., 2024, Cystic Fibrosis
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