Cystic Fibrosis in Children
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Direct answer
Cystic fibrosis is autosomal recessive failure of the CFTR chloride channel, producing salty sweat, thick airway secretions and pancreatic insufficiency — the child with chronic productive cough, failure to thrive with steatorrhoea, and clubbing in early childhood. Diagnosis rests on a sweat chloride of 60 mmol/L or more by pilocarpine iontophoresis, supported by CFTR genetics and newborn immunoreactive trypsinogen screening. Management is daily airway clearance with inhaled mucolytics, aggressive antibiotic strategy against Staphylococcus aureus and Pseudomonas aeruginosa, pancreatic enzyme and fat-soluble vitamin replacement, and — for eligible genotypes — CFTR modulators such as the elexacaftor–tezacaftor–ivacaftor triple combination that change disease trajectory rather than symptoms alone.
What you must remember
- Inheritance: autosomal recessive CFTR mutations; F508del is the commonest worldwide, though the Indian mutation spectrum is heterogeneous and classic panels miss many local variants.
- Sweat chloride at or above 60 mmol/L is diagnostic; 30–59 mmol/L is intermediate and demands repeat testing plus genetics. Collect in duplicate from a child who is well-hydrated, not oedematous and above about 3 kg.
- Neonatal clue: meconium ileus in 10–15 per cent — abdominal distension and failure to pass meconium with a microcolon on contrast study; older equivalent is distal intestinal obstruction syndrome.
- Pancreatic insufficiency affects around 85 per cent: steatorrhoea, failure to thrive, fat-soluble vitamin A, D, E and K deficiency and rectal prolapse; a subset stays sufficient and may present with pancreatitis.
- Respiratory signature: chronic wet cough, recurrent infections with Staphylococcus aureus then Pseudomonas aeruginosa, bronchiectasis with clubbing, nasal polyposis, and eventual respiratory failure — the main determinant of survival.
- Distinctive Indian scenario: any child with unexplained bronchiectasis, chronic diarrhoea with failure to thrive, or "refractory asthma" with clubbing deserves a sweat test, because under-diagnosis remains the norm.
- Salt-loss presentations in hot climates: hypochloraemic metabolic alkalosis with hyponatraemia (pseudo-Bartter) in infants during summer.
- Respiratory care: daily physiotherapy, inhaled dornase alfa or hypertonic saline, and staged antibiotics — eradicate early Pseudomonas with inhaled tobramycin or colistin, then chronic suppression.
- Nutrition: pancreatic enzyme replacement with every feed and fat-containing snack, high-calorie high-fat diet, and routine fat-soluble vitamin supplementation.
- CFTR modulators: ivacaftor for gating mutations, and the triple elexacaftor–tezacaftor–ivacaftor combination effective for F508del homozygotes and many heterozygotes, now licensed down to young children in several jurisdictions.
- Other organ issues: CF-related diabetes from the second decade (annual oral glucose tolerance testing), infertility in males (congenital bilateral absence of vas deferens), and delayed puberty.
A typical exam case
A two-year-old has been admitted three times for "pneumonia", is below the third centile despite a voracious appetite, passes bulky greasy stools, and has early clubbing. The mother recalls a cousin who died of "lung trouble". This is the classical post-neonatal CF presentation in India: recurrent lower respiratory infections plus failure to thrive with steatorrhoea. Send a sweat chloride (60 mmol/L would confirm), pancreatic faecal elastase for insufficiency, and genetics where available. Start the package that defines survival: twice-daily physiotherapy, enzyme replacement with meals, vitamin supplementation, high-energy diet, and prompt treatment of exacerbations with eradication therapy on first Pseudomonas isolation.
The second examinable child is the newborn with distension, bilious vomiting and no meconium at 48 hours, with a microcolon on contrast study: meconium ileus, virtually pathognomonic of cystic fibrosis — sweat test later, genetics now. The third is the adolescent with stable lungs but new weight loss and polyuria: annual glucose tolerance testing catches CF-related diabetes. Genotype then drives eligibility for modulators — knowing which CFTR mutations the child carries is no longer academic but therapeutic.
Where students slip
Candidates treat cystic fibrosis as a respiratory disease with digestive side-effects; the marks go to the multi-system picture — salt loss, diabetes, infertility, nasal polyps and rectal prolapse are all regularly examined. The sweat test has technical traps: oedema and malnutrition falsely lower chloride, samples must be adequate and duplicated, and a single intermediate result is not a diagnosis. On therapy, older answer sheets still recommend "postural drainage alone" or omit Pseudomonas eradication; the strategy of early eradication and chronic suppression is the expected modern answer. Finally, forgetting that CF remains under-diagnosed in India rather than rare loses easy clinical-reasoning marks.
Frequently asked questions
What sweat chloride value diagnoses cystic fibrosis?
Sixty mmol/L or more on pilocarpine iontophoresis, confirmed on a repeat sample; values of 30–59 mmol/L are intermediate and require further testing with genetics and clinical review.
Which neonatal intestinal presentation is virtually diagnostic of cystic fibrosis?
Meconium ileus — failure to pass meconium with distal obstruction and a microcolon on contrast study, occurring in roughly 10–15 per cent of affected newborns.
How is pancreatic insufficiency in cystic fibrosis managed?
Pancreatic enzyme replacement with every meal and snack, a high-calorie high-fat diet, and routine supplementation of fat-soluble vitamins A, D, E and K, with growth monitored closely.
Why is early Pseudomonas aeruginosa acquisition treated aggressively?
Initial infection can be eradicated with inhaled antibiotics such as tobramycin or colistin, delaying chronic mucoid colonisation that drives bronchiectasis and respiratory decline.