Cystic fibrosis

Question 1

What is cystic fibrosis?

Cause & pathophysiology

Answer 1

Autosomal recessive condition resulting in mutated CF transmembrane conductrance regulator (CFTR) gene on chromosome 7.

CFTR is a Cl- channel.

In airways;

• Normally
  
  • Cl- out via CFTR
  • Na+ & H20 follows
  • Mucus not too thick
• CF
  
  • Cl- not leaving
  • INC NaCl + H₂0 in
  • Mucus very thick, as reduced airway surface liquid

In skin;

• Normally
  
  • Cl- in via CFTR
  • Na+ in via CFTR & Na+ channels
  • Sweat not too salty
• CF
  
  • No Cl- in via CFTR
  • INC NaCl out
  • Sweat very salty

Question 2

What are the clinical features of CF?

Answer 2

Neonate;

• Failure to thrive, meconium ileus, rectal prolapse

Children & young adults;

• Respiratory;
  
  • Cough, wheeze, recurrent infections, bronchiectasis, pneumothorax, haemoptysis, resp. failure, cor pulmonale
• Gastrointestinal;
  
  • Pancreatic insufficiency (DM, steatorrhoea), distal intestinal obstruction syndrome (meconium ileus equivilent), gallstones, cirrhosis
• Other;
  
  • Male infertility, osteoporosis, arthritis, vasculitis, nasal polyps, sinusitis, hypertrophic pulmonary osteoarthropathy (HPOA)

Signs;

• Cyanosis
• Finger clubbing
• Bilateral course crackles

Question 3

How is CF diagnosed?

What tests would you perform?

Answer 3

• Sweat test (sweat sodium & chloride >50nmol/L, normally Cl>Na)
• Genetics (screening for known common CF mutations)
• Faecal elastase (screen for exocrine pancreatic insufficiency)

Tests;

• Blood
  
  • FBC, U&E, LFT, clotting, vit A,D&E levels, glucose tolerance test
• Bacteriology
  
  • Cough swab, sputum cultur
• Radiology
  
  • CXR (hyperinflation, bronchiectasis)
  • Abdo US (fatty liver, cirrhosis, chronic pancreatitis
• Spirometry (obstructive defect)
• Aspergillus serology/ skin test
• Biochemistry; faecal fat analysis

Question 4

How is CF managed?

Answer 4

By MDT.

CHEST;

• Physiotherapy
• Antibiotics
• Mucolytics
• Bronchodilators

GI;

• Pancreatic enzyme replacement
• Fat soluble vitamin supplements (A,D,E,K)
• Ursodeoxycholic acid for impaired liver function
• Liver transplantation

Other;

• CF-related diabetes?
• Screen/ treat osteoporosis
• Treat arthritis, sinusitis, vasculitis, fertility and fenetic counselling

Advanced lung disease;

• Oxygen, diuretics (cor pulmonale), non-invasice ventilation, lung/heart transplantation