Cystic fibrosis Flashcards
What is cystic fibrosis?
Cystic fibrosis (CF) is an autosomal recessive genetic condition affecting mucus glands
Genetic mutation of which gene casues cystic fibrosis?
It is caused by a genetic mutation of the cystic fibrosis transmembrane conductance regulatory gene on chromosome 7
How many people carry/are affected by cystic fibrosis?
Around 1 in 25 are carriers of the mutation and 1 in 2500 children have CF
The key consequences of the cystic fibrosis mutation are:
- Thick pancreatic and biliary secretions that cause blockage of the ducts, resulting in a lack of digestive enzymes such as pancreatic lipase in the digestive tract
- Low volume thick airway secretions that reduce airway clearance, resulting in bacterial colonisation and susceptibility to airway infections
- Congenital bilateral absence of the vas deferens in males. Patients generally have healthy sperm, but the sperm have no way of getting from the testes to the ejaculate, resulting in male infertility
How does cystic fibrosis present?
- Cystic fibrosis is screened for at birth with the newborn bloodspot test
- Meconium ileus is often the first sign of cystic fibrosis. This presents as not passing meconium within 24 hours, abdominal distention and vomiting
- If cystic fibrosis is not diagnosed shortly after birth it can present later in childhood with typical signs and symptoms, recurrent lower respiratory tract infections, failure to thrive or pancreatitis
Symptoms of cystic fibrosis
- Chronic cough
- Thick sputum production
- Recurrent respiratory tract infections
- Abdominal pain and bloating
- Steatorrhoea (due to a lack of lipase)
- Parents may report the child tastes particularly salty when they kiss them, due to the concentrated salt in the sweat
- Failure to thrive
Signs of cystic fibrosis
- Low weight or height on growth charts
- Nasal polyps
- Finger clubbing
- Crackles and wheezes on auscultation
- Abdominal distention
Causes of Clubbing in Children
- Hereditary clubbing
- Cyanotic heart disease
- Infective endocarditis
- Cystic fibrosis
- Tuberculosis
- Inflammatory bowel disease
- Liver cirrhosis
Methods of diagnosing cystic fibrosis
- Newborn blood spot testing is performed on all children shortly after birth and picks up most cases
- The sweat test is the gold standard for diagnosis
- Genetic testing for CFTR gene can be performed during pregnancy by amniocentesis or chorionic villous sampling, or as a blood test after birth
Describe the sweat test for cystic fibrosis
A patch of skin is chosen for the test, typically on the arm or leg. Pilocarpine is applied to the skin on this patch. Electrodes are placed either side of the patch and a small current is passed between the electrodes. This causes the skin to sweat. The sweat is absorbed with lab issued gauze or filter paper and sent to the lab for testing for the chloride concentration. The diagnostic chloride concentration for cystic fibrosis is more than 60mmol/l.
Common colonisers in cystic fibrosis:
- Staphylococcus aureus
- Haemophilus influenza
- Klebsiella pneumoniae
- Escherichia coli
- Burkhodheria cepacia
- Pseudomonas aeruginosa
What are the consequences of a pseudomonas colonisation in cystic fibrosis?
Colonisation with pseudomonas leads to a significant increase in morbidity and mortality in patients with CF.
How is pseudomonas colonisation treated?
Pseudomonas colonisation can be treated with long term nebulised antibiotics such as tobramycin. Oral ciprofloxacin is also used.
Management of cystic fibrosis
- Chest physiotherapy several times a day is essential to clear mucus and reduce the risk of infection and colonisation
- Exercise improves respiratory function and reserve, and helps clear sputum
- High calorie diet is required for malabsorption, increased respiratory effort, coughing, infections and physiotherapy
- CREON tablets to digest fats in patients with pancreatic insufficiency (these replace the missing lipase enzymes)
- Prophylactic flucloxacillin tablets to reduce the risk of bacterial infections (particularly staph aureus)
- Treat chest infections when they occur
- Bronchodilators such as salbutamol inhalers can help treat bronchoconstriction
- Nebulised DNase (dornase alfa) is an enzyme that can break down DNA material in respiratory secretions, making secretions less viscous and easier to clear
- Nebulised hypertonic saline
- Vaccinations including pneumococcal, influenza and varicella
Patients with cystic fibrosis require regular monitoring and screening for:
- colonisation of bacteria like pseudomonas
- diabetes
- osteoporosis
- vitamin D deficiency
- liver failure
