Cystic Fibrosis: Case Study

Cystic fibrosis (CF) is a disease caused by defective chloride transportation. The defect in chloride transportation is a result of metamorphosis within the cystic fibrosis gene leading to abnormalities of cyclic adenosine monophosphate (cAMP). Six categories of defects due to gene mutations include: total lack of gene synthesis; defective gene maturation and premature degradation; disorganized regulation; poor chloride conductance; weakened transcription owing to promoter abnormality; or hastened channel regeneration from the cell exterior (Ramsey, Davies, & McElvaney, 2011).

The gene mutations have low penetrance, which prevents the genotype from predicting the severity or occurrence of the disease. Defects in cystic fibrosis genetic composition lower chloride discharge and increase mucus dehydration. The lower mucus hydration makes it easier for bacteria to adhere to it, which increases inflammation and infection (Filburn, Lumeng, & Nasr, 2014).

The autosomal recessive inheritance of the cystic fibrosis gene means that most patients are heterozygotes or carriers as they have one homozygote and one heterozygote allele. Two heterozygous parents may therefore produce a child with the disease (Brooks, 2014, para. 12).

The following Punnett squares describe the Mendelian autosomal recessive inheritance of CF:

I

II

III

As earlier stated, the inheritance of cystic fibrosis is from two carriers. In Punnett diagram I, both parents are carriers of the recessive allele (c), therefore there is a one in four (25%) chance of an offspring with both c alleles resulting in cystic fibrosis. In Punnett diagrams II and III, there is no chance of inheritance since the recessive allele (c) is seen in only one parent.

The production of mucus from the airways is reinforced by Goblet cells and cilia. Goblet cells are specialized cells in the respiratory tract that secrete mucin (the sol or fluid component of mucus). In cystic fibrosis, mucin secretion is diminished leading to thickened mucus. Movement of cilia in the airway aids the clearance of viscous mucus (Ramsey et al., 2011). Mucus, high in viscosity, results in obstruction and impairs the ciliary function.

The functional defects of the goblet cells and cilia contribute to the pathogenesis of cystic fibrosis (Filburn et al., 2011). Pseudostratified epithelium, composed of goblet, ciliated, intermediate, and basal cells are seen in the normal respiratory tract. However, hyperplastic and metaplastic cellular changes (especially in the goblet/mucous-secreting cells) are observed in the respiratory linings of cystic fibrosis patients.

The typical symptoms of upper respiratory infection – fever, cough, fatigue, and runny nose – and those of gastrointestinal disease – anorexia and weight loss – are seen. Chronic diarrhea with pale fatty stool is also seen. Infants with cystic fibrosis may present with chronic and recurrent cough that may be productive of mucoid and later purulent sputum. Recurrent wheezing, pneumonia, atypical asthma, pneumothorax, chest pain, hemoptysis, and digital clubbing are all respiratory complications of cystic fibrosis (Brooks, 2014, para. 18).

Meconium ileus, steatorrhea, failure to thrive, bilious vomiting, intussusception, or rectal prolapse and features of insufficiency of the exocrine pancreas such as malabsorption, flatulence or foul-smelling flatus, recurrent abdominal pain and distension are also seen in the gastrointestinal system. Children of cystic fibrosis may present with undescended testes, hydrocele and delayed puberty. Clinical signs of the index case include fever (101.7⁰F), tachycardia (HR = 122bpm), tachypnea (RR – 32cpm) and use of accessory muscles.

The gold standard for testing cystic fibrosis is the sweat test. This test involves the quantitative measurement of the amount of chloride in sweat. The upper limit value of chloride used is 29 mmol/L. A value of chloride in sweat 30mmol/L and above is significant and values >= 60mmol/L are diagnostic of cystic fibrosis. Sweat-chloride concentration of 30 – 59 mmol/L is considered intermediate (Brooks, 2014, para. 4).

In cystic fibrosis, defective chloride transportation across epithelial cells of sweat glands results in the excess amount of chloride measured in the sweat. The mutation of the CFTR protein, which is present in cystic fibrosis results in a defect in chloride transport across the epithelial cells of sweat glands and consequently in increased sodium and water reabsorption (LeGrys, Yankaskas, Quittell, Marshall, & Mogayzel, 2007). This is responsible for the significantly high amount of chloride measured in the sweat.

The pancreatic enzymes involved in cystic fibrosis are pancreatic lipase, pancreatic amylase, and protease. Pancreatic lipase aids in the breakdown of fats, pancreatic amylase aids in the breakdown of carbohydrate, and protease aids in the breakdown of protein.

• Zosyn (1.5 gm. every 6 hours IV): This is a combined antibiotic that contains penicillin (piperacillin) and a beta-lactamase inhibitor (tazobactam). These act against bacteria replicated in the respiratory and gastrointestinal infections such as Pseudomonas aeroginosa.
• Albuterol (2.5 mg via nebulizer TID): This is a beta-adrenergic agent that activates receptors and helps in relaxing the smooth muscles. Albuterol enhances the generation of cAMP through adenylate cyclase activation for bronchial relaxation.
• Flucticasone (propionate 100mq, 1 puff BID): This is attached to the glucocorticoid receptors, alters the protein fusion transcription, reduces fibroblast proliferation, prevents macrophage buildup at swollen areas, and reduces deposition of collagen.
• Pancrelipase ((Creon) 8000USP lipase + 30,000 USP units amylase + 30,000 units protease with each meal): The amylase, lipase, and protease systems of pancrelipase digest starch, fat, and protein, respectively.

Poor airway clearance as a result of obstruction from excessive mucus.

• Advice on regular exercise and coughing to relieve the airways. Deep inhalation helps lung expansion and chest excursions.
• Changing patient’s position frequently induces release of secretion.
• Administration of digoxin and diuretics to improve heart rate and clear mucus.
• Frequent monitoring of respiratory rate and pattern to note breathlessness and institute management.

Malnutrition due to loss of appetite and calorie losses.

• Monitor nutrition and weight to ascertain anorexia.
• Use of bronchodilators to relieve construction as severe breathlessness can stop the patient from eating.
• Encourage the patient to eat frequent small amounts with long rest periods in between to avoid breathlessness.
• Remove unpleasant sights or smells around the patient to help improve appetite.
• Encourage relatives to provide patient’s favorite meals to induce eating.

Anxiety as a result of breathlessness.

• Keep the patient company because feelings of loneliness when dyspneic can result in anxiousness.
• Encourage patient to take slow breaths to improve breathing and relieve anxiety.
• Teach slow deep breathing movements. This can help in muscle relaxation and distract the patient from anxiety.

References

Brooks M. (2014) FDA OKs Expanded Use of Ivacaftor (Kalydeco) in Cystic Fibrosis: Medscape Medical News. Web.

Filburn A., Lumeng C. & Nasr S. (2011). Infant pulmonary function testing guides therapy in cystic fibrosis lung disease. Respiratory Medicine CME. 4(1), 17-19.

LeGrys V., Yankaskas J., Quittell L., Marshall B. & Mogayzel, P. (2007). Diagnostic sweat testing: the Cystic Fibrosis Foundation guidelines. Journal of Pediatrics, 151(1), 85-89.

Ramsey, B., Davies J. & McElvaney N., (2011). A CFTR potentiator in patients with cystic fibrosis and the G551D mutation. New English Journal of Medicine, 365(18), 1663-72.