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Cystic Fibrosis (CF)

Study guide:

Definitions:  

  • CF is a multi-systemic disorder characterized by autosomal recessive inheritance.

 

Epidemiology:

  • Most common lethal genetic disease in Caucasians.

  • Inherited Multi-system disorder of children and adult.

  • A carrier rate of 1: 25.

  • Common in Caucasian.

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Pathophysiology:

  • CF is a result of mutations on a gene called cystic fibrosis transmembrane conductance regulator (CFTR)  Expressed largely in epithelial cells of the airways, gastrointestinal tract, sweat glands and genitourinary system.

  • It is a single polypeptide chain includes 1480 Amino acids and located on the long arm of chromosome 7 in the region of 7q31.2.

  • The amino acid that is mainly being affected is phenylalanine.

  • This gene mainly functions as a chloride channel in the apical cell membrane and regulated by cyclic AMP.

  • When a mutation happens to this gene, it changes the secondary and tertiary structure of the protein. That leads to closed chloride channel in response to elevated cyclic AMP in epithelial cells causing thick secretion from exocrine glands and blockage of secretory ducts giving rise to signs and symptoms in CF.

  • The primary system to be affected is the respiratory tract by the following mechanisms:

    • Decreased excretion of chloride into the airway lumen.

    • Increased reabsorption of sodium into the epithelial cells.

    • Less excretion of water and increased viscosity and tenacity of airway secretions (thick mucus).

Recurrent respiratory infections in CF:

  • S. aureus: early

  • P. aeruginosa: most common

    • B. cepacia: worst prognosis

    • Aspergillus fumigatus

Sign & Symptoms by Age Group:

Table 1: Adopted from Cleveland clinic, edited by LtMed.

Diagnostic criteria for CF:

Figure 1: Diagnostic Criteria adopted from Update of CF by Trisha Brown.

Diagnosis:

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Figure 2: Diagnosis of CF.

Treatment:

  • Oxygen therapy as necessary.

  • Airway clearance therapy.

  • Aerosol treatment: normal saline and albuterol (beta 2 agonist).

  • Mucolytic (DNAse):

    • Inhaled rhDNase to break down the massive amounts of DNA as a result of neutrophils breakdown.

  • Antibiotics:

    • Same antibiotics for bronchiectasis (please check Bronchiectasis study guide for information).

    • Inhaled aminoglycosides are exclusively limited to CF patients.

  • CFTR modulators (Potentiators and Correctors).

  • Pancreatic enzymes replacement.

  • Vitamins and minerals supplement.

  • Noninvasive ventilation (improves symptoms in chronic respiratory failure with no survival benefit).

  • Lung transplant:

    • Only in cases of advanced disease not responsive to medical therapy.

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Complications:

  • The most common cause of death in CF patients is lung diseases in general and respiratory infections to be specific:

    • Pneumococcal and influenza vaccination is a must for every CF patient.

  • CF is the most common cause of exocrine pancreatic dysfunction. 

Figure 3: Complications of CF.

References:

  1. George, R. (2005). Chest medicine. Philadelphia, PA: Lippincott Williams & Wilkins.

  2. Grippi, M., Elias, J., Fishman, J., Kotloff, R., Pack, A., Senior, R. and Siegel, M. (n.d.). Fishman's pulmonary diseases and disorders.

  3. Kumar, P. and Clark, M. (n.d.). Kumar & Clark's clinical medicine.

  4. Walker, B., Colledge, N., Ralston, S. and Penman, I. (n.d.). Davidson's principles and practice of medicine.

  5. Rowe SM, Miller S, Sorscher EJ. Cystic fibrosis. N Engl J Med 2005; 252:1992–2001.

  6. Davis PB. Therapy for cystic fibrosis the end of the beginning. N Engl J Med 2011; 365:1734–1735.

  7. Cvetnic, William G, Eduardo Pino, and Christine E Koerner. USMLE Step 2 CK Pediatrics. [New York]: Kaplan, 2014. Print.

  8. O'Connell, Theodore X, Thomas Blair, and Ryan Pedigo. Crush Step 1. 2014.Print.

  9. Cvetnic W, Pino E, Koerner C. USMLE step 2 CK pediatrics. [New York]: Kaplan; 2011.

  10. Hall J, Premji A. Toronto Notes for Medical Students, Inc. © 2015. 2015.

  11. Le T, Bhushan V, Sochat M, Sylvester P, Mehlman M, Kallianos K. First aid for the® USMLE.

  12. Dalcin P, Abreu e Silva F. Cystic fibrosis in adults: diagnostic and therapeutic aspects. Jornal Brasileiro de Pneumologia [Internet]. 2008 [cited 27 March 2016];34(2):107-117. Available from: http://www.scielo.br/scielo.php?pid=s1806-37132008000200008&script=sci_arttext&tlng=en (Figure 1).

  13. 348. Cystic Fibrosis [Internet]. Clevelandclinicmeded.com. 2016 [cited 27 March 2016]. Available from: http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/pulmonary/cystic-fibrosis/ (Figure 2).

  14. Walker, B., Colledge, N., Ralston, S. and Penman, I. (n.d.). Davidson's principles and practice of medicine (Figure 3).

 

 

Written by:          Abdulrahman Alqahtani

 

Reviewed by:      Nawaf AlKharashi

                            Areej Madani

 

Format editor:    Haifa Al Issa

 

Web Publisher: Seba AlMutairi 

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