Cystic Fibrosis

Published on 10/06/2015 by admin

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Last modified 22/04/2025

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Cystic Fibrosis

Barbara A. Chini, MD

Basic Information

Definition

Cystic fibrosis (CF) is an inherited, multisystem disease of exocrine gland function that is primarily characterized by diffuse obstruction and chronic infection of the airways and poor digestion resulting from exocrine pancreatic insufficiency. Although multiple organ systems are affected, progressive lung destruction (i.e., bronchiectasis) is the major cause of morbidity and mortality in those affected with CF.

Synonym

Mucoviscidosis

ICD-9-CM Codes

277.00 Cystic fibrosis, pancreatic
518.89 Cystic fibrosis, pulmonary

Epidemiology & Demographics

• One of the most common fatal genetic disorders among whites
• Autosomal recessive inheritance
• Estimated incidence: 1 case per 3200 whites; 1 case per 15,000 blacks; 1 case per 11,000 Native Americans; 1 case per 31,000 Asian Americans; 1 case per 9500 Hispanics
• Carrier frequency: 1 in 32 overall in the United States

Clinical Presentation

History

• A family history of CF may be reported (16%).
• Multiple organ systems are affected, most commonly the sweat ducts, pancreas, and airways.
• CF most often manifests in early childhood with persistent respiratory illness (50%), malnutrition and poor growth (34%), abnormal stools (26%), or a combination of these features.
• Signs and symptoms may vary widely by age:

image Neonate: meconium ileus or peritonitis (15%)
image Infancy: obstructive jaundice, hypochloremic alkalosis, hyponatremic dehydration, heat prostration, steatorrhea, hypoproteinemia, edema, salty taste
image Infancy and childhood: failure to thrive, bronchiolitis, recurrent wheezing
image Childhood and older: rectal prolapse, nasal polyposis, panopacification of sinuses, pancreatitis, unexplained cirrhosis, gallstones, allergic bronchopulmonary aspergillosis
image Adolescence and adulthood: cor pulmonale, glucose intolerance, diabetes mellitus, biliary cirrhosis, hemoptysis
image Any age: absence of the vas deferens, azoospermia, recurrent pneumonia or wheezing, chronic cough (often productive), staphylococcal pneumonia, mucoid pseudomonas in lung, bronchiectasis, digital clubbing

Physical Examination

• Respiratory system

image Chronic productive cough
image Recurrent or persistent crackles or wheezing
image Diminished breath sounds
image Barrel chest deformity, hyperinflation
image Use of accessory muscles of respiration; tachypnea
image Chronic sinusitis, nasal polyps, widening of the nasal bridge

• Gastrointestinal system

image Poor weight gain
image Rectal prolapse
image Abdominal distention
image Loss of subcutaneous fat and muscle
image Edema, hepatomegaly

• Reproductive system

image Absence or atresia of vas deferens
image Testicular hernia, hydrocele, undescended testes
image Delayed puberty

• Skeletal system

image Hypertrophic osteoarthropathy
image Digital clubbing

• Other difficulties

image Acrodermatitis enteropathica
image Enlarged submaxillary glands
image Bulging fontanelle (i.e., vitamin A deficiency)

Etiology

• The basic defect is an abnormality of chloride transport in apical membrane epithelial cells.
• The responsible gene is on the long arm of chromosome 7, and it codes for the CF transmembrane conductance regulator (CFTR protein).
• More than 800 gene mutations are known.
• The most prevalent mutation of CFTR is the deletion of one phenylalanine residue at amino acid 508 (ΔF508).
• Genetic heterogenicity occurs and may partially account for the wide spectrum of disease severity and rate of progression.

image An individual genotype poorly predicts pulmonary disease progression.

• The patient is unable to clear mucous secretions easily.

image Inadequate water in mucous secretions (“sticky mucous”)
image Persistent infection of the lower respiratory airways

Diagnosis

Differential Diagnosis

• Bronchiectasis
• Chronic reactive airways disease
• Immotile cilia syndrome
• Immunodeficiency
• Malabsorption syndromes
• Protein-calorie malnutrition

Workup

The diagnosis of CF is suspected on clinical grounds or from the family history.

Laboratory Tests

• Newborn screening: A few U.S. states screen newborns for CF by measuring immunoreactive trypsin (IRT) in blood. Most infants who have CF have elevated IRT levels, but there are many false-positive results. The diagnosis must be confirmed by sweat test or by genotyping.
• Genotyping: There are commercial genotyping tests for about 100 specific mutations in the CFTR gene.

image Genotyping identifies about 95% of all CF alleles.
image A patient in whom two alleles are not identified by commercial genotyping still can have CF because there are more than 800 mutations.

• Sweat chloride test: The diagnosis of CF can be confirmed by a sweat chloride concentration greater than 60 mEq/L in the presence of appropriate clinical manifestations (i.e., chronic pulmonary disease or pancreatic insufficiency, or both) or an appropriate family history.

image The test should be performed in an experienced, reliable laboratory.
image A positive result must always be confirmed by a second test.
image False-positive results are few, but they may be caused by untreated Addison’s disease, ectodermal dysplasia, glycogen storage diseases, or untreated hypothyroidism.

• Pulmonary function testing: Tests offer evidence of obstruction, flow limitation, or air trapping.
• Sputum culture: Staphylococcus aureus or mucoid forms of Pseudomonas aeruginosa from sputum strongly suggest CF.

Imaging Studies

• Chest radiograph: peribronchial cuffing, mucous plugging, infiltrates, atelectasis, fibrosis, bronchiectasis, hyperinflation
• Sinus films: panopacification of sinuses
• Computed tomography of the chest: can demonstrate air trapping and bronchiectasis long before radiographs show changes

Treatment

Nonpharmacologic Therapy

• There is no cure for CF, but the significantly increasing life span appears to be linked to early and aggressive management of the disease.
• Treatment plans must be individualized to account for age and for type and severity of symptoms.
• Hospitalize all newly diagnosed patients to facilitate verification of the diagnosis, to provide education for the family, and to determine the baseline disease status.
• A multidisciplinary team should include a nurse, respiratory therapist, social services advisor, dietitian, psychologist, and physician.
• Maintain hydration, particularly in a hot environment and during ongoing losses.
• Perform airway clearance techniques daily to assist with clearing of mucus.
• Neonates with CF may present with meconium ileus or meconium peritonitis, requiring immediate surgical intervention (15% of CF patients).
• MediPort placement may be required for frequent intravenous administration of antibiotics.
• A gastrostomy tube and fundoplication may be required to optimize the patient’s nutritional status.
• Complications of progressive CF may require surgical intervention.

image Lobectomy for chronic, recalcitrant atelectasis (controversial) or recurrent hemoptysis
image Bronchial artery embolization for recurrent hemoptysis
image Chest tube for pneumothorax
image Pleurodesis for recurrent pneumothorax
image Lung transplantation for end-stage lung disease

Acute General Rx

• Primarily directed at respiratory and nutritional support
• Inhalation therapies: bronchodilators aid daily airway clearance of mucus, aerosolized antibiotics, human recombinant DNAase
• Antibiotics

image Oral: Use at first sign of increasing lower respiratory tract symptoms to cover S. aureus, nontypable H. influenzae, and P. aeruginosa (e.g., amoxicillin, ciprofloxacin, clindamycin).
image Intravenous: Use when limited response to oral and inhalation therapy and when symptoms are worsening. Usually, two antibiotics are necessary to cover suspected pathogens.

Chronic Rx

• Primarily directed at respiratory and nutrition support
• Inhalation therapies: bronchodilators aid daily airway clearance of mucus, aerosolized antibiotics, human recombinant DNAase
• Anti-inflammatory drugs (i.e., corticosteroids): for chronic reactive airways disease and allergic bronchopulmonary aspergillosis
• Nutrition

image Pancreatic enzymes are replaced.
image Fat-soluble vitamin deficiencies: Replace vitamins A, D, E, and K by supplementation.
image Increased caloric need requires increased intake of high-calorie foods.

• Immunizations: maintain schedule, with special attention to pertussis and yearly influenza vaccinations

Disposition

• Frequent outpatient visits after an initial diagnosis and hospitalization are essential.
• Patients should be seen by the multidisciplinary CF team every 3 or 4 months. As the disease progresses, more frequent appointments may be necessary.

Referral

• All patients with CF should be referred to a CF care center accredited by the Cystic Fibrosis Foundation for coordinated care by a multidisciplinary CF team.
• In addition to the multidisciplinary CF team, patients may require consultation with experts in endocrinology, gastroenterology, rheumatology, and surgery.

Pearls & Considerations

Comments

• Although most common in whites, CF is also seen in blacks and Native Americans.
• Patients may present with predominantly respiratory or gastrointestinal symptoms.
• Patients may present with right upper lung collapse, failure to thrive, or hyponatremic dehydration.

Patient/Family Education

Information is available from the Cystic Fibrosis Foundation (www.cff.org).

Suggested Readings

Boat TF. Cystic fibrosis. In: Behrman RE, editor. Nelson Textbook of Pediatrics. 16th ed. Philadelphia: WB Saunders; 2000:1315-1327.

Davis PB. Cystic fibrosis. Pediatr Rev. 2001;22:257.

Gibson RL, et al. State of the art: pathophysiology and management of pulmonary infections in cystic fibrosis. Am J Respir Crit Care Med. 2003;168:918.

MacLusky I. Cystic fibrosis for the primary care pediatrician. Pediatr Ann. 1993;22:541.

Wilmott RW, Fiedler MA. Recent advances in the treatment of cystic fibrosis. Pediatr Clin North Am. 1994;41:431.

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