Cystic Fibrosis

Cystic fibrosis is a chronic, progressive, inherited disease that affects the exocrine (mucus-secreting) glands. The disease is transmitted as an autosomal recessive trait and is the most common fatal genetic disease of white children. When both parents are carriers of the recessive gene, they have a 25% chance of transmitting the disease with each pregnancy.

Cultural Tip The incidence of cystic fibrosis is highest in people of northern European ancestry. The disease is less common in Blacks, Native Americans, and people of Asian ancestry. It occurs with equal frequency in both sexes.

Cystic fibrosis is incurable, but medical research is being conducted to find better treatment. Life expectancy has greatly increased. Previously, patients with cystic fibrosis died by about age 16; today they live to age 28 or older.

Causes and pathophysiology

The gene responsible for cystic fibrosis encodes a protein that involves chloride transport across epithelial membranes. More than 100 specific mutations of the gene have been identified. The immediate causes of symptoms are increased viscosity of bronchial, pancreatic, and other mucous gland secretions and consequent destruction of glandular ducts. Cystic fibrosis accounts for almost all cases of pancreatic enzyme deficiency in children.

Signs and Symptoms

• Thick, viscous mucus secretions in the lungs
• Repeated infections: The accumulation of sticky, thick mucus in the lungs creates a favorable environment for infectious microorganisms to inhabit and flourish.
• Stools, pale or clay colored, foul smelling, or stools that float
• Recurrent pneumonia
• Chronic cough, possibly with blood streaking
• Wheezing
• Bronchitis
• Chronic sinusitis
• Asthma
• Nasal polyps (fleshy growths inside the nose)
• Abdominal pain, flatulence
• Fatigue

Diagnostic tests

According to the Cystic Fibrosis Foundation, a definitive diagnosis requires:

Two clearly positive sweat tests, using pilocarpine solution (a sweat inducer), and the presence of an obstructive pulmonary disease, confirmed pancreatic insufficiency or failure to thrive, or a family history of cystic fibrosis.

Chest X-rays that show early signs of lung obstruction

Stool specimen analysis that shows the absence of trypsin, suggesting pancreatic insufficiency.

The following test results may support the diagnosis:

Deoxyribonucleic acid testing can now locate the presence of the Delta F 508 deletion (found in about 70% of cystic fibrosis patients, although the disease can cause more than 100 other indications). This test can also be used for carrier detection and prenatal diagnosis in families with a previously affected child.

If pulmonary exacerbation exists, pulmonary function tests can reveal decreased vital capacity, elevated residual volume due to air entrapments, and decreased forced expiratory volume in 1 second.

A liver enzyme test may reveal hepatic insufficiency; a sputum culture may reveal organisms that patients typically and chronically colonize, such as Pseudomonas and Staphylococcus.

A serum albumin level helps to assess nutritional status, and electrolyte analysis is used to assess for dehydration.

Treatment

Because cystic fibrosis has no cure, the goal of treatment is to help the patient lead as normal a life as possible. Specific treatments depend on the organ systems involved.

• To combat electrolyte loss through sweat, the patient should generously salt his food and, during hot weather, take salt supplements.
• Oral pancreatic enzymes taken with meals and snacks offsets pancreatic enzyme deficiencies. Such supplements improve absorption and digestion and help satisfy hunger on a reasonable caloric intake. The patient should also follow a diet that is high in fat, protein, and calories and includes vitamin A, D, E, and K supplements.
• To manage pulmonary dysfunction, the patient should undergo chest physiotherapy, nebulization to loosen secretions followed by postural drainage, and breathing exercises several times daily to help remove lung secretions. But he shouldn't receive antihistamines, which dry mucous membranes, making mucus expectoration difficult.
• Dornase alfa, a pulmonary enzyme given by aerosol nebulizer, helps to thin airway mucus, improving lung function and reducing the risk of pulmonary infection.
• A patient with pulmonary infection needs to loosen and remove mucopurulent secretions by using intermittent nebulizer and postural drainage to relieve obstruction. Use of a cool-mist tent is controversial because mist particles may become trapped in the esophagus and stomach, never reaching the lungs.
• Broad-spectrum antibiotics are used to control infection.
• Oxygen therapy is used as needed.
• Heart-lung transplantation may reduce the effects of the disease.
• Since the discovery of the basic genetic defect of cystic fibrosis, new treatments have been explored. Experimental treatments include drugs such as amiloride and gene therapy. Researchers have targeted the lungs for gene therapy because the most serious pathology occurs there. They hope to insert corrected genetic material into lung stem cells, which produce new lung cells. Lung stem cells might be reached through an aerosolized delivery system currently under study.

Prevention

There is no way to prevent cystic fibrosis. Screening of family members of a cystic fibrosis patient may detect the cystic fibrosis gene in between 60 and 90% of carriers, depending on the test used.