Cystic fibrosis is a generalized dysfunction of the exocrine glands that affects multiple organ systems. Transmitted as an autosomal recessive trait, it's the most common fatal genetic disease in white children.
Cystic fibrosis is a chronic disease. With improvements in treatment over the past decade, the average life expectancy has risen from age 16 to age 28 and more.
The gene responsible for cystic fibrosis (located on chromosome 7) encodes a protein that involves chloride transport across epithelial membranes; over 100 specific mutations of the gene are known. (See Cystic fibrosis transmission risk.) The immediate causes of symptoms in cystic fibrosis are increased viscosity of bronchial, pancreatic, and other mucous gland secretions and consequent obstruction of glandular ducts. Cystic fibrosis accounts for almost all cases of pancreatic enzyme deficiency in children.
In the United States, the incidence of cystic fibrosis is highest in Whites of northern European ancestry (1 in 2,000 live births) and lowest in Blacks (1 in 17,000 live births), Native Americans, and people of Asian ancestry. The disease occurs equally in both sexes.
The clinical effects of cystic fibrosis may become apparent soon after birth or may take years to develop. They include major aberrations in sweat gland, respiratory, and GI function. Sweat gland dysfunction is the most consistent abnormality. Increased concentrations of sodium and chloride in the sweat lead to hyponatremia and hypochloremia and can eventually induce fatal shock and arrhythmias, especially in hot weather.
Respiratory symptoms reflect obstructive changes in the lungs: wheezy respirations; a dry, nonproductive paroxysmal cough; dyspnea; and tachypnea. These changes stem from thick, tenacious secretions in the bronchioles and alveoli and eventually lead to severe atelectasis and emphysema. Children with cystic fibrosis display a barrel chest, cyanosis, and clubbing of the fingers and toes. They suffer recurring bronchitis and pneumonia as well as associated nasal polyps and sinusitis. Death typically results from pneumonia, emphysema, or atelectasis.
The GI effects of cystic fibrosis occur mainly in the intestines, pancreas, and liver. One early symptom is meconium ileus; the neonate with cystic fibrosis doesn't excrete meconium, a dark green mucilaginous material found in the intestine at birth. He develops symptoms of intestinal obstruction, such as abdominal distention, vomiting, constipation, dehydration, and electrolyte imbalance. As the child gets older, obstruction of the pancreatic ducts and resulting deficiency of trypsin, amylase, and lipase prevent the conversion and absorption of fat and protein in the GI tract. The undigested food is then excreted in frequent, bulky, foul-smelling, pale stools with a high fat content. This malabsorption induces poor weight gain, poor growth, ravenous appetite, distended abdomen, thin extremities, and sallow skin with poor turgor. The inability to absorb fats results in a deficiency of fat-soluble vitamins (A, D, E, and K), leading to clotting problems, retarded bone growth, and delayed sexual development. Males may experience azoospermia and sterility; females may experience secondary amenorrhea but can reproduce. A common complication in infants and children is rectal prolapse secondary to malnutrition and wasting of perirectal supporting tissues.
In the pancreas, fibrotic tissue, multiple cysts, thick mucus, and eventually fat replace the acini (small, saclike swellings normally found in this gland), producing symptoms of pancreatic insufficiency: insufficient insulin production, abnormal glucose tolerance, and glycosuria. About 15% of patients have adequate pancreatic exocrine function for normal digestion and, therefore, have a better prognosis. Biliary obstruction and fibrosis may prolong neonatal jaundice. In some patients, cirrhosis and portal hypertension may lead to esophageal varices, episodes of hematemesis and, occasionally, hepatomegaly.
The following test results may support the diagnosis:
❑ Chest X-rays indicate early signs of obstructive lung disease.
❑ Stool specimen analysis indicates the absence of trypsin, suggesting pancreatic insufficiency.
❑ 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 mutations). It allows prenatal diagnosis in families with a previously affected child.
❑ Pulmonary function tests reveal decreased vital capacity, elevated residual volume due to air entrapments, and decreased forced expiratory volume in 1 second. This test is used if pulmonary exacerbation already exists.
❑ Liver enzyme tests may reveal hepatic insufficiency.
❑ Sputum culture reveals organisms that cystic fibrosis patients typically and chronically colonize, such as Staphylococcus and Pseudomonas.
❑ Serum albumin measurement helps assess nutritional status.
❑ Electrolyte analysis assesses hydration status.
The aim of treatment is to help the child lead as normal a life as possible. The type of treatment depends on the organ systems involved.
To combat electrolyte losses in sweat, salt foods generously and, in hot weather, administer sodium supplements.
To offset pancreatic enzyme deficiencies, give oral pancreatic enzymes with meals and snacks, as ordered. Maintain a diet that's low in fat, but high in protein and calories, and provide supplements of water-miscible, fat-soluble vitamins (A, D, E, and K).
Management of pulmonary dysfunction includes chest physiotherapy, postural drainage, and breathing exercises several times daily to aid removal of secretions from lungs. Antihistamines are contraindicated because they have a drying effect on mucous membranes, making expectoration of mucus difficult or impossible. Aerosol therapy includes intermittent nebulizer treatments before postural drainage to loosen secretions.
Dornase alfa or DNase (recombinant human deoxyribonuclease), genetically engineered pulmonary enzymes given by aerosol nebulizer, helps thin airway mucus, improving lung function and reducing the risk of pulmonary infection.
Treatment of pulmonary infection requires:
❑ broad-spectrum antimicrobials
❑ oxygen therapy as needed
❑ loosening and removal of mucopurulent secretions, using an intermittent nebulizer and postural drainage to relieve obstruction. Use of a mist tent is controversial because mist particles may become trapped in the esophagus and stomach and never even reach the lungs.
Lung transplantation may be considered in some cases. Genetic research is ongoing, with researchers hoping to cure cystic fibrosis by artificially inserting a “healthy” gene into a person through gene therapy. The gene would be inserted by using an intranasal form.Research on correcting the disorder before birth is promising.
❑ Throughout this illness, teach the patient and his family about the disease and its treatment. The Cystic Fibrosis Foundation can provide educational and support services.
❑ Although many males with cystic fibrosis are infertile, females may become pregnant (due to increased life expectancies). As a result, more cystic fibrosis patients are now facing difficult reproductive decisions. Refer such patients (or the parents of an affected child) for genetic counseling so they can discuss family planning issues or prenatal diagnosis options if they're considering having more children.
❑ Be aware that some patients have recently undergone lung transplants to reduce the effects of the disease. Also, aerosol gene therapy shows promise in reducing pulmonary symptoms.
Research indicates that the genetic defect responsible for cystic fibrosis has also been identified in individuals experiencing some forms of unexplained pancreatitis.
Review other book chapters online related to Fibrosis:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X 
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