Cystic Fibrosis

– An inherited disease of the exocrine glands that results in multisystem involvement primarily by affecting the respiratory and gastrointestinal systems. It typically is characterized by chronic obstructive pulmonary disease, abnormally high loss of electrolytes through the sweat glands, and pancreatic enzyme insufficiency, leading to digestive impairments and malabsorption syndrome.

Causes and Incidence

Cystic fibrosis (CF) is caused by a defective gene that is inherited from both parents as an autosomal recessive trait. The gene is responsible for encoding a membrane-associated protein called cystic fibrosis transmembrane conductance regulator (CFTR). The exact function of CFTR is unknown, but research shows that it is closely tied to chloride transport. Current research focuses on the causes of seemingly unrelated multisystem effects.

CF is the most common lethal genetic disease among white children and young adults in the United States, with an incidence of 1 in approximately every 2,400 live births. Blacks also are affected, but the rate is about 1 in 17,000 births. CF is rare in Asians and Native Americans.

Disease Process

In CF, the exocrine glands are affected in one of three ways: (1) they produce and become obstructed by thickened, sticky mucus; (2) they produce excess normal secretions; or (3) they secrete excess sodium and chloride. The lungs are normal at birth, but bronchioles and bronchi soon become clogged with thick mucous plugs, leading to associated opportunistic infections and overinflation of the lungs. Bronchial walls thicken and airways remain filled with purulent secretions, leading to fibrosis and atelectasis. Chronic hypoxemia leads to hypertrophy of the pulmonary arteries, which leads to pulmonary hypertension and right ventricular hypertrophy. The pancreatic ducts also become clogged with mucous plugs, which interfere with pancreatic enzyme activity. Digestive enzymes fail to reach the small intestine, and as a result, digestion and absorption of nutrients are markedly impaired, leading to excess fat and protein in the stools. The biliary tracts in the liver become plugged with mucus and fibrose over time. Salivary glands and bile ducts may also become clogged. Sweat glands secrete abnormal levels of sodium and chloride, leading to excessive loss of these electrolytes.

Symptoms

Signs and symptoms vary widely, involve several systems, and change as the disease progresses. Some children show manifestations at birth, whereas others do not develop symptoms for years. Manifestations range from mild to life threatening. The earliest sign is a meconium ileus, seen at birth in about 10% of infants with CF. All children display sweat gland abnormalities, 85% to 90% have pancreatic and gastrointestinal (GI) tract involvement, and 50% show respiratory involvement.

Sweat glands/skin
Salty tasting skin; salt crystals on nose, forehead and hairline; dehydration, alkalosis in heat or with fever

Pancreas/GI tract
Meconium ileus, with cramps, nausea, vomiting, abdominal distention; frequent, bulky, oily, and foul-smelling stools; normal or voracious appetite; weight loss, failure to thrive; pot belly, wasted buttocks, thin extremities; sallow skin; anemia, easy bruising; rectal prolapse

Respiratory tract
Wheezing, dry cough, rhinitis, gagging; dyspnea; intercostal retractions, use of accessory muscles to breathe; barrel chest, digital clubbing, cyanosis; repeated episodes of upper respiratory infection (URI), bronchial pneumonia

Reproductive system
Delayed onset of puberty; amenorrhea, viscous cervical secretions that block sperm entry in women; sterility in men

Potential Complications

Complications are numerous and can include biliary cirrhosis, esophageal varices, portal hypertension, diabetes mellitus, pneumothorax, cor pulmonale, congestive heart failure, peptic ulcer, intestinal obstruction, intussusception, pancreatitis, cholecystitis, and cardiac arrhythmias. CF is a terminal disease. However, the median death rate has climbed, from 7 1/2 years in 1966 to 28 years in 1993. A few individuals have survived to 50 years of age or older.

Diagnostic Tests

Clinical evaluation
Any of the above manifestations, particularly salty skin, failure to thrive, and frequent URIs; family history

Quantitative pilocarpine
Sodium or chloride concentration .60 mEq/L

Iontophoresis sweat test
To obtain definitive diagnosis

Treatments

Surgery
Heart-lung or liver transplantation with advanced disease; treatment of complications (e.g., resection of bowel obstructions, cholecystectomy, portal shunt for esophageal varices).

Drugs
Antibiotics to treat pulmonary infections; amiloride HCl (aerosol) to inhibit sodium and water reabsorption in the lungs; DNase and other drugs to thin mucus; alphaantitrypsin to reduce inflammation; pancreatic enzyme replacements (e.g., pancrelipase); bronchodilators to aid breathing.

General
Diet therapy, with 50% increase in normal caloric and protein intake, high fat intake, multivitamins, water-miscible vitamin E, sodium supplements, enteral supplementation in severe cases Prophylaxis against respiratory infection with pertussis, measles, and flu vaccines Chest physiotherapy to increase movement of mucus from lungs (postural drainage, percussion, vibration, and assisted coughing; oxygen therapy for hypoxia; exercise to stimulate mucus movement) Long-term psychologic counseling for individual and family; genetic counseling for parents; support groups; home care, respite care.