Cystic fibrosis is a genetic disease that occurs in 1 in 2,000 live births among whites, 1 in 17,000 live births among blacks, and 1 in 50,000 live births among Asians. The cystic fibrosis (CF) gene has been localized to the seventh chromosome. The classic triad entails chronic sinopulmonary disease, pancreatic insufficiency and an elevated sweat electrolyte concentration. With appropriate therapy, more patients are surviving into adulthood with the mean survival rate at approximately 27 years of age.

The CF gene is responsible for the production of a protein termed the Cystic Fibrosis Transmembrane conductance regulator (CFTR), which results in failure of chloride and sodium ion transport across cell membranes. Clinically, this defect manifests as impaired functioning of various exocrine glands throughout the body. Exocrine dysfunction results in the production of excessively thick and tenacious mucus, sweat with an abnormal salt (NaCl) and potassium content, and obstruction and fibrosis of the ducts of the pancreas, biliary system, and vas deferens. Progressive pulmonary disease characterized by obstruction, air trapping, and recurrent infections may be complicated by pneumothorax, massive hemoptysis or cor pulmonale. Pulmonary complications are the leading cause of premature death experienced by afflicted patients. Other clinical abnormalities include recurrent pancreatitis, appendicitis, cholelithiasis, cholecystitis, obstructive azoospermia with resultant infertility among male patients, thickened cervical mucus, and hypertrophic osteoarthropathy. Clubbing is a physical finding that manifests early in the disease course and may be a useful diagnostic clue.

Pancreatic insufficiency with resultant fat malabsorption are common gastrointestinal manifestations and are present in 85% of cases. Other potential complications associated with the gastrointestinal system include rectal prolapse, diabetes mellitus, cholelithiasis, biliary cirrhosis (may or may not be associated with concomitant portal hypertension and hypersplenism), malnutrition with vitamin and essential fatty acid deficiencies, and pancreatitis.

Male patients are usually (98%) azoospermic. Female patients may suffer decreased levels of fertility; however, some may be able to conceive so they should be counseled regarding contraception. Genetic counseling should also be offered to all patients.

Recurrent pulmonary complications are a frequent manifestation. Staphylococcus aureus and Hemophilus influenzae are frequent underlying pathogens and colonizers in young patients. As patients mature, Pseudomonas aeruginosa becomes a frequent etiologic agent and colonizer which proves impossible to effectively eradicate. Infections secondary to respiratory syncytial virus (RSV) are an often fatal complication in afflicted infants.

The diagnosis is established based on clincial symptoms, a history of CF in a sibling, an elevated sweat chloride concentration, identification of CF mutations, or demonstration of nasal epithelia abnormalities. A positive sweat chloride test exists when the chloride content is greater than 60 mEq/L, or when the chloride content is higher than the sodium content. For the test to be accurate, between 50 and 100 microL of sweat should be collected. The diagnosis can be established in the fetus via the analysis for genetic markers from chorionic villus sampling. In neonates, elevated immunoreactive trypsinogen levels result from obstruction of the pancreatic duct with a resultant leak of this enzyme into the blood. Therefore, continuously elevated levels of this enzyme detected during the first 4 to 6 weeks of life should provoke physicians to perform a sweat test to establish or eliminate the diagnosis.

Therapy is supportive and is directed at replacement of digestive enzymes, nutritional supplementation, clearance of airway mucus, and aggressive chemotherapy directed against recurrent pulmonary infections. Pancreatin or pancrelipase are both effective for pancreatic enzyme replacement, and their efficacy may be enhanced when given 1 hour after an H2 receptor blocker to decrease stomach acid. Patients should be given dietary advice to increase caloric intake to 1.5 to 2 times the normal requirement. Diets should be further supplemented by multivitamins with minerals and vitamin E. The vitamins used in therapy must be water soluble. Pulmonary therapy should consist of aggressive chest percussion and postural drainage, inhaled bronchodilators and aggressive chemotherapy for infections. Oral antibiotics (trimethoprim-sulfamethoxazole, ciprofloxacin, and cefaclor) are effective against S. aureus and H. influenzae. However, P. aeruginosa is resistant to oral therapy and hospitalization for intravenous antibiotics to include combined aminoglycoside (tobramycin, gentamicin, or amikacin) along with either a broad-spectrum semisynthetic penicillin (piperacillin, azlocillin, or meziocillin) or third-generation cephalosporin (ceftazidime) is required. Inhaled antibiotics (aerosolized tobramycin) may also be useful.