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For further information, see CMDT Part 9-09: Cystic Fibrosis

Key Features

Essentials of Diagnosis

  • Pulmonary disease

    • Chronic or recurrent productive cough, dyspnea, and wheezing

    • Recurrent airway infections or chronic colonization of the airways with

      • Haemophilus influenzae

      • Pseudomonas aeruginosa

      • Staphylococcus aureus

      • Burkholderia cenocepacia

    • Bronchiectasis and scarring on chest radiographs

    • Airflow obstruction on spirometry

  • Extrapulmonary disease

    • Sinus disease

    • Gastrointestinal disease

      • Pancreatic insufficiency

      • Recurrent pancreatitis

      • Hepatobiliary disease

      • Meconium ileus

      • Distal intestinal obstruction

    • Genitourinary problems

      • Male infertility

      • Urogenital abnormalities

  • Sweat chloride concentration > 60 mEq/L on two occasions

  • Presence of two disease-causing mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene

  • Abnormal nasal potential difference

General Considerations

  • Most common fatal hereditary disorder of Whites in the United States

  • Caused by abnormalities in a membrane chloride channel (the cystic fibrosis transmembrane conductance regulator [CFTR] protein) that results in altered chloride transport and water flux across the apical surface of epithelial cells

  • At least 1000 mutations to the CFTR gene are described, with "ΔF508" accounting for approximately 60% of cases

  • Pathophysiology results from production of an abnormal mucous in exocrine glands, which leads to tissue destruction and, in the respiratory tract, impairs mucociliary clearance

  • Variety of mutations is reflected in wide range of pulmonary and nonpulmonary manifestations

Demographics

  • Affects 1 in 3200 Whites; 1 in 25 is a carrier

Clinical Findings

Symptoms and Signs

  • Disease should be suspected in young adults with a history of chronic lung disease, pancreatitis, or infertility

  • Productive cough, decreased exercise tolerance, and recurrent hemoptysis are typical

  • Patients also often complain of chronic rhinosinusitis symptoms, steatorrhea, diarrhea, and abdominal pain

  • Patients with cystic fibrosis are often malnourished with low body mass index

  • Other findings include

    • Digital clubbing

    • Increased anteroposterior chest diameter

    • Hyperresonance on percussion

    • Apical crackles

  • Nearly all male patients have congenital absence of the vas deferens with azoospermia

  • Biliary cirrhosis and gallstones may occur

Differential Diagnosis

  • Chronic obstructive pulmonary disease

  • Asthma

  • α1-Antiprotease deficiency

  • Bronchiolitis

  • Celiac disease

  • Chronic sinusitis

Diagnosis

Laboratory Tests

  • Arterial blood gases reveal hypoxemia, with compensated respiratory acidosis in advanced disease

  • Pulmonary function tests

    • A mixed obstructive and restrictive pattern

    • Reduced FVC, airflow rates, and total lung capacity

    • Air trapping and reduced diffusion capacity are common

  • Genotyping, measurement of nasal membrane potential difference, semen analysis, or assessment of pancreatic function can play a role in diagnosis

  • Sputum cultures

    • Frequently show S aureus and P aeruginosa

    • Occasionally show H influenzae, Stenotrophomonas maltophilia, and Burkholderia cepacia

Imaging Studies

  • Hyperinflation is seen early on chest radiographs

  • Peribronchial cuffing, mucus plugging, bronchiectasis, atelectasis, small rounded peripheral opacities, and increased interstitial markings are common

  • High-resolution ...

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