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ESSENTIALS OF DIAGNOSIS

ESSENTIALS OF DIAGNOSIS

  • Autosomal recessive disorder.

  • Pulmonary disease: chronic or recurrent productive cough, dyspnea, and wheezing; recurrent airway infections or chronic colonization of the airways with H influenzae, P aeruginosa, S aureus, or Burkholderia cenocepacia; bronchiectasis and scarring on chest radiographs; airflow obstruction on spirometry.

  • Extrapulmonary disease: sinus disease (chronic sinusitis and nasal polyposis); GI disease (pancreatic insufficiency, recurrent pancreatitis, hepatobiliary disease, meconium ileus, and distal intestinal obstruction); genitourinary problems (absent vas deferens and male infertility).

  • Diagnosis: sweat chloride concentration > 60 mEq/L on two occasions; or presence of two disease-causing mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene; or sweat chloride concentration 30–59 mEq/L plus one disease-causing mutation in CFTR gene.

GENERAL CONSIDERATIONS

Cystic fibrosis is the most common cause of severe chronic lung disease in young adults and the most common fatal hereditary disorder of White persons in the United States. It is an autosomal-recessive disorder affecting about 1 in 3000 White persons; 1 in 25 is a carrier. Cystic fibrosis is 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. Over 2000 different mutations of the CFTR gene have been identified with potential to cause disease. The most common mutation is ΔF508. Mutations of the CFTR gene have been divided into five different classes: class I (defective protein production), class II (defective protein processing), class III (defective regulation), class IV (defective conduction), and class V (reduced amounts of functional CFTR protein).

CLINICAL FINDINGS

A. Symptoms and Signs

Cystic fibrosis should be suspected in an adult with a history of chronic lung disease (especially bronchiectasis), pancreatitis, or infertility. Cough, sputum production, decreased exercise tolerance, and recurrent hemoptysis are typical complaints. Patients also often complain of chronic rhinosinusitis symptoms, steatorrhea, diarrhea, and abdominal pain. Patients with cystic fibrosis are often malnourished with low BMI. Digital clubbing (Figure 6–42), increased anteroposterior chest diameter, hyperresonance to percussion, and apical crackles are noted on physical examination. Sinus tenderness, purulent nasal secretions, and nasal polyps may also be seen. Nearly all men with cystic fibrosis have congenital bilateral absence of the vas deferens with azoospermia. Biliary cirrhosis and gallstones may occur.

B. Laboratory Findings

ABG studies often reveal hypoxemia and, in advanced disease, a chronic, compensated respiratory acidosis. PFTs show a mixed obstructive and restrictive pattern. There is a reduction in FVC, airflow rates, and TLC. Air trapping (high ratio of RV to TLC) and reduction in pulmonary diffusing capacity are common.

C. Imaging

Hyperinflation is seen early in the disease process. Peribronchial cuffing, mucus plugging, bronchiectasis (ring shadows and cysts), increased interstitial markings, small ...

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