Ease Into Prep with a USMLE^® Step 2 CK Question of the Day

The correct answer is B. This patient has cystic fibrosis (CF). Due to a mutation in the cystic fibrosis transmembrane regulator (CFTR) gene, transport of chloride ions by epithelial cells is deranged. This leads to thick, viscous secretions in the lungs, pancreas, liver, intestine, and reproductive tract. The salt content in sweat gland secretions is also increased. Most CF patients will have multiple organ systems affected, as in this patient with frequent respiratory infections and pancreatic insufficiency. His history of failure to thrive in early childhood is likely due to malabsorption and malnutrition. Treatment includes pulmonary medications to open the airways and thin secretions, control of infections, therapy to clear airways of secretions, nutritional support, and pancreatic enzyme replacement + fat-soluble vitamin replacement.

Deficiency of a serine protease inhibitor (choice A) causes lung destruction in alpha-1 antitrypsin deficiency, another inherited disorder that affects the lungs.

Excess fluid in alveoli impairing gas exchange, decreasing compliance, and increasing pulmonary arterial pressure (choice C) characterizes acute respiratory distress syndrome (ARDS), a distinct type of respiratory failure. ARDS has many etiologies, the most common being sepsis.

Mast cell activation leading to bronchial wall thickening (choice D) describes the pathophysiology of asthma. In cystic fibrosis, bronchiectasis develops, which includes bronchial wall thickening plus airway dilatation (which can be observed by CT scan), and mast cells are not implicated.

Paralysis of airway cilia (choice E) is caused by smoking and contributes to increased respiratory infections in smokers, as well as chronic cough.