Which are common manifestations of cystic fibrosis?

Choice A rationale Salty skin is caused by the dysfunction of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) protein, which impairs chloride and water transport across epithelial cells, including those in sweat ducts. The unabsorbed chloride remains in the sweat, leading to an elevated sodium chloride concentration on the skin, a basis for the diagnostic sweat test. Choice B rationale Barrel chest is a consequence of chronic hyperinflation of the lungs due to air trapping, a result of progressive small-airway obstruction from thick, tenacious mucus. Over time, the increased residual volume and functional residual capacity alter the chest wall's shape, increasing its anterior-posterior diameter. Choice C rationale Digital clubbing is a painless, symmetric enlargement of the tips of the fingers and toes, a sign of chronic hypoxemia and pulmonary disease. In cystic fibrosis, the progressive lung destruction and resultant impaired gas exchange lead to sustained low blood oxygen levels, triggering the development of clubbing. Choice D rationale Bradycardia (abnormally slow heart rate) is not a common manifestation of cystic fibrosis; in fact, chronic hypoxemia and the increased metabolic demands of respiratory distress often lead to tachycardia (abnormally fast heart rate). Bradycardia is usually a late, ominous sign of severe decompensation. Choice E rationale Steatorrhea, the passage of foul-smelling, fatty stools, results from the failure of the exocrine pancreas to secrete sufficient digestive enzymes (lipase, protease, amylase) into the small intestine. The thick mucus blocks the pancreatic ducts, preventing the essential enzymes from reaching the chyme for proper fat absorption.