The correct answer is a. The first step is the evaluation of urinary potassium excretion. A urinary potassium-creatinine ratio value exceeding 1.5 is evidence of inappropriate urinary potassium excretion in the face of hypokalemia and helps to rule out diarrhea or laxative abuse as the cause.
The correct answer is c. The urinary potassium excretion is inappropriate for someone with hypokalemia. This indicates that the likely cause is not lower gastrointestinal loss of potassium. Upper gastrointestinal loss could still be a proximate cause as the predominant mechanism for hypokalemia in that situation is renal due to secondary hyperaldosteronism and bicarbonate in the tubular fluid acting as a nonreabsorbable anion. The actual potassium loss from gastric losses is not very much as potassium concentration is only 5 mEq/L to 10 mEq/L in gastric fluid.
The correct answers are d, e, f, and g. The presence of hypertension and mild metabolic alkalosis indicates that all causes of primary and secondary hyperaldosteronism as well as Liddle syndrome and the various forms of AME have to be considered. Blood pressure would not be typically elevated with Bartter or Gitelman syndrome, but the abuse of diuretics in hypertensive patients should still be considered.
The correct answers are c and d. Since we are considering the causes of hypokalemia associated with metabolic alkalosis and hypertension, measurements of plasma aldosterone concentration and plasma renin activity are necessary to differentiate the various conditions. Hypomagnesemia is not a cause of hypertension nor is diuretic abuse. Diuretic abuse in a hypertensive patient might be a possibility, but it would be of value to first document an elevated level of both renin and aldosterone. A plasma cortisol measurement may be of value later, but it should not be the initial test in trying to make this differentiation.
The correct answers are b and c. Two aspects of the dietary history are very important. She denies ingesting licorice, but apparently ingests large amounts of grapefruit. Acquired AME is seen with ingestion of licorice and grapefruit. Dietary flavinoids present in licorice and in grapefruit inhibit the enzyme 11-β-hydroxysteroid dehydrogenase, allowing cortisol to occupy the mineralocorticoid receptor.
The correct answer is c. The differential response to amiloride is indicative of Liddle syndrome. The mechanism of AME caused by either a genetic defect or an acquired abnormality in 11-β-hydroxysteroid dehydrogenase (due to licorice or grape fruit in the latter case) is enhanced mineralocorticoid activity by virtue of occupation of the mineralocorticoid receptor by glucocorticoids. Thus, the symptoms should respond to receptor occupation by spironolactone. In contrast, Liddle syndrome is due to enhanced activity of the sodium channel which is unaffected by Spironolactone, but is blocked by amiloride.
The correct answers are a and b. Genetic testing can confirm the defect in Liddle syndrome. At that point, family members should be evaluated, so that any of them with hypertension can receive appropriate treatment. Diagnosis of AME syndrome is usually done by demonstration of an excess of free urinary cortisol over free urinary cortisone in a 24-hour urine collection, although genetic testing can identify the congenital defect