A 24-year-old woman is brought to the emergency department due to feeling lightheaded every time she stands up. The patient has no significant medical problems. She left her boyfriend 4 months ago as he was "eating too much" and has since had decreased appetite and lost 5 kg (11 lb). The patient has also missed her last 2 menstrual periods. She does not use tobacco, alcohol, or illicit drugs. Family history is significant for coronary artery disease and congestive heart failure. Her temperature is 36.7 C (98 F), blood pressure is 100/70 mm Hg, and pulse is 88/min while supine. On standing, blood pressure is 80/55 mm Hg and pulse is 120/min. Other than dry skin and mucous membranes, the patient's physical examination is unremarkable. Initial laboratory results are as follows: Which of the following is the most likely underlying etiology for this patient's symptoms?

Question

A 24-year-old woman is brought to the emergency department due to feeling lightheaded every time she stands up.  The patient has no significant medical problems.  She left her boyfriend 4 months ago as he was "eating too much" and has since had decreased appetite and lost 5 kg (11 lb).  The patient has also missed her last 2 menstrual periods.  She does not use tobacco, alcohol, or illicit drugs.  Family history is significant for coronary artery disease and congestive heart failure.  Her temperature is 36.7 C (98 F), blood pressure is 100/70 mm Hg, and pulse is 88/min while supine.  On standing, blood pressure is 80/55 mm Hg and pulse is 120/min.  Other than dry skin and mucous membranes, the patient's physical examination is unremarkable.  Initial laboratory results are as follows:  Which of the following is the most likely underlying etiology for this patient's symptoms?

Quizplus · Accepted Answer

Explanation: This young woman has dizziness due to orthostatic hypotension. In addition, she has abnormal serum and urine electrolytes, including hyponatremia, hypokalemia, hypochloremia, and increased urinary sodium and potassium. Diuretic abuse, which leads to hypovolemia, best explains the laboratory findings in this patient as follows: orthostatic hypotension Normally, dehydrated patients with hyponatremia are expected to have low urine sodium (<20 mEq/L); however, this patient has elevated urine sodium, which suggests salt wasting (eg, diuretic use, cerebral salt wasting [CSW], adrenal insufficiency). Normally, patients with hypokalemia respond by reducing urine potassium excretion, except in cases of renal potassium wasting (eg, diuretic use, hyperaldosteronism, renal tubular acidosis). Hypochloremia is likely a result of diuresis and contraction alkalosis; urine chloride levels can vary. Surreptitious diuretic use is sometimes employed as a means to lose weight. Patients may gain access to these medications from family members who have been appropriately prescribed these medications. (Choice A) CSW presents with hypovolemia and hyponatremia with high urine sodium (>20 mEq/L). However, CSW always occurs due to a neurologic insult (injury or surgery). (Choice C) Laxative abuse will also lead to hypotension and hypovolemia. However, elevated urine sodium indicates that sodium loss is through the urinary tract (eg, diuretic use) rather than the gastrointestinal tract (eg, laxative use). (Choice D) Low caloric intake causes weight loss secondary to wasting of muscle mass and fat and could also lead to electrolyte abnormalities. However, elevated urine sodium and potassium are not expected. (Choice E) Mineralocorticoid deficiency can lead to wasting of sodium and water, but serum potassium levels are increased in such patients. (Choice F) Self-induced vomiting may lead to hypovolemia, hypokalemia, and hyponatremia. However, urinary sodium will be low as the kidneys try to conserve water by maximally resorbing sodium and water. Educational objective: Diuretic abuse leads to increased excretion of water and electrolytes by the kidneys, resulting in dehydration, weight loss, orthostatic hypotension, hyponatremia, and hypokalemia. Urinary sodium and potassium will be elevated. Patients sometimes abuse diuretics to induce weight loss. References: Diuretic abuse and central pontine myelinolysis. (http://www.ncbi.nlm.nih.gov/pubmed/2486385)

A 24-Year-Old Woman Is Brought to the Emergency Department Due