A 16-year-old girl is evaluated in the emergency department for syncope. She has no other medical conditions and does not use tobacco, alcohol, or illicit drugs. Her blood pressure is 95/65 mm Hg and pulse is 106/min. The remainder of the physical examination is within normal limits. Laboratory values are as follows.

The patient's urine chloride is low at 8 mEq/L.
Which of the following is the most likely diagnosis?

Question

A 16-year-old girl is evaluated in the emergency department for syncope. She has no other medical conditions and does not use tobacco, alcohol, or illicit drugs. Her blood pressure is 95/65 mm Hg and pulse is 106/min. The remainder of the physical examination is within normal limits. Laboratory values are as follows.

The patient's urine chloride is low at 8 mEq/L.
Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

This patient has several electrolyte abnormalities including hyponatremia, hypokalemia, hypochloremia, and metabolic alkalosis. Potential causes of metabolic alkalosis with hypokalemia include vomiting, diuretic use, or abnormal renal sodium handling (eg, Gitelman and Bartter syndromes). The urine chloride level can distinguish among these diagnoses. Patients with gastric losses reabsorb chloride from the urine due to both volume depletion and hypochloremia, leading to low urinary chloride. In contrast, patients taking diuretics or who have abnormal renal sodium handling are unable to reabsorb chloride and inappropriately lose it in the urine (Choice B). This patient likely has surreptitious vomiting due to bulimia. Persistent self-induced vomiting can cause hypovolemia (leading to hypotension and tachycardia), scarring on the dorsal hands, dental erosions, and puffy cheeks from parotid hypertrophy. (Choice A) Anxiety disorder can present with multiple symptoms including palpitations, sleep disturbances, headaches, and possible hyperventilation with dizziness. However, anxiety alone does not cause the laboratory abnormalities seen in this patient. (Choices C and D) Ecstasy (MDMA) is a sympathomimetic that can cause hypertension, tachycardia, hyperthermia, and possible hyponatremia. Other findings include agitation, hyperactivity, anxiety, and altered mentation. Primary hyperaldosteronism typically presents with hypertension, hypokalemia, and metabolic alkalosis. Absence of hypertension in this patient makes either of these diagnoses less likely. Educational objective: Etiologies of metabolic alkalosis with hypokalemia include vomiting, diuretic use, or abnormal renal sodium handling (eg, Gitelman and Bartter syndromes). Urinary chloride level is typically low in patients with vomiting and high in patients with diuretic use or abnormal renal sodium handling. __________ References: Hypokalemia: a practical approach to diagnosis and its genetic basis. (http://www.ncbi.nlm.nih.gov/pubmed/17584063) Clinical evaluation of hypokalemia in anorexia nervosa. (http://www.ncbi.nlm.nih.gov/pubmed/2634141)

A 16-Year-Old Girl Is Evaluated in the Emergency Department for Syncope