A 60-year-old man with alcoholism is admitted after being found unresponsive in the street. No other history is available.
His temperature is 37.1 C (98.8 F), blood pressure is 130/86 mm Hg, pulse is 110/min and regular, and respirations are 20/min. On examination, the patient is disheveled and appears chronically ill. He has decreased muscle mass and no subcutaneous fat. He responds to painful stimuli and has slurred speech. Carpal spasm was noted in the hand of the arm in which his blood pressure was taken. Mucous membranes are dry and there is no moisture in the axillae. He has nystagmus on end lateral gaze of both eyes. No other focal neurologic findings are present.
Laboratory results are as follows:

Intravenous thiamine and fluids consisting of 3 L normal saline/5% dextrose containing 40 mEq of potassium are administered over 4 hours. Electrolytes are re-measured with the following results:

Which of the following is the most likely cause of this patient's hypokalemia?

Question

A 60-year-old man with alcoholism is admitted after being found unresponsive in the street.  No other history is available.
His temperature is 37.1 C (98.8 F), blood pressure is 130/86 mm Hg, pulse is 110/min and regular, and respirations are 20/min.  On examination, the patient is disheveled and appears chronically ill.  He has decreased muscle mass and no subcutaneous fat.  He responds to painful stimuli and has slurred speech.  Carpal spasm was noted in the hand of the arm in which his blood pressure was taken.  Mucous membranes are dry and there is no moisture in the axillae.  He has nystagmus on end lateral gaze of both eyes.  No other focal neurologic findings are present.
Laboratory results are as follows:

Intravenous thiamine and fluids consisting of 3 L normal saline/5% dextrose containing 40 mEq of potassium are administered over 4 hours.  Electrolytes are re-measured with the following results:

Which of the following is the most likely cause of this patient's hypokalemia?

Quizplus · Accepted Answer

11ec193a_96c3_465d_853d_5d1c8cb38427_MD0002_00 This poorly nourished man with alcoholism has hypocalcemia and hypokalemia (neither improved with intravenous potassium replacement) consistent with magnesium deficiency. This is commonly seen in the intensive care unit setting and in community-dwelling older individuals on restricted diets ("tea and toast" diet). Magnesium is required as a cofactor for over 300 enzyme systems and directly regulates sodium, potassium, and calcium channels. Magnesium deficiency can therefore result in widespread organ dysfunction. Two laboratory features commonly present with hypomagnesemia are hypocalcemia (40% of patients) and hypokalemia (60% of patients). Hypocalcemia is due to decreased parathyroid hormone (PTH) secretion and PTH resistance (impaired calcium mobilization from bone). Hypokalemia is due to renal potassium wasting. In a patient with hypomagnesemia, administration of potassium typically does not restore serum potassium concentration to normal until body magnesium stores are replenished. (Choice A) Catecholamines (via beta-2 adrenergic receptors) can cause a shift of potassium from extra- to intracellular sites, thereby lowering serum potassium concentration. Although modest volume depletion and alcohol withdrawal can result in increased plasma catecholamines, the hypokalemia is usually responsive to potassium replacement and should correct to normal levels. (Choice C) Primary hyperaldosteronism can result in significant hypokalemia, metabolic alkalosis, hypernatremia, and hypertension. This patient's mild increase in blood pressure is most likely due to early alcohol withdrawal, and his normal sodium and serum bicarbonate make primary hyperaldosteronism less likely. (Choice D) Refeeding can result in a shift of potassium from extra- to intracellular sites and thereby lower serum potassium. This cellular shift may be promoted by insulin and can modestly decrease serum potassium. The hypokalemia that occurs with refeeding usually corrects with potassium replacement. (Choice E) Renal tubular acidosis is commonly associated with hypokalemia due to renal potassium losses. This patient's normal serum bicarbonate does not support a diagnosis of renal tubular acidosis. Educational objective: Hypomagnesemia is often associated with hypocalcemia and hypokalemia. Persistent hypokalemia despite potassium replacement should prompt a check of serum magnesium. __________ References: Magnesium homeostasis and clinical disorders of magnesium deficiency (http://www.ncbi.nlm.nih.gov/pubmed/8173141) Mechanisms of hypocalcemia in magnesium deficiency (http://www.ncbi.nlm.nih.gov/pubmed/17804670)

A 60-Year-Old Man with Alcoholism Is Admitted After Being Found