Finding the cause of severe hypokalemia

To the Editor: We read with great interest the article in the December issue by Dr. Leiva-Murillo and colleagues¹ in which the authors present a salient diagnostic approach for hypokalemia. One additional diagnostic consideration in the typical evaluation of severe hypokalemia is the presence of a covert eating disorder in the form of bulimia nervosa.

Regardless of the specific mode of purging used (self-induced vomiting, stimulant laxatives, or diuretics), these behaviors are frequently associated with the presence of hypokalemia, often with a concomitant metabolic alkalosis.² Because many patients with bulimia are often of normal body weight, these individuals can hide their history and can go undetected in the absence of anorexia nervosa and its characteristic thin habitus. Moreover, these patients tend to frequent busy emergency departments, urgent care centers, and student health centers, where clinicians have limited time to delve into the potential causes of the hypokalemia.

A helpful approach to follow is that the presence of hypokalemia in an otherwise healthy-appearing young person may be a sine qua non of a covert eating disorder. It is important to make this diagnosis, given the lethality of eating disorders and the potential for the subsequent development of hypokalemic nephropathy³ and edema due to pseudo-Bartter syndrome as a direct result of purging behaviors.⁴

Finally, similar to the patient whose case was presented in the article, patients with hypokalemia due to bulimia are treated with potassium chloride. Occasionally, on recheck a few hours later, the serum potassium level remains low. It is important to understand that the efficacy of potassium repletion is abrogated unless the contraction alkalosis resulting from dehydration due to purging behaviors is also corrected. This is known as pseudo-Bartter syndrome and is caused by the excessive aldosterone levels found in chronic bulimia resulting from increased aldosterone secretion to prevent critical dehydration from purging.

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