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Metabolic Abnormalities in Bulimia Nervosa

Am Fam Physician. 2004 Mar 15;69(6):1530-1532.

Persons with anorexia nervosa eventually become visibly recognizable because of their severely underweight status. In contrast, those affected by bulimia are typically of normal weight and are not as easily detected. This disorder is characterized by binge eating and purging. Mehler reviews the diagnosis and treatment of bulimia, using a hypothetical case of a 20-year-old woman noted to have severe hypokalemia and metabolic alkalosis.

Bulimia is most common in late adolescent females. Comorbidity with other psychiatric disorders is typical, and patients with a concomitant personality disorder (e.g., borderline, narcissistic, and antisocial disorders) have a worse prognosis. Although most bulimics purge by vomiting, abuse of laxatives or diuretics also occurs. The number of times a bulimic patient purges can vary widely, from as seldom as once or twice weekly to as often as 10 times per day.

The medical complications of bulimia relate to the method and frequency of purging. Repeatedly induced vomiting can lead to the loss of dental enamel, increased dental caries, swollen salivary glands, Mallory-Weiss esophageal tears, and gastroesophageal reflux. Laxative abusers can develop severe constipation on withdrawal of laxatives, related to damage to the myenteric plexus. The typical electrolyte abnormalities associated with bulimia are hypokalemia and metabolic acidosis. Different purging methods result in different constellations of serum and urine electrolyte disturbances (see accompanying table). The author notes that although severe hypokalemia in an otherwise healthy young female specifically suggests bulimia, most patients who purge do not develop electrolyte abnormalities. Therefore, screening for hypokalemia or other electrolyte derangements is not a sensitive means for detecting purging.

Electrolyte Levels Usually Associated with Purging

Serum levels Urine levels
Method of purging Sodium Potassium Chloride Bicarbonate pH Sodium Potassium Chloride

Vomiting

Increased, decreased, or normal

Decreased

Decreased

Increased

Increased

Decreased

Decreased

Decreased

Laxatives

Increased or normal

Decreased

Increased or decreased

Decreased or increased

Decreased or increased

Decreased

Decreased

Normal or decreased

Diuretics

Decreased or normal

Decreased

Decreased

Increased

Increased

Increased

Increased

Increased


Reprinted with permission from Mehler PS. Bulimia nervosa. N Engl J Med 2003;349:876.

Electrolyte Levels Usually Associated with Purging

View Table

Electrolyte Levels Usually Associated with Purging

Serum levels Urine levels
Method of purging Sodium Potassium Chloride Bicarbonate pH Sodium Potassium Chloride

Vomiting

Increased, decreased, or normal

Decreased

Decreased

Increased

Increased

Decreased

Decreased

Decreased

Laxatives

Increased or normal

Decreased

Increased or decreased

Decreased or increased

Decreased or increased

Decreased

Decreased

Normal or decreased

Diuretics

Decreased or normal

Decreased

Decreased

Increased

Increased

Increased

Increased

Increased


Reprinted with permission from Mehler PS. Bulimia nervosa. N Engl J Med 2003;349:876.

Treatment of the medical complications associated with bulimia is usually possible, but the underlying disorder can be challenging to manage. Fluoridated mouthwash and tooth-paste can help ameliorate dental caries, and the use of sour candies may decrease salivary gland swelling. Antacid medications help reduce reflux symptoms, and nonstimulant laxatives may be used to decrease constipation in those with previous stimulant laxative abuse. Oral repletion of low potassium is typically accomplished with 40 to 80 mEq per day of supplementary potassium, until a normal serum potassium level is achieved. Patients with severe hypokalemia and metabolic alkalosis need volume repletion with intravenous normal saline to turn off the renin-angiotensin-aldosterone system and allow normalization of potassium levels.

Cognitive-behavioral therapy has demonstrated efficacy in the treatment of bulimia, but more than 60 percent of patients in one follow-up survey cited by the author still had residual eating disorder features six years after treatment. Disturbances in serotonergic systems have been postulated as contributing to bulimia. The selective serotonin reuptake inhibitor fluoxetine is the only medication that has been approved by the U.S. Food and Drug Administration for treatment of bulimia. Higher dosages of fluoxetine, up to 60 mg daily, may be necessary for effective control. Even with a combination of psychotherapy and pharmacologic treatment, remission rates in studies of bulimic patients averaged less than 50 percent.

Mehler PS. Bulimia nervosa. N Engl J Med. August 28, 2003;349:875–81.


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