**2.3 Identifying hyponatremia**

*Weight Management*

excelling on the cross-country team.

**2. Eating disorders and hyponatremia**

**2.1 Three main types of eating disorders**

leading to a BMI that is less than 18.5 kg/m<sup>2</sup>

purging over the last 3 months.

**2.2 Electrolyte disturbances**

purging by using laxatives or diuretics to lose weight.

otherwise good health and no psychiatric concerns. She is doing well in school and

Eating disorders are characterized by a disturbance in eating or eating related behavior and body image associated with substantial distress and psychosocial impairment and/or jeopardizing physical health [1]. Anorexia Nervosa, Bulimia Nervosa, and Binge Eating Disorder are the most well-known and best understood eating disorders. Other recognized eating disorders include avoidant/restrictive food intake disorder, pica, and rumination disorder. This classification scheme is mutually exclusive, such that during one-episode patients can carry only one diagnosis at a time. In this chapter we discuss the diagnostic categories that lead to hyponatremia and then focus on

Anorexia Nervosa is distinguished by severe restriction in nutritional intake

fat, gaining weight, and distortion in body shape and image. This is accompanied by behaviors that continue to interfere with weight gain and that stimulate weight loss. These behaviors include exercising, restricting food, eating low calorie foods, or

As defined by DSM-5 [1], anorexia nervosa—restricting subtype describes an individual whose weight loss has been accomplished primarily by dieting and fasting and has not engaged in recurrent episodes of binge eating or purging in the last 3 months. In Anorexia nervosa—binge-eating/purging subtype, the individual meets criteria for anorexia nervosa and has engaged in episodes of binge-eating and

Bulimia Nervosa is characterized by recurrent episodes of binge eating and compensatory behavior aimed at preventing weight gain, occurring at least once a week for at least 3 months. Like in the binge-purge subtype of Anorexia Nervosa, these purging behaviors may include self-induced vomiting, misuse of diuretics, or

If untreated and persistent, these two types of eating disorders result in electrolyte and acid-base disturbances, affecting serum and urine sodium, potassium, and chloride, and serum bicarbonate and pH [3]. Common electrolyte disturbances include hypokalemia and hyponatremia [4]. Hyponatremia is defined by a serum sodium concentration of <135 mEQ/L. Patients who purge consistently lose sodium through fluid output; self-induce vomiting, laxatives abuse leading to diarrhea; and diuretic abuse, leading to excessive urination. This decrease in effective circulating vascular volume stimulates the release of antidiuretic hormone (ADH) from the pituitary gland leading to water reabsorption through the kidneys. The body's attempt to preserve volume leads to dilution of the sodium already present in circulation. Hyponatremia in our eating disordered patients can be associated with low, normal or high serum tonicity. Hyponatremia associated with hypovolemia is as a result of low serum tonicity. Hyponatremia may also result from excessive water

laxatives, or excessive exercise. Patients may also restrict by fasting.

intake or impaired renal sodium reabsorption due to chronic starvation.

in adults, an intense fear of becoming

pal episodes? 2. What additional investigation would you find helpful?

detecting and treating hyponatremia in the eating disordered patient [2].

1. What additional questions might you ask to elucidate the cause of her synco-

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A quick screen can be utilized to investigate eating disordered patterns. Clinicians should use a validated eating disorder questionnaire, like the Eating Disorder Questionnaire Online (EDQ-O) or the SCOFF (Sick Control, One, Fat, Food) questionnaire to assess for the presence of an eating disorder [5]. On physical examination, patients who purge consistently or who restrict may appear volume depleted with orthostatic decreases in blood pressure, increases in pulse rate and decreased skin turgor. In addition to a basic metabolic panel, urine electrolyte screens should be completed to help elucidate the etiology of the hyponatremia. Patients who misuse prescribed diuretics or who use copious amounts of over the counter diuretics will not have low urine sodium. On the other hand, patients who self-induce vomiting or diarrhea will have low urinary sodium because of increased sodium retention through the kidneys.
