**Abstract**

Eating disorders, psychotic illnesses, and substance use disorders are some of the more common psychiatric conditions encountered in clinical practice that are associated with hyponatremia. The mechanisms that lead to hyponatremia vary, and at times hyponatremia may be a result of a drug side effect or drug-drug interaction. Additionally, hyponatremia from a non-psychiatric condition may lead to psychiatric symptomatology. Given the potential for hyponatremia to cause significant morbidity and potential mortality, clinicians are urged to consider screening for plasma sodium in patients at risk of hyponatremia, such as patients in the three categories of psychiatric conditions described above. Treatment of hyponatremia consists of various acute interventions, with consideration that treatment of the underlying psychiatric condition may help to diminish or eliminate the frequency of hyponatremic episodes in the long run.

**Keywords:** hyponatremia, anorexia nervosa, bulimia nervosa, psychosis, alcohol use disorder

#### **1. Introduction**

Sodium abnormalities can be seen in various psychiatric diseases. Common conditions include eating disorders, psychotic illnesses, and certain substance use disorders. Additionally, hyponatremia of any cause, including from drug side effects in patients being treated for psychiatric illnesses, can cause or worsen psychiatric conditions and may lead to medical comorbidities. References used in this chapter include articles from an online PubMed search of hyponatremia and psychosis spanning the past 50 years, and various Up-to-date review articles. In this chapter we dissect these conditions and open with a typical patient case.

#### **1.1 Case**

Lucia is a 19 year old junior majoring in Mathematics and Literature. She runs cross-country and has fainted multiple times while training with her teammates. On the recommendation of her coach she went to the student medical center for a wellness check. She looks thin and athletic. Vital sign checks show postural hypotension and orthostatic increase in pulse rate. Her BMI is calculated at 18 kg/m2 . She reports

otherwise good health and no psychiatric concerns. She is doing well in school and excelling on the cross-country team.

1. What additional questions might you ask to elucidate the cause of her syncopal episodes? 2. What additional investigation would you find helpful?

#### **2. Eating disorders and hyponatremia**

#### **2.1 Three main types of eating disorders**

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

Anorexia Nervosa is distinguished by severe restriction in nutritional intake leading to a BMI that is less than 18.5 kg/m<sup>2</sup> in adults, an intense fear of becoming 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 purging by using laxatives or diuretics to lose weight.

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 purging over the last 3 months.

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

#### **2.2 Electrolyte disturbances**

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 intake or impaired renal sodium reabsorption due to chronic starvation.

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*Hyponatremia and Psychiatric Diseases DOI: http://dx.doi.org/10.5772/intechopen.90011*

**2.3 Identifying hyponatremia**

sodium retention through the kidneys.

**2.4 Treatment**

**3.1 Psychotic illnesses**

**3.2 Bipolar illness**

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

Treatment depends on the severity of hyponatremia. In the case of patients with eating disorders, psychiatrists and nutritionists should be consulted and involved in treatment and care to facilitate discontinuation of purging, and excessive water drinking [6]. Some hospitals have developed protocols for treating such patients, including observed meals and caloric counting to ensure a smooth recovery when

food is re-introduced and for prevention of refeeding syndrome [7].

**disorder (OCD) affecting serum sodium**

with delusional skin infestation leading to hyponatremia [10].

**3. Psychotic illnesses, bipolar illnesses, and obsessive-compulsive** 

One of the most common psychotic illnesses that affect serum sodium is schizophrenia. As defined by DSM-5 [1], schizophrenia is characterized by two of more of the following symptoms including delusions, hallucinations, disorganized speech, grossly disorganized or catatonic behavior, and negative symptoms (i.e. diminished emotional expression) that are present for a significant portion of a 1-month period and continuous signs of disturbance in functioning level present for at least 6 months. Patients with schizophrenia can experience primary psychogenic polydipsia (PPD), characterized by an increase of fluid intake along with excretion of excessive amounts of dilute urine exceeding 40–50 mL/kg of body weight [8]. It is hypothesized that this occurs in patients with schizophrenia due to elevated levels of dopamine that stimulate the thirst center [8]. In patients with schizophrenia, polydipsia prevalence is estimated at 6–20%, and complications can include not just hyponatremia but rhabdomyolysis as well [9]. Severe water intoxication has also been reported in a patient

PPD has also been implicated in psychiatric patients with bipolar I disorder in a manic state whose increase in fluid intake can lead to hyponatremia [8]. As defined by DSM 5, a manic episode is a distinct period of abnormally and persistently elevated, expansive or irritable mood with increased activity or energy lasting at least 1 week that is not attributable to physiological effects of substances with three or more of the following symptoms present including inflated self-esteem,
