Lupine Publishers| Hyponatremia in Psychiatric Inpatients: A Native Pilot Study

 Lupine Publishers| Journal of Neurology and Brain Disorders

Abstract

Introduction: Hyponatremia is one of the most frequent ion and water disorders and severe hyponatremia is associated with well-known clinical symptoms and manifestations. In the present assessment the incidence and clinical profile of hyponatremia have been probed among a great sample of non-western psychiatric inpatients and compared with the available data in literature regarding prevalence and other associated clinical characteristics.

Methods: All inpatients with idiopathic hyponatremia during the last sixty-four months had been included in the present study. Clinical diagnosis, as well, was in essence based on ‘Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5)’. Statistical significance had been defined as a p value ≤0.05.

Results: While the annual incidence of hyponatremia in current evaluation was around 0.01%, the annual incidence of mortality due to hyponatremia was around 0.001%. It was significantly more prevalent among male psychiatric inpatients (p<0.04) and patients with duration of illness in excess of one year (p<0.04). Furthermore, it was meaningfully more evident among schizophrenic patients (p<0.007), in comparison with remaining primary psychiatric disorders. There was no significant relationship between hyponatremia and symptomatic profile, or serum level of sodium and occurrence of seizure.

Conclusion: Hyponatremia was significantly more prevalent among male patients and cases with duration of illness in excess of one year. Furthermore, it was meaningfully more evident among schizophrenic patients.

Keywords: Hyponatremia; Psychiatric disorders; Psychotropic drugs; Schizophrenia

Introduction

Hyponatremia (serum sodium concentration < 136mEq/L) is one of the most frequent ion and water disorders. It is generally due to disproportionate renal water retention. Severe hyponatremia (<125mEq/L) is associated with well-known clinical symptoms and manifestations. However, even mild reductions in sodium blood levels have been shown to be associated with increased mortality and with the risk of falls and fractures. The diagnosis of hyponatremia, although requiring simple clinical and laboratory tests, may be complex and difficult [1]. Hyponatremia is a prevalent and potentially dangerous medical comorbidity in psychiatric patients, too [2]. Hyponatremia can occur in the context of water intoxication, where water consumption exceeds the maximal renal clearance capacity along with a low serum and urine osmolality. Cross‐sectional studies of chronically ill, hospitalized psychiatric patients have found the prevalence of water intoxication to be approximately 5% [3]. It may occur, as well, due to drug‐induced Syndrome of Inappropriate Antidiuretic Hormone (SIADH), where the kidney retains an excessive quantity of solute‐free water. In this situation, serum osmolality is low and urine osmolality is relatively high. The prevalence of SIADH has been estimated to be as high as 11% in acutely ill psychiatric patients [4]. Risk factors for antidepressant induced SIADH (increasing age, female gender, medical co‐morbidity and polypharmacy) seem to be less relevant in the population of patients treated with antipsychotic drugs [5]. Overall prevalence of antipsychotic‐induced hyponatremia has been estimated at 0.004% [6] and 26.1% [5] of patients. Mild to moderate hyponatremia presents as confusion, nausea, headache and lethargy.

As the plasma sodium falls, these symptoms become increasingly severe and seizures and coma can develop. So, while monitoring of plasma sodium is desirable for all those receiving antipsychotics, signs of confusion or lethargy should provoke thorough diagnostic analysis, including plasma sodium determination and urine osmolality [3]. Prevalence of polydipsia in a population of chronic psychiatric patients can be as high as 6 to 17% [7]. Schizophrenia represents 80% of cases reported [8]. Early onsets of psychiatric disorder and long duration of that or poor response to psychopharmacotherapy have been identified as significant risk factors for appearance of hyponatremia [9]. Patients with hyponatremia may be asymptomatic or present with nausea, anorexia, muscle cramps, weakness, fatigue, confusion and disorientation. Severe hyponatremia may result in serious neurologic sequelae such as coma and seizures, and death. Advanced age, too, appears to be a risk factor for this adverse effect, as does the concomitant use of diuretics [10]. Like other psychotropic medications, it is suspected that atypical antipsychotics can induce hyponatremia by either stimulating antidiuretic hormone release from the brain or enhancing antidiuretic hormone activity in the kidneys [10]. Currently, there are no reliable estimates of incidence or risk of hyponatremia from atypical antipsychotic drugs in older adults [11]. On the other hand, while acute hyponatremia is characterized by onset of symptoms <48h, chronic hyponatremia develops over >48h and most patients have chronic hyponatremia. The serum sodium concentration is usually above 120meq/L. Brain adapts itself to hyponatremia by generation of idiogenic osmoles. This is a protective mechanism that reduces the degree of cerebral edema; it begins on the first day and is complete within several days. Hence in chronic hyponatremia patients may appear asymptomatic [12]. Mild chronic hyponatremia is not benign as previously thought and can directly contribute to increased morbidity and possibly, mortality [13,14]. In the present assessment the incidence and clinical profile of hyponatremia have been probed among a great sample of non-western psychiatric inpatients and compared with the available data in literature regarding prevalence and other associated clinical characteristics.

Methods

Razi psychiatric hospital in south of capital city of Tehran, as one of the largest and oldest public psychiatric hospitals in the Middle East, which has been established formally in 1917 and with a capacity around 1375 active beds, had been selected as the field of study in the present retrospective assessment. For evaluation, all inpatients with idiopathic hyponatremia during the last sixty-four months had been included in the present study. Clinical diagnosis, as well, was in essence based on ‘Diagnostic and Statistical Manual of Mental Disorders, 5^th edition (DSM-5)’ [15].

Statistical Analysis

Analysis of dependent variables had been accomplished by ‘t-test’ and appraisal of independent variables had been explored by means of ‘comparison of proportions’. Statistical significance, as well, had been defined as a p value ≤0.05. MedCalc Statistical Software version 15.2 was used as statistical software tool for analysis.

Results

As said by results, among 20118 psychiatric patients hospitalized in razi psychiatric hospital, during the last sixty-four months (April of 2014-August 2019), eighteen patients had been diagnosed as hyponatremic, whether symptomatic or asymptomatic, during their inpatient treatment, based on laboratory checkups. So, the annual incidence of hyponatremia in the current inpatients’ evaluation was around 0.01%. In spite of referral to intensive care unit and given medical treatment, one elderly chronic female patient died by reason of hyponatremia. Accordingly, in the present survey the annual incidence of mortality because of hyponatremia was around 0.001%. Also, with regard to gender difference and in keeping with results, while there was no significant difference regarding age between male (mean: 43.92±9.51y/o) and female (mean: 52.50±8.34y/o) patients (t = 1.962, p< 0.08, CI 95%: -18.29, 1.13), hyponatremia was significantly more prevalent among male psychiatric inpatients (z= 2.00, p<0.04, CI 95%:0.006, 0.660). besides, concerning chronicity of psychiatric disorders, comparison of proportions showed that hyponatremia was significantly more prevalent among psychiatric patients with duration of illness in excess of one year (p<0.04) (twelve patients in the chronic wards versus six patients in the acute districts of the hospital). Moreover, with respect to prevalence of primary psychiatric disorders among patients, who have experienced hyponatremia during the last 64 months, schizophrenia (n=13) was significantly more prevalent in comparison with remaining disorders [mental retardation (n=1), schizoaffevtive (n=1), bipolar disorder (n=2) and major depressive disorder (n=1)] (z=2.66, p<0.007, CI 95%: -0.11, 0.77). While, eleven patients had different clinical symptoms due to hyponatremia (Table 1), seven cases were asymptomatic, and diagnosis had been confirmed based on merely coincidental checkup. Quantitatively, analysis revealed no significant difference between those groups (z=1.33, p<0.18, CI 95%: -0.54, 0.10). Also, though mean total plasma level of sodium was around 121.72±4.97, there was no significant difference between serum level of sodium in seizure cases (mean total= 119.75±1.29) and non-seizure patients (mean total=122.64±5.06) (t = 1.929, p< 0.28, CI 95%: -6.07, 0.29).

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