Management of psychogenic polydipsia and hyponatremia in an acute mental health unit

To the Editor

Psychogenic polydipsia is a clinical condition characterized by excessive oral fluid intake in the absence of physiologic stimulus to drink. It is a recognised phenomenon in patients with psychiatric disorders (Dundas et al., 2007). The aetiology of psychogenic polydipsia remains unclear. However the complications, which include headaches, visual disturbances, seizures, cerebral oedema, renal failure or congestive heart failure, are mostly due to hyponatremia and can be life threatening (Vieweg et al., 1985). We report a case that highlights the difficulties in managing psychogenic polydipsia and its complications in an acute mental health unit.

A 30 year old male, with a diagnosis of paranoid schizophrenia was admitted to the acute mental health unit with deteriorating mental state in the setting of medication non-compliance. He did not have a previous recorded history of psychogenic polydipsia. Past medical history included a diagnosis of photosensitive epilepsy, and the last seizure was five years ago. His physical examination and investigations on admission were normal, including a serum sodium level of 136mmol/L, a normal CT head scan and urine drug screen. He was treated with risperidone 6mg nocte. During the course of the admission he developed a generalised tonic clonic seizure, lasting for 2 minutes. The sodium level at that time was 122mmol/L. He was clinically euvolemic. His serum osmolality was 259mmol/kg and the urine osmolality was 70mmol/kg with a urine sodium level of <10mmol/L, which excluded the syndrome of inappropriate antidiuretic hormone hypersecretion as a cause for hyponatremia. The serum cortisol and thyroid function tests were normal. Retrospectively staff had noticed him to be drinking increasing amounts of fluids during the admission. A diagnosis of psychogenic polydypsia induced hyponatremia was made and fluid restriction of two litres per day was started.

Despite repeated instructions, he continued to drink fluids from the patients’ kitchen area and also from the bathroom taps, and required to be transferred to the psychiatric intensive care unit (ICU) for closer supervision. He required intensive one-on-one staffing and constant monitoring of his fluid intake in order to maintain strict fluid restriction. All cups had to be removed from the patients’ kitchen areas and rubbish bins had to be emptied of used cups and containers to prevent him from drinking excessive water. Fluid balance charts, staff education of the importance of fluid restriction and development of individualised strategies to maintain fluid restriction with the input from the charge nurse and nurse specialists were required. On day one after initiation of fluid restriction, his serum sodium improved to 127mmol/L and on day two it was 128mmol/L. On day four, the serum sodium normalised to 135mmol/L. Strict monitoring and 14 days of ICU admission was required to regulate his fluid intake and ensure serum sodium levels were within normal limits. As his mental state improved, his fluid intake also improved.

This case highlights the difficulties of managing psychogenic polydipsia in patients who are acutely unwell with low levels of insight. The treatment requires multidisciplinary approach using fluid restriction, behavioural and pharmacological modalities (Verghese et al., 1996). The case also shows that even mild to moderate hyponatremia may be sufficient to trigger seizures in a patient with an underlying seizure disorder who is also on antipsychotic medication, which are known to lower the seizure threshold (Okazaki et al., 2007; Haddad et al., 2008). The prevalence of polydipsia has been reported to be up to 20% of patients with chronic schizophrenia (De Leon et al., 1994). Therefore it is important to recognise this condition early and develop individualised management strategies for patients in acute mental health units.