Extreme hyponatraemia due to primary polydipsia and quetiapine-induced SIAD

Summary Hyponatraemia is the most common electrolyte disturbance in hospitalised patients and is associated with numerous adverse outcomes. Patients with schizophrenia are particularly susceptible to hyponatraemia, in part due to the close association between this condition and primary polydipsia. We report the case of a 57-year-old woman with schizophrenia and primary polydipsia who was receiving inpatient psychiatric care. She became increasingly confused, had multiple episodes of vomiting, and collapsed 1 week after being commenced on quetiapine 300 mg. On examination, she was hypertensive and her Glasgow coma scale was nine. She had a fixed gaze palsy and a rigid, flexed posture. Investigations revealed extreme hyponatraemia with a serum sodium of 97 mmol/L. A CT brain demonstrated diffused cerebral oedema with sulcal and ventricular effacement. A urine sodium and serum osmolality were consistent with SIAD, which was stimulated by the introduction of quetiapine. The antidiuretic effect of vasopressin limited the kidney’s ability to excrete free water in response to the patients' excessive water intake, resulting in extreme, dilutional hyponatraemia. The patient was treated with two 100 mL boluses of hypertonic 3% saline but deteriorated further and required intubation. She had a complicated ICU course but went on to make a full neurological recovery. This is one of the lowest sodium levels attributed to primary polydipsia or second-generation antipsychotics reported in the literature. Learning points The combination of primary polydipsia and SIAD can lead to a life-threatening, extreme hyponatraemia. SIAD is an uncommon side effect of second-generation anti-psychotics. Serum sodium should be monitored in patients with primary polydipsia when commencing or adjusting psychotropic medications. Symptomatic hyponatraemia is a medical emergency that requires treatment with boluses of hypertonic 3% saline. A serum sodium of less than 105 mmol/L is associated with an increased risk of osmotic demyelination syndrome, therefore the correction should not exceed 8 mmol/L over 24 h.

GLP1 Receptor Agonists Reduce Fluid Intake in Primary Polydipsia

Background Primary polydipsia, characterized by excessive fluid intake, carries the risk of water intoxication and hyponatremia, but treatment options are scarce. Glucagon-like peptide-1 (GLP-1) reduces appetite and food intake. In experimental models, they also play a role in thirst and drinking behavior in. The aim of this trial was to investigate whether GLP-1 receptor agonists reduce fluid intake in patients with primary polydipsia. Methods: In this randomized, double-blind, placebo-controlled, 3-week crossover-trial, 34 patients with primary polydipsia received weekly dulaglutide (Trulicity®) 1.5mg and placebo (0.9% sodium chloride). During the last treatment week, patients attended an 8-hour evaluation visit with free water access. The primary endpoint was total fluid intake during the evaluation visits. The treatment effect was estimated using a linear mixed-effects model. In a subset of 15 patients and matched controls, thirst perception and neuronal activity in response to beverage pictures were assessed by functional MRI. Results Median [IQR] total fluid intake was 2250ml [1600-2600] on dulaglutide versus 2400ml [1850-3400] on placebo. Patients on dulaglutide reduced fluid intake by 490ml [95%-CI -780, -199], p=0.002, corresponding to a relative reduction of 17%. 24-hour urinary output was reduced by -943ml [95%-CI -1473, -413]. Thirst perception in response to beverage pictures was higher in patients with primary polydipsia versus controls and lower on dulaglutide versus placebo, but functional neuronal activity was similar between groups and treatments. Conclusion: GLP-1 receptor agonists reduce fluid intake and thirst perception in patients with primary polydipsia and could therefore be a novel treatment option for these patients.

A Subset of Primary Polydipsia, “Dipsogneic Diabetes Insipidus”, in Apparently Healthy People Due to Excessive Water Intake: Not Enough Light to Illuminate the Dark Tunnel

Dipsogenic diabetes insipidus (DDI) is a subtype of primary polydipsia (PP), which occurs mostly in healthy people without psychiatric disease. In contrast, PP is characterized by a polyuria polydipsia syndrome (PPS) associated with psychiatric illness. However, the pathogenesis of DDI is not well established and remains unexplored. In order to diagnose DDI, the patient should exhibit excessive thirst as the main symptom, in addition to no history of psychiatric illness, polyuria with low urine osmolality, and intact urine concentrating ability. Treatment options for DDI remain scarce. On this front, there have been two published case reports with successful attempts at treating DDI patients. The noteworthy commonalities in these reports are that the patient was diagnosed with frequent excessive intake of water due to a belief that drinking excess water would have pathologic benefits. It could therefore be hypothesized that the increasing trend of excessive fluid intake in people who are health conscious could also contribute to DDI. Hence, this review provides an overview of the pathophysiology, diagnosis, and treatment, with a special emphasis on habitual polydipsia and DDI.

Incidence of hyperkalemia during hypertonic saline test for the diagnosis of diabetes insipidus

Objective Hyperkalemia has been reported upon different hypertonic saline infusion protocols. Since hypertonic saline test has recently been validated for the differential diagnosis of diabetes insipidus (DI), we aimed to investigate the course of plasma potassium during the test. Design We analyzed data of 90 healthy volunteers and 141 patients with polyuria–polydipsia syndrome (PPS) from two prospective studies evaluating the hypertonic saline test. Our primary outcome was the incidence rate of hypertonic saline-induced hyperkalemia > 5 mmol/L. Methods Participants received a 250 mL bolus of 3% NaCl solution, followed by 0.15 mL/min/kg body weight continuously infused targeting a plasma sodium level of 150 mmol/L. Blood samples and clinical data were collected every 30 min. Results Of the 231 participants, 16% (n = 37/231) developed hyperkalemia. The incidence of hyperkalemia was higher in healthy volunteers and in patients with primary polydipsia (25.6% (n = 23/90) and 9.9% (n = 14/141), respectively), and only occurred in 3.4% (n = 2/59) of patients with diabetes insipidus. Hyperkalemia developed mostly at or after 90-min test duration (81.1%, n => 30/37). Predictors of hyperkalemia (OR (95% CI)) were male sex (2.9 (1.2–7.4), P => 0.02), a plasma potassium at baseline > 3.9 mmol/L (5.2 (1.8–17.3), P => 0.004), normonatremia at 30-min test duration (3.2 (1.2–9.5), P => 0.03), and an increase in potassium levels already at 30-min test duration as compared to baseline (4.5 (1.7–12.3), P => 0.003). Hyperkalemia was transient and resolved spontaneously in all cases. Conclusion The hypertonic saline test can lead to hyperkalemia, especially in patients with primary polydipsia who experience a longer test duration. Monitoring potassium levels in these patients is recommended.