Characteristics and outcomes of patients with profound hyponatraemia due to primary polydipsia

Objective: Hyponatraemia due to excessive fluid intake (ie primary polydipsia [PP]) is common. It may culminate in profound hyponatraemia-carrying considerable risk of morbidity. However, data on patients with PP leading to hyponatraemia are lacking. Herein, we describe the characteristics of polydiptic patients hospitalized with profound hyponatraemia and assess 1-year outcomes.

Design: Substudy of the prospective observational Co-MED Study.

Patients: Patients with an episode of profound hyponatraemia (≤125 mmol/L) due to PP in the medical emergency were eligible and classified into psychogenic polydipsia (PsyP), dipsogenic polydipsia (DiP) and beer potomania (BP).

Measurements: Symptoms, laboratory findings and factors contributing to hyponatraemia (comorbidities, medication and liquid intake) were assessed. A 1-year follow-up was performed to evaluate recurrence of hyponatraemia, readmission rate and mortality.

Results: Twenty-three patients were included (median age 56 years [IQR 50-65], 74% female), seven had PsyP, eight had DiP and eight had BP. Median serum sodium of all patients was 121 mmol/L (IQR 114-123), median urine osmolality 167 mmol/L (IQR 105-184) and median copeptin 3.6 mmol/L (IQR 1.9-5.5). Psychiatric diagnoses, particularly dependency disorder (43%) and depression (35%), were highly prevalent. Factors provoking hyponatraemia were found in all patients (eg acute water load, medication, stress). During the follow-up period, 67% of patients were readmitted, 52% of these with rehyponatraemia, and three patients (38%) with BP died.

Conclusion: Patients with PP are more likely to be female and to have addictive and affective disorders. Given the high recurrence, rehospitalization and mortality rate, careful monitoring and long-term follow-up including controls of serum sodium, education and behavioural therapy are needed.