Endocrine Abstracts

Background

The pathophysiology of primary polydipsia, a disorder with increased fluid intake, is poorly understood. A dysregulation in the hypothalamic-pituitary-adrenal axis (HPA) is speculated and arises mainly from research in patients witch a schizophrenia spectrum disorder but data is contradictory. The aim of this study was to investigate markers of HPA axis activity in patients with primary polydipsia compared to healthy controls.

Methods

In this exploratory analysis data from 34 patients with primary polydipsia and 20 healthy volunteers of two different prospective studies with the same study design were combined. The main outcomes were differences in circadian rhythm of serum and salivary cortisol, 24-hour urinary free cortisol, and cortisol levels before and after ACTH stimulation between patients with primary polydipsia and healthy volunteers.

Results

34 patients with primary polydipsia (68% female) aged 29.5 years (IQR 26.0, 38.8) with a median body mass index (BMI) of 23.1 kg/m² (IQR 20.7, 25.5) were included in the analysis. Circadian rhythms of serum cortisol levels (P = 0.9), urinary free cortisol levels (P = 0.17), and serum cortisol upon ACTH stimulation (P = 0.77) were similar between patients with primary polydipsia and healthy volunteers. Circadian rhythms of salivary cortisol levels were significantly lower in patients with primary polydipsia as compared to healthy volunteers with an estimated difference of –3.7 nmol/l (95%-CI –5.5, –1.8 nmol/l, P = < 0.001).

Conclusion

Our results suggest no difference in HPA axis activity between patients with primary polydipsia and healthy volunteers. The observed difference in salivary cortisol levels may be linked to the increased amount of water consumed by patients with primary polydipsia rather than altered stress response. Our results improve the psychopathological understanding increased fluid intake.