Endocrine Abstracts

Inroduction: Polydipsia -excessive oral intake of liquids, with/without thirst- can induce euvolemic hyponatremia. Adequate inhibition of AVP secretion induced by low plasma osmolality (POsm) is reflected in a urinary osmolality (UOsm) ≤100 mOsm/kg. However, increased fluid intake can also reveal underlying non-osmotic AVP secretion, induced by pain, nausea, and/or SIADH, with UOsm >100. Iatrogenic polydipsia is characterized by increased liquid intake without thirst, following the recommendations of health professionals. Polydipsia can also be secondary to increased fluid intake to correct dryness of the mouth. Primary care in Madrid recommends a minimum water intake of 2–3 liters daily for adults during summer months, to avoid dehydration - characterized by hypernatremia. We describe cases in which patients presented marked hyponatremia induced by increased fluid intake.

Methods: Retrospective analysis of 22 adult patients presenting euvolemic hyponatremia associated with elevated fluid intake, attended in Endocrinology of a general hospital in Madrid over 12 months. Initial Nadir serum sodium (SNa)-associated POsm was available in 20/22, initial urinary electrolytes and urine osmolality in 9/22, Creatinine in 22/22, GFR/MDRD-4 in 20/22. All presented normal cortisol and thyroid hormone levels. Sodium in mmol/L, Osm in mOsm/kg. SPSS 25.

Results: 12/22 were women. Age: 74.5(IQR:73) Median fluid intake: 3250 ml(IQR:4400). 12/22 episodes were during the summer. In 7/22 increased fluid intake was induced by specific recommendations of health care professionals, another 7 by health campaigns, 3 by dryness of the mouth. Two patients presenting UOsm≤100 were diagnosed with primary polydipsia. 19/21 presented UOsm> 100: 6/19 with nausea/pain, 13/19 SIADH. 3 patients required initial 3% hypertonic saline therapy. Four SIADH patients required tolvaptan treatment to normalize SNa. The rest responded to ‘fluid hygiene’: drinking/swallowing only when thirsty. 21/21 patients with prior SNa available had presented previous hyponatremic episodes: SNa 130(IQR:1). In one patient UOsm was unavailable, making diagnosis impossible.

Conclusions: Polydipsia can induce marked hyponatremia, is often iatrogenic, and can reveal underlying SIADH. In this series, all patients with available SNa records had presented prior episodes of hyponatremia. Physicians must be cautious when recommending drinking without thirst to patients with a prior history of hyponatremia, even in hot, dry climates.