Hyponatremia due to preserved non-osmotic arginine vasopressin secretion in adipsic diabetes insipidus: a case report with review of literature

Abstract

Adipsic diabetes insipidus (ADI) is characterized by central diabetes insipidus and an impaired thirst response to hyperosmolality, leading to hypernatremia. Hyponatremia observed in patients with ADI has been considered a complication of desmopressin therapy. Herein, we present a case of impaired thirst sensation and arginine vasopressin (AVP) secretion without desmopressin therapy, in which hyponatremia developed due to preserved non-osmotic AVP secretion. A 53-year-old woman with hypopituitarism, receiving hydrocortisone and levothyroxine, experienced hyponatremia three times over 5 months without desmopressin treatment. The first hyponatremic episode (120 mEq/L) was complicated by a urinary tract infection with a plasma AVP level of 33.8 pg/mL. Subsequent hyponatremia episodes occurred after administration of antipsychotic (124 mEq/L) and spontaneously (125 mEq/L) with unsuppressed plasma AVP levels (1.3 and 1.8 pg/mL, respectively). Hypertonic saline infusion did not affect AVP or copeptin levels. Regulating water intake using a sliding scale based on body weight prevented the recurrence of hyponatremia without the use of desmopressin. Except during infection, plasma AVP levels (1.3 ± 0.4 pg/mL) were not significantly correlated with serum sodium levels (r_s = -0.04, p = 0.85). In conclusion, we present a unique case of impaired thirst sensation and AVP secretion in which hyponatremia developed without desmopressin therapy. Preserved non-osmotic AVP secretion, possibly stimulated by glucocorticoid deficiency, may contribute to the development of hyponatremia in patients with ADI.

Keywords: Copeptin; Desmopressin; Hypopituitarism; Syndrome of inappropriate antidiuresis (SIAD).

Fig. 1. Serum sodium and plasma arginine vasopressin (AVP) levels and water intake

Serum sodium level (closed circles and lines) fluctuations during treatment. In contrast, plasma AVP levels (open triangles and dotted lines) were primarily low and detectable, except at one point (bottom graph). The patient had free access to drinking water, and the water intake was approximately 500–1,500 mL/day before day 115 (top graph). *Missing values. Abbreviation: AVP, arginine vasopressin. IV, intravenous.

Fig. 2. Association between plasma arginine vasopressin (AVP) and serum sodium levels

Except at one point, plasma AVP levels were low and detectable, regardless of serum sodium levels. Abbreviation: AVP, arginine vasopressin.