Dual Aetiology of Diabetes Insipidus in Pregnancy: Vasopressinase-Mediated and Central Mechanisms.

Diabetes insipidus (DI) is a heterogeneous disorder characterised by polyuria and polydipsia due to impaired arginine vasopressin (AVP) secretion or action. We describe a 36-year-old pregnant woman who presented at 28 weeks' gestation with weakness, severe hypokalaemia from renal potassium wasting, hypernatraemia and polyuria with dilute urine. Vasopressinase-mediated DI was suspected; there was no response to AVP, but desmopressin (dDAVP) produced a rapid clinical improvement, confirming the diagnosis. However, postpartum recurrence of symptoms prompted further evaluation, with imaging suggestive of lymphocytic infundibuloneurohypophysitis, necessitating reinitiation of dDAVP. This case highlights the diagnostic complexity of DI in pregnancy and the need to remain vigilant for central causes, even when vasopressinase-mediated DI is initially suspected.