Central Diabetes Insipidus — ESENeph MCQ

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ModerateElectrolyte DisordersCentral Diabetes InsipidusESENeph

A 35-year-old man presents with a serum sodium of 158 mmol/L. He has polyuria (6 L/day) and polydipsia. Urine osmolality is 85 mOsm/kg (dilute). After administration of Desmopressin, urine osmolality increases to 650 mOsm/kg. What is the diagnosis?

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Correct answer: D — Central (cranial) diabetes insipidus

Dilute urine (osmolality <300 mOsm/kg) in the context of hypernatraemia indicates diabetes insipidus. The response to Desmopressin (a V2 receptor agonist) differentiates central from nephrogenic DI. A significant increase in urine osmolality (>50% or >600 mOsm/kg) confirms central DI (the kidneys respond to ADH but the pituitary is not producing enough). In nephrogenic DI, the kidneys fail to respond to Desmopressin. Primary polydipsia shows dilute urine but normal serum sodium.

Reference: Bichet 2019 – Diabetes Insipidus Review; Spasovski et al 2014