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Central diabetes insipidus — RACP Paediatrics MCQ

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ModerateEndocrineCentral diabetes insipidusRACP Paediatrics

A 5-year-old presents with polyuria (5 L/day), polydipsia, and nocturia. Blood glucose is normal. Serum osmolality is elevated (305 mOsm/kg) and urine osmolality is inappropriately dilute (120 mOsm/kg). After DDAVP administration, urine osmolality rises to 650 mOsm/kg. MRI shows absence of the posterior pituitary bright spot. What is the most likely diagnosis?

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Correct answer: B — Central diabetes insipidus

Elevated serum osmolality with inappropriately dilute urine that concentrates after DDAVP indicates central (cranial) diabetes insipidus. Loss of the posterior pituitary bright spot on MRI is characteristic. Causes include idiopathic, CNS tumours (craniopharyngioma, germinoma, LCH), post-neurosurgery, and infiltrative disease. Desmopressin (DDAVP) is the treatment.

Reference: RCH Melbourne – 2023 – Diabetes Insipidus CPG; RACP Paediatric Curriculum – Endocrine