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Central Diabetes Insipidus — RACP Paediatrics MCQ

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HardEndocrinologyCentral Diabetes InsipidusRACP Paediatrics

A 13-year-old boy presents with excessive thirst and polyuria. He is not diabetic (normal glucose, HbA1c). Serum sodium is 150 mmol/L. Urine osmolality is 80 mOsm/kg (very dilute) despite serum hyperosmolality. After desmopressin administration, urine osmolality rises to 600 mOsm/kg. What is the diagnosis?

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Correct answer: D — Central diabetes insipidus

Central diabetes insipidus (CDI) is characterised by inability to concentrate urine due to ADH deficiency. Serum hyperosmolality with dilute urine confirms diabetes insipidus. A response to exogenous desmopressin (urine osmolality concentrates >50% above baseline) confirms central (not nephrogenic) DI. MRI pituitary is required to exclude an underlying lesion (craniopharyngioma, Langerhans cell histiocytosis).

Reference: RCH Melbourne – 2024 – Clinical Practice Guidelines: Diabetes Insipidus