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ICI Diabetes Insipidus Hypernatraemia — SCE Medical Oncology MCQ

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HardLung CancerICI Diabetes Insipidus HypernatraemiaSCE Medical Oncology

A 60-year-old man with NSCLC on pembrolizumab + chemotherapy develops immune-related diabetes insipidus. His serum sodium is 155 mmol/L. He is polyuric (6 L/day). Urine osmolality is 95 mOsm/kg. What immediate treatment is needed?

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Reveal the answer and explanation

Correct answer: A — Desmopressin (DDAVP) and free water replacement — central diabetes insipidus from posterior pituitary/stalk hypophysitis causes inability to concentrate urine, leading to hypernatraemia and dehydration

ICI-induced central diabetes insipidus (from posterior pituitary/infundibular hypophysitis) presents with polyuria, polydipsia and hypernatraemia (serum Na >145). Unlike SIADH (hyponatraemia), DI causes hypernatraemia from inability to concentrate urine (low urine osmolality despite high serum osmolality). Treatment: desmopressin (DDAVP) intranasal/SC replaces ADH function, plus free water replacement (NOT normal saline, which worsens hypernatraemia). ICI should be held. Anterior pituitary function must also be assessed.

Reference: ESMO 2024 irAE Management; BNF Desmopressin