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Syndrome of inappropriate antidiuresis — SCE Acute Medicine MCQ

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EasyAcute Renal and Metabolic EmergenciesSyndrome of inappropriate antidiuresisSCE Acute Medicine

A 73-year-old man presents with vomiting, weakness, confusion or collapse. Relevant history includes diabetes, kidney disease, endocrine disease or a treatment trigger. On assessment, volume status and bedside physiology are abnormal. Investigations show euvolaemic hypotonic hyponatraemia with high urine sodium after carbamazepine. What is the most likely underlying cause/mechanism?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Inappropriate antidiuretic hormone activity causing impaired free-water excretion

The key discriminator is that euvolaemic hypotonic hyponatraemia with high urine sodium after carbamazepine, which makes Inappropriate antidiuretic hormone activity causing impaired free-water excretion the single best answer. Adrenal steroid deficiency is less appropriate because it does not address the dominant acute risk in the vignette; Portal hypertensive bleeding would fit a different presentation or later stage of care. Oxygen supply-demand mismatch and Impaired free-water excretion from ADH activity are suboptimal because they would either delay time-critical treatment or follow the wrong acute pathway. Teaching point: SCE-style acute medicine questions usually test prioritisation using physiology, timing and a guideline-defined threshold, rather than isolated factual recall.

Reference: Society for Endocrinology hyponatraemia guidance