22nd May 2025

You are asked to review an 84-year-old gentleman by nursing staff as the laboratory has rang the ward demonstrating one of your patient’s has a serum sodium of 123 mmol/L.

You are asked to review an 84-year-old gentleman by nursing staff as the laboratory has rang the ward  demonstrating one of your patient’s has a serum sodium of 123 mmol/L. His serum osmolality is reduced at 250 mOsmol/Kg.  This patient was admitted 2 weeks earlier with a new diagnosis of small cell lung cancer. On assessment he is noted to be euvolaemic and is clinically stable.

Which of the following is not a cause of euvolaemic hyponatraemia?