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Psychogenic Polydipsia — MRCPsych Paper B MCQ

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HardSchizophrenia & PsychosisPsychogenic PolydipsiaMRCPsych Paper B

A 48-year-old man with schizophrenia and established psychogenic polydipsia is found confused on a psychiatric ward and has a generalised tonic-clonic seizure. His serum sodium is 118 mmol/L, and the duration of the hyponatraemia is uncertain. Initial ABC measures have been instituted, capillary glucose is normal, and the seizure has terminated following intravenous lorazepam. What is the immediate next management priority?

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Correct answer: C — Activate emergency medical transfer for monitored hypertonic saline treatment

This is severe symptomatic hyponatraemia causing hyponatraemic encephalopathy. Confusion and a seizure at a sodium concentration of 118 mmol/L require an emergency medical response, transfer to a closely monitored acute-care environment, and senior-led hypertonic saline treatment. Treatment aims for a small initial sodium rise sufficient to reverse neurological symptoms, with frequent monitoring because excessive correction can cause osmotic demyelination. Fluid restriction is part of subsequent management of psychogenic polydipsia but is inadequate as sole treatment during seizures or encephalopathy. Increasing the antipsychotic dose does not treat the immediate emergency. Demeclocycline has no role in acute resuscitation and is principally associated with selected chronic SIADH management. Desmopressin is not initial treatment; specialists may use it if rapid spontaneous overcorrection develops.

Reference: Royal Devon University Healthcare NHS Foundation Trust. Emergency Management of Severe Hyponatraemia Pathway, v1.1, sections on indications, administration and monitoring; approved 2023. https://www.royaldevon.nhs.uk/media/sxidezst/emergency-mmnagement-ofsevere-hyponatraemia-pathway_final301123_redacted.pdf