skip to main content

Hyperprolactinaemia Investigation — MRCPsych Paper B MCQ

Instant feedback + full explanation. One question, done properly.

HardSchizophrenia & PsychosisHyperprolactinaemia InvestigationMRCPsych Paper B

A 36-year-old man with schizophrenia is clinically stable on paliperidone long-acting injection. He reports reduced libido and has gynaecomastia. Two fasting, low-stress samples show monomeric prolactin concentrations of 2400 mU/L and 2520 mU/L. Thyroid, renal and liver function are normal. Paliperidone cannot safely be interrupted to determine whether the prolactin concentration normalises. Which investigation is most appropriate to exclude a structural pituitary cause?

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

Reveal the answer and explanation

Correct answer: B — Dedicated pituitary MRI

The correct answer is B. This patient has persistent, symptomatic monomeric hyperprolactinaemia despite exclusion of hypothyroidism and significant renal or hepatic dysfunction. Paliperidone is a recognised prolactin-raising antipsychotic, but because it cannot safely be withdrawn to demonstrate normalisation, a structural pituitary lesion should be excluded with dedicated pituitary MRI. CT provides poorer soft-tissue and sellar detail and is generally reserved for situations in which MRI is contraindicated. Formal perimetry assesses the functional consequences of a lesion approaching the optic chiasm but cannot exclude a microadenoma. The dexamethasone suppression and insulin tolerance tests assess other hypothalamic-pituitary-adrenal disorders and do not identify a prolactinoma.

Reference: Royal United Hospitals Bath NHS Foundation Trust. Hyperprolactinaemia: A Guide for GPs, Investigations and Management in Primary Care, version 2. 2025. https://www.ruh.nhs.uk/pathology/documents/clinical_guidelines/PATH_026_Hyperprolactinaemia_A_Guide_for_GPs.pdf