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TSH-secreting pituitary adenoma — SCE Endocrinology MCQ

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HardThyroidTSH-secreting pituitary adenomaSCE Endocrinology

A 45-year-old man has headaches and sweating. Thyroid tests show TSH 5.2 mU/L, free T4 34 pmol/L and free T3 9.1 pmol/L on repeat testing. Alpha-subunit is elevated and pituitary MRI shows a 12 mm sellar lesion. What is the most likely diagnosis?

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Correct answer: C — TSH-secreting pituitary adenoma

Inappropriately non-suppressed TSH with high thyroid hormones and raised alpha-subunit plus pituitary macroadenoma strongly suggests TSHoma. Thyroid hormone resistance can look similar biochemically but usually lacks a raised alpha-subunit and pituitary mass effect. The pearl is to repeat tests and consider assay interference before definitive localisation.

Reference: Society for Endocrinology pituitary guidance, NICE NG145