Factitious thyrotoxicosis — SCE Endocrinology MCQ

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HardThyroidFactitious thyrotoxicosisSCE Endocrinology

A 38-year-old man has thyrotoxicosis with TSH <0.01 mU/L and free T4 34 pmol/L. He has no goitre, no eye signs and serum thyroglobulin is undetectable. Radioiodine uptake is very low. What is the most likely diagnosis?

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Correct answer: A — Factitious thyrotoxicosis

Very low uptake with undetectable thyroglobulin suggests exogenous thyroid hormone ingestion. Thyroiditis also has low uptake but thyroglobulin is usually raised because hormone leaks from damaged thyroid tissue. Graves' disease and toxic adenoma usually show increased uptake.

Reference: NICE NG145; Endocrine Society Thyroid Guidance