A 35-year-old woman has palpitations and a 9 kg weight loss over 3 months. Her free thyroxine is 48 pmol/L (reference 10–22 pmol/L), TSH is less than 0.01 mIU/L (reference 0.4–4.0 mIU/L), and radioactive iodine uptake is low. Serum thyroglobulin is undetectable, and she reports taking an over-the-counter thyroid preparation. Which mechanism best explains the biochemical pattern?
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