Two weeks after receiving iodinated contrast for a CT scan, a 70-year-old woman with a long-standing multinodular goitre presents with tremor, weight loss and new-onset atrial fibrillation. Free T4 is elevated and radioiodine uptake is heterogeneous. The mechanism responsible is:

• A Autonomous hormone synthesis by nodular tissue in response to the sudden iodine load ✓
• B Transient inhibition of thyroid hormone release by high intrathyroidal iodide
• C TSH receptor-stimulating antibodies triggered by the contrast agent
• D Granulomatous destruction of follicles releasing preformed hormone

Explanation

This is the Jod-Basedow phenomenon: autonomous nodules escape normal autoregulation and use the large iodine load to synthesise and secrete excess hormone, causing iodine-induced thyrotoxicosis. Option B describes the Wolff-Chaikoff effect, an opposite protective fall in hormone synthesis. Stimulating antibodies indicate Graves disease, and granulomatous follicle destruction with a painful neck indicates subacute thyroiditis, neither of which fits this history.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.