A patient receives a large dose of iodinated contrast dye for a CT scan. Within hours, serum T4 and T3 fall slightly and remain low for several days before recovering spontaneously. Which phenomenon explains this transient fall?
- A Jod-Basedow phenomenon, iodide-triggered hormone overproduction followed by depletion
- B Wolff-Chaikoff effect, acute iodide-induced inhibition of organification ✓
- C Permanent destruction of thyroid peroxidase by iodide radicals
- D Downregulation of the sodium-iodide symporter leading to glandular atrophy
Correct answer: B. Wolff-Chaikoff effect, acute iodide-induced inhibition of organification
Explanation
An abrupt rise in intrathyroidal iodide transiently inhibits thyroid peroxidase-mediated organification and coupling, and also reduces hormone release, lowering T4 and T3. In normal glands this Wolff-Chaikoff effect escapes within days as iodide transport downregulates. The Jod-Basedow phenomenon is the opposite response, where iodide induces hormone overproduction in autonomous thyroid tissue. The recovery here is spontaneous and complete, excluding permanent enzyme destruction.
Reference: Ganong's Review of Medical Physiology, 26th ed.
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