A patient with Graves disease is started on a large dose of Lugol iodine before surgery, and thyroid hormone levels fall within days. Which phenomenon explains this acute fall?

• A Wolff-Chaikoff effect ✓
• B Jod-Basedow phenomenon
• C Escape from autoregulation
• D TSH surge from iodide loading

Explanation

An acute rise in intrathyroidal iodide transiently inhibits thyroid peroxidase-mediated organification and hormone synthesis, an autoregulatory response called the Wolff-Chaikoff effect. This underlies the use of iodine before thyroidectomy to reduce gland vascularity and hormone output. The Jod-Basedow phenomenon is the opposite event, where excess iodide induces thyrotoxicosis in susceptible glands such as multinodular goiter.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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