The Wolff-Chaikoff effect is a clinically important phenomenon in thyroid physiology. It refers to:

• A Iodine deficiency causing thyroid hypertrophy via TSH-mediated RAIU increase
• B Chronic iodine excess causing thyrotoxicosis (Jod-Basedow phenomenon)
• C Iodine-induced autoimmune thyroiditis (Hashimoto's) exacerbation
• D Acute high-dose iodine load transiently inhibiting thyroid hormone synthesis by blocking organification ✓

Explanation

When the thyroid gland is acutely exposed to a large iodine load (e.g., contrast media, amiodarone, Lugol's iodine), the organification of iodine is transiently blocked — the Wolff-Chaikoff effect. This is mediated by inorganic iodide accumulating intracellularly and inhibiting thyroid peroxidase (TPO)-mediated iodide oxidation and MIT/DIT coupling. Normally, the gland 'escapes' this block within 1–2 weeks as iodide transport downregulates. The Wolff-Chaikoff effect is exploited clinically with Lugol's iodine to prepare hyperthyroid patients for surgery or to block thyroid hormone synthesis in thyroid storm.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.