A healthy adult ingests a large single dose of iodide. Within hours, thyroid hormone synthesis falls sharply even though serum TSH is unchanged. This transient suppression, which escapes spontaneously after days of continued iodide exposure, is called the:

• A Jod-Basedow phenomenon
• B Hershberger effect
• C Plummer effect
• D Wolff-Chaikoff effect ✓

Explanation

Acute iodide excess transiently inhibits thyroid peroxidase-mediated organification and coupling, reducing hormone synthesis; this autoregulatory Wolff-Chaikoff effect protects against iodide-induced thyrotoxicosis. After several days the thyroid escapes by downregulating the sodium-iodide symporter, restoring normal synthesis. The Jod-Basedow phenomenon is the opposite event: iodide-induced hyperthyroidism in glands with autonomous function such as nodular goiter. Plummer refers to toxic autonomous nodules, not acute iodide blockade.

Reference: Williams Textbook of Endocrinology, 14th ed.

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