The occurence of hypehyroidism following administration of supplemental iodine to subjects in endemic area of iodine deficiency is due to ?
**Core Concept**
The development of hyperthyroidism in individuals with iodine deficiency after receiving supplemental iodine is a classic example of the Wolff-Chaikoff effect and its subsequent rebound phenomenon. This condition is also known as iodine-induced thyrotoxicosis.
**Why the Correct Answer is Right**
In individuals with iodine deficiency, the thyroid gland adapts to the low iodine levels by increasing the production of thyroid-stimulating hormone (TSH) and reducing the expression of the sodium-iodide symporter (NIS) on the thyroid follicular cells. When supplemental iodine is administered, it initially inhibits the enzyme thyroid peroxidase (TPO), leading to a temporary decrease in thyroid hormone synthesis (Wolff-Chaikoff effect). However, as the body adapts to the increased iodine levels, the expression of NIS is upregulated, and thyroid hormone production resumes, often resulting in an overproduction of thyroid hormones, leading to hyperthyroidism.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the pathophysiology of iodine-induced hyperthyroidism.
**Option B:** This option is incorrect because it does not address the underlying mechanism of the Wolff-Chaikoff effect and its rebound phenomenon.
**Clinical Pearl / High-Yield Fact**
It is essential to note that the risk of iodine-induced hyperthyroidism is higher in individuals with pre-existing thyroid autoimmunity, such as Graves' disease, and in those with a history of thyroid surgery or radiation exposure.
**Correct Answer:** C. The rebound phenomenon after the initial Wolff-Chaikoff effect leads to an overproduction of thyroid hormones, resulting in hyperthyroidism.