Which scenario exemplifies the Jod-Basedow phenomenon?

• A. Hyperthyroidism triggered by excess iodine intake in susceptible individuals
• B. Hypothyroidism triggered by iodine deficiency
• C. No relation to iodine intake
• D. It is the same as Wolff-Chaikoff effect

Answer: (A)

Jod-Basedow is iodine-induced hyperthyroidism that occurs when a person has autonomous thyroid tissue (such as nodular goiter or Graves’–type tissue) and then receives an excess iodine load. In iodine-deficient individuals, the thyroid can become nodular and gain the ability to take up iodine and synthesize thyroid hormone independently of normal regulatory controls. When a large amount of iodine becomes available—through iodinated contrast, iodine-rich supplements, or dietary iodine—these autonomous areas ramp up hormone production, leading to thyrotoxicosis. This is why hyperthyroidism triggered by excess iodine in susceptible individuals is the classic scenario for Jod-Basedow. It’s not about iodine deficiency causing hypothyroidism, it’s not a scenario with no iodine effect, and it’s not the Wolff-Chaikoff effect (which is an initial, usually temporary suppression of thyroid hormone synthesis in response to high iodine that can “escape” in normal glands).