- Definition
- A reduction in thyroid hormone levels caused by ingestion of a large amount of iodine.
- Serves as a protective autoregulatory mechanism to prevent the synthesis of excessive amounts of thyroid hormone (T3/T4) in the setting of high iodine load.
- Pathophysiology
- Excess plasma iodide → transient inhibition of thyroid peroxidase (TPO).
- Result: ↓ Organification of iodide (incorporation of iodine into thyroglobulin) → ↓ T3/T4 synthesis.
- Escape Phenomenon: The effect is usually temporary (~10 days). The thyroid “escapes” inhibition by downregulating the Sodium-Iodide Symporter (NIS), thereby decreasing intrathyroidal iodine concentration to allow organification to resume. t
- Outcome: Transient Hypothyroidism (protective mechanism).
- Clinical Associations:
- Amiodarone toxicity (Amiodarone-induced hypothyroidism).
- Treatment for Thyroid Storm (e.g., Lugol’s solution, Potassium Iodide).
- Contrast: Opposite of Jod-Basedow phenomenon (Iodine load → Hyperthyroidism).