Wolff-Chaikoff block

The thyroid gland also regulates its uptake of iodide and thyroid hormone synthesis by intrathyroidal mechanisms that are independent of TSH. These mechanisms are primarily related to the level of iodine in the blood. Large doses of iodine inhibit iodide organification (Wolff-Chaikoff block, see Figure 38-1). In certain disease states (eg, Hashimoto s thyroiditis), this can inhibit thyroid hormone synthesis and result in hypothyroidism. Hyperthyroidism can result from the loss of the Wolff-Chaikoff block in susceptible individuals (eg, multinodular goiter). 

High doses of iodide can also transiently block thyroid hormone synthesis through inhibition of the organification process. This is known as the Wolff-Chaikoff effect. In certain susceptible individuals the thyroid cannot escape from the transient inhibitory effect of iodide on the organification mechanism. As a result, hypothyroidism may develop after prolonged excess iodide administration. The hypothyroidism is usually transient and thyroid function returns to normal after iodide withdrawal. 

Hypothyroidism induced by iodine is well documented and it has been postulated that is is the iodide ion that is responsible, a phenomenon classically known in the Wolff-Chaikoff effect (37) This blocking effect has been shown to be enhanced by antithyroid antibodies (38,39), antipyrine (40) and lithium (41) The pathogenesis of the clinical entity known as "iodide goiter (37) in which goiter and/or hypothyroidism appears and subsides concomittantly with iodide intake and withdrawal, has been related to the Wolff-Chaikoff effect that had been demonstrated in animal In our laboratory a few cases of iodide goiters were discovered by means of XRF (see example in Fig 3) A correlation could be established between the clinical state of the patient and its TITI, demonstrating the validity of the pathogenic hypothesis Because an important part of iodine ean be washed out by perchlorate in these cases, it has been... 

---