Iodine-induced hyperthyroidism antithyroid drugs

Blockers are usually used as adjunctive therapy with antithyroid drugs, RAI, or iodides when treating Graves disease or toxic nodules in preparation for surgery or in thyroid storm. /3-Blockers are primary therapy only for thyroiditis and iodine-induced hyperthyroidism. 

Hyperthyroidism and toxicity Iodine-induced hyperthyroidism A mild increase in the incidence of hyperthyroidism worldwide has been described following iodized salt programs (Connolly et al. 1970, Stewart et al. 1971, Bauch 1985, Koutras etal. 1999, Joseph 1989, Meng etal. 1989, Lobbers etal. 1989, Pickardt 1989). Joseph et al. (1980) reported that iodine intakes of < 100 xg per day pose no risk for patients with autonomous tissue due to iodine deficiency critical amounts are between 100 and 200 jg I per day. The absence of iodine deficiency in the Japanese population accounts for the absence of iodine-induced thyrotoxicosis (Nagataki 1987). Hyperthyroidism is easily controlled with antithyroid drugs. 

The main use of antithyroid drugs in toxic adenoma and toxic multinodular goiter is therefore to attain a euthyroid state before the patient may undergo other modes of therapy. Another use is to block iodine uptake prior to the exposure to radiographic contrast agents in patients at risk of iodine-induced hyperthyroidism. 

Color-flow Doppler sonography can be of use in distinguishing the two types, because type 1 is associated with increased vascularity and type 2 is not. In a retrospective study of 24 patients with amiodarone-induced hyperthyroidism in an iodine-replete environment, 13 had little or no vascularity, of whom seven were prednisolone-responsive of 11 patients with increased vascularity, four responded to antithyroid drugs alone and only one of seven responded to prednisolone (37). Euthyroidism was achieved twice as rapidly in patients with low vascularity than in those with increased vascularity. Thus, responsiveness to prednisolone was not consistently predicted by lack of vascularity, but the presence of flow appeared to correlate with non-responsiveness to prednisolone. 

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