Iodine-induced hyperthyroidism prevention

Dunn JT, Semigran MJ, Delange F. The prevention and management of iodine-induced hyperthyroidism and its cardiac features. Thyroid 1998 8(1) 101—6. 

The beneficial effects of iodine supplementation in the prevention and control of developed thyroid abnormalities due to iodine deficiency have been discussed so far in this chapter. However, supplementation with excess iodine, including the improvement of a previous iodine-deficient state, may cause thyroid dysfunctions, viz., iodine-induced hypothyroidism/iodide goiter in susceptible subjects (Roti and Vagenakis, 2000) and iodine-induced hyperthyroidism (IIH) especially in individuals over 40 years of age and who have been iodine deficient for a long period in the past (Vidor et ai, 1973). It may also increase the ratio of papillary/follicular carcinomas (Slowinska-Klencka et ai, 2002). In other words, both low and excess intake of iodine is related to further risk of thyroid disease. Although a daily intake of up to 1000 pg/day by a normal adult individual is quite safe (WHO, 1994), the upper limit is much lower in a population that has been exposed to iodine deficiency in the past. Therefore, to prevent IDD, the recommended iodine requirement in an adult individual is fixed within a narrow range of 150 rg/day (Knudsen et ai, 2000). Iodine supplementation under certain conditions in certain populations causes adverse effects, e.g., iodide goiter and iodine-induced hypothyroidism, IIH, iodine-induced thyroiditis and thyroid cancer. 

For the prevention or treatment of iodine-induced hyperthyroidism, a thionamide drug may be combined with perchlorate (3 X 300 mg/day for 7—14 days), an iodine uptake blocking agent. 

Another important group, the National IDD Advisory Committee (NIDDAC) chaired by Professor Chen Zupei, has played a crucial role in the national program. Under the leadership of the MOH, NIDDAC provides scientific and technical guidefines, standards and recommendations. It also provides evidence for poficy development (IDD Newsletter, 1998). Since 1993 NIDDAC has re-evaluated and standardized the measmement of thyroid gland size by palpation and ultrasound standardized urinary iodine testing methods. It has also evaluated the technical aspects and the application of neonatal TSH in IDD monitoring, iodine excess and excessive dietary iodine-induced goiter, and the role of iodized oil in the prevention and control of IDD and iodine-induced hyperthyroidism (Chen, 2002). 

Frequency, Pathogenesis, Prevention and Treatment of Iodine-Induced Hyperthyroidism... 

Hermida JS, Jarry G, Tcheng E, Moullart V, Arlot S, Rey JL, Schvartz C. Prevention des recidives d hyperthyroidie a l amiodarone par l iodel31. [Prevention of recurrent amiodarone-induced hyperthyroidism by iodine-131.] Arch Mai Coeur Vaiss 2004 97(3) 207-13. 

Prophylactic iodization may be effective in preventing iodine-induced thyroid dysfunction in iodine-deficient areas. However, iodine prophylaxis itself can cause hyperthyroidism, especially in older individuals (Fradkin and Wolff 1983 Roti and degli Uberti, 2001). Thus, prophylaxis must be carefully designed, if iodization is initiated. 

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