Distribution and Administration of Potassium Iodide in the Event of a Nuclear Incident (2004) / Chapter Skim
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2 Thyroid Physiology
2 Thyroid Physiology
Pages 14-29
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From page 14... ...
and triiodothyronine (T3) are necessary for growth and development and they stimulate all aspects of cell metabolism, including protein synthesis and oxygen consumption.
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From page 15... ...
T3 binds to T3 nuclear receptors in the cells of the peripheral tissues and stimulates a wide variety of genomic events that result in enhanced protein synthesis and increased metabolism. Central nervous system control of thyroid function resides in the anterior hypothalamus, which synthesizes and secretes a tripeptide, thyrotropin-releasing hormone (TRH)
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From page 16... ...
Abnormalities in thyroid function may be mild and are usually diagnosed on the basis of low or high serum TSH and normal circulating free T4 and T3 concentrations; again, this emphasizes the use of serum TSH in diagnosing thyroid dysfunction. Physiologic Need for Iodine and Sources of iodine It has been recognized for more than 50 years that iodine is an essential component of the thyroid hormones, T4 and T3, and that severe iodine deficiency (less than 50 fig iodine intakes daily)
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From page 17... ...
- 7 . ~ The thyroid responds to dietary iodine deficiency by enlarging and more actively transporting iodine from the blood, thereby concentrating sufficient iodine to maintain normal function.
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iodine into the thyroid. Thyroid radioiodine uptake is elevated in patients with hyperthyroidism, is usually low in hypothyroid patients, and varies inversely with iodine intake.
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Large doses of AT are, therefore, given to treat patients with hyperthyroidism; those who have large nodular goiters that are causing local compressive symptoms on the trachea and esophagus, and those who cannot tolerate thyroid surgery; and to ablate functioning residual normal or malignant thyroid tissue after definitive surgery for thyroid cancer. The very large doses used to treat thyroid cancer occasionally lead to radiation-induced salivary gland inflammation and loss of taste because iodine is also concentrated by the salivary glands.
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From page 20... ...
As noted earlier, the presumed low dietary iodine intake in the Chornoby} area probably resulted in an increased uptake of radioactive iodines. How K} Works Under normal circumstances, excess iodine decreases NIS on the thyroid-cell surface, thereby inhibiting the farther entrance of iodine into the thyroid.
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From page 21... ...
Although iodate is used in some European countries and is also stable, it has traditionally not been used as a blocking agent in the United States and is not as readily
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From page 22... ...
According to the IAEA International Basic Safety Standards, the generic optimized intervention level for iodine blockade is 100 mGy (10 red) of avertable committed absorbed dose to the thyroid due to radioiodine.
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WHO recommends different intervention levels for different age groups and pregnant and lactating women. The intervention level for neonates, infants, children, and adolescents up to ~ ~ years old and for pregnant and lactating women is, because of the higher radiation risks in this group, only one-tenth of that for adults up to 40 years old.
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From page 24... ...
For this reason, a generic intervention level of 100 mGy (10 red) has been specified in the International Basic Safety Standards; but it does not obviate consideration of the IAEA practicality of planning to implement iodine prophylaxis for specific age groups.
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From page 25... ...
The single intervention level of 50 mGy (5 red) for all exposed people under the age of 40 years was chosen based upon the FDA guidelines for pregnant women, infants, and children (FDA, 2001a)
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From page 26... ...
It should be understood that most of these are very rare. Extremely rare disorders reported to be aggravated by excess iodine ingestion include dermatitis herpetiformis Duhring, ioderma tuberosum, hypocomplementemia vasculitis, and myotonia congenita.
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From page 27... ...
Therefore, people over 40 probably should not take KI tablets after a nuclear incident as they are at virtually no risk of developing thyroid cancer from the radiation, and are more likely than younger people to develop side effects from the KI. In contrast with iodine-induced hypothyroidism, excess iodine ingestion may induce hyperthyroidism or Tod Basedow disease, especially in regions of iodine deficiency, including many countries in Western Europe.
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From page 28... ...
Adult Elderly Secondary to transplacental passage of iodine or exposure of neonate to topical or parenteral iodine-rich substances Occasionally reported in infants drinking iodine-rich water In Japanese subjects with high iodine intake where Hashimoto's thyroiditis has been excluded Reported in elderly subjects with and without possible defective organification and autoimmune thyroiditis Chronic nonthyroidal illness Cystic fibrosis Chronic lung disease (including Hashimoto's thyroiditis) Chronic dialysis treatment Thalassemia major Anorexia nervosa Underlying thyroid disease Hashimoto's thyroiditis Euthyroid patients previously treated for Graves disease with ]
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From page 29... ...
THYROID PHYSIOLOGY Table 2.7 Risk Groups for Iodine-Induced Hyperthyroidism 29 Underlying thyroid disease Iodine supplementation for endemic iodine-deficiency goiter iodine administration to patients with euthyroid Graves disease especially those in remission after antithyroid drug therapy Nontoxic nodular goiter Autonomous nodules Nontoxic diffuse goiter No underlying thyroid disease Iodine administration to patients with no recognized underlying thyroid disease, especially in areas of mild to moderate iodine deficiency Iodine may also be useful in some clinical situations other than a need to prevent iodine deficiency (Table 2.~. Table 2.S Medical Uses of Stable iodine Treatment and prevention of iodine deficiency goiter Thyroid storm · Preoperative preparation of toxic goiter · Post ~3~l therapy of Graves disease · As sole therapy of Graves disease (when sensitive to antithyroid drugs)
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