Thyroid enlargement

Adverse reactions are related to the iodine content of the drug the toxicity is often expressed as skin reactions, thyroid enlargement, and interference with thyroid function studies. Headache and diarrhea also occur. Chronic use of clioquinol, a closely related agent, has been linked to a myelitislike illness and to optic atrophy with permanent loss of vision. 

A normal rate of thyroid hormone synthesis depends on an adequate dietary intake of iodine. Iodine is naturally present in water and soil, although some soils contain very low amounts. As a result, seafood is a more reliable source of iodine than crop plants. Approximately 1.6 billion people in more than 100 countries live in areas where natural sources of dietary iodine intake are marginal or insufficient. A minimum of 60 j.g of elemental iodine is required each day for thyroid hormone synthesis, and at least 100 j.g/day is required to eliminate thyroid follicular cell hyperplasia and thyroid enlargement (i.e., iodine deficiency goiter). 

The etiology and pathogenesis of hypothyroidism are outlined in Table 38-5. Hypothyroidism can occur with or without thyroid enlargement (goiter). The laboratory diagnosis of hypothyroidism in the adult is easily made by the combination of a low free thyroxine and elevated serum TSH (Table 38-2). 

Other additional studies or pertinent information that lend support to this MRL It is well documented in intermediate-duration studies that the thyroid is a target of PBBs showing a spectrum of effects, including decreases in serum T3 and T4 hormone, thyroid enlargement, effects in the follicular cells (e.g., reduced size, hyperplasia with columnar appearance, and papillary projections) and accumulation of colloid droplets (Akoso et al. 1982 Byrne et al. 1987 Gupta and Moore 1979 Kasza et al. 1978 Norris et al. 1975 NTP 1983 Sepkovic and Byrne 1984 Sleight et al. 1978). 

Because of interference with iodine uptake, hypothyroidism and goiter can result (935). The condition is reversible, but an obstructive syndrome due to thyroid enlargement has been observed (935). 

Nontoxic goiter is a syndrome of thyroid enlargement without excessive thyroid hormone production. Enlargement of the thyroid gland is usually due to TSH stimulation from inadequate thyroid hormone synthesis. The most common cause of nontoxic goiter worldwide is iodide deficiency, but in the USA, it is Hashimoto s thyroiditis. Less common causes include dietary goitrogens, dyshormonogenesis, and neoplasms (see below). 

Metallic Mercury. A 13-year-old boy exposed to mercury vapors for 2 weeks developed a thyroid enlargement with elevated triiodothyronine, and thyroxine and low thyroid-stimulating hormone levels (Karpathios et al. 1991). Serum-free thyroxine (T4) and the ratio of free thyroxine to free 3,5,3 -triiodo-... 

Primary goitrous hypothyroidism results when the synthesis of T4 and T3 is impaired, either because of some extrinsic factor or because of an intrinsic, inherited defect in thyroid hormone biosynthesis. As a result, the positive feedback loop causes compensatory thyroid enlargement (goiter) through the hypersecretion of TRH and TSH. Primary nongoitrous hypothyroidism is characterized by loss or atrophy of thyroid tissue, resulting in decreased production of thyroid hormones despite maximum stimulation by TSH. Hashimotos thyroiditis is the most frequent cause of primary hypothyroidism in developed countries where iodine intake is sufficient. Worldwide, iodine deficiency is the most common cause of goitrous hypothyroidism. The... 

Laboratory tests most commonly used to evaluate patients for thyroid gland dysfunction are listed in Table 52-1. Familiarity with normal physiology and with pathophysiology is important if these tests are to be properly used and selected. However, it is important to note that normal serum thyroid hormone concentrations do not exclude thyroid disease, and abnormal thyroid tests do not always indicate thyroid disease. Diffuse or nodular thyroid enlargement, for example, maybe seen in euthyroid patients. ... 

Graves disease " is an autoimmune syndrome that may include hyperthyroidism, diffuse thyroid enlargement, exophthalmos, pretibial myxedema, and thyroid acropachy (Figs. 73 and 73-5). Graves disease is the most common cause of hyperthyroidism. The prevalence of Graves disease is estimated to be 3 per... 

Thyrotoxicosis factitia should be suspected in a thyrotoxic patient without infiltrative ophthalmopathy or thyroid enlargement. The RAID uptake is at low levels because the patient s thyroid gland func-... 

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