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HISTORY AND EPIDEMIOLOGY
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Long before the thyroid was recognized as a functional endocrine gland, it was believed to serve a cosmetic function, especially in women. Egyptian paintings often emphasize the full and beautiful necks of women with enlarged thyroid glands. Early theories on the physiologic function of the thyroid gland included lubrication of the trachea, diversion of blood flow from the brain, and protection of women from “irritation” and “vexation” from men.33 Although poorly defined in historical accounts, symptoms resembling hypothyroidism and myxedema that were successfully treated with ground sheep thyroid were described 500 years ago. In the 16th century, Paracelsus described the association between goiter (thyroid gland enlargement) and cretinism.69 A syndrome of cardiac hyperactivity, goiter, and exophthalmos was first described in 1786.82 Graves and von Basedow33 further detailed this syndrome and its relationship to the thyroid gland 50 years later.
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In 1891, injection of ground sheep thyroid extract was formally described as a treatment for myxedema.33 Shortly afterward, oral therapy was determined to be equally effective. Seaweed, which contains large amounts of iodine, was used to treat goiter (hypothyroidism) in Chinese medicine as early as the third century a.d. In 1863, Trousseau101 fortuitously discovered a treatment for Graves disease when he inadvertently prescribed daily tincture of iodine instead of tincture of digitalis to a tachycardic, thyrotoxic young woman.
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Sir Charles R. Harington described the chemical structure and performed the first synthesis of thyroxine (tetraiodothyronine {T4}) in 1926.84 Triiodothyronine (T3) was not isolated and synthesized until the 1950s.33 Prior to this, desiccated thyroid gland from animal sources was commonly used to treat hypothyroidism. Despite becoming essentially obsolete in the modern medical community, unprocessed, desiccated thyroid can be easily purchased via the Internet and in health food stores as a thyroid supplement.95 A pharmaceutical grade porcine derived thyroid supplement originally produced by Armour, is still available by prescription from several manufacturers. Unfortunately, the misguided use of both organic and synthetic thyroid supplements as vitality agents, stimulants, and weight-loss aids has become increasingly common. Two epidemics of “hamburger thyrotoxicosis” that occurred in the United States in the mid 1980s secondary to consumption of ground beef contaminated with bovine thyroid gland demonstrated the potential widespread toxicologic sequelae after a community unknowingly ingested thyroid hormone.38,51
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Today, hypothyroidism and hyperthyroidism are relatively common endocrine disorders. The global incidence of neonatal hypothyroidism is one per 3000 to 4500 births. It is estimated that hypothyroidism affects 1% to 5% of US adults. It is more prevalent in whites than people of Hispanic or African American descent. In the elderly, the prevalence of hypothyroidism increases to 15% by the age of 75 years. Worldwide, iodine deficiency is the leading cause of hypothyroidism. According to US retail pharmaceutical statistics for prescription drugs, levothyroxine (both generic and brand combined; T4) has consistently ranked in the ...