Thyroid gland disorders

Thyroid disorders may be divided into over- and underproduction of the thyroid hormones. These may be caused by thyroid gland disorders or disorders of the pituitary gland (TSH production) or hypothalamus (thyrotropin-releasing hormone release). Thyroid hormone deficiency in infancy may cause mental retardation if it is not corrected immediately after birth. For this reason, many states require thyroid function tests in all newborns. In adults, thyroid deficiency may be caused by Hashimoto s thyroiditis, an immune disorder, or dietary iodine deficiency, in which case it is called simple goiter. The term "myxedema" has been used to refer to hypothyroidism of whatever cause. Myxedemas may... 

Myopathy is the term used broadly for affections of the skeletal musculature, in which the muscular symptoms in no way arise from disordered function of the central or peripheral nervous system. Within this definition are included, therefore, such widely differing conditions as the polymyositis syndrome, endocrine myopathies associated with thyroid gland disorders, and the muscular dystrophies. 

Thyroid Gland Disorders. The elimination half-life of theophylline is markedly prolonged in hypothyroidism. Conversely, clearance is increased in hyperthyroidism, but reduces toward normal values after initiation of treatment for this disorder. ... 

X lO kJ/mol. If a patient with a th Toid disorder is given this isotope and 7.45 pg is incorporated into the thyroid gland, how much energy will the gland receive in one day ... 

C. Thyroid clubbing (acropachy). (Reprinted, with permission, from Jameson JL, Weetman AP. Disorders of the thyroid gland. In Kasper DL, Braunwald E, Fauci AS, et al, (eds.) Harrison s Principles of Internal Medicine. 16th edition. New York McGraw-Hill 2004 2114.)... 

Secondary hyperlipoproteinemias, which arise from a disordered lipid tissue metabolism or its impaired control, are observed in diabetes mellitus, thyroid gland hypofunction, alcoholism, etc. 

Newborn screening is used just after birth to identify genetic disorders that can be treated early in life. Millions of babies are tested each year in the United States. All states currently test infants for phenylketonuria (a genetic disorder that causes mental retardation if left untreated) and congenital hypothyroidism (a disorder of the thyroid gland). Most states also test for other genetic disorders. 

Worldwide, the most common thyroid disorder is hypothyroidism resulting from dietary iodine deficiency. In iodine-replete areas of the world, most thyroid disorders are the result of autoimmune disease. The symptoms manifested in hypothyroid and hyperthyroid states are largely independent of any underlying disorder of the thyroid gland itself they are a function of the degree of hormone deficiency or excess. 

Biosynthetic defects in thyroid hormonogenesis may also result in an inability of the thyroid gland to produce sufficient hormone and may be due to inherited enzymatic deficiencies or the ingestion of natural or therapeutically administered antithyroid agents. An example in the latter category is lithium, widely used to treat psychiatric disorders and associated with the development of hypothyroidism and goiter. It is concentrated by the thyroid, where it inhibits thyroidal I uptake, incorpora-... 

Burman KD and Wartofsky L. Iodine effects on the thyroid gland Biochemical and clinical aspects. Rev Endocr Metab Disord 2000 l(l-2) 19-25. 

Laboratory animals fed PBBs had body weight loss, skin disorders, and nervous system effects, and their livers, kidneys, thyroid glands, and immune systems were seriously injured. Some animals fed high amounts died. PBBs also caused birth defects in animals, but it is not known for sure whether PBBs make males or females infertile. Most of the effects in animals occurred after they ate large amounts of PBBs for short periods or smaller amounts for several weeks or months. In a lifetime study in rats and mice treated orally with PBBs at doses higher than those expected from environmental exposure, body weight loss and effects on the livers, kidneys, and thyroid glands were observed. A few studies tested animals exposed to PBBs by skin contact. These... 

The thyroid gland, located in the neck, absorbs much of the iodine that enters the body in food and drink. This image of the gland was obtained by giving a patient the radioactive isotope iodine-131. Such images are useful in diagnosing metabolic disorders. 

Patients with an underlying disorder of the thyroid gland may be more predisposed to this complication. 

In the treatment of hyperthyroidism the dose of 131I is usually a few millicuries and is either roughly estimated or calculated according to the size of the thyroid gland, the uptake of a tracer dose of iodine, and the type of thyroid disorder (diffuse or nodular), with doses ranging from 80 to 150 microCi (3.0-5.5 MBq) per gram of thyroid tissue (3,4). 

CaR expression is greatest in the parathyroid glands, calcitonin-secreting C-cells of the thyroid gland, and kidney, but the CaR is also found in the two other key organs that participate in calcium homeostasis gut and bone (Brown and MacLeod, 2001). This review will focus on the structure and function of the CaR, its role in normal physiology and in various disorders of Ca -sensing, and the development of CaR-based therapeutics. 

Hypothyroidism, known as myxedema in adults, when severe, is the most common disorder of the thyroid gland. Worldwide, hypothyroidism is most often the result of endemic iodine deficiency. In nonendemic areas, where iodine is sufficient in the diet, chronic autoimmune thyroiditis (Hashimoto s thyroiditis) accounts for the majority of cases. This disorder is primarily characterized by high levels of circulating antibodies against a key enzyme (thyroid peroxidase) in the processing of iodine in the thyroid gland. Blocking antibodies directed at the TSH receptor may also be present. Thyroid destruction may also occur via apoptotic cell death. 

In areas where there is also low iodine in the diet a further complication may arise. The thiocyanate that is formed from the cyanide inhibits the uptake of iodine into the thyroid gland. Iodine is used to make hormones that regulate the metabolism of the body, and its deficiency leads to goitre (enlarged thyroid) and cretinism (mental retardation) in the offspring of women with the disorder. 

Calcitonin is a 32-amino-acid polypeptide hormone that was hrst purihed in 1962 by Copp and Cheney (121). It was originally thought as a product from parathyroid glands, but later it was discovered to be made by the C cells of the thyroid gland. Calcitonin participates in calcium and phosphorus metabolism, lowers plasma calcium and phosphate levels, and it has been used as a drug for bone and mineral disorders for a long time. 

Many structural or functional abnormalities of the thyroid gland can lead to thyroid hormone deficiency (Box 52-2). Primary hypothyroidism is frequently caused by diseases or treatments that directly destroy thyroid tissue or interfere with thyroid hormone biosynthesis. Secondary hypothyroidism occurs as a result of pituitary or hypothalamic disease and/or disorders. 

For example, inclusion of 0.02 % KI, potassium iodide, in ordinary table salt has nearly eUminated goiter in the United States. Goiter is a disorder of the thyroid gland caused by a deficiency of iodine. Alineral water tastes better than purer, distilled water. 

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