Thyroid gland hypothyroidism

This infant has an underactive thyroid gland (hypothyroidism). Replacement hormone treatment will prevent her from being seriously retarded. 

Iodine. Of the 10—20 mg of iodine in the adult body, 70—80 wt % is in the thyroid gland (see Thyroid and antithyroid preparations). The essentiahty of iodine, present in all tissues, depends solely on utilisation by the thyroid gland to produce thyroxine [51-48-9] and related compounds. Well-known consequences of faulty thyroid function are hypothyroidism, hyperthyroidism, and goiter. Dietary iodine is obtained from eating seafoods and kelp and from using iodized salt. 

The thyroid gland, located in the base of the neck, exerts i key role on growth and metabolism. In contrast with that of some of the other endocrine glands, this control is effected Ihrough a pair of relatively simple molecules, thyroxine, and its close congener, triiodothyronine. Cases of thyroid deficien-cy (hypothyroidism) are common enough to warrant the production... 

Decreased activity of the thyroid gland results in hypothyroidism and, in severe cases, myxoedema. It is often of immunological origin and the manifestations are low metabolic rate, slow speech, lethargy, bradycardia, increased sensitivity to cold, and mental impairment. Myxoedema includes a characteristic thickening of the skin. Therapy of thyroid tumours is another cause of hypothyroidism. Thyroid deficiency... 

Lithium is concentrated in the thyroid gland and can impair thyroid hormone synthesis. Although goiter is uncommon, as many as 30% of patients develop at least transiently elevated thyroid-stimulating hormone values. Lithium-induced hypothyroidism is not usually an indication to discontinue the drug. Patients can be supplemented with levothyroxine if continuation of lithium is desired.30... 

Despite the availability of a wide array of thyroid hormone products, it is clear that synthetic levothyroxine (LT4) is the treatment of choice for almost all patients with hypothyroidism. LT4 mimics the normal physiology of the thyroid gland, which secretes mostly T4 as a prohormone. As needed, based on metabolic demands, peripheral tissues convert thyroxine (T4)... 

The most common causes of hypothyroidism are listed in Table 41-2. Up to 90% of patients with autoimmune thyroiditis have circulating anti-TPOAbs. The autoimmune inflammatory response results in a lymphocytic infiltration of the thyroid gland and its eventual destruction. 

Patients with mild or subclinical hypothyroidism do not need to be started on the full replacement dose because they still have some endogenous hormone production. Start these patients on 25 to 50 meg/day, and titrate every 6 to 8 weeks based on TSH levels. Over time, it is likely that the LT4 dose will need to be increased slowly as the patient s thyroid gland loses residual function. 

The vast majority of hypothyroid patients have thyroid gland failure (primary hypothyroidism). The causes include chronic autoimmune thyroiditis (Hashimoto s disease), iatrogenic hypothyroidism, iodine deficiency, enzyme defects, thyroid hypoplasia, and goitrogens. 

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. 

Tyrosine (Tyr or Y) (4-hydroxyphenylalanine ((5)-2-amino-3-(4-hydroxyphenyl)-propanoic acid)) is a polar, neutral, aromatic amino acid with the formula H00CCH(NH2)CH2C6H50H and is the precursor of thyroxin, dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline), and the pigment melanin. Being the precursor amino acid for the thyroid gland hormone thyroxin, a defect in this may result in hypothyroidism. Tyr is extremely soluble in water, a property that has proven useful in isolating this amino acid from protein hydrolysates. The occurrence of tyrosine- 0-sulfate as a constituent of human urine and fibrinogen has been reported. ... 

The Class III effects of amiodarone develop over several weeks. This time-course is similar to that seen in thyroid gland ablation [25]. It is well known that patients with hypothyroidism have long QT intervals which are indicative of prolonged action potentials. Amiodarone has been shown to inhibit the conversion of thyroxine (T4) to triiodothyronine (T3) both in human subjects [26] and in vitro [27]. It has been argued that the Class III effects of amiodarone are due to its effects on thyroid hormones [28]. Others, however, argue that there is no relationship between prolongation of ventricular refractory period by amiodarone and thyroid state [29]. 

Hypothyroidism Goiter (enlarged thyroid gland), decreased reflexes, intolerance of cold weather, depression... 

Levothyroxine is used to treat hypothyroidism (an underactive thyroid gland). Thyroid hormone can be made from beef and pork thyroid, but this lacks standardization and it is difficult to control dosage. The synthetic drug is more desirable. Levothyroxine is one of two important thyroid hormones. It is converted into the second important hormone, liothyronine, in the body. The key step in the synthesis of structures such as levothyroxine is the substitution of an iodonium salt by an iodinated phenol. Siql-like reactions on an aromatic ring are not common, but an iodonium salt provides a good leaving group. 

Diseases associated with thyroid glands are the result of either excess production of thyroid hormone (hyperthyroidism), or its insufficiency (hypothyroidism). Both cases can result in a goiter. 

Hypothyroidism (myxedema) results when there is a breakdown of thyroid hormone production in the thyroid gland. Treatment consists of replacing this hormone with aforementioned drugs. Treatment with levothyroxine, 3,5,3, 5 -tetraiodothyronine, is preferred. Lyothyronin, L-3,5,5 -triiodothyronine, is also used, as is lotrix, a mixture of levothyroxine and levothyronine in a 4 1 ratio. Of the drugs of animal origin, thyroidin and thy-roglobulin (proloid) are used. 

Hypothyroidism Hypothyroidism may occur with long-term lithium administration. Patients may develop enlargement of thyroid gland and increased thyroid-stimulating hormone levels. 

TSH, or thyrotropin, is a glycosylated protein of two subunits, a and p. TSH stimulates the thyroid gland to produce thyroid hormones. Deficiencies are treated by giving thyroxine itself rather than TSH, but TSH is available for diagnostic purposes to differentiate between pituitary and thyroid gland failure as causes of hypothyroidism (see Chapter 65). 

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