McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 7 Thyroid and parathyroid agents

• Lack of TSH due to pituitary disease • Lack of TRH related to a tumour or disorder of the hypothalamus Hypothyroidism is the most common type of thyroid dysfunction. It is estimated that approximately 5% to 10% of women older than 50 years of age are hypo- thyroidic. Hypothyroidism is also a common finding in elderly men. The symptoms of hypothyroidism can be

varied and vague, such as obesity and fatigue (Box 37.2), and are frequently overlooked or mistaken for signs of normal ageing (Table 37.1). Children who are born without a thyroid gland or who have a non-functioning gland develop a condition called cretinism . If untreated, these children will have poor growth and development and mental retardation because of the lack of thyroid hormone stimulation.

The evidence

BOX 37.2

Thyroid hormones for obesity Treatment trends for obesity have changed over the years. Not long ago, one of the suggested treatments was the use of thyroid hormone.The thinking was that obese people had slower metabolisms and therefore would benefit from a boost in metabolism from extra thyroid hormone. If an obese person is truly hypothyroid, this might be a good idea. Unfortunately, many of the people who received thyroid hormone for weight loss were not tested for thyroid activity and ended up with excessive thyroid hormone in their systems.This situation triggered a cascade of events.The exogenous thyroid hormone disrupted the hypothalamic–pituitary–thyroid control system, resulting in decreased production of thyrotropin- releasing hormone (TRH) and thyroid-stimulating hormone (TSH) as the hypothalamus and pituitary sensed the rising levels of thyroid hormone. Because the thyroid was no longer stimulated to produce and secrete thyroid hormone, thyroid levels would actually fall. Lacking stimulation byTSH, the thyroid gland would start to atrophy. If exogenous thyroid hormone were stopped, the atrophied thyroid would not be able to immediately respond to theTSH stimulation and produce thyroid hormone. Ultimately, these people experienced

an endocrine imbalance. What’s more, they did not lose weight—and in the long run may actually have gained weight as the body’s compensatory mechanisms tried to deal with the imbalances. Today, thyroid hormone is no longer considered a good choice for treating obesity. Other drugs have come and gone, and new drugs are released each year to attack other aspects of the problem. Many people, especially middle-aged people who may recall that thyroid hormone was once used for weight loss, ask for it as an answer to their weight problem. People have even been known to “borrow” thyroid replacement hormones from others for a quick weight loss solution or to order the drug over the Internet without supervision or monitoring. Obese people need reassurance, understanding and education about the risks of borrowed thyroid hormone. Insistent people should undergo thyroid function tests. If the results are normal, they should receive teaching about the controls and actions of thyroid hormone in the body and an explanation of why taking these hormones can cause problems. Obesity is a chronic and frustrating problem that poses continual challenges for healthcare providers. Stimulated: hyperactive reflexes, anxiety, nervousness, insomnia, tremors, restlessness, increased basal temperature Stimulated: tachycardia, palpitations, increased pulse pressure, systolic hypertension, increased sensitivity to catecholamines Skin is flushed, warm, thin, moist, sweating; hair is fine and soft; nails are soft and thin Increased, overactive cellular metabolism: low-grade fever; intolerance to heat; increased appetite with weight loss; muscle wasting and weakness, thyroid myopathy Localised with accumulation of mucopolysaccharides in eyeballs, ocular muscles; periorbital oedema, lid lag, exophthalmos; pretibial oedema Altered tendency toward oligomenorrhoea, amenorrhoea Hyperthyroidism

■■ TABLE 37.1 Signs and symptoms of thyroid dysfunction Clinical effects Hypothyroidism

Central

Depressed: hypoactive reflexes, lethargy, sleepiness, slow speech, emotional dullness Depressed: bradycardia, hypotension, anaemia, oliguria, decreased sensitivity to catecholamines Skin is pale, coarse, dry, thickened; puffy eyes and eyelids; hair is coarse and thin; hair loss; nails are thick and hard intolerance to cold; decreased appetite, higher levels of fat and cholesterol; weight gain; hypercholesterolaemia Accumulation of mucopolysaccharides in the heart, tongue and vocal cords; periorbital oedema, cardiomyopathy, hoarseness, and thickened speech Decreased function: menorrhagia, habitual abortion, sterility, decreased sexual function

nervous system

Cardiovascular system

Skin, hair and nails

Metabolic rate Decreased: lower body temperature;

Generalised

myxoedema

Ovaries

Goitre

Rare; simple non-toxic type may occur

Diffuse, highly vascular; very frequent