C H A P T E R 3 7
Thyroid and parathyroid agents
555
• 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.
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.
The evidence
BOX 37.2
■■
TABLE 37.1 Signs and symptoms of thyroid dysfunction
Clinical effects
Hypothyroidism
Hyperthyroidism
Central
nervous
system
Depressed: hypoactive reflexes, lethargy,
sleepiness, slow speech, emotional dullness
Stimulated: hyperactive reflexes, anxiety,
nervousness, insomnia, tremors, restlessness,
increased basal temperature
Cardiovascular
system
Depressed: bradycardia, hypotension,
anaemia, oliguria, decreased sensitivity to
catecholamines
Stimulated: tachycardia, palpitations, increased
pulse pressure, systolic hypertension, increased
sensitivity to catecholamines
Skin, hair and
nails
Skin is pale, coarse, dry, thickened; puffy eyes
and eyelids; hair is coarse and thin; hair loss;
nails are thick and hard
Skin is flushed, warm, thin, moist, sweating; hair
is fine and soft; nails are soft and thin
Metabolic rate Decreased: lower body temperature;
intolerance to cold; decreased appetite, higher
levels of fat and cholesterol; weight gain;
hypercholesterolaemia
Increased, overactive cellular metabolism:
low-grade fever; intolerance to heat; increased
appetite with weight loss; muscle wasting and
weakness, thyroid myopathy
Generalised
myxoedema
Accumulation of mucopolysaccharides in the
heart, tongue and vocal cords; periorbital
oedema, cardiomyopathy, hoarseness, and
thickened speech
Localised with accumulation of
mucopolysaccharides in eyeballs, ocular
muscles; periorbital oedema, lid lag,
exophthalmos; pretibial oedema
Ovaries
Decreased function: menorrhagia, habitual
abortion, sterility, decreased sexual function
Altered tendency toward oligomenorrhoea,
amenorrhoea
Goitre
Rare; simple non-toxic type may occur
Diffuse, highly vascular; very frequent
