A condition in which the thyroid gland, which is located in the
neck, does not make sufficient thyroid hormone to meet the
body's requirements. Hypothyroidism is often referred to as an "underactive
What causes hypothyroidism?
Almost all hypothyroidism is caused by autoimmune disease. In
this condition, which is called Hashimoto's thyroiditis or
Hashimoto's disease, the immune system goes awry and begins to
destroy the thyroid gland. This is a gradual process. It is not
usually associated with thyroid gland discomfort, but may cause
the gland to enlarge or shrink in size. The autoimmune disease
is restricted to the thyroid gland; consequently, treatment with
thyroid hormone (also known as L-thyroxine) completely corrects
Previous treatments for hyperthyroidism (an
overactive thyroid gland) may also result in hypothyroidism.
These treatments include radioactive iodine therapy or previous
thyroid surgery. Patients who undergo total removal of thyroid
gland for thyroid cancer will also develop hypothyroidism.
Hypothyroidism may also arise from a inflammatory condition
called de Quervain's thyroiditis.
How common is
Hypothyroidism is relatively common. It affects between 1 in 100
to 3 in 100 women of child-bearing age. It is more common in
women than in men, and it becomes more common with age.
Hypothyroidism occurs in up to 5 to 10 percent of older women.
What are the symptoms of
Hypothyroidism slows metabolism and affects essentially every
system in the body. Symptoms include generalized fatigue, weight
gain, thinning (brittle) hair, dry scaly skin, thin nails that
break easily, constipation, alterations in menses, aching
muscles, and slow heart rate. You may notice changes in
behavior, such as decreased ability to concentrate, reading and
calculating are more difficult, and you may experience decreased
interest in personal relationships or work. Hypothyroidism can
cause or worsen depression.
How is hypothyroidism tested?
A blood test is performed. It measures your thyroid hormone (thyroxine
or T4) and TSH (Thyroid-stimulating hormone) levels.
How are the thyroid test results
An elevation of TSH is a very sensitive index of reduced thyroid
function. Somewhat like the thermostat in your home, when
thyroid hormone levels fall, TSH (the furnace) is switched on to
stimulate the thyroid gland. When thyroid hormone levels are low
for a long time, TSH levels rise to a high level. Thus,
hypothyroidism is characterized by a TSH level that is above the
normal range and a thyroxine level that is below or at the low
end of the normal range (everyone's set point is a little
different). Your doctor can assist in the interpretation of
these results, or you may wish to see a physician (an
Endocrinologist) who specializes in hormonal disorders. A
medication called L-Thyroxine (L-T4) is used to replace the
missing thyroid hormone. It is chemically identical to those
made by your own thyroid gland. Consequently, when the correct
doses are prescribed and restore your metabolism to normal, the
treatment is not accompanied by side effects.
L-thyroxine has to be taken long-term. Once
it is discontinued or interrupted for a short time, your level
of thyroid hormone may start to fall again. Long term thyroxine
treatment is very safe--do not confuse it with HRT (HRT refers
to female hormone replacement).
During pregnancy, patients with
hypothyroidism often need to increase their dose of thyroxine.
This is to ensure that the developing fetus gets adequate
thyroid hormone. Your endocrinologist would help you to stay on
the correct dose throughout your pregnancy.