Hypothyroidism results when the
thyroid produces an insufficient amount of thyroid hormone. It affects 11 million
Americans and is the most common form of thyroid disease; it is more than four
times as prevalent as hyperthyroidism. Whereas hyperthyroidism is most common
in younger women, hypothyroidism generally affects women in their 50's to 60's:
by age 60, one in 6 women will have an under active thyroid. Even though it
is much more common than hyperthyroidism, it is much more frequently undiagnosed,
because its symptoms are easily attributed -- by patients themselves as well
as their physicians -- to aging, menopause, fatigue or stress. In fact, a recent
survey of 1,000 women over age 40 conducted by Louis Harris in conjunction with
the American Medical Women's Association (AMWA) found that nearly 2 out of 3
women do not know what "hypothyroidism" means. This was despite the
fact that more than half of these women experienced three or more symptoms commonly
associated with hypothyroidism over the past year. Of those women, 3 out of
4 never discussed those symptoms with their physician.
In 9 out of 10 cases, hypothyroidism
results from a problem in the thyroid gland itself. The most common cause of
hypothyroidism is Hashimoto's disease (or Hashimoto's thyroiditis), a condition
in which the immune system produces antibodies that destroy the thyroid. In
all types of hypothyroidism, the less thyroid hormone produced, the more TSH
released by the pituitary. This acts on the thyroid gland to enlarge it, which
may cause a "goiter". Other causes of hypothyroidism include complications
of thyroid or parathyroid surgery, radioiodine treatments for hyperthyroidism,
or a congenital thyroid birth defect. Short-term hypothyroidism may also be
the result of certain types of thyroid inflammation or viral thyroid infections.
Goiters themselves may also be caused by a dietary insufficiency of iodine.
Rarely, in about 1 in 20 cases, hypothyroidism may be caused by a problem
in the hypothalamus or pituitary gland rather than in the thyroid gland itself.
Under normal circumstances, the
hypothalamus signals the pituitary gland to produce TSH. When a medical problem
affects either the hypothalamus or the pituitary gland, the chain of signals
from the brain to the thyroid may be interrupted. If this happens, the thyroid
gland may not receive the pituitary's message to produce thyroid hormones, even
though the thyroid itself can function perfectly. This type of hypothyroidism,
called "secondary hypothyroidism," may be caused if the pituitary
is damaged by a tumor, infection, sarcoidosis, or cancer.
Hypothyroidism in pregnancy may
be a bigger problem than previously recognized. It affects one in 50 pregnant
women. While only one in every
4,000 babies is born with clinical
hypothyroidism, a recent study (8/99) in the prestigious New England Journal
of Medicine (NEJM) showed that untreated thyroid disease in pregnant mothers
may result in a child having impaired psychological development, as well as
significantly decreased IQ scores, motor skills, language skills, and reading
abilities. . . even though the baby's thyroid function is normal. Ask your
doctor whether you should be screened for thyroid disease if you are planning
to become pregnant or if you are early in your current pregnancy. It is also
important to recognize that five to eight percent of women develop thyroid disorders
after giving birth.
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Created: 11/2/2000  - Donnica Moore, M.D.