Thyroid Disease
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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.