| Signs and symptoms |
The signs and symptoms of hypothyroidism vary widely, depending on the severity of the hormone deficiency.
At first, you may barely notice symptoms such as fatigue and sluggishness, or you may simply attribute them to getting older. But as your metabolism continues to slow, you may develop more obvious signs and symptoms, including:
- Increased sensitivity to cold.
- Constipation.
- Pale, dry skin.
- A puffy face.
- Hoarse voice.
- Elevated blood cholesterol levels.
- Unexplained weight gain. Many people attribute their weight gain to an underactive thyroid, but
this is true only in a small percentage of cases. Hypothyroidism will rarely cause you to gain more
than 10 to 20 pounds — most of which is fluid.
- Heavier-than-normal menstrual periods.
- Depression.
Advanced hypothyroidism, known as myxedema, is very rare, but when it occurs it can be life-threatening. Its symptoms include drowsiness and intense intolerance to cold followed by profound lethargy and unconsciousness.
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| Causes |
Your thyroid gland produces two main hormones, thyroxine (T-4) and triiodothyronine (T-3). They maintain the rate at which your body uses fats and carbohydrates, help control your body temperature, influence your heart rate and help regulate the production of protein. Your thyroid gland also produces calcitonin, a hormone that regulates the amount of calcium in your blood.
The rate at which these hormones are released is controlled by your pituitary gland and your hypothalamus — an area at the base of your brain that acts as a thermostat for your whole system. Here's how the process works:
The hypothalamus signals your pituitary gland to make a hormone called thyroid-stimulating hormone (TSH). Your pituitary gland then releases TSH — the amount depends on how much thyroxine and triiodothyronine are in your blood. Finally, your thyroid gland regulates its production of hormones based on the amount of TSH it receives.
Although this process usually works well, the thyroid sometimes fails to produce enough hormones. This may be due to a number of different factors, including:
- Autoimmune disease (Hashimoto's thyroiditis). Autoimmune disorders occur when your immune
system produces antibodies that attack your own tissues. Sometimes this process occurs within the
thyroid gland. Scientists aren't sure why the body produces antibodies against itself. Some think a
virus or bacteria might trigger the response, while others believe a genetic flaw may be involved.
Most likely, autoimmune diseases result from more than one factor. But however it happens, these
antibodies affect the thyroid's ability to produce hormones.
- Treatment with radioactive iodine. The most common treatment for people who produce too
much thyroid hormone (hyperthyroidism) is radioactive iodine. The radioactive material becomes
concentrated in the thyroid gland, reducing its function. Often, however, function is reduced too
much, resulting in hypothyroidism. Antithyroid drugs such as methimazole (Tapazole) — also used to
treat conditions in which the thyroid produces too much thyroid hormone — may cause hypothyroidism as
well.
- Radiation therapy. Radiation used to treat cancers of the head and neck can affect your
thyroid gland and may lead to hypothyroidism.
- Thyroid surgery. Removing all or a large portion of your thyroid can diminish or halt
hormone production.
- Medications. A number of medications can contribute to hypothyroidism. One of the most common is lithium (Lithonate, Lithane), which is used to treat certain psychiatric disorders. If you're taking medication, ask your doctor about its effect on your thyroid gland.
- Congenital disease. Approximately 1 in 5,000 babies in the United States is born with a
defective thyroid gland or no thyroid gland at all. In most cases, no one knows why the thyroid gland
didn't develop normally, but some children have an inherited form of the disorder. Often, infants with
congenital hypothyroidism appear perfectly normal at birth. That's one reason why doctors now
recommend that all newborns receive thyroid tests when they're between 24 and 72 hours old.
- Pituitary disorder. About 1 percent of cases of hypothyroidism are caused by the failure of
the pituitary gland to produce enough TSH — usually due to a benign tumor of the pituitary gland.
- Pregnancy. Some women develop hypothyroidism during or after pregnancy, often because they
produce antibodies to their own thyroid gland. Left untreated, hypothyroidism increases the risk of
miscarriage, premature delivery and preeclampsia — a condition that causes a significant rise in a
woman's blood pressure during the last 3 months of pregnancy. It can also seriously affect the
developing fetus.
- Iodine deficiency. The trace mineral iodine — found primarily in seafood, seaweed, plants grown in iodine-rich soil, and iodized salt — is essential for the production of thyroid hormones. Before the 1920s, it wasn't unusual for people to develop hypothyroidism because they consumed too little of this mineral. But the addition of iodine to table salt has virtually eliminated this problem in the United States. In other parts of the world, however, as many as 200 million people may suffer from iodine deficiencies.
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| Risk factors |
Although anyone can develop hypothyroidism, it occurs mainly in women over age 40, and the risk of developing the disorder increases with age. You also have an increased risk if you:
- Have a close relative, such as a parent or grandparent, with an autoimmune disease
- Have diabetes, making it more likely you'll develop hypothyroidism during or after pregnancy
- Have been treated with radioactive iodine or antithyroid medications
- Have had thyroid surgery (thyroidectomy)
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| When to seek medical advice |
See your doctor if you're feeling tired for no reason or have any of the other symptoms of hypothyroidism, such as dry skin, a pale, puffy face, constipation or a hoarse voice.
You'll also need to see your doctor for periodic testing of your thyroid function if you've had previous thyroid surgery or treatment with radioactive iodine or antithyroid medications.
If you have high blood cholesterol, talk to your doctor about whether hypothyroidism may be a cause. And if you're receiving hormone therapy for hypothyroidism, schedule follow-up visits as often as your doctor recommends. Initially, it's important to make sure you're receiving the correct dose of medicine. And over time, the dose you need to keep your thyroid functioning normally may change.
| Screening and diagnosis |
Because hypothyroidism is more prevalent in older women, some endocrinologists recommend that women age 60 and over be screened for the disorder during routine annual physical examinations. Some doctors also recommend that pregnant women be tested for hypothyroidism.
In general, your doctor may test for an underactive thyroid if you're feeling increasingly tired or sluggish, have dry skin, constipation and a hoarse voice, or have had previous thyroid problems or goiter.
Diagnosis of hypothyroidism is based on your symptoms and the results of blood tests that measure levels of TSH and sometimes the levels of the thyroid hormone thyroxine. Low levels of thyroxine and high levels of TSH indicate an underactive thyroid. That's because your pituitary produces more TSH in an effort to stimulate your thyroid gland into producing more thyroid hormone.
In the past, doctors weren't able to detect hypothyroidism until symptoms were fairly advanced. But by using the sensitive TSH test, doctors are now able to diagnose thyroid disorders much earlier — often before you ever experience symptoms. Because the TSH test is the best screening test, your doctor will likely check TSH first and follow with a thyroid hormone test if needed.
TSH tests also play an important role in managing hypothyroidism. They help your doctor determine the right dosage of medication, both initially and over time.
| Complications |
Untreated hypothyroidism can lead to a number of health problems. Constant stimulation of your thyroid to release more hormones may cause the gland to become larger — a condition known as goiter. Hashimoto's thyroiditis, an autoimmune inflammation of the thyroid, is one of the most common causes of a goiter. Although generally not uncomfortable, a large goiter can affect your appearance and may interfere with swallowing or breathing.
Hypothyroidism may also be associated with an increased risk of heart disease, primarily because high levels of low-density lipoprotein (LDL) cholesterol — the "bad" cholesterol — can occur in people with an underactive thyroid. Hypothyroidism also can lead to an enlarged heart.
Depression may occur early in hypothyroidism and may become more severe over time. Hypothyroidism can also cause decreased sexual desire (libido) in both men and women and can lead to slowed mental functioning.
Myxedema is a rare, life-threatening condition that is the result of long-term, undiagnosed hypothyroidism. Its symptoms include intense cold intolerance and drowsiness followed by profound lethargy and unconsciousness. A myxedema coma may be triggered by sedatives, infection or other stress on your body. If you have symptoms of myxedema, you need immediate emergency medical treatment.
Babies born to women with thyroid disease may have a higher risk of birth defects than babies born to healthy mothers. Doctors have long known that these children are more prone to intellectual and developmental problems, but recent studies also show a link between hypothyroid pregnancies and birth defects such as cleft palate. A link also exists between hypothyroid pregnancies and heart, brain and kidney problems.
Infants with untreated congenital hypothyroidism are also at risk of serious problems with both physical and mental development. But if the condition is diagnosed within the first few months of life, the chances of normal development are excellent.
| Treatment |
Standard treatment for an underactive thyroid involves daily use of the synthetic thyroid hormone levothyroxine (Levothroid, Synthroid). The oral medication restores adequate hormone levels, shifting your body back into normal gear.
Soon after starting treatment, you'll notice that you're feeling less fatigued. The medication also gradually lowers cholesterol levels elevated by the disease and may reverse any weight gain. Treatment with levothyroxine is usually lifelong.
To determine the right dosage of levothyroxine, your doctor generally checks your level of TSH after 2 to 3 months. Excessive amounts of the hormone can accelerate bone loss, which may make osteoporosis worse or add to your risk of this disease.
If you have coronary artery disease or severe hypothyroidism, your doctor may start treatment with a smaller amount of medication and gradually increase the dosage. Progressive hormone replacement allows your heart to adjust to the increase in metabolism.
Levothyroxine causes virtually no side effects when used in the appropriate dose and is relatively inexpensive. If you change brands, let your doctor know to ensure you're still receiving the right dosage. Also, don't skip doses or stop taking the drug because you're feeling better. If you do, the symptoms of hypothyroidism will gradually return. People with hypothyroidism need to take medication for the rest of their lives.
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| Complementary and alternative medicine |
Although most doctors recommend synthetic thyroxine, natural extracts containing thyroid hormone derived from the thyroid glands of pigs are also available. These products — Armour Desiccated Thyroid Hormone and Westhroid — more closely resemble natural thyroid hormones because they contain both thyroxine and triidothyronine. Synthetic thyroid medications contain thyroxine only.
Extracts are available by prescription only and shouldn't be confused with the glandular concentrates sold in natural foods stores. Glandulars are dried concentrates of glands derived from animals. These products aren't regulated by the Food and Drug Administration, and their potency isn't guaranteed. What's more, using them raises concerns about exposure to bovine spongiform encephalopathy — commonly known as mad cow disease. Some, but not all, glandular products are derived from range-fed cattle from New Zealand or Argentina, which are more likely to be disease-free.
— October 8, 2002 —