The thyroid gland is a butterfly-shaped organ located in front of the windpipe (trachea) above the breastbone and just below the voice box (larynx or Adam's Apple). It is an endocrine gland, meaning that it secretes special proteins called hormones into the blood stream. Other hormone-secreting glands include the pancreas, pituitary gland, adrenal glands ovaries and testes. The hormones produced act as chemical signals to control various body functions.
The thyroid gland is critically involved in the regulation of blood pressure, weight, energy levels and mood, growth and development in children and fertility. Each of the thyroid hormones, thyroxin (T4) and triiodothyronine (T3), contain iodine. Iodine-containing thyroid hormone is stored in the thyroid gland as a complex protein called thyroglobulin. Release of thyroid hormone is controlled by the pituitary gland's release of a hormone called TSH.
Thyroid hormones are unique in that they require trace amounts of iodine for biological activity. Iodine is a potent trace mineral found in seafood but not naturally abundant in other foods. By the 1920s it was realized that in land-locked places diets were often iodine-deficient. Since that time, iodine has been added to table salt in North America. We now get sufficient iodine in our food even if we eat a low-salt diet. However, approximately 1.5 billion people worldwide are still at risk of iodine deficiency. Surprisingly, sea salt does not contain enough iodine unless it has been iodized. Even salty fast foods may not contain iodine!
Yes, although some are more at risk. About four per cent of Canadians suffer from some form of thyroid disease. The most common condition, hypothyroidism, is caused by an underactive thyroid. It occurs roughly four times more often in women than men. The thyroid can also become overactive, resulting in hyperthyroidism. It is about ten times more common in women than in men. Pregnancy can cause phases of both hypo- and hyperthyroidism. About one in every 4,000 newborns has an underactive thyroid (congenital hypothyroidism). This condition must be treated at birth to prevent mental retardation. In Canada, a law ensures all newborns are tested for thyroid levels within the first few days of life.
At the other end of the age spectrum, the elderly are more likely to suffer from hypothyroidism than are the young or middle-aged. By age 60, 17 per cent of women and eight per cent of men show signs of hypothyroidism. Since symptoms may not be typical, thyroid testing can help solve undiagnosed conditions in the elderly. If you are over 60, symptoms of an underactive thyroid may include arthritis, bowel movement changes, psychiatric problems, congestive heart failure, problems with balance, an unexplained high cholesterol or some combination of the above. If you are over 60 and have an overactive thyroid, symptoms may include one or more of muscle weakness, depression, atrial fibrillation, fast pulse, nervousness, or excessive weight loss. Thyroid diseases are not contagious but, since they can be genetic, may be more common in some families.
The most common cause of hypothyroidism in iodine-sufficient areas of the world is a chronic inflammation of the thyroid called Hashimoto's Disease (also called Hashimoto's Thyroiditis or chronic autoimmune thyroiditis). The precise cause is not clear, but it is an autoimmune reaction thought to be linked with a combination of genetic susceptibility and environmental factors such as infection or stress. The body's natural protective immune mechanism mistakenly begins to destroy the thyroid as if it were foreign material. Hashimoto's Disease runs in some families. Those with other autoimmune conditions, including insulin-dependant diabetes or rheumatoid arthritis, are slightly more at risk.
Other types of thyroiditis can also eventually result in the thyroid producing too little hormone. The most common form follows a viral respiratory illness. It may begin with a short period of too much hormone being released, after which levels become too low. It resolves without treatment within six to 18 months.
Hypothyroidism occurs in about five per cent of women after childbirth but disappears six to 12 months after delivery. Once again, this condition often starts with a short (up to four month) period of hyperthyroidism followed by a hypothyroid phase. If there has been a major loss of blood around the time of delivery, permanent damage to the pituitary gland can result in secondary hypothyroidism.
Hypothyroidism can occur after radiation treatment of cancer in other parts of the neck. It can also be a result of pituitary gland problems, or a side effect of certain drugs such as lithium (used to treat bipolar disorder).
The most common cause of hyperthyroidism is another autoimmune condition called Graves' Disease. It occurs most often in young women, and tends to run in families. Graves' Disease can appear some months after recovery from an immune system-suppressing event such as pregnancy or severe psychological stress. Smoking doubles the risk! Another cause is toxic nodular goiter. This condition occurs mainly in those over age 50. It results from benign (non-cancerous) areas of enlargement in the thyroid. A third, rare cause results from pituitary tumors that produce increased levels of Thyroid Stimulating Hormone (TSH).
Certain medications can produce hyperthyroidism. One example is amiodarone, a heart medication that contains iodine. Amiodarone can also cause other types of thyroid disease, including hypothyroidism. Too much salt, although unhealthy for other reasons, will not cause hyperthyroidism.
The most common symptoms and signs associated with thyroid disease are compared in Table 1. Many of these are non-specific, which means they occur in a variety of different diseases. This can make it difficult for doctors to arrive at a quick diagnosis without the benefit of several blood tests. However, routine testing in adults without signs or symptoms suggestive of thyroid disease should not be done.
In extreme cases, abnormal thyroid hormone levels can have serious results. If the level gets very low a condition called myxedema can occur. In its worst form, it can cause coma and death. Extremely high levels of thyroid hormone can cause seizures and mental illness (thyroid storm). Thankfully, these extremes are very rare these days.
Yes, especially hypothyroidism. Subclinical (very mild) hypothyroidism is more common than once thought. Changes in the regulation of the thyroid can occur before symptoms appear. If thyroid problems are suspected, your doctor can order a blood test to measure TSH production. A high level of TSH indicates low thyroid output even if there are no symptoms yet and other thyroid tests appear normal. Conversely, a low level of TSH almost always means a high thyroid hormone level.
Not really, since cancer of the thyroid is relatively rare. It only accounts for around 1.5 per cent of all cancers in women and about 0.5 per cent of all cancers in men. Thyroid cancers often become apparent as a thyroid nodule (lump). Roughly five per cent of the public has thyroid nodules but only five to ten per cent of those are cancerous and need to be removed. Despite the fact that cancer is unlikely, if you feel a lump near your thyroid gland, have your doctor check it. Additional tests such as an ultrasound, a fine needle aspirate (biopsy) of thyroid tissue, or a thyroid scan using radioactive Iodine can be done for further examination.
If a lump is found on the thyroid of a child, an adolescent, or a male, there is a higher chance of it being cancerous. Those who have had radiation to their neck for other reasons or who have rapidly growing thyroid glands are also at higher risk. Anyone with a close relative who has had thyroid cancer is ten times more at risk than the general population.
Several different kinds of thyroid cancer exist and each one responds differently to treatment. The good news is that surgical cure rates can be as high as 95 per cent, depending on the type of cancer. Papillary carcinoma accounts for approximately 90 per cent of thyroid cancer and generally has a very good prognosis.
In the future, genetic testing will likely make it possible to tell who is at higher risk for thyroid cancers. Through genetic testing it is now possible to determine if the children of parents with 'medullary' thyroid cancer will develop the same cancer. The test determines whether these children have a certain gene. If the gene is present, there is a 90-95 per cent chance they will go on to develop medullary thyroid cancer. The thyroid gland can then be removed preventatively and thyroid hormone replacements used.
American Academy of Otolaryngology:
American Thyroid Association:
National Institute of Health
An excellent resource is the book The Harvard Medical School Guide to Overcoming Thyroid Problems,
published by McGraw-Hill.
Hypothyroidism: Regardless of the cause of an underactive thyroid, treatment is the same. Treatment is easy, very effective and inexpensive. It consists of simply replacing the missing amount of hormone with synthetic product identical to the body's own. The most common replacement (or supplement) is levothyroxine (Synthroidª, Eltroxinª and others) taken once a day. Synthetic levothyroxine is identical to the levothyroxine the thyroid normally produces. With treatment, symptoms gradually disappear. Depending on the type of hypothyroidism, treatment may be lifelong.
You should be careful to always make sure you get the same brand of thyroid replacement with each prescription. Brands differ in how much levothyroxine they contain. It is crucial that your body receives exactly the same amount each day. Similarly, generic thyroid replacement drugs should be used with caution. Be aware that many drugs interfere with thyroid medication. If you are taking thyroid medication, check with your doctor before taking other medications (prescription or otherwise). For instance, over-the-counter antacids, calcium and iron preparations may decrease the effect of thyroxin. Starting or stopping estrogen may change thyroid supplement requirements.
Hyperthyroidism: The treatment of patients with overactive thyroid glands is more complex. There are several different methods:
Radioactive Iodine (I131) is now considered the treatment of choice for adults. Radioactive iodine is taken as a capsule or liquid. It is absorbed only by the thyroid gland, leaving all other tissues in the body untouched. The radiation level is very low but since it is concentrated in the thyroid, the thyroid shrinks and produces fewer hormones. Those prescribed radioactive iodine should be aware that lifelong follow up with the doctor is necessary. Fifty percent of people eventually become hypothyroid and need to take levothyroxine pills for the rest of their lives. As well, hyperthyroidism affects many organ systems. As such, anyone diagnosed with hyperthyroidism and treated with radioactive iodine needs close lifelong monitoring by a doctor. Radioactive iodine can not be used during pregnancy or while nursing.
Antithyroid medications are often preferred for children and are a second choice for adults. They block the production of thyroid hormones. The two main drugs are propylthiouracil and methimazole (Tapazoleª). These drugs are generally safe and effective but need the supervision of specialists when used during pregnancy. It can take several weeks for hormone levels to return to normal. Other types of drugs can be used to control symptoms in the meantime. Anyone taking these medications should be monitored closely to be sure the thyroid gland is not producing too much or too little hormone. Drug side effects such as stomach discomfort, allergies, or rarely, a drastic reduction in the white blood cell counts, may also occur. After treatment for 18 - 24 months, up to 50 per cent of people return to a normal thyroid state and do not need further medication.
Surgery for hyperthyroidism, which involves removal of part or all of the thyroid, is no longer as common. It is most often performed on those who are very young, have huge goiters, or when thyroid cancer is suspected.
Thyroid diseases are complex and varied. If you have concerns about thyroid disease, contact your doctor for further information and assessment.