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Thyroid Disease
What is thyroid disease?
Thyroid disease is a term describing a range of medical problems associated with the small, butterfly-shaped thyroid gland located just below the Adam's apple in the neck.
Although it weighs less than an ounce, the thyroid secretes hormones - thyroxine and triiodothyronine - that control the metabolism of nearly all tissues in the body. Essentially, the thyroid regulates the speed at which the cells in your body function, from how fast and steadily your heart beats to how well your nervous system works to how quickly your cells burn calories.
The thyroid also has a secondary function, producing the hormone calcitonin, which regulates the level of calcium in your blood.
Thyroid problems can range from minor to serious - and potentially life-threatening - including:
- Simple enlargement of the thyroid gland (goiter)
- Overproduction of thyroid hormones (hyperthyroidism)
- Underproduction of thyroid hormones (hypothyroidism)
- Inflammation (thyroiditis)
- Immune system dysfunction (Graves' disease)
- Nodular problems
- Cancer
Although among the range of thyroid problems the mechanisms of the disorders are generally understood, in some cases specific causes are not known. Symptoms can vary. Some of these problems can be treated relatively simply with drugs or hormone supplements. Some may require surgery or radiation therapy. Although the consequences of some can be serious, generally with appropriate treatment the prognosis for all is good.
The physicians of Connecticut Surgical Group have extensive experience in the treatment of thyroid problems and work closely together to ensure the best approach for each patient's situation.
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What is the anatomy of the thyroid gland?
Located in the front of the neck just below the Adam's Apple, the thyroid is often described as resembling a butterfly in its shape - two wing-like lobes connected by a band of tissue called the isthmus. Within the neck, the thyroid is sited in front of the larynx, or voice box. During gestation, the thyroid originates at the base of the tongue, but normally migrates to its location in the mid-neck in the course of fetal development.
The four pea-sized parathyroid glands, which regulate the calcium level within our bodies, are located just behind the thyroid. Although they share partial nomenclature and blood supply, the parathyroids are not related to the thyroid in function. For more information on the parathyroid glands, click here.
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How does the thyroid gland work?
The thyroid is the last of a complex chain of glands that are all involved in regulating thyroid hormones, beginning with the hypothalamus gland in the brain and continuing with the pituitary gland at the base of the brain.
It is important to understand that iodine is essential to the production of the thyroid hormones thyroxine and triiodothyronine, and that they are essential to regulating the body's metabolism. Thyroid cells constitute the only tissue in the body that can absorb iodine, and their role is to convert the iodine the body ingests with its food into the thyroid hormones.
Thyroid tissue does this by combining the iodine with the amino acid tyrosine. As they are distributed through the bloodstream, the thyroid hormones have an effect on every cell in the body, affecting electrical nerve impulses, the rate and rhythm of the heartbeat, the rate at which cells convert calories to energy, even your levels of anxiety and irritability.
In the brain, the hypothalamus initiates the production of thyroid hormones by signaling the pituitary at the base of the brain to stimulate the thyroid. The hypothalamus sends its signal by producing a hormone that tells the pituitary to release its own substance, Thyroid Stimulating Hormone (TSH). The hypothalamus is often described as determining at what levels the presence of thyroid hormones should be set, and the pituitary as the "thermostat" that reads the current thyroid hormone levels in the bloodstream and controls the thyroid to keep the desired level maintained.
Under the stimulation of TSH, the thyroid releases the thyroid hormones into the blood stream, increasing and decreasing the supply as the pituitary directs it.
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What are the risk factors for developing thyroid disease?
With such a range of disorders, specific risk factors will vary according to the specific problem. However, in general, some thyroid problems (such as autoimmune diseases) tend to run in families, the risk for most thyroid disorders increases with age - especially over age 40 - and women are more likely to experience it than men.
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How is thyroid disease diagnosed?
By and large, your doctor will diagnose your thyroid disease based on symptoms, risk factors and blood tests to measure your levels of TSH generated by the pituitary and thyroid hormones produced by the thyroid.
Depending on the problem being considered, additional studies may include a radioactive iodine uptake test and a thyroid scan. The first involves ingestion of a small amount of radioactive iodine and measurement of its concentration in the thyroid gland several times over the following two to 24 hours.
A thyroid scan involves using a gamma camera to visualize the absorption of a short-lived radioisotope within the gland - the camera captures the radiation emitted from the areas in which the isotope has been absorbed, indicating which areas of the gland are functioning and which aren't.
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What is a goiter?
A goiter is a benign but significant growth in the size of a thyroid gland, forming an enlarged lump at the base of the neck. If the pituitary reads that thyroid hormones are low, it may dispatch increased levels of its own thyroid stimulating hormone to the thyroid - causing the thyroid gland to enlarge. Although traditionally goiters have been associated with a deficiency of iodine in the diet, in American society today - where foods containing iodine are plentiful - goiter is more likely to be a function of a breakdown in hormone production in the thyroid (and the resulting increase in the pituitary's stimulating hormone).
Although a goiter can be dramatic and unattractive in appearance, it is not necessarily serious in and of itself. A small-to-moderate goiter that is not affecting surrounding structures can be stabilized by the use of thyroid hormone supplements. While the goiter won't shrink, it shouldn't grow.
If a goiter enlarges to the extent that it is pressing into other structures of the neck - such as the larynx, trachea, esophagus or even the chest - it may interfere with breathing and swallowing. Symptoms may include a cough, hoarseness and choking, especially during sleep. If the goiter becomes a physical or medical problem, surgical removal may be called for.
Although a goiter might be removed surgically because of its appearance, generally by the time it becomes a cosmetic issue it is also a medical one.
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What is hyperthyroidism?
Hyperthyroidism is the production of excessive amounts of the thyroid hormones, a phenomenon that can speed up your body's metabolism by as much as 100 percent. This can lead to serious problems such as unexplained weight loss, racing heartbeat, cardiac arrhythmia, hand tremors and muscle weakness.
This overfunctioning of the thyroid gland may be caused by the autoimmune disorder Graves' disease, by nodules in the thyroid that produce too much thyroxine (one of the thyroid hormones) or by the inflammation problem of thyroiditis. Each is described in more detail below.
Symptoms of hyperthyroidism may include:
- Development of a goiter
- Unexplained, sudden weight loss
- Runaway heartbeat or irregular heartbeat (cardiac arrhythmia)
- Changes in your skin
- Brittle hair
- Anxiety, irritability and even physical tremors
- Weakness in the muscles of your arms and thighs
- Increased bowel movements
- Increased sweating
- Lightened menstrual flow and less-frequent menstrual periods
- Sleep problems
Treatment techniques may include:
- Radioactive iodine. Since the thyroid cells are the only cells in the body that absorb iodine, ingestion of a radioactive iodine agent in capsule or liquid form will disrupt thyroid tissue cells, cause the gland to shrink and reduce the symptoms over a period of months. This is intended to cause thyroid hormone levels in the blood to return to normal, but some patients will find themselves experiencing underproduction of thyroid hormones. This is actually an easy problem to treat, however, involving use of thyroid hormone supplements.
- Anti-thyroid medications. These are drugs intended to interfere with your thyroid gland's ability to use iodine to produce thyroid hormones. It results in a permanent solution for some patients and only a temporary one for others.
- Surgery. Surgical removal of part or all of your thyroid gland is a solution for some hyperthyroidism patients. Depending on the clinical evaluation of your needs, this could range from removal of a part of one lobe to removal of the entire gland. As with radioactive iodine treatment, patients who undergo thyroidectomy may subsequently experience underproduction of thyroid hormones and have to take thyroid hormone supplements thereafter. As stated, this is actually an easy problem to treat through the use of thyroid hormone supplements.
Surgical options are discussed in more detail below.
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What is hypothyroidism?
The opposite of hyperthyroidism, hypothyroidism involves underproduction of thyroid hormones and a slowing of body metabolism. An inability of the thyroid gland to produce sufficient amounts of thyroid hormones can result from a range of causes.
Potential causes include:
- Autoimmune disorders that cause your body's own antibodies to attack your thyroid gland
- Other past or present inflammations of the thyroid
- Radioactive iodine treatments that may have overcompensated for hyperthyroidism
- Surgical removal of the thyroid gland
- Radiation therapy to treat cancers of the head and neck
- Some medications, such as the psychiatric drug lithium
- Autoimmune problems during pregnancy
- Birth defects involving the thyroid gland
- Iodine deficiency
- Malfunction of the pituitary gland
Possible symptoms of hypothyroidism include:
- Unexplained weight gain
- Muscle weakness, cramps and aches
- General fatigue
- Increased difficulty tolerating cold
- Dry, pale skin
- Coarse, dry hair
- Constipation
- Hoarseness
- Heavier menstrual flow
- Depression
Symptoms of hypothyroidism tend to develop slowly, and only half of the patients are diagnosed before symptoms have progressed. If not treated, hypothyroidism can result in development of a goiter in response to the pituitary gland's constant transmission of stimulating hormone to attempt to cause increased production of thyroid hormones.
Treatment
Treatment of hypothyroidism is relatively straightforward, with the use of levothyroxine, a synthetic hormone. Administered orally on a daily basis, it restores the thyroid hormones to appropriate levels. Your levels will be checked periodically to ensure that your dosage is correct.
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What is thyroiditis?
Inflammation of the thyroid gland can result from a number of causes - and from unknown causes - with varying results. In some cases, thyroiditis may cause excess discharge of thyroid hormones, resulting in symptoms of hyperthyroidism. In some patients, it may cause a decrease in production of thyroid hormones. In some cases, it may cause fever and pain.
A form of chronic thyroiditis called Hashimoto's thyroiditis is an autoimmune disorder that interferes with the thyroid's ability to produce thyroid hormones but not its ability to absorb iodine. The pituitary's transmission of stimulating hormone continues. Provision of hormone replacements usually will correct the problem and often lead the gland to decrease in size.
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What is Graves' disease?
Graves' disease (named for the 19th Century physician Robert Graves) is an autoimmune disorder that is often described as a cause of hyperthyroidism - in fact, the most commonly occurring underlying cause. It's also sometimes referred to by the name diffuse toxic goiter, reflecting the fact that the entire gland is enlarged.
In patients with Graves' disease, the immune system generates antibodies that attach to sites on the thyroid gland that lead it to increase production of the thyroid hormones. In addition, Graves' patients can experience redness and thickening of the skin on the lower legs, and inflammation around the eyes.
Although most Graves' patients don't have obvious eye issues, the ophthalmology aspects may involve swelling of tissues around the eyes, making the eyes appear to bulge, and blurred or double vision. The inflammation can be treated with corticosteroids to reduce swelling, or possibly ophthalmic surgery to relieve compression. Treatment of the hyperthyroidism may also lead over time to resolution of the eye issues.
Graves' disease can be a serious issue and requires medical consultation. It's unclear what causes it, but it appears to run in families. It affects women more often than men, and occurs most often in the 30s and 40s age groups.
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What are thyroid nodules?
Nodules are lumps or tumors that develop within the thyroid gland. They occur in some five percent of the population. Although when thyroid cancer develops it usually originates within a nodule, it's important to emphasize that the overwhelming majority of thyroid nodules are benign, or noncancerous.
Nodules can, however, also be a cause of hyperthyroidism, or the overproduction of thyroid hormones. A nodule that is "hot" has lost its regulatory capability, causing the cells within it to produce excessive amounts of hormones - and the characteristics of hyperthyroidism (a "cold" nodule underproduces hormone). The rest of the gland makes enough hormone.
Detection of a nodule can lead to several tests, including fine needle aspiration to assess whether it is benign or cancerous, and an ultrasound scan to obtain a visual image of the nodule.
In a fine needle aspiration procedure, your doctor (sometimes under x-ray guidance) will insert a very thin needle through the skin tissue and into the nodule within the gland itself to draw out cells for analysis by a pathologist.
An ultrasound scan, using high speed radio waves to visualize the nodule, will yield an image defining its structure. Sharp edges, lack of blood flow and the presence of fluid rather than living tissue usually indicate a benign nodule. The presence of multiple nodules within the gland usually suggests a benign status, as well.
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What is thyroid cancer?
The good news is that thyroid cancer tends to grow quite slowly, it's treatable, and the overwhelming majority of patients demonstrate excellent long-term survival rates.
There are four main types of thyroid cancer, named according to the appearance of their cells - papillary, follicular, medullary and anaplastic. The most commonly occurring are papillary and follicular.
While the causes are not known, it is clear that thyroid cancer is more likely to be found in people exposed in the past to low-dosage x-ray treatments in the head and neck for such issues as enlarged tonsils and acne. Individuals who lived or served in the area of the South Pacific where nuclear bomb testing was conducted are known to have a higher incidence of thyroid disease. Because it's slow-growing, thyroid cancer generally takes 20 years or more following exposure to radiation to manifest itself.
Treatment options are varied, including surgery, radiation treatment through external radiation generating machines or through the use of radioactive iodine, and traditional chemotherapy. In the iodine treatment, radioactive iodine is ingested with the intention that the radioactivity of the substance, as it is absorbed by the thyroid tissue, will destroy cancerous cells.
Papillary thyroid cancer
Papillary cancer cells, so-called because under a microscope they display multiple nipple-like projections, represents as many as 80 percent of all thyroid cancer cases.
It's a very slow-growing cancer. Some thyroid glands display tiny segments of papillary cancer cells without any medical implications - no indication of enlargement to malignant tumors. If it develops into a lump within the gland, it's considered a risk for continued growth and expansion to other parts of the body.
However, thyroid cancer is a disease in which the original cancer is of more concern than its spread. It's most likely avenue of spread is through the lymph system, but because it's so slow-growing, the outlook in these cases remains good. The outlook is less promising when the tumor itself has grown out of the thyroid and into surrounding tissues. Generally, for patients for whom the tumor is confined to the thyroid itself, the mortality rate after 25 years is less than one percent.
Follicular thyroid cancer
Follicular thyroid cancer, representing as many as 15 percent of all thyroid cancer cases, is so-called because it affects the normal follicle-shaped cells that make up the thyroid gland. In about 30 percent of patients, it presents little risk of spreading, but in the majority of patients it carries with it a risk of expanding to other parts of the body through the bloodstream.
Medullary thyroid cancer
Medullary thyroid cancer develops in the thyroid gland's "C cells," tissue involved in the thyroid's secondary function of producing calcitonin. This is the hormone responsible for regulating the level of calcium in your blood. Medullary cancer accounts for about five percent of all thyroid cancer cases. It can spread quickly to the lymph nodes in the neck but spreads slowly to more distant organs.
The standard treatment for this cancer is total removal of the thyroid gland and associated lymph nodes and other tissues in the neck. Ten-year survival rates are about 90 percent for cases in which the cancer is contained in the thyroid, 70 percent if it has spread to the lymph nodes in the neck and 20 percent if it has reached other organs.
Anaplastic thyroid cancer
Anaplastic thyroid cancer accounts for less than three percent of all thyroid cancer cases, but it is the most aggressive type and carries with it the lowest survival rate - a three-year survival rate of about 10 percent. By the time it's diagnosed, it has spread to the lymph nodes in some 90 percent of patients and it is not unusual for it to have spread to other organs.
Treatment approaches include surgery, radiation therapy and chemotherapy, but usually its development is very far along by the time it is diagnosed.
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What are the surgical options for thyroid disease?
Surgery for thyroid problems can involve removal of a small amount of tissue, an entire lobe, a lobe plus the isthmus, almost all of both lobes, or the entire gland.
- A partial lobectomy (involving a section of one lobe) might be performed for a benign nodule that is located well into the upper or lower half of the structure. In terms of current treatments, this procedure is seldom done these days, however.
- A lobectomy, removal of the entire lobe, is more likely to be performed. This can reflect concern about potentially cancerous tissue, hot or cold nodules and goiters based on one lobe.
- A lobectomy with an isthmusectomy, removing a full lobe plus the isthmus, might be performed if there are concerns about a larger amount of troublesome tissue.
- A subtotal thyroidectomy is a more extensive option involving removal of a full lobe, the isthmus and part of the opposite lobe - in other words, most but not all of the gland.
- A thyroidectomy is the procedure in which the entire thyroid is removed. When dealing with cancer, many surgeons prefer to ensure that all suspicious tissue has been excised by removing the entire gland.
Thyroid surgery is accomplished through an incision from three to five inches long across the central region of the neck. With access to the thyroid, the surgeon can excise the segment of tissue appropriate to the problem. Major concerns are to avoid damaging the nerves serving the larynx (and vocal cords) and preserving blood supply and the four pea-size parathyroid glands, which are located adjacent to the thyroid.
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What should I think about in dealing with my thyroid disease?
The consequences of the varied forms of thyroid disease can be serious, even life-threatening. But it is important to remember that effective treatments exist and that outcomes generally are quite good. Don't hesitate to seek medical assistance.
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For Additional Information:
You can find additional information about thyroid disease at web sites sponsored by government agencies, societies and healthcare institutions. It should perhaps be noted that the World Wide Web is open to many sources posting questionable information and promises, and you are encouraged to seek information from established, reputable organizations.
Likely sources include:
The American Cancer Society
www.cancer.org
The American College of Surgeons
www.facs.org
The American Thyroid Association
www.thyroid.org
Endocrine Web.com
www.endocrineweb.com
The National Digestive Diseases Information Clearinghouse
www.niddk.nih.gov
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