Thyroid for Dummies (46 page)

But how low is too low? If a reading of 0.3 is good, is a reading of 0.1 better?

A study published in
Thyroid
in 1999, addressed this issue. The researchers had two groups of cancer patients: in one group, TSH levels were suppressed to below 0.1; in the other group TSH levels were kept between 0.4 and 0.1.

The study found that residual thyroid tissue was no more suppressed when the TSH was less than 0.1 than when it was less than 0.4. The research shows that thyroid cancer patients should receive suppressive doses of T4 but that greater suppression is no better than lesser degrees of suppression.

The advantage of taking the least suppressive dose of thyroid hormone possible is that you have less risk of developing osteoporosis or rapid heartbeats, particularly if you are middle-aged or older.

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Anticipating Drug Interactions

So many drugs interact with thyroid hormones that you must check with your doctor whenever you are placed on a new medication or taken off an old medication (look at Chapter 10).

Thyroid function is often affected not only when you start a new medication, but also if you are taken off an old medication or the dosage is changed significantly.

The way to avoid a problem is to perform (or ask your doctor or pharmacist to perform) a search for interactions between thyroid hormone and the drugs you need to take.

Drugs can affect thyroid function at any level. They can increase or decrease the release of thyrotrophin-releasing hormone, which affects how much thyroid-stimulating hormone (TSH) your body makes. They can increase or decrease the release of thyroid hormone from the thyroid. They can change the ratio of T4 hormone versus T3. They can affect the uptake of thyroid hormone into cells. They can increase or decrease the action of thyroid hormone within the cells.

The major drugs to take care with are the following (refer to Chapter 10): ߜ Amiodarone

ߜ Aspirin (in doses greater than 3,000 milligrams)

ߜ Corticosteroids

ߜ Iodine

ߜ Iron tablets

ߜ Lithium

ߜ Oestrogen

ߜ Propranolol

Chances are that you will take one or more of these drugs in your lifetime.

Just about every drug affects thyroid function in one way or another.

Fortunately, most of the effects are overcome as the normal thyroid gland makes some adjustment. But if you’re on a fixed treatment dose of thyroid hormone, your thyroid cannot adjust as it would normally. Ask your doctor about having your thyroid function tested four to six weeks after you start a new medication or stop an old one.

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Protecting Your Thyroid from Radiation

Between 1920 and 1960, many people received irradiation treatment that increases their risk for thyroid cancer. Close to 10 per cent of people receiving this treatment have developed thyroid cancer to date.

If you received irradiation to your neck area as a child because of enlarged tonsils, acne, an enlarged thymus, or some other condition, you are at increased risk for thyroid cancer and should inform your doctor. And if you’ve had any kind of radiation treatment to your head, chest, or neck in the past, it’s important to perform the ‘Neck Check’ described earlier in this chapter. If you feel something unusual in your thyroid shape or size, see your doctor. In fact, see your doctor anyway as changes are often subtle and the incidence of thyroid cancer is definitely higher if you’ve had irradiation therapy. The exception here is that radiation treatment for hyperthyroidism does not increase your risk of cancer.

A thyroid scan or a thyroid ultrasound (check out Chapter 4) usually finds any significant abnormality that exists. If one is found, the usual next step is a fine needle biopsy of the thyroid.

What about follow-up if nothing is found? It’s probably a good idea to have an examination of your thyroid on at least an annual basis if you have a history of thyroid exposure to radiation (other than for treatment for hyperthyroidism).

However, should cancer occur, it’s no more dangerous than thyroid cancer not associated with radiation, as long as it’s treated properly.

Keeping Up-to-Date with

Thyroid Discoveries

This book is an excellent start in your quest for knowledge about the thyroid gland and how it affects you. Given the pace of research, however, a book cannot keep you completely up-to-date with new findings about the thyroid gland. You need to seek them out for yourself. Where do you look?

In Appendix B, you find the Internet sites that are most accurate and reliable with respect to thyroid function and disease. These include Web sites of large organisations, sites belonging to individuals and groups who are advocates for various thyroid conditions, and government sites that provide information about the thyroid.

Drug companies that make thyroid medications have Web sites that contain information about their products and often general information about the thyroid as well.

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Part VI

Appendixes

"Bad skin, lifeless hair, hoarse voice, loss
of hearing—Thyroid disease has done

wonders for my pop music career."

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In this part . . .

Appendix A is a glossary of the terms you encounter

as you read and hear about the thyroid gland, its

function, and its diseases. All the strange words you meet for the first time in the text of the book are listed here and defined. Appendix B shows you where to look for more

information as well as the latest research findings on the thyroid. There is a huge amount of research focusing on every aspect of normal thyroid function and abnormal

thyroid conditions. This book gives you a good working knowledge of the subject, but there is always more to know, and these Web sites are where to find it.

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Appendix A

A Glossary of Key Terms

Acute thyroiditis:
A sudden-onset bacterial or fungal infection of the thyroid.

Allele:
One of two or more genes that determine which enzyme is made or which body characteristic prevails.

Antigen:
A foreign protein that prompts the production of antibodies to destroy it.

Autoimmune thyroiditis:
Inflammation of the thyroid associated with the production of antibodies against thyroid tissue – also known as Hashimoto’s thyroiditis or chronic thyroiditis.

Beta-blocking agent:
One of a group of drugs given to block some of the adverse effects of excess thyroid hormone.

Chromosome:
One of 23 pairs in the nucleus of every human cell that carry all the genes that determine the characteristics of the body.

Chronic thyroiditis:
Another name for autoimmune thyroiditis.

Cretinism:
A syndrome affecting children; its most outstanding feature is mental retardation that results from a lack of iodine during pregnancy.

Cyst:
A sac-like structure containing fluid.

Dominant gene:
The gene that determines which particular enzyme or body characteristic is expressed when two different genes are present.

Ectopic thyroid:
Thyroid tissue found in an abnormal site, such as the base of the tongue.

Exophthalmos:
Eye disease associated with Graves’ disease.

Fine needle aspiration biopsy (FNAB):
The process of putting a tiny needle into tissue, in this case the thyroid, for the purpose of determining the nature of that tissue. This process is particularly helpful for identifying thyroid cancer.

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Free thyroxine (FT4):
The tiny fraction of the T4 hormone that is not bound to protein and is therefore available to enter cells.

Free thyroxine index (FTI):
An obsolete test once used to determine thyroid function. The product of multiplying the total T4 by the T3 resin uptake.

Free triiodothyronine (FT3):
The tiny fraction of the T3 hormone that is not bound to protein and is therefore available to enter cells.

Gestational transient thyrotoxicosis:
A brief period of hyperthyroidism during pregnancy that results from the large production of human chorionic gonadotrophin (which acts as a thyroid stimulator).

Goitre:
An enlarged thyroid gland.

Graves’ disease:
An autoimmune condition that combines hyperthyroidism, eye disease, and skin disease.

Hashimoto’s thyroiditis:
Another name for autoimmune or chronic thyroiditis.

Heterozygous:
Possessing two different genes for an enzyme or trait.

Homozygous:
Possessing two of the same gene for an enzyme or trait.

Human chorionic gonadotrophin (HCG):
A hormone made in the placenta that shares some properties with thyroid-stimulating hormone.

Hyperthyroidism:
An over-active state due to the excessive production or intake of thyroid hormone.

Hypothyroidism:
An under-active state due to the diminished production or intake of thyroid hormone.

Isthmus of the thyroid:
The thyroid tissue that connects both lobes of the thyroid.

Leptin:
A hormone produced in fat cells that signals the brain that the intake of calories is excessive.

Levothyroxine:
The generic name for thyroxine (T4) medication.

Liothyronine:
The generic name for triiodothyronine (T3) medication.

Medullary thyroid cancer:
A cancer in the thyroid associated with cells called parafollicular or C-cells, which make a hormone called calcitonin.

Multinodular goitre:
An enlargement of the thyroid associated with many nodules or outgrowths.

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Multiple endocrine neoplasia (MEN):
Hereditary production of tumours in several endocrine glands – one of the types of tumour is medullary thyroid cancer.

Mutation:
An unexpected change in an enzyme or body characteristic due to an alteration in a particular gene.

Myxoedema:
Another name for hypothyroidism.

Postpartum thyroiditis:
Inflammation of the thyroid, after a pregnancy, that is associated with thyroid autoantibodies and may go through stages of hyperthyroidism, normal thyroid function, and hypothyroidism. It may resolve or end in hypothyroidism. It is often accompanied with depression.

Pyramidal lobe of the thyroid:
An accessory lobe rising from the isthmus of the thyroid.

Recessive gene:
A gene that determines an enzyme or body characteristic only when it is present on both chromosomes. (Otherwise the dominant gene prevails.)

Resin T3 uptake:
A test of thyroid function (now obsolete) that provides an assessment of the amount of T4 bound to protein compared to the free T4.

Riedel’s thyroiditis:
A rare form of thyroid inflammation that is often associated with thyroid antibodies. It results in fibrosis of thyroid tissue, and sometimes parathyroid tissue, with tight adherence to the trachea.

Silent thyroiditis:
A form of thyroiditis that is identical to postpartum thyroiditis but occurs at any time of life.

Subacute thyroiditis:
A viral inflammation of the thyroid gland that is associated with pain in the thyroid.

Subclinical hypothyroidism:
An elevation of the TSH, with a normal free T4

level and minimal to no symptoms of hypothyroidism.

Thiocyanate:
A chemical found in some foods that may interfere with thyroid function.

Thyroglobulin:
Material in the follicle of the thyroid in which thyroid hormones are stored.

Thyroid agenesis:
Developmental failure to produce a thyroid gland in the foetus.

Thyroid autoantibodies:
Proteins that react against the thyroid, sometimes to suppress or destroy it and sometimes to stimulate it.

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Thyroid dysgenesis:
Failure of the thyroid to grow or move into its proper place in the neck (attached to the trachea below the Adam’s apple).

Thyroid hypoplasia:
Production of a thyroid gland that is inadequate for the needs of the body.

Thyroid scan and uptake:
Use of radioactive iodine to outline the thyroid, determine if tissue is actively producing thyroid hormone, and determine the level of activity of the gland.

Thyroid-stimulating hormone (TSH):
A hormone from the pituitary gland that stimulates the thyroid to produce more hormone.