Kathryn Jean Lucas, MD
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Morehead City, North Carolina 28557

Thyroid Information

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HYPOTHYROIDISM At a snail’s pace

By: K. Jean Lucas, M.D.

WHAT IS HYPOTHYROIDISM?

As the name of this condition implies, hypothyroidism is present when the thyroid is not able to produce enough thyroid hormone to meet the demands of the body. In the early stages of this disorder, a person may have virtually no symptoms but laboratory tests may show a mildly elevated TSH. Thyroid stimulating hormone, as discussed above, is the most sensitive test in diagnosing thyroid disorders. When the TSH is elevated, even when the T4 is in the "normal range", the body is sensing that not enough thyroid hormone is being produced.

As the hypothyroidism becomes more severe, the following symptoms may be present. Not all of these symptoms may be present in individual patients.

WHY DO PEOPLE BECOME HYPOTHYROID?

The most common reason to develop hypothyroidism is from an autoimmune disorder in which antibodies attack the thyroid and gradually damage it enough to decrease its function. This disorder is inherited and predominates in women. It occurs commonly as women age or after childbirth.

If a person has had surgery to remove the thyroid, radical neck surgery to remove a cancer, or have been treated with radioactive iodine therapy for hyperthyroidism, the thyroid will not work because of removal or destruction of the thyroid tissue.

If the pituitary is damaged, contains a tumor or cyst, or does not produce enough TSH for any reason, the thyroid hormone levels will be low and the TSH will not respond to low T4 levels by increasing. In this situation, other hormones will also be affected by the pituitary problem and will need to be checked. The pituitary controls the ovaries, testes, adrenal, and thyroid. It is extremely rare to have only a TSH deficiency without any other abnormalities in pituitary function.

HOW IS HYPOTHYROIDISM TREATED?

As with any hormone deficiency, hormone replacement therapy is given to patients who are unable to produce adequate levels on their own. Brand name thyroxine (Synthroid, Levothroid, Levoxyl) is the preferred therapy for hypothyroidism. The T4 in these preparations is converted in the body to the active form of T3 for use by the tissues of the body. By allowing the body to convert the T4 into T3, the levels of thyroid hormone in the body are more constant and consistent.

Prior to the availability of synthetic T4, pig and cow thyroids were ground up and dried and given as desiccated thyroid. Brand names of the preparations include Armour thyroid. Although this type of replacement is natural (at least for cows and pigs), it is often variable in dose from batch to batch. It also contains T4 and T3. The T3 is a rapid acting thyroid hormone and leads to an erratic level of thyroid hormone in the body. In this case, the most natural way of replacing thyroid hormone is to use synthetic T4 and allow the body to convert what it needs into T3.

The dose of thyroid hormone that a hypothyroid patient will be started on will depend on:

1. the age of the patient: in older patients, a lower than normal dose will be started at first in order not to change the body’s functioning and heart rate too quickly
2. the body weight of the patient. The more one weighs, the higher the dose needs to be in order to correct the thyroid hormone deficit.
3. the amount of the thyroid that has been destroyed. If the disease is in its early stages, the full dose of thyroid hormone replacement is not needed at that time. However, as time goes on the full replacement will eventually be needed as the thyroid fails further.
4. the presence of heart disease. The dose will need to be much lower and gradually increased over time in order to prevent stimulation of the heart and precipitate a heart attack or rapid heart rhythm.
5. the goal of therapy. In some patients, suppression of a nodule or previous thyroid cancer will require a higher dose of thyroid hormone than replacement of thyroid hormone alone would indicate.

IS THE THYROID HORMONE DOSE CORRECT?

After a patient has been on a dose of thyroid hormone for at least 6 weeks, the levels of thyroid hormone and TSH can be determined. If the TSH is still elevated, then the body is sensing that it is not receiving enough thyroxine to carry out its daily functions. The dose of thyroxine will need to be increased. On the other hand, if the dose of thyroid hormone is too much, the TSH will be suppressed (lower than normal) and the dose will need to be lowered.

Symptoms of receiving too much or too little thyroid hormone may also be present in individual patients but usually are not enough to determine the correct dose of thyroxine. Several months may be required by the body to readjust to a normal level of thyroid hormone. For example, the body temperature is not a reliable measure of adequate thyroid hormone replacement because of the variation of body temperature throughout the population and through the day in each individual.

Over time, the thyroid dose may need to be modified. The reasons for changes in thyroid hormone are as follows:

1. further destruction of the thyroid by the autoimmune process
2. aging
3. changes in body weight
4. pregnancy or the initiation of birth control pills or oral estrogens at menopause may necessitate a change in dose to a higher level.

After the dose is stabilized and the TSH is normal, thyroid levels and TSH need to be checked at least once a year. Usually the prescription of the thyroid medication is only able to filled for this length of time as well.

Since hypothyroidism is an inherited disorder, one may want to have other members of the family (especially the females) checked for the presence of this disease. The TSH test is the best way of screening for the presence of thyroid disease.

OPTIMIZING THYROID HORMONE THERAPY

Take your thyroid hormone every day, preferably at the same time of day. If possible, take it on an empty stomach, but if trying to do this prevents you from remembering your dose, then take it with breakfast daily.

See your physician at least once a year and try to understand why you are taking this medication and the purpose of the medication.

Avoid generic brands of thyroid hormone. In this case, even though they may be less expensive to buy, they will give you varying amounts of thyroid hormone in your body and will require more testing in order to make sure you are receiving the correct dose. In this way, generic brands incur more expense.

Do not change brand names without checking with your physician.

If your symptoms change or you develop symptoms of being on too much thyroid hormone or too little thyroid hormone, alert your physician.

Notify your physician when you become pregnant, start birth control pills, or oral estrogens, since the dose of thyroid hormone may need to be changed.

If you forget to take the thyroid hormone pill that morning, take it later in the day. If you completely miss a day, do not take an extra one the next day. Thyroid hormone lasts a long time in the body and if you occasionally miss a dose, the level will not significantly change. However, if you routinely miss 2 doses or more per week, then over time, the levels of thyroid hormone obtained by your physician will be lower than they should be. You should let your physician know if you are frequently missing doses so that the lab tests you receive will be interpreted in light of this information.

"Do Not Take if You Have Thyroid Disease"

Many medications including those for cough and colds will contain a warning on the package, "Do not take this medication if you have thyroid disease." or "Consult your doctor before taking this medication." If your thyroid hormones levels are in the normal range, then you should be able to take any medication that a person without hypothyroidism should be able to take. However, if you are too much thyroid hormone or are hyperthyroid, then decongestant medications, medications or beverages with caffeine, and asthma medications, may increase the symptoms of too much thyroid hormone and cause palpitations, nervousness, and tremor.

If you are still hypothyroid, you should avoid sedating medications such as antihistamines or sleeping aids because the effect of these medications will be increased because of the hypothyroidism.

DRUG INTERACTIONS WITH THYROID HORMONE

• Iron supplements will decrease the absorption of thyroid hormone taken at the same time. One should take these preparations at different times of the day.
• Antacids containing aluminum hydroxide (amphogel, alternagel) and carafate will decrease the absorption of thyroid hormone if taken at the same time.
• Questran and clofibrate will decrease the absorption of thyroid hormone and will need to be taken at different times of the day.
• Oral estrogens and oral contraceptives may cause a decrease in the active level of thyroid hormone and may require the thyroid hormone dose to be raised.
• Seizure medication such as Dilantin and Tegretol may decrease the levels of thyroid hormone measured by laboratory tests. Usually the TSH does not increase and no dosage adjustment is necessary.
• Steroid hormones such as Prednisone, Medrol, or Decadron may decrease thyroid hormone levels and decrease TSH.

When a patient is hypothyroid, most medication levels in the blood will increase because of the decrease in metabolic rate. Levels of certain medications will need to be monitored by your physician until the thyroid levels are back to normal.

FOR FURTHER INFORMATION

	YOUR THYROID: A Home Reference, L.C. Wood, D.S.Cooper, & E.C. Ridgway, 1982.
	THE THYROID GLAND: A Book for Thyroid Patients, Joel Hamburger, 1988.
	HOW YOUR THYROID WORKS, H. Jack Baskin, 1991.
	COULD IT BE MY THYROID? Sheldon Rubenfeld, 1995
	THE THYROID FOUNDATION OF AMERICA, INC. Box B-ACC 630 Massachusetts General Hospital Boston, MA 02114
	THE THYROID SOCIETY FOR EDUCATION AND RESEARCH 1-800-THYROID (1-800-849-7643)

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Copyright © 1999-2011 K. Jean Lucas, MD, All Rights Reserved

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