Hypothyroidism is almost always due to disease within your thyroid gland that causes a decrease in the production of thyroid hormone. The most common cause of this disorder is autoimmune thyroid disease, which is transmitted genetically and affects women much more often than men. Excellent tests, particularly the blood TSH level, are available to diagnose the condition accurately, and treatment with thyroid hormone (thyroxine ) should restore you to good health. Because the condition runs in families, some of your relatives should be checked for thyroid problems by their own physicians.
When the thyroid gland fails to produce a normal amount of thyroid hormone, hypothyroidism results. Thyroid hormones act upon receptors in tissues throughout your body controlling the rate at which various things happen, such as the speed of chemical reactions, the rate of tissue growth, and the rate at which electrical impulses travel in your nerves and muscles.
So when you become hypothyroid, many of the affected bodily functions simply slow down.
As your thyroid begins to fail, you may feel perfectly well, for often the only suggestion of a problem will be a slight enlargement of your thyroid gland (goiter), appearing as a lump or swelling in front of your neck. Then, as your thyroid hormone level falls further, you may begin to feel tired and listless, perhaps chilly when those about you are comfortably warm. As your skin, hair, and fingernails grow more slowly, they become thickened, dry, and brittle. Some hair loss may be noticed. Then, as your hypothyroidism becomes more severe, changes may occur in the tissues beneath your skin that lead to a characteristic puffy, swollen appearance known as myxedema. This is often particularly apparent around your face and eyes.
Your circulation is affected and your heart rate slows, but you probably won't notice this unless someone happens to count your pulse (it may be below 60 beats per minute). Since your intestinal activity slows down, you may become constipated. A few pounds of weight gain may occur due to water retention, but you are not likely to get fat due to hypothyroidism alone because your appetite and zest for food decrease rather than increase when you become hypothyroid. Your muscles may become sore and you may be awakened at night with leg cramps. Muscle swelling may occur and may make your tongue (which is a muscle) bigger. Your nervous system may be affected in several ways. You may notice some memory loss, decreased ability to think, depression, and you may become more sensitive to medications, so that weak sedatives cause prolonged sleep. Some patients experience tingling in their fingers, or loss of balance and difficulty in walking.
If you are a younger woman, changes in your reproductive system may cause longer, heavier, and more frequent menstruation. Your ovaries may stop producing an egg each month, and, if so, it may be difficult for you to get pregnant. If pregnancy does occur, you are a little more likely to have a miscarriage than if you had a healthy thyroid.
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The causes of hypothyroidism vary somewhat with the age when the disorder begins. Some children born with severe hypothyroidism have never developed enough thyroid tissue to supply adequate amounts of thyroid hormones for their bodily needs. Other hypothyroid infants may have an inherited defect in the production of thyroid hormones within their thyroid gland. In some underdeveloped countries, dietary iodine deficiency is an important added cause of serious hypothyroidism in newborn babies.
The most common cause of thyroid gland failure in older children and adults is a silent, ongoing inflammation of the thyroid (without evidence of infection), known as chronic lymphocytic thyroiditis. It is also known as Hashimoto's disease, in honor of the Japanese physician who described it. The thyroid fails because inflammation and scarring damage the thyroid tissue.
Thyroid failure is also very common among patients who have been treated in the past for an overactive thyroid. Here, hypothyroidism may occur immediately after a treatment that destroys or removes part of the thyroid (radioactive iodine or an operation), but, in most instances, the thyroid doesn't fail until months or years later. Such a delayed onset of hypothyroidism suggests that the original treatment is not the only cause of thyroid failure in such patients. Coexistent chronic lymphocytic thyroiditis may be a factor as well.
Less commonly, the thyroid may fail temporarily after a viral infection or because of a medication. For example, if an antithyroid drug used to control an overactive thyroid is given in too large a dose, hypothyroidism may result and last until the dosage of that drug is reduced. Lithium, a psychiatric drug, can also cause hypothyroidism in some people. Furthermore, some individuals have thyroid glands that are very sensitive to iodine. They can develop hypothyroidism as a side effect if they are given iodine in a medication such as amiodarone (a heart medicine). Individuals who eat seaweed (kelp, dulse, etc.) or take supplements which contain seaweed extracts can take in excessive amounts of iodine. Hypothyroidism can also develop in patients who receive large amounts of x-rays to the neck area as part of cancer treatment.
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If your physician suspects hypothyroidism, he or she will first perform a medical examination to look for evidence that your thyroid level is low. The most important test in making a certain diagnosis of this condition is your TSH blood level. When your thyroid gland fails, your pituitary begins to produce increased amounts of TSH, in an effort to stimulate your thyroid more and return it to normal function. If your thyroid is damaged, it cannot increase its activity and your blood level of TSH rises and remains high. Detecting an increased level of TSH in your blood also provides solid evidence that your hypothyroidism is due to disease within your thyroid gland, and is not a result of inadequate stimulation of your thyroid by a diseased pituitary gland.
A word should be said about a dangerous recent trend in the lay press to minimize the importance of thyroid blood tests in the diagnosis and management of hypothyroidism. The thyroid tests available 20 or 30 years ago were simply not specific enough to tell if a person was truly hypothyroid. Very accurate and relatively inexpensive tests are available today, however, and they should always be used by your physician to help make a diagnosis of hypothyroidism. Such a diagnosis should never be based solely on complaints of weight gain, fatigue, or infertility, or on such nonspecific findings as dry skin or a low body temperature. Well-informed physicians do not start patients on thyroid medication until blood tests, and most importantly, the TSH level, confirming the diagnosis are obtained. Blood tests are essential in determining the cause and severity of the hypothyroidism, and in assessing the adequacy of thyroid therapy. The level of the thyroid hormones (T4 and T3) may also be checked, but these tests are less sensitive than the TSH level in making a decision about the diagnosis of primary hypothyroidism or the dose of medication that you might require.
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Hypothyroidism is treated with thyroid hormone tablets containing precisely the same chemical compound that your thyroid normally produces and therefore, you will not be allergic to it. Moreover, the hormones are not destroyed by stomach juices, so they can be given by mouth. Finally, if taken correctly, thyroid hormone has no unwanted effects on any body tissues.
Today, many different thyroid hormone preparations are manufactured. For many years, however, the only thyroid hormone medications available were made from animal thyroid glands. These preparations were very useful, but they contain not only thyroxine (T4), but also a second, more rapidly acting thyroid hormone, triiodothyronine (T3). Most doctors prefer to administer thyroid hormone tablets that do not contain T3 for two reasons. First, the body normally makes T3 from T4; in fact, much of our T4 is changed into T3 under normal circumstances, as it is used by the body. Second, the blood T3 level can become abnormally high after taking medication that contains T3. The abnormally high T3 level can cause a rapid pulse and increase the workload of the heart, which can be dangerous for anyone with underlying heart disease. For these reasons, most physicians now treat hypothyroidism with tablets of pure T4 rather than tablets that contain both T4 and T3.
Recently, there has been renewed interest in the question of whether T4 plus a little T3 might be better for some people than T4 alone. A study published in the February 11, 1999 issue (Vol. 340, No. 6) of the New England Journal of Medicine suggested that some patients with hypothyroidism may feel better taking a medication that includes a combination of triiodothyronine (T3) along with thyroxine (T4). However, the addition of T3 could lead to complications for certain patients. While this approach to treatment is not new, it is not the treatment most widely accepted and prescribed by most physicians for their hypothyroid patients.
Most physicians prefer to treat hypothyroid patients with pure T4 because treatment with rapid-acting T3 produces abnormally high peak levels of T3 in the blood. This could cause increased risk for heart rhythm problems or heart attacks especially in older individuals and anyone with heart disease. Because in most individuals the body converts T4 to T3 as needed, pure thyroxine (T4) alone is the medication that the vast majority of physicians prescribe for hypothyroid patients. A change in thyroid hormone dose, or adding T3 in some form may be a help for some patients. Some people may have health concerns such as depression, memory problems, muscle aches, or weight gain which may need different treatment including other medication.
There is an increasing tendency today to use generic forms of drugs as opposed to more expensive forms sold under a trade name. Although generic drugs are generally less expensive, generic thyroid preparations have always presented the question of unreliable potency. Tests conducted in the United States have shown this variability of potency in generic T4 tablets. In fact, only three kinds of T4 tablets are found to be consistently reliable: Synthroid, Levothroid, and Levoxyl. These tablets have a nearly identical color code (thyroxine tablets of different potencies come in different colors), which helps to avoid confusion about thyroid hormone dosage. A wide variety of dosage strengths are available to enable the physician to precisely tailor the dose to the patient. Synthroid is available in the United States and Canada, while Levothroid and Levoxyl are marketed only in the United States. Other brands are available in Canada and Europe.
When changing a patient from a dessicated thyroid tablet to T4, physicians usually start at a slightly lower dose of T4 because many older preparations are not reliably potent. For example, someone who has taken two or three grains of dessicated thyroid may be started on 75 to 125 micrograms of thyroxine. In fact, few patients ever need more than 100 to 200 micrograms of thyroxine per day.
Even when hypothyroidism is severe, a few months of thyroid treatment should lead to complete recovery and a return to good health. At that time, your physician will probably measure your blood levels of T4 and TSH to be sure that your dosage of thyroid hormone is correct. If you are taking too much T4 your blood level of TSH will be too low and the blood level of T4 may be above the normal range. On the other hand, if your dose of T4 is too low, your blood level of TSH will still be high and the T4 level may be low.
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The smooth control of thyroid hormone levels that physicians achieve by using pure thyroxine preparations is due to the slow rate at which thyroxine is used up by the body. In fact, if a normal person's thyroid suddenly stopped working, it would take about seven days for the body to use up just half of the T4 already in the blood. Therefore, if you are hypothyroid and taking thyroxine tablets to correct your thyroid deficiency, you will not feel suddenly sick even if you stop your thyroxine tablets abruptly. Furthermore, because you won't notice a sudden change in the way you feel, you may incorrectly assume that your thyroid condition no longer exists and you may stop taking your medication entirely. Unfortunately, when your hypothyroidism does recur, its onset may be so gradual that you may not realize that you are becoming ill again until your symptoms are pronounced.
If you are hypothyroid, it is important that you see your physician periodically for checkups. Since most hypothyroidism tends to get worse progressively over months and years, a dose of thyroid hormone that was correct several years ago may well be inadequate as thyroid replacement now. Therefore, your physician will probably want to measure your serum T4 and TSH periodically to be sure that a change in hormone dosage is not indicated. We recommend that patients should be tested at least once each year to be sure that the control of the thyroid condition is correct.
An exception to this rule applies if you become pregnant. Pregnancy often increases the thyroid hormone requirement. Therefore, if you become pregnant while taking thyroid hormone for hypothyroidism, we recommend that you have your TSH level checked as soon as you know you are pregnant, and again in each trimester. If the value is high your doctor will increase your dose of medication until you have safely delivered your child. Then your dose will be reduced to the previous level.
A word might be said about treating certain of the less common causes of thyroid failure. For example, subacute thyroiditis, which may be due to a viral infection, may only temporarily decrease thyroid function. If a patient needs any thyroxine treatment for a transient hypothyroid condition, it should be only a matter of weeks or months before he or she can stop the drug and remain well. And when hypothyroidism is due to iodine ingestion or an antithyroid drug, simply stopping or decreasing the dose of the drug may be all that is required. In every such instance, your physician has the necessary tests available as a guide in properly taking care of you. A very special example of this is the hypothyroidism that occurs immediately after delivering a child. This condition is known as postpartum thyroiditis and is found in approximately 5 to 8 percent of all women in the postpartum period. It usually occurs 2 to 12 months after delivery and may be preceded by hyperthyroidism due to thyroid hormone leaching out of the inflamed thyroid. If hypothyroidism develops it commonly requires treatment with thyroid hormone. Surprisingly, this form of hypothyroidism is usually not permanent and typically goes away spontaneously after 6 to 12 months. Thus, in this type of hypothyroidism, your doctor will discontinue the thyroid medication to see if the problem has disappeared. However, hypothyroidism is permanent in 10 - 25% of women with this disorder.
Since the pituitary gland at the base of your brain controls and stimulates your thyroid, a tumor or other problem that involves the pituitary can cause secondary thyroid failure. Since your pituitary also controls other glands, including your reproductive organs and adrenal glands, it is usually an easy matter for your physician to tell if this is the case. For example, a woman with secondary (pituitary) hypothyroidism will usually stop menstruating when her diseased pituitary gland stops stimulating her ovaries properly. Physicians have at their disposal both x-ray techniques and laboratory tests to evaluate the function of your pituitary gland as well as your thyroid. If there is indeed a pituitary problem, you will probably require treatment for other hormonal deficiencies in addition to the thyroid. If your pituitary fails because of a tumor, specific treatment may be directed at the pituitary gland itself. Fortunately, pituitary tumors respond to both surgical and radiation treatment. Just as with primary hypothyroidism, you will need careful and prolonged follow-up, for in addition to thyroid hormone requirements, the amounts of other hormones you take may vary with time. Thus, periodic blood tests and x-rays of the pituitary area will probably be recommended by your physician.
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