Hypothyroidism occurs when there are not enough of the thyroid hormones, T4 and T3, circulating in the blood. This disorder may also be described as an underactive thyroid. It is the most common form of thyroid dysfunction and affects approximately two out of 100 people. More women than men have underactive thyroid glands.
There are several causes of hypothyroidism:
Hashimoto's thyroiditis, an autoimmune disease, is the leading cause of hypothyroidism in North America. For reasons not fully understood, the body's immune system mistakenly produces antibodies that help to attack healthy thyroid cells, damaging the thyroid gland and affecting its ability to produce enough thyroid hormone.
Secondary hypothyroidism is a rare condition caused by a diseased pituitary gland. A healthy pituitary gland produces TSH, an essential hormone for production of thyroid hormone in the thyroid gland. In secondary hypothyroidism, little or no TSH is produced by the pituitary; therefore, the thyroid gland is not stimulated to make sufficient thyroid hormone.
Congenital hypothyroidism is caused by the failure of a baby's thyroid gland to develop normally while in the womb. After birth, normal physical and mental development depends on an adequate supply of thyroid hormone. In North America, all newborns are routinely tested for congenital hypothyroidism in order to prevent severe developmental disorders. Thyroid hormone replacement should begin shortly after the diagnosis of congenital hypothyroidism. Lifelong treatment with levothyroxine is usually necessary for patients born with this condition.
Since the signs and symptoms of hypothyroidism can also be the signs and symptoms of other, unrelated diseases, it is important for you to be examined by your physician and have appropriate laboratory tests performed. A physician usually begins by asking you about your medical history and then performing a physical examination. The most precise and accurate way to make a diagnosis of hypothyroidism is to measure blood concentrations of TSH and the thyroid hormone T4. A low level of T4 and a high TSH will confirm the diagnosis. Your blood may also be tested for the presence of certain thyroid antibodies to determine whether Hashimoto's thyroiditis is the cause of the hypothyroidism.
Hypothyroidism, including secondary hypothyroidism, can be treated simply, safely, and effectively by replacing the thyroid hormone T4. The preferred drug used for this purpose is synthetic T4, a man-made thyroid hormone that is identical to the body's; it's chemical name is levothyroxine. Fortunately, almost everyone can take levothyroxine. Hypothyroid patients are usually advised to take one tablet daily. The amount prescribed is based upon your physical examination and the levels of TSH and thyroid hormone in yout blood. Because most cases of hypothyroidism are permanent, lifelong thyroid hormone replacement will be necessary.
The majority of patients can be started with the anticipated full thyroid hormone replacement dose. However, older patients and those with a history of heart disease are sometimes given smaller doses that are gradually increased every few weeks. It may take eight weeks or more before the full effect of levothyroxine is noticed. Sometimes, adjustments in the strength of the tablets are necessary. You should never take more thyroid hormone than prescribed in an attempt to speed up your treatment or to lose weight. Adverse reactions are mainly caused by levothyroxine overdose. An overdose of thyroid hormone can cause symptoms of hyperthyroidism (an overactive thyroid): feeling hot, trembling hands, and/or palpitations.
Since hypothyroidism can influence the effects of antidiabetic drugs or anticoagulants, patients on these medications may be monitored more frequently as they begin treatment with levothyroxine. In addition, patients who become pregnant or begin taking estrogens may require higher doses of levothyroxine. Finally, certain drugs can interfere with the body's absorption of thyroid medication and should, therefore, be taken at least four hours after levothyroxine. Antacids, the cholesterol-lowering drug cholestyramine, and drugs containing iron are examples of such preparations. It is important that your physician is aware of all the medications, including over-the-counter preparations, you are taking.
Consult a physician in cases of chest pain, increased pulse rate, palpitations, excessive sweating, heat intolerance, and nervousness after beginning levothyroxine treatment.
Myxedema coma is a rare, life-threatening form of hypothyroidism. It can occur either in patients with undiagnosed, untreated hypothyroidism or in diagnosed hypothyroid patients who do not take their prescribed thyroid hormone replacement for months. The signs and symptoms of myxedema coma consist of a progressive worsening of the signs and symptoms of hypothyroidism, eventually leading to respiratory failure and a loss of consciousness. Treatment includes hospitalization in an Intensive Care Unit, intravenous thyroid hormone, and, frequently, life support with a respirator.
Once the proper dose of levothyroxine is established, you should be seen by your physician at least once a year for a physical examination and measurement of thyroid function. Occasionally, adjustments in the amount of the prescribed levothyroxine are required. Reasons for changing the dosage include:
Laboratory tests for some patients will show elevated TSH and normal or slightly low thyroid hormone levels. Often these patients have none of the signs and symptoms normally associated with hypothyroidism. This condition is called subclinical hypothyroidism. Your physician must decide whether you should be treated immediately or observed over time. Since research has shown that cholesterol levels and heart function improve for some patients when treated with levothyroxine, it is becoming more common for physicians to treat patients for subclinical hypothyroidism when it is first detected.
EM Pharma's ThyroCare™ brochures were developed to promote a greater understanding of thyroid disease and the diagnostic and treatment options available. If you have, or suspect you have, a thyroid disorder, your physician is in the best position to advise and treat you. We encourage you to discuss your questions and concerns with him or her.