Hypothyroidism

Just as too much thyroid hormone causes hyperthyroidism and increased metabolism; too little thyroid hormone causes hypothyroidism resulting in a slowed metabolism. When the thyroid gland fails to produce enough thyroid hormone, it is usually because the thyroid gland is failing or has been removed; however, about two percent of hypothyroid patients have a normal thyroid gland and are producing too little thyroid hormone because the pituitary gland (which controls the thyroid) is failing to produce TSH. Since the pituitary gland controls the adrenal glands, ovaries, and testicles; disease of the pituitary gland is usually more serious than simple thyroid failure. Therefore pituitary function must be checked in all patients who are hypothyroid. The pituitary hormone (TSH) goes up with primary thyroid failure, whereas the TSH is low when the pituitary gland is responsible for hypothyroidism.

Like symptoms of hyperthyroidism, the symptoms of hypothyroidism are vague at first and often attributed to overwork, stress, or growing older.

When hypothyroidism occurs, all the body's metabolic processes slow down. Heart rate slows, body temperature drops with an increased sensitivity to cold; hair and nails grow more slowly. Constipation frequently occurs because of slowed intestinal activity. Thinking becomes slow with memory loss and sometimes difficulty with calculations such as balancing ones checkbook. Skin becomes dry, muscles become sluggish and may cramp, (arms and legs tend to go to sleep), and there is an increased need for sleep. In women menstrual periods become heavy and infertility is common. Many men experience impotence. Weight gain, while much discussed, is usually limited to less than fifteen pounds. The weight is not due to over eating, but to decreased utilization of calories (less activity). In general, hypothyroid patients complain of chronic tiredness and loss of energy.

In primary thyroid failure, there is frequently an enlargement of the thyroid gland (goiter), but in secondary thyroid failure (disease of the pituitary gland) the thyroid gland does not enlarge. Hoarseness can occur with either type of hypothyroidism since there may be swelling (edema) of the vocal cords; but hoarseness and difficulty swallowing are much more common if there is a goiter.
In the past, thyroid tests were notoriously unsensitive to borderline hypothyroidism and it was common practice to put patients on thyroid replacement if they presented with certain symptoms. These symptoms included unexplained fatigue, hair loss, overweight, infertility, menstrual irregularity, short stature, etc. Although an occasional patient did seem to respond to treatment, the majority of patients showed no improvements and they were then faced with the possible need to keep taking thyroid hormone indefinitely.

Today, thyroid tests are among the most sensitive tests in medicine, and all patients who really need to be on thyroid hormone replacement will show an abnormality on at least one thyroid test. Therefore one should never take thyroid pills as a "test trial" without checking the thyroid function first. Once a person is placed on thyroid hormone it is impossible to check their thyroid function without stopping the hormone.

The causes for hypothyroidism are numerous. In the past many cases resulted from previous thyroid surgery. Since thyroid surgery used to be more common than it is today, we now see more cases due to previous radioactive iodine treatment than due to surgery. Undoubtedly many cases are familial or hereditary since over 50% of hypothyroid patients have relatives with a history of thyroid disease or goiter. Also, the newer tests for diagnosis are picking up more cases of borderline hypothyroidism that were not recognized by the older thyroid tests that were not sensitive to slight degrees of under function.

About 1 in 4,500 children are born low thyroid. If not recognized shortly after birth and treatment started immediately, these children become mentally retarded. For that reason most countries check  all children born in hospitals for hypothyroidism at birth. Hashimoto's Thyroiditis (discussed later) is a very common reason for hypothyroidism in older children and young adults.

Iodine deficiency, while a common reason for hypothyroidism in the first part of the last  century, no longer exist in most western countries because of the iodination of salt and the use of iodine as a food preservative in so many foods. Indeed, hypothyroidism has occurred because of too much iodine in certain patients. The ingestion of large amounts of iodine in vitamins, cough medicines, or as a dye used in x-raying the gallbladder or kidney has actually caused hypothyroidism.

Certain drugs such as lithium, Amiodarone, kelp, or antithyroid pills can cause hypothyroidism. Patients who have received radiation for Hodgkins Disease, tongue cancer, or other types of cancer frequently become hypothyroid several months to several years after their treatment.

Although newspaper and magazine articles have been written about using underarm temperature, basal metabolic rate test, ankle jerk reflex, and other means of diagnosing hypothyroidism, the most accurate test for hypothyroidism is a blood test. A low T4 (or T3) and a high TSH (in primary hypothyroidism) are typical. The TSH tends to be the first test to become abnormal in patients becoming hypothyroid. The finding of a normal T7 and TSH virtually rules out any possibility of hypothyroidism. When patients are found to be hypothyroid, thyroid antibodies and a thyroid scan are frequently done to find out the cause for the hypothyroidism.

Putting patients on thyroid hormone because of symptoms of fatigue, weight gain, infertility, etc. should never be done without first testing the blood. This will confirm the diagnosis and can be used as a baseline in assessing the treatment later. To go back and check a patient's thyroid after being on thyroid replacement is always more difficult and requires stopping the medication.

It was only around hundred twenty years ago in 1891 that a 26 year old English physician, George Murray, reported to the British Medical Association that he had cured a case of myxedema (hypothyroidism) by injecting sheep's thyroid gland into the patient. This was the first report of a patient being cured of this condition. The next year several physicians found that patients could be treated simply by eating sheep's thyroid glands; the usual dose was one- half of a sheep's thyroid served raw taken once a week. By 1893 a London pharmacy was making dried extract of thyroid glands, and thyroid extract remained the treatment for over fifty years.

These desiccated preparations of animal thyroid glands are hard to standardize and be sure of exact potency. Furthermore, the animal thyroid contained impurities that might alter the thyroid function tests or cause unwanted symptoms.

Today, synthetic thyroid hormone (L-thyroxine), identical to human thyroid hormone, is used as replacement. We have found that generic thyroid hormone is not as reliable as the brand names in treating hypothyroidism. It is good to insist that your pharmacy always use the brand name as the cost is only a few cents a day different from generic preparations. Since the thyroid hormone is a normal body constituent, it acts like the body's own hormone; therefore, one won't be allergic to it, and it does not cross react with other medications. Unlike most medications (including many hormones) which are "foreign chemicals" in the body and are rapidly excreted within 24 hours, synthetic L-thyroxine acts like the body's own hormone and stays in the body until it is used up. The half-life (time it takes for one-half of the medication to be used up) is 6.7 days as opposed to several hours for most medications.

Iron supplements and vitamin preparations containing iron interfere with the absorption of L-thyroxine from the intestine. Therefore, patients who take iron pills or multivitamins with minerals should take them at a separate time from their L-thyroxine.

The main problem is to give enough thyroid but not give too much. Fortunately, the new thyroid tests used today make this fairly simple. Once a person's dose is determined, it generally is checked only once a year. Children and adolescents are generally checked every six months. For patients to increase their dose because of obesity or fatigue is incorrect and often harmful. The TSH and T4 are much more accurate determinations of thyroid level than are any symptoms.

Obesity is becoming more and more common  and is not a thyroid disease. As stated, the weight gain with hypothyroidism is modest and some patients actually lose weight (apparently too tired to eat). Most people who are overweight are overweight because they eat more than they need and are not physically active. Obesity alone, without other symptoms, is almost never due to hypothyroidism. Hypothyroid patients who are overweight remain overweight after treatment unless they go on a diet and exercise program to lose weight.

In trying to treat overweight with thyroid hormone, an analogy may be made to a fractured limb; the orthopedic surgeon puts a cast on the broken arm or leg and it corrects the problem. However, to put a cast on a leg or on an arm that hurts from arthritis but is not broken will certainly not help and may worsen the arthritis. Likewise, giving thyroid to a person who has a normal thyroid gland will not help and may actually worsen the problem by increasing appetite and decreasing energy.

The most important thing to remember about thyroid replacement is that it remains permanent. Once a thyroid gland has failed it is extremely unlikely to ever function normally again. Stopping thyroid replacement will ultimately result in recurrent hypothyroidism and can cause the thyroid gland to start growing (develop a goiter). Symptoms of hypothyroidism may not occur immediately after stopping the thyroid hormone but gradually develop over the next few months or even years. Therefore once a person is started on thyroid replacement, he or she should continue it throughout life.

Since hypothyroidism tends to run in families it is good to let your relatives know the disease exists so that they may be checked by their physician. Children who become hypothyroid during childhood usually stop growing and frequently have an obvious goiter.