THE THYROID GLAND

This gland is located in the lower neck, just below the Adam’s apple and above the breastbone. It is shaped like a butterfly with the wings on either side of the windpipe. Its function is to provide the body with thyroid hormones, chemicals that are essential for the normal functioning of the body. The major thyroid hormone released by the gland is thyroxine.

It is quite clear that each cell in the body depends on thyroxine to work normally. Because this is so critical, the body has an elaborate regulatory mechanism involving the brain (hypothalamus), which monitors the levels of thyroxine in the blood and adjusts the activity of the pituitary gland, and the pituitary gland which produces the thyroid stimulating hormone (TSH) which regulates the thyroid hormone production by the thyroid gland.

We can divide thyroid problems into two broad categories: those that involve the thyroid gland structure (what the thyroid looks like), and those that involve thyroid function (how the thyroid works).

ABNORMALITIES OF THYROID STRUCTURE

An enlarged thyroid gland is called a goiter. Goiters are common and may be present in up to 15% of the population. Usually, an enlarged thyroid gland produces no symptoms.

The thyroid may be enlarged diffusely (simple goiter) or may be irregular in shape and "lumpy" (multinodular goiter). Goiters may occur for a variety of reasons. Formerly in this country, and currently in several parts of the world, the most common cause was a dietary deficiency of iodine, an element essential for thyroid hormone production. The most common cause of goiter in US is a chronic inflammation of the thyroid which appears to be a result of the body mistakenly identifying the thyroid as "foreign" tissue and trying to "reject" it. This process, called chronic thyroiditis, can result in both simple and multinodular goiters.

It needs to be emphasized that these abnormalities in thyroid structure say little about how the thyroid is working. Thus, a patient can have a very large lumpy goiter that produces adequate amounts of thyroid hormones. On the other hand, some patients may have normal sized glands that may be very overactive or underactive.

Occasionally, a patient's thyroid will be found to have a single lump (nodule). A nodule may be cystic (a cavity filled with fluid) or solid. If solid, it is important to ascertain that the nodule is not neoplastic, a thyroid cancer. A radioisotope scan, an ultrasound examination, and a fine-needle aspiration biopsy, may be essential in making a definitive diagnosis. About one in fifteen women and one in sixty men in the Unites States will have a thyroid nodule. Most are not cancers and very few cause ill effects. When a thyroid nodule is detected we must ascertain the following: 1. Is the nodule cancerous. 2. Is it producing a pressure on adjacent structures. and 3. Is the nodule producing an excessive amounts of thyroid hormone.

Most nodules produce no symptoms. They are frequently found during examination of the thyroid gland. Sometimes they produce discomfort, tenderness upon touch or even marked pain. An enlarged thyroid gland (a goiter) may cause a discomfort upon swallowing, or produce cough, shortness of breath on exertion, or a “tickle” in the throat. These symptoms may occur with benign or malignant growths.

ABNORMALITIES OF THYROID FUNCTION

Too much or not enough thyroid hormone results in a variety of symptoms involving every organ system of the body. Both hormonal states pose severe risks to health and need to be diagnosed and treated appropriately.

TOO MUCH THYROID HORMONE (HYPERTHYROIDISM or GRAVES DISEASE *).

There are many causes of too much thyroid hormone. Some of these are transient and can be treated expectantly but most are chronic and require active treatment. The symptoms of excess thyroid hormone may vary from virtually none to severe weight loss (primarily of body protein, not of body fat), profound weakness, irregular heartbeat, heart failure, circulatory collapse and even death. In the past, as recently as the 1800's, the mortality rates were as high as 50% in patients with Grave’s disease. Fortunately, now, there are three different methods for successful treatment of this disease. The selection of an appropriate treatment alternative depends, among others, on the cause of the hyperactivity, as well as on a variety of other factors.

TREATMENT

1. Drugs
Antithyroid drugs, such as propylthiouracil (PTU) or methimazole (Tapazole) exert their therapeutic action by interfering with incorporation of iodine into the thyroid hormone molecules. This results in a decrease in active thyroid hormone production. These medications can be used to treat mild hyperthyroidism, to obtain rapid effect before ultimate therapy is decided upon, as a temporary therapy in elderly patients, as a primary form of therapy in patients who respond well to it and prefer it over other forms of therapy. A long term remission may occur in substantial percentage of the patients and in some of these the disease may “burn out “ and render the patient hypothyroid. The hypothyroidism is then treated indefinitely.

2. Radioiodine
The majority of patients with hyperthyroidism are treated with radioactive iodine. The iodine is administered by mouth , it passes into the blood stream and eventually is taken up by the thyroid gland where it remains for a long enough time to destroy the thyroid hormone producing cells. Within several days it is eliminated from the body and the radioactivity of the iodine quickly decays. Most patients's hyperthyroid states are corrected within several weeks and hypothyroidism requiring treatment with thyroid hormone may develop. This is easily treated with appropriate amounts of thyroid hormone. Radioactive iodine has been used clinically since the 1940’s. No serious complications were noted. In the USA over 70% of adult patients with hyperthyroidism are treated with radioiodine. There is also an increased use of radioiodine in the treatment of hyperthyroidism in children with almost no complications.

3. Surgery
Hyperthyroidism can be successfully treated by means of surgery in which the hyperactive thyroid gland is removed. To prevent complications during surgery the hyperthyroidism is treated prior to surgery with antithyroid medications like propyl thiouracil or Tapazole to control the hyperthyroid state and shortly before surgery with non radioactive iodine to decrease the vascularity of the gland. Complications that may result from thyroid surgery include accidental removal of the parathyroid glands (which may result in serious calcium deficiency requiring life long treatment) or an accidental injury to the recurrent laryngeal nerve (which may result in speech problems and voice changes).

Once the thyroid gland is removed, depending how complete was the surgery, the patient may become euthyroid, the hyperthyroid state may recur with time or the patient may become permanently hypothyroid. As with induction of hypothyroidism in hyperthyroid patient with one of the above mentioned medical treatments (antithyroid drugs or radioiodine) appropriate replacement therapy with thyroid hormone is essential for life and when properly administers results in full recovery.

TOO LITTLE THYROID HORMONE (HYPOTHYROIDISM).
Hypothyroidism, lack of or low thyroid hormone levels, may some times be transient but much more often it is a permanent condition resulting from irreversible damage to the thyroid gland. Again, the symptoms involve every organ system and can vary from mild depression to profound changes in mentation with decreased memory, cold intolerance, increased somnolence and severe muscle weakness. Those patients with profound hypothyroidism (myxedema) have thickened dry skin and tend to accumulate a gelatinous material around their organs and under their skin. This gives them a puffy look and accounts for the 10-15 pound weight gain that is seen in about half of patients with hypothyroidism. If not treated, the myxedema will progress to kidney failure, heart failure, coma and death. Fortunately, patients with hypothyroidism can be treated with thyroid hormone preparations which are identical to the thyroxine that the thyroid gland normally secretes. Thus, by monitoring the levels in the blood, and adjusting the dose of the thyroid hormone prescribed, the physician can perfectly reproduce the functioning of the normal thyroid. Patients so treated are absolutely normal with regard to the thyroid function and should expect no symptoms of hypothyroidism.

THYROID AND BODY FAT

As indicated above, about half the number of patients with hypothyroidism gain weight but this weight gain is not due to fat. Some of these patients may decrease their physical activity, resulting in an increase in fat, but it needs to be stressed that there is little direct effect of thyroid hormone on body fat. Thus, obesity has little to do directly with abnormalities of thyroid function. The prescription of thyroid hormone to stimulate weight reduction is not only an ineffective remedy but also a dangerous undertaking.

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