Diseases of the thyroid gland

Diseases of the thyroid glandThe thyroid gland is an H-shaped gland which lies in the front of the neck overlying the wind­pipe. It consists of a large lobe on each side, the lobes being connected by a narrow band called the isthmus. The entire gland is composed of numerous microscopic follicles which secrete the hormone thyroxine. This hormone is about 65 per cent iodine, and its chief function is to accelerate metabolism; it is necessary for normal growth and devel­opment.

A method of measuring the rate of the vari­ous chemical processes occurring in the body (metabolism) is by the BMR, or basal meta­bolic rate.

Insufficient production of the thyroid hor­mone in the young results in a condition known as cretinism; the cretin is an individual char­acterized by small stature, retarded mental de­velopment, and underdevelopment of the sexual organs. In adults, hypoactivity of the thyroid gland results in a condition known as myx­edema; the individual is overweight, mentally and physically sluggish, with sparse hair and boggy tissues. In these conditions the rate of all the metabolic processes is slow. Marked im­provement may be brought about by administer­ing thyroid extract in these conditions of under­active thyroid gland.

Any abnormal enlargement of the thyroid gland is called a goiter. Such may be of normal function, or hypoactive or hyperactive. Simple goiter is a diffuse enlargement of the entire gland. It is due to a deficiency of iodine in the diet. The gland enlarges, apparently in attempts to mannfacture sufficient hormone. A promi­nent swelling in the neck occurs and may cause symptoms of pressure on the windpipe with shortness of breath or difficulty in swallowing. Often marked benefit may follow medical measures, but if the symptoms of pressure are pronounced, the excess of the gland may have to be removed surgically (subtotal thyroidec­tomy) .

Exophthalmic goiter, or toxic goiter, or hyperplastic goiter, is a diffuse enlargement of the thyroid gland with overgrowth of the follicles and overproduction of thyroxine. All the metabolic processes of the body are stimu­lated to overactivity. The patient loses weight; the pulse rate is increased; tremors develop; there is excess sweating and hot flashes; the eyes are pushed forward, a condition known as exoph­thalmos, or “pop-eyes”; apprehension and nerv­ousness increase. As the disease progresses, weight loss continues and the patient becomes emaciated. Pressure symptoms from the en­larging gland may occur.

Treatment of this toxic goiter rests with sur­gical removal of most of the overactive gland tissue (subtotal thyroidectomy). The incision is made across the lower front of the neck and the thyroid exposed. The major portion of the lobes and the isthmus are excised, leaving only a small amount of gland tissue at the lower por­tion of the lobe on each side. Only a small amount of gland tissue is necessary for normal function, but the amount of gland that is ex­cised is judged by the degree of overactivity. The incision is closed by plastic surgery tech­nique for cosmetic reasons. In cases of severe overactivity of the thyroid, extensive and pro­longed preoperative preparations may be neces­sary. This may include a period of absolute rest in a quiet atmosphere removed from disturbing noises and sights and avoiding all forms of ap­prehension; sedatives may be used, and drugs which suppress the thyroid gland’s activity may be needed in the preparation for surgery.

In the recent atomic years radioactive iodine has been used in the treatment of overactive thyroid. The gland is known to absorb and uti­lize iodine for the formation of its hormone. Iodine which has been rendered radioactive is given by mouth to be absorbed by the thyroid gland. Here it gives off rays which partially de­stroy the gland’s cells. The radioactivity is of short duration but the effect on the gland per­manent. This is a therapeutic course of radio­active iodine, but the activity of the gland may be studied beforehand by a tracer dosage. For this test a small harmless amount of radioactive iodine is given and is absorbed by the thyroid gland; then the amount of radiation given off from the gland is measured by a recording in­strument (such as the Geiger counter). This test is of accurate value in determining the magnitude of treatment necessary, either surgi­cally or by radioactive iodine.

Adenomatous goiter, or nodular goiter, is a condition wherein a benign tumor develops in the gland to form a lump in the gland sub­stance. Often these nodules are multiple. The gland may become overactive and the symptoms of toxic goiter ensue, but most are of normal activity.

In some cases, these benign nodules may un­dergo malignant change. Therefore the best treatment is surgical removal of the greater portion of the gland containing the tumor (sub­total thyroidectomy). This is particularly neces­sary in younger individuals since the chances of the benign nodule becoming cancerous are greater, as the life expectancy is longer with more years for possible malignant change.

Thyroidectomy (thyroid-out) may be of one lobe or both, and may be subtotal (partial) or total. In the case of cancer of the thyroid, obviously total thyroidectomy must be per­formed; x-ray may be employed.

Inflammation of the thyroid gland is called thyroiditis. It may be acute or chronic and symptoms of overactivity may occur. Treatment may be by medical means or with x-ray, and occasionally partial thyroidectomy is necessary.

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