Hyperthyroidism generally encompasses several different disorders with the common feature of excessive production of thyroid hormone. The two most common forms of hyperthyroidism are Graves disease and toxic multi-nodular goiter.

Causes

The production of thyroid hormone is normally regulated by the pituitary gland, which secretes thyroid-stimulating hormone (TSH) when a need for thyroid hormone is present and decreases secretion of TSH when it senses an adequate supply of the hormone. Generally speaking, some malfunction occurs in hyperthyroidism, and the thyroid is no longer sensitive to this regulatory mechanism. Graves disease is probably caused by the presence of an abnormal chemical stimulator of thyroid hormone production. In toxic multinodular goiter, nodules of thyroid tissue form, and these nodules secrete abnormally large amounts of thyroid hormone, independent of the amount of hormone in the body.

Symptoms

Because thyroid hormone is involved in so many vital processes, including maintenance of body temperature, conversion of food to energy, and regulation of growth and fertility, the effects of an excess of that hormone are many and varied. The symptoms common to all forms of hyperthyroidism include rapid heartbeat, weight loss despite increased appetite and food intake, generalized hyperactivity, tremors (shakiness), increased sweating, severe nervousness and emotional instability, alteration of menstruation and fertility, and muscle weakness.

In addition to these symptoms, patients with Graves disease often have bulging eyes. Their skin is characteristically warm, moist, and velvety, and there may be areas of raised, thickened, sometimes itchy skin on the legs and feet that have the texture of orange peel. The thyroid gland is frequently enlarged, smooth, and soft. This disease occurs most often in those in their 30s and 40s. It is more common in women than in men.

In toxic multinodular goiter, the thyroid gland is lumpy but not uniformly enlarged. This condition occurs most often in the middle-aged and elderly.

Diagnosis

The diagnosis of hyperthyroidism is made on the basis of the patient's medical history and findings from a physical examination as well as various laboratory studies. Significant elevation of the level of thyroid hormone in the blood can be detected with special blood tests. The diagnosis can be further established through the use of nuclear medicine scans obtained after the
injection of radioactive iodine, which becomes concentrated in the thyroid gland. The nuclear medicine study yields not only a picture of the gland but also an estimate of the degree of hyperactivity.

Treatment

Specific treatment of hyperthyroidism depends on which condition is present. However, treatment of the hyperthyroid state in general has several common elements. The drug propranolol, a beta-blocker, is commonly used to help prevent the effects of the hormonal overstimulation that greatly contributes to the tremors, increased heart rate, and sweating. This drug, although it diminishes symptoms, does not decrease the amount of thyroid hormone being produced. Therefore, an antithyroid drug, such as propylthiouracil, is necessary.

Antithyroid drugs work by actually interfering with the production of thyroid hormone. However, this is usually only a temporary solution; when the drug is stopped, the excess production sometimes resumes. The definitive therapy for hyperthyroidism is the destruction or removal of most or all of the thyroid gland. This is achieved by using radioactive iodine or surgery.

Graves disease is usually first treated by blocking hormonal overstimulation with propranolol. Simultaneously, an antithyroid drug is started. This drug may be maintained for a long period of time. If relapse occurs (which it frequently does) or if the level of thyroid hormone is not normalized, the question then is how to reduce the amount of thyroid tissue. Whether surgery or radioactive iodine is used depends on many complex factors. Both treatments frequently result in too little thyroid hormone in the blood, but this problem is easily remedied by supplementation with synthetic thyroid hormone.



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