Overview of Hyperthyroidism
Causes, Evaluation, and Treatment of a Hyperactive Thyroid Gland
Sep 5, 2008
The thyroid gland is the endocrine organ in the neck that regulates overall body metabolism. The thyroid hormone it produces stimulates cells to perform multiple necessary functions. However, if this gland is hypoactive (hypothyroidism) or hyperactive (hyperthyroidism), a variety of abnormalities may occur.
The following is an overview of the causes, clinical manifestations, diagnosis, and treatment of hyperthyroidism.
Causes
The thyroid gland secretes thyroid hormone in response to thyroid-stimulating hormone (TSH) from the pituitary gland, which in turn is secreted in response to thyrotropin-releasing hormone (TRH) from the hypothalamus in the brain. Hyperthyroidism, often used interchangeably with the term "thyrotoxicosis," usually results from problems in the thyroid gland.
There are several causes of hyperthyroidism. The most common is Graves disease, an autoimmune disorder in which thyroid-stimulating antibodies bind to the TSH receptor in the thyroid gland and constantly stimulate production of thyroid hormone. Another cause is subacute thyroiditis, a self-limiting condition in which the thyroid gland releases a large burst of stored thyroid hormone, goes through a hypothyroid state, and returns to normal. Other causes of hyperthyroidism include solitary or multinodular toxic goiters, excess iodine, dermoid tumors in the ovary producing thyroid hormone (struma ovarii), molar pregnancy, and choriocarcinoma.
Clinical Manifestations
Hyperthyroidism is associated with effects across multiple body systems, including anxiety, tremor, excess sweating, heat intolerance, weight loss, increased appetite, and heart palpitations. If caused by Graves disease, hyperthyroidism can also result in abnormalities of the eyes, including a prominent wide-eyed stare, eye pain, tearing, and double vision.
For some patients, the condition is extreme and becomes life-threatening. Such hyperthyroidism is called a thyroid storm. This is characterized by an abrupt and sudden occurrence of severe hyperthyroid symptoms. They may also be accompanied by mental confusion, nausea, vomiting, diarrhea, and cardiovascular shock.
Diagnosis
The tests that are necessary to diagnose hyperthyroidism are levels of TSH and levels of free thyroid hormone, both T4 and T3. Any cause of hyperthyroidism results in elevated T4 and T3, and TSH levels are generally very low because excessive T4 and T3 levels provide strong negative feedback to stop the production of TSH by the pituitary gland.
If a physician suspects Graves disease, he or she may also check for autoimmune thyroid antibodies.
Treatment
The treatment of hyperthyroidism depends on the cause. For hyperthyroidism due to a constantly overactive thyroid gland, the antithyroid drugs propylthiouracil and methimazole can inhibit the thyroid peroxidase enzyme necessary to produce thyroid hormone. These drugs are usually given on a temporary basis prior to the definitive treatment, which can be surgical resection of the thyroid (partial or subtotal thyroidectomy) or radioactive iodine to destroy thyroid tissue. Additional treatment options include propanolol to slow the heart, if necessary, and iodine for emergency treatment of thyroid storm.
There are also patients who have subclinical hyperthyroidism, characterized by depressions in TSH levels but otherwise normal levels of T4 thyroid hormone and minimal to no signs of hyperthyroidism. Such patients can either be treated or just be monitored; the decision is made on a case-by-case basis.
