Hyperthyroidism (overactive thyroid) is a condition caused by too much thyroid hormone in the body. It is also known as thyrotoxicosis.
The thyroid gland is located in the front of the neck, just below the larynx (voice box). It helps to maintain a healthy metabolism (the process by which foods are transformed into basic elements which can be utilized by the body for energy or growth) by producing and releasing iodine-containing hormones called thyroxine (T4) and triiodothyronine (T3).
T4 helps in regulating the body's growth, metabolism, digestion, body temperature and heartbeat. When the body produces too much of this hormone, it causes exaggerated bodily responses.
The causes of hyperthyroidism include:
- Grave's disease, also known as toxic diffuse goiter (enlargement of the thyroid gland) and is the most common form of hyperthyroidism (in about 75 percent of all cases) affecting the entire thyroid gland. Grave's disease is considered an autoimmune disorder (a condition in which the body's immune system develops antibodies against its own thyroid gland cells).
- Plummer's disease (involves a single mass or adenoma)
- pituitary tumors
- thyroiditis (inflammation of the thyroid gland caused by excessive amounts of thyroid hormone leaking out of the thyroid gland and into the blood)
- too much thyroid hormone medication
- excessive dietary intake of iodine (found in seaweed and liver)
The symptoms of hyperthyroidism may include:
- goiter (enlarged thyroid gland)
- mental impairment, memory lapses, diminished attention span
- trembling hands
- itchy skin
- unexplained weight loss despite increased appetite
- heart palpitations
- heat intolerance
- increased sweating
- muscle weakness
- hair loss
- increase in bowel movements
- decrease in menstrual periods
- eye irritation
- protruding eyeballs (Grave's disease only)
If the person is exhibiting extreme irritability, high blood pressure, rapid heart rate, vomiting, fever up to 106, and delirium, they may have thyroid storm. Thyroid storm is a complication of Grave's disease that comes on suddenly and may be caused by a stressful event, such as injury, surgery or infection. Immediate treatment is necessary.
The diagnosis of hyperthyroidism is often obvious from the patient's symptoms and appearance. However, to confirm the diagnosis, blood tests may be done for TSH (thyroid-stimulating hormone) or other thyroid hormones.
Additionally, the doctor may do a thyroid scan. The thyroid scan, or iodine uptake test, involves the patient swallowing a solution containing radioactive iodine. The physician then uses a scanning device to measure the amount of iodine that has been absorbed by the thyroid; an elevated level further confirms that the gland is overactive.
There is no one treatment that is best for all patients with hyperthyroidism. Many factors will influence the doctor's choice of treatment, including the patient's age, the form of hyperthyroidism, the severity of the disease and other medical conditions which may be affecting the patient's health.
Currently, there are three principal ways to treat hyperthyroidism: drug therapy, radioactive iodine therapy and surgery.
Drug therapy includes using two types of drugs to control the hyperthyroidism. Initially, the doctor will prescribe either methimazole (Tapazole) or propylthiouracil (PTU) pills which are antithyroid agents. These drugs block the amount of thyroid hormone in the blood and make it more difficult for iodine to get into the thyroid gland.
Although these drugs have blocked the amount of thyroid hormone in the blood, there are still high levels of circulating thyroid hormone in the blood. To combat this, the doctor may also prescribe beta-blocker drugs, such as propranolol (Inderal), to block the action of the circulating thyroid hormone.
Radioactive iodine therapy is an alternative if drug treatment fails. The patient is given a capsule or a drink of water containing radioactive iodine. After being swallowed, the "radioiodine" is rapidly absorbed by the overactive thyroid cells and over a period of several weeks, the radioactive iodine damages the cells.
The result is the thyroid shrinks in size, thyroid production falls and blood levels return to normal. The radioactivity disappears from the body within a few days. Hyperthyroidism can reoccur from several months to many years after this therapy.
Surgery is the preferred treatment for people with a large goiter who chronically relapse after drug therapy and for people who refuse or who are not candidates for the radioactive iodine therapy.
The surgery, called a thyroidectomy, involves the surgical removal of part of the thyroid gland. If only a single lump or nodule within the thyroid is producing too much hormone, the surgeon can take out just that small part of the gland. If the entire gland is overactive, which is more often the case, a total thyroidectomy is needed.
Sometimes, the surgeon can leave a small portion of the thyroid intact – just enough to produce adequate amounts of thyroid hormone. Depending on how much of the gland is left after surgery, the patient may need subsequent thyroid replacement therapy.