Hyperthyroidism

The thyroid makes two hormones, T4 and T3, which can affect every cell in the body. These hormones regulate our metabolism, affecting how many calories we burn, heat production, and body weight. In short, the thyroid “runs” our body through energy metabolism. For example, the thyroid hormones have direct effects on the heart rate, which beats faster and harder under the influence of thyroid hormones. Every cell in the body will respond to increases in thyroid hormone with an increase in the rate at which they use energy.
Hyperthyroidism is a condition of excess thyroid hormone on the body. Although there are several causes of hyperthyroidism, most of the symptoms patients experience are the same regardless of the cause.

Common symptoms and signs of hyperthyroidism:
• Palpitations
• Heat intolerance
• Nervousness
• Insomnia
• Shortness of breath
• Loose stools
• Light or absent menstrual periods
• Fatigue
• Fast heart rate
• Tremor
• Weight loss
• Muscle weakness
• Warm moist, oily skin
• Hair loss
• Staring gaze

Causes of Hyperthyroidism

There are multiple causes of hyperthyroidism. Most often, the entire gland is overproducing thyroid hormone, which is called Graves’ disease. Less commonly, a single large area of the thyroid gland or multiple small areas causes excess hormone secretion. We call this a single “hot” nodule or multi-nodular hyperthyroidism. Thyroiditis (inflammation of the thyroid due to viral infection) can also cause hyperthyroidism.

Graves Disease

The most common cause of hyperthyroidism is Graves’ disease. Grave’s disease is caused by an enlarged thyroid (an enlarged thyroid is also called a goiter) which produces way too much thyroid hormone. Graves’ disease is an autoimmune disease which causes the production of a protein or antibody which is made by the patient’s own immune system. This antibody stimulates the patient’s thyroid gland to overproduce thyroid hormones.

There are three distinct clinical aspects of Graves’ disease:
1. Over stimulation of the thyroid gland (hyperthyroidism)
2. Inflammation of the muscles around the eyes, causing swelling (Grave’s ophthamopathy)
3. Thickening of the skin over the lower legs (pretibial myxedema)

Most patients with Graves’ disease, however, have no obvious eye involvement or skin changes. Their eyes may feel irritated or they may look like they were staring. One out of 20 people with Graves’ disease will suffer more severe eye problems, which can include bulging of the eyes, severe inflammation, double vision, or blurred vision. These severe eye problems are more common in smokers and tobacco cessation in smokers can prevent or eliminate the risk of Grave’s eye diseases. Serious eye problems can be prevented if recognized and treated, however, permanent eye damage may even cause blindness. Thyroid and eye involvement in Graves’ disease generally run a parallel course, eye problems are typically transient and resolve slowly after hyperthyroidism is treated. However, the eye problems may develop or worsen despite treatment of the hyperthyroidism and yearly eye evaluation is important.

Other Features Graves’ Disease:
1. Graves’ disease affects women more often than men (about 8:1 ratio)
2. Graves’ disease is often called diffuse toxic goiter because the entire thyroid gland is enlarged, usually moderately enlarged, and sometimes quite big.
3. Graves’ disease can happen at any age but is more common in the 30s and 40s.
4. Graves’ disease has a genetic component and does run in families

Other Less Common Causes of Hyperthyroidism

Hyperthyroidism can also be caused by a single over functioning nodule within the thyroid or by multiple nodules. These thyroid nodules are benign (non-cancerous) lumps or tumors in the gland. A single nodule or multiple nodules can produce excessive amounts of thyroid hormones. This condition is called “toxic nodular goiter” or multi-nodular hyperthyroidism. Without normal regulatory control, the cells in this nodule produce thyroid hormone at an increased rate causing the symptoms of hyperthyroidism. Inflammation or viral infection of the thyroid gland, called thyroiditis, can lead to the release of excess amounts of thyroid hormones that are normally stored in the gland. In subacute thyroiditis, the inflammation of the gland is believed to be caused by a virus. When the virus infects the thyroid, the thyroid cells dump their stored hormone into the bloodstream and cause a transient increase of thyroid hormone (hyperthyroid phase) followed by a healing phase. During the healing phase, the thyroid makes too little thyroid hormone (hypothyroid phase) followed by normal thyroid function (euthyroid phase). A more common painless form of thyroiditis occurs in one out of 20 women, a few months after delivering a baby and is, therefore, known as postpartum thyroiditis. This is usually only a temporary hyperthyroidism, but does recur with each subsequent pregnancy. Hyperthyroidism can also occur when patients take excessive doses of thyroid hormone. Other forms of hyperthyroidism are even rarer. It is important for your doctor to determine which form of hyperthyroidism you may have since the best treatment options will vary depending on the underlying cause.

Making the Diagnosis of Hyperthyroidism

The diagnosis of hyperthyroidism is usually done by a combination of blood tests and nuclear medicine tests. Levels of the thyroid hormones, T4 and T3, are measured in blood, and one or both may be high.

The most useful test to diagnose hyperthyroidism is the level of thyroid-stimulating hormone (TSH). TSH is a hormone secreted from part of the brain called the pituitary gland; its purpose is to stimulate the thyroid to produce thyroid hormone and increase thyroid growth. The pituitary monitors thyroid hormone levels, and keeps the blood thyroid hormone in balance. A low blood TSH suggests that the pituitary is shut off due to too much thyroid hormone in the blood, which is produced by an overactive thyroid.

Other tests are used to distinguish among the various causes of hyperthyroidism. The nuclear medicine iodine scan (also simply called a thyroid scan) is used to diagnosis the potential causes of hyperthyroidism by taking a picture of an isotope given intravenously which is taken up into the thyroid. The scan can diagnose diffuse uptake (Grave’s), a solitary “hot” nodule or multiple small nodules which cause thyroid cells to make too much hormone. In the case of thyroiditis the thyroid gland is infected, does not take up the isotope and has little to no uptake. Because the thyroid gland is the only place in the body that uses iodine to make thyroid hormones, measuring how much radioactive iodine that the gland absorbs can also be a useful way to make a diagnosis of hyperthyroidism. The tiny dose of radiation this test uses is small and has no side effects. Radioactive thyroid scan and uptake tests are also useful to determine what treatment should be used in a patient with hyperthyroidism.

Common Tests Used to Diagnose Hyperthyroidism
• Thyroid-stimulating hormone (TSH) is associated with a low (suppressed) TSH level.
• Thyroid hormones (T3, T4) may be increased. Usually T4, T3 or both hormone measurements are high but may be normal in early hyperthyroidism.
• A thyroid scan and uptake are essential for the diagnosis of the cause of the hyperthyroidism and may guide treatment.
• Occasionally, thyroid stimulating immunoglobulin (TSI) is measured because TSI is one antibody which is sometimes elevated in Grave’s disease and can be helpful to diagnose Grave’s disease under certain circumstances when a thyroid uptake and scan are not possible.

Treatment Options for Hyperthyroidism

Beta Blockers (Propranolol, Metoprolol, Atenolol)
There are effective treatments for hyperthyroidism. The symptoms of hyperthyroidism (such as tremor and palpitations) can usually be improved quickly by medications called beta blockers, such as Propranolol or Metoprolol. These drugs block the effect of the thyroid hormone but don’t cure the hyperthyroidism and do not decrease the amount of thyroid hormone. For patients with transient forms of hyperthyroidism (thyroiditis or those taking excess thyroid medication), beta blockers maybe the only treatment required. Once the hyperthyroidism resolves, the beta blocker can be tapered off.

Anti-Thyroid Drugs (Propylthiouracil, Methimazole)

For patients with sustained forms of hyperthyroidism, such as Graves’ disease or toxic nodular goiter, other drugs and anti-thyroid medications are often used. These drugs prevent the thyroid from producing hormones and, therefore, “shut down” the thyroid hormone production.
Methimazole and propylthiouracil (PTU) are the most commonly used drugs which interfere with the thyroid gland’s ability to make thyroid hormone and are usually very effective in controlling hyperthyroidism within a few weeks. The anti-thyroid drugs rarely cure the hyperthyroidism and hyperthyroidism reoccurs about 70-80% of the time after the drugs are discontinued. However, this therapy may result in a “cure” of hyperthyroidism in 20-30% of patients with Grave’s disease.
Anti-thyroid drugs can have side effects such as rash, itching, or fever, which are uncommon. About 5% of people get a rash which can vary from being very minor to very severe. Rarely, patients treated with these medications can reduce white blood cells and patients taking anti-thyroid drugs should be aware that they must stop their medication and call their doctor immediately if they develop a fever, severe sore throat or any sign of infection. An extremely rare complication can be inflammation of the liver, which can cause severe fatigue, yellowing of the skin or other serious symptoms. This is an emergency and the patient should seek immediate medical attention.

Radioactive Iodine Treatment

Radioactive iodine is the most widely-recommended permanent treatment of hyperthyroidism. This treatment takes advantage of the fact that thyroid cells are the only cells in the body which have the ability to concentrate iodine. If you give radioactive iodine in a sufficient dose, it will only concentrate in the thyroid cells and kill them, a permanent way to stop hyperthyroidism. Because iodine is not absorbed by any other cells in the body, there is very little radiation exposure (or side effects) for the rest of the body. Radioiodine can be taken by mouth and does not require hospitalization (see Radioactive Iodine Treatment). This form of therapy often takes 6-12weeks before the thyroid is killed, but the radioactive medicine is completely gone from the body within a few days. 90% of patients are cured with a single dose, 10% need a second dose, and 1% need a third dose of radioactive iodine. It may take as long as 6-12 months for its full effect on the thyroid cells.
The intended effect of radioactive iodine treatment is to destroy the thyroid gland which results in permanent hypothyroidism. Once the thyroid is destroyed, the patient will need lifelong thyroid hormone replacement. There is no evidence that radioactive iodine treatment of hyperthyroidism causes cancer of the thyroid gland or damages any other parts of the body. It does not interfere with a woman’s chances of becoming pregnant and delivering a healthy baby in the future. Radioiodine ablation treatment has been a successful advancement to curing many causes of hyperthyroidism with very few, if any, side effects. However, it is important that women should avoid pregnancy for at least 6 months after radioactive iodine treatment. Radioactive iodine should never be given to a pregnant woman because it can injure the fetus. So women of child bearing age need to be screened for pregnancy before considering radioactive iodine ablation.

Side effects from radioactive iodine are very few (see Radioactive Iodine Treatment). Greater than 95% of patients treated have no side effects. Occasionally, mild to severe neck pain may occur 1-2 weeks after the treatment. The neck pain is usually mild and last only 1-2 weeks and is frequently treated with Acetaminophen (Tylenol) and/or Ibuprofen (Motrin). Sometimes the neck pain can be severe and this should be promptly brought to the doctor’s attention for additional treatment. A very rare complication is a sudden worsening of hyperthyroidism and its symptoms because of “radiation thyroiditis”. This sudden hyperthyroidism is very rare which could be serious. So if hyperthyroid symptoms get worse, call you doctor immediately.

Surgical Removal of the Gland or Nodule

Another permanent cure for hyperthyroidism is to surgically remove all or part of the gland or nodule, but is less commonly used as a treatment compared to radiation therapy. However, some hyperthyroid patients will need to have surgical removal of their thyroid. Examples where surgery is necessary are those patients who cannot tolerate medicines, the medicine does not work well, have severe Grave’s eye disease, refuse radioactive iodine, or have an emergent need to normalize thyroid levels, such as some cardiac patients. Other situations, such as those with hyperthyroidism due to a single hot nodule or multiple hot nodules which do not take up radioactive iodine may be candidates for surgical treatment, as well. Surgical complications are rare; a small risk of injury to structures near the thyroid gland in the neck including the nerve to the voice box (the recurrent laryngeal nerve) is less than 1%, if done by an experienced endocrine surgeon. Even rarer is damage to the four parathyroid glands during surgery, which can result in hypoparathryoidism. Like radioactive iodine treatment, surgery often results in hypothyroidism. Whenever hypothyroidism occurs after treatment of an overactive thyroid gland, it can be easily treated with thyroid hormone replacement.