Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone. This disorder occurs in about 1% of all Americans and affects women much more often than men. In its mildest form, hyperthyroidism may not cause noticeable symptoms; however, in some patients, excess thyroid hormone and the resulting effects on the body can have significant consequences.
Causes of Hyperthyroidism
Hyperthyroidism can be caused by a number of things:
- Toxic nodule - A single nodule or lump in the thyroid can produce more thyroid hormone than the body needs and lead to hyperthyroidism.
- Toxic multinodular goiter - If the thyroid gland has several nodules, those nodules can sometimes produce too much thyroid hormone causing hyperthyroidism. This is most often found in patients over 50 years old. In many cases, a person may have had a multinodular goiter for several years before it starts to produce excess amounts of thyroid hormone.
- Graves' disease - Graves' disease is an autoimmune disorder in which the body's immune system attacks the thyroid. Patients with Graves’ disease often have enlargement of the thyroid gland and become hyperthyroid. In some patients, the eyes may be affected. Patients may notice the eyes become more prominent, the eyelids do not close properly, a gritty sensation and general irritation of the eyes, increased tear production, or double vision. Like other autoimmune diseases, this condition may occur in other family members and is much more common in women than in men.
- Sub-acute thyroiditis - This type of hyperthyroidism can follow a viral infection which causes inflammation of the thyroid gland. This inflammation causes the thyroid to release excess amounts of thyroid hormone into the blood stream which leads to hyperthyroidism. Over time the thyroid usually returns to its normal state. Because the stored thyroid hormone has been released, patients may become hypothyroid (where their thyroid gland produces too little thyroid hormone) for a period of time until the thyroid gland can build up new stores of thyroid hormone.
- Postpartum thyroiditis - Some women develop mild to moderate hyperthyroidism within several months of giving birth, which usually lasts 1 to 2 months. This is often followed by several months of hypothyroidism. Most women recover and have normal thyroid function.
- Excessive Iodine ingestion - Some food sources with high concentrations of iodine, such as over the counter supplements, kelp tablets, some expectorants, amiodarone (a medication used to treat certain heart rhythm problems) and x-ray dyes, may occasionally cause hyperthyroidism in some patients. In most cases, the hyperthyroidism usually resolves when the supplement is discontinued.
- Overmedication with thyroid hormone - Patients who take too much thyroid hormone replacement can also develop hyperthyroidism. Patients should have their thyroid hormone levels evaluated by a physician at least once each year and should NEVER give themselves "extra" doses unless directed by a physician. Changes in thyroid medication should always be guided by thyroid function testing.
Symptoms of Hyperthyroidism
When hyperthyroidism develops, patients may experience some of the following signs or symptoms:
- fast or irregular heartbeat
- anxiety or irritability
- trembling of the hands
- weight loss despite eating the same amount or even more than usual
- hot flashes and increased perspiration
- loss of scalp hair
- separation of fingernails from the nail bed
- muscle weakness, especially in the upper arms and thighs
- loose or frequent bowel movements
- skin changes
- an unexplainable change in the menstrual cycle in women
- an increased chance of miscarriage
- irregular heart rhythm or palpitations
- loss of calcium from the bones leading to decreased bone density
How is Hyperthyroidism Diagnosed?
There are signs and symptoms of hyperthyroidism that can be identified by a physician. Signs and symptoms of hyperthyroidism are often non-specific and can also be associated with many other causes. Laboratory tests are used to confirm the diagnosis of hyperthyroidism and probable cause. A primary care physician may make the diagnosis of hyperthyroidism, but help may be needed from an endocrinologist, a physician who is a specialist in thyroid and other endocrine diseases.
The best test to determine overall thyroid function is the thyroid stimulating hormone (TSH) level. TSH is produced in the brain and travels to the thyroid gland to stimulate the thyroid to produce and release more thyroid hormone. A high TSH level indicates that the body does not have enough thyroid hormone. A TSH level lower than normal indicates there is usually more than enough thyroid hormone in the body and may indicate hyperthyroidism. When hyperthyroidism develops, free thyroxine (T4) and free triiodothyronine (T3) levels rise above normal. Other laboratory studies may help identify the cause of hyperthyroidism. Thyroid-stimulating immunoglobulins (TSI) can be identified in the blood when Graves' disease is the cause of hyperthyroidism. Thyroid peroxidase antibodies and other anti-thyroid antibodies are also seen in some disorders leading to hyperthyroidism.
Treatments for Hyperthyroidism
Currently, there are several effective treatments available for hyperthyroidism depending on the cause, severity, and several other factors. The most common treatments for hyperthyroidism include antithyroid medications, radioactive iodine, and thyroid surgery.
Antithyroid medication (most often methimazole) decreases thyroid hormone production. Antithyroid medicine does not cure the disease but works while the patient takes the medication. It is not usually recommended as a long term solution, although in some patients the hyperthyroidism does go into remission and the medication can be discontinued. If the hyperthyroidism does not go into remission after two years, a more definitive treatment is often recommended (thyroidectomy or radioactive iodine).
Radioactive iodine (RAI) is a common treatment for hyperthyroidism. The thyroid is one of the few organs in the body that avidly takes up iodine. This allows radioactive iodine to selectively damage the thyroid gland without affecting other parts of the body. The thyroid gland is eventually destroyed and disappears and the body no longer produces its own thyroid hormone. In general, this treatment can be used in patients with Graves' disease or in those patients with nodules in the thyroid gland causing hyperthyroidism. Not all cases of hyperthyroidism respond well to radioactive iodine.
After radioactive iodine most patients will require thyroid hormone replacement with levothyroxine (Synthroid, Levothroid, and other brand names). Thyroid hormone levels will be checked frequently at the beginning, and then often are only checked once a year after the correct dose of thyroid hormone for the patient has been determined.
Some patients will have their hyperthyroidism treated by having part or all of their thyroid surgically removed.
Deciding which treatment for hyperthyroidism is the right treatment is made on a case by case basis according to each individual patient’s medical, social, and family history. Often, surgical thyroidectomy is recommended over RAI in the following circumstances:
- Large thyroid causing compressive symptoms unlikely to be treated adequately with RAI
- Significant compression of adjacent structures and compressive symptoms
- Moderate to severe Graves’ eye disease
- Failed medical therapy
- Adverse reaction to antithyroid medications
- Need for rapid reversal of hyperthyroidism
- Fear of radiation exposure, inability to comply with radiation safety guidelines
- Co-existent thyroid nodules and need to rule out possibility of thyroid cancer
- Small children at home
- Pregnancy, desire for pregnancy within next 4-6 months, or lactation
- Patient desire
What’s Special About University of Michigan’s Treatment of Graves’ Disease?
UM is one of the few places in the country that has a multidisciplinary group dedicated to the treatment of patients with Graves’ disease. UM’s multidisciplinary group consists of endocrinologists, endocrine surgeons, ophthalmologists, nuclear medicine physicians, rheumatologists and psychiatric professionals. Our group sees Graves’ disease patients from around the country and is involved with one of the most well-known national organizations concentrating on helping patients and families coping with Graves’ disease and Graves’ eye disease. Our group routinely publishes papers with new research results on Graves’ disease.
The ophthalmologists in our group specialize in the treatment of Graves’ eye disease which can require complex management. Most ophthalmologists have little experience treating patients with Graves’ disease and Graves’ eye disease. For those patients with Graves’ eye disease, it is the severity of the eye disease which drives the selection of the type of treatment for hyperthyroidism if these two problems occur together.
While those patients with no Graves’ eye disease or only mild eye disease may be candidates for any of the three types of treatments for hyperthyroidism, those who have moderate to severe eye disease are often referred for surgical thyroidectomy as RAI has a higher chance of worsening the eye disease than surgery does.