Hyperthyroidism is a disorder in which your thyroid gland makes and releases more thyroid hormone than your body needs. Your doctor may say you have an "overactive thyroid," or refer to the condition as "overactive thyroid disease."
Your thyroid gland is located in the front of your neck. Hormones released by the thyroid affect nearly every part of your body from your brain to your skin and muscles. They play a crucial role in controlling how your body uses energy, a process called metabolism. This includes how your heart beats and even how you burn calories.
Women are five to 10 times more likely to develop hyperthyroidism than men.
Causes of Hyperthyroidism
The causes of hyperthyroidism include:
Graves' disease . The most common cause of hyperthyroidism is an autoimmune condition called Graves' disease. The body's immune system creates an antibody that causes the gland to make an excessive amount of thyroid hormone. Graves' disease runs in families, and usually affects younger women.
Thyroiditis. Thyroiditis is inflammation of the thyroid. A virus or problem with the immune system causes the gland to swell, leaking thyroid hormone into the bloodstream. There are several types of thyroiditis.
- Subacute: A sudden, painful form of thyroiditis of unknown cause. The thyroid usually heals on its own after a few months. The thyroid can become underactive for a while before it returns to normal.
- Postpartum: This type of thyroiditis affects women after pregnancy. One to two women out of every 10 women develop hyperthyroidism after having a baby. It usually lasts a month or two, followed by several months of underactive thyroid (hypothyroidism). In most women, the thyroid returns to normal.
- Silent: This type is similar to postpartum thyroiditis but is not related to pregnancy. The thyroid produces too much hormone but patients do not develop a painful thyroid gland. Some people may develop hypothyroidism afterwards.
- If one nodule causes hyperthyroidism, it is called a single toxic nodule.
- If several nodules cause the thyroid to become overactive, the condition is called toxic multinodular goiter.
Excess iodine. You may also develop hyperthyroidism if you eat, drink, or are otherwise exposed to substances that contain a high amount of iodine. Iodine is used by the body to make thyroid hormone. Kelp or seaweed supplements and the medication amiodarone (Cordarone, Pacerone), once used to treat irregular heartbeats, are examples of medicines that contain a lot of iodine.
Thyroid medications. Taking too much thyroid hormone medication can wreak havoc on your thyroid gland and cause hyperthyroidism. If you have been prescribed thyroid replacement hormone (for hypothyroidism), never take an extra dose, even if you missed one, without first talking to your doctor.
Symptoms of Hyperthyroidism
Symptoms of hyperthyroidism may be vague and can often mimic other illnesses and conditions. If you have a very mild form of hyperthyroidism, you may not notice any symptoms. Symptoms are often particularly subtle in the elderly. However, an overactive thyroid often leads to discomfort or even disability that disrupts your everyday activities or routines.
Thyroid enlargement, called a goiter, occurs in most people with hyperthyroidism. You may see or feel a lump in the front of your neck. Sometimes only your doctor will be able to detect a goiter.
Other symptoms of hyperthyroidism include:
- Anxiety, nervousness, and irritability
- Frequent, loose bowel movements
- Difficulty sleeping
- Double vision
- Eyes that bulge out, or "protrude" (in patients with Graves' disease)
- Hair changes, including brittle hair, thinning hair, and hair loss from scalp
- Irregular heart beat (arrhythmia), especially in older adults
- Menstrual cycle changes, including lighter bleeding and less frequent periods
- Muscle weakness, especially in the thighs and upper arms
- Rapid fingernail growth
- Rapid heartbeat, usually over 100 beats per minute
- Shaky hands
- Thinning skin
- Weight loss despite increased appetite
Make an appointment with your health care provider if you have any of these symptoms. It is important to note that these symptoms can be due to other medical conditions and disorders ranging from anxiety to a tumor of the adrenal gland.
How Is Hyperthyroidism Diagnosed?
Blood tests can confirm a diagnosis of hyperthyroidism. Blood tests include those for thyroid-stimulating hormone (TSH). This is a hormone released by the pituitary gland to stimulate the thyroid to make thyroid hormone. Other blood tests include measures of thyroid hormone levels (typically elevated) and thyroid-stimulating antibody (called thyroid-stimulating immunoglobin test) to check for Graves' disease. If your test results are abnormal, your doctor may also order the following tests:
- Thyroid ultrasound to check for nodules or inflammation
- Radioactive iodine uptake test to see your thyroid’s absorption of iodine
- Thyroid scan to see where iodine is in the thyroid
How Is Hyperthyroidism Treated?
There are several different ways to treat hyperthyroidism. Before choosing the one that's best for you, your doctor will consider your age, overall heath, severity of your symptoms, and specific cause of your overactive thyroid.
Treatment options include:
- Anti-thyroid drugs. These medications, including propylthiouracil (PTU) and methimazole (Tapazole), help prevent the thyroid gland from making new hormone. This doesn't permanently damage the thyroid, but some people may have serious side effects.
- Radioactive iodine (RAI) taken by mouth. Overactive thyroid cells quickly absorb this iodine and soon die. This prevents the release of thyroid hormone. Any remaining radioactive iodine disappears from the body within a few days. It may take a few months for the therapy to relieve hyperthyroidism symptoms, and a second dose may be needed. People who have this treatment will develop an underactive thyroid (hypothyroidism), and will need thyroid hormone supplements for the rest of their life. This therapy cannot be done during pregnancy.
- Surgery to remove all or part of the thyroid, called a thyroidectomy. Most people who have this procedure eventually develop an underactive thyroid and will need to take thyroid hormone-replacement medication for the rest of their life.
- Beta-blockers to slow down your heart rate. These medicines do not lower your thyroid hormone levels but help relieve symptoms related to a rapid heart rate.
After treatment, you will need regular blood tests to check your thyroid hormone levels. Your doctor may need to adjust your medication dose from time to time.
Complications of Hyperthyroidism
It is important to maintain regular, lifelong visits with your doctor if you have hyperthyroidism. Untreated or improperly treated, an overactive thyroid can lead to severe, even life-threatening problems.
Complications linked to hyperthyroidism include:
- Irregular heart rhythm (atrial fibrillation)
- Congestive heart failure
- Osteoporosis and bone fractures (hyperthyroidism causes your bones to lose calcium faster than usual)
Thyrotoxic crisis is a sudden worsening of hyperthyroidism symptoms that can be deadly if not treated right away. Seek immediate medical help if you or someone you know has hyperthyroidism and develops the following symptoms:
- Agitation or signs of delirium
- Decreased awareness
- Very fast pulse