What is hyperthyroidism

Hyperthyroidism, also called overactive thyroid or thyrotoxicosis, is when the thyroid gland makes more thyroid hormones than your body needs. The thyroid gland is a small, butterfly-shaped gland in the front of your neck, just above your collarbone (see Figures 1 to 3). Your thyroid is one of your endocrine glands, which make hormones. Thyroid hormones control the rate of many activities in your body, so they affect nearly every organ in your body, even the way your heart beats. These include how fast you burn calories and how fast your heart beats. All of these activities are your body’s metabolism. If your thyroid is too active, it makes more thyroid hormones than your body needs. This is called hyperthyroidism.

About 1.2 percent of people in the United States have hyperthyroidism ¹. That’s a little more than 1 person out of 100.

Hyperthyroidism is more common in women, people with other thyroid problems, and those over 60 years old. Graves’ disease, an autoimmune disorder where the immune system stimulates the thyroid to produce too much hormone, is the most common cause of overactive thyroid. Other causes include thyroid nodules, thyroiditis, consuming too much iodine, and taking too much synthetic thyroid hormone.

Overactive thyroid symptoms can vary from person to person. Hyperthyroidism symptoms may include

• Being nervous or irritable
• Mood swings
• Fatigue or muscle weakness
• Heat intolerance
• Trouble sleeping
• Hand tremors
• Rapid and irregular heartbeat
• Frequent bowel movements or diarrhea
• Weight loss
• Goiter, which is an enlarged thyroid that may cause the neck to look swollen

To diagnose hyperthyroidism, your doctor will do a physical exam, look at your symptoms, and do thyroid tests. Treatment is with medicines, radioiodine therapy, or thyroid surgery. No single treatment works for everyone.

If left untreated, hyperthyroidism can cause serious problems with the heart, bones, muscles, menstrual cycle, and fertility. During pregnancy, untreated hyperthyroidism can lead to health problems for the mother and baby.

If hyperthyroidism isn’t treated, it can cause some serious health problems, including:

• Heart problems. A rapid heart rate, a heart rhythm disorder (called atrial fibrillation) that can lead to blood clots, stroke or congestive heart failure, and other heart-related problems.
• An eye disease called Graves’ ophthalmopathy that can cause double vision, light sensitivity, and eye pain, and rarely can lead to vision loss
• Thinning bones and osteoporosis. Too much thyroid hormone can prevent your body from absorbing calcium into your bones. You can get calcium in your Or your doctor may recommend a calcium supplement.
• Thyrotoxic crisis or thyroid storm. A sudden worsening of hyperthyroidism symptoms that leads to a fever, rapid pulse, and delirium. Signs of delirium include decreased awareness, confusion, and restlessness. See a doctor right away if this occurs.
• Infertility. Too much thyroid hormone can make it hard for some women to get pregnant. An overactive thyroid also can be harmful to the mother and baby during pregnancy. Most doctors test women’s thyroid hormone levels at this stage.

Who is more likely to develop hyperthyroidism?

Women are 2 to 10 times more likely than men to develop hyperthyroidism ².

You are more likely to have hyperthyroidism if you:

• have a family history of thyroid disease
• have other health problems, including:
  • pernicious anemia, a condition caused by a vitamin B12 deficiency
  • type 1 diabetes
  • primary adrenal insufficiency, a hormonal disorder
• eat large amounts of food containing iodine, such as kelp, or use medicines that contain iodine, such as amiodarone, a heart medicine
• are older than age 60, especially if you are a woman
• were pregnant within the past 6 months

What is the thyroid gland

The thyroid gland is the largest adult gland to have a purely endocrine function, weighing about 25-30 g. The butterfly-shaped thyroid gland is located adjacent to the trachea just inferior to the larynx (voice box) and is named for the nearby shield like thyroid cartilage of the larynx.

The thyroid gland is composed of right and left lateral lobes, one on either side of the trachea, that are connected by an isthmus in front of the trachea. About 50% of thyroid glands have a small third lobe, called the pyramidal lobe. It extends superiorly from the isthmus.

Microscopic spherical sacs called thyroid follicles make up most of the thyroid gland. The wall of each follicle consists primarily of cells called follicular cells, most of which extend to the lumen (internal space) of the follicle. A basement membrane surrounds each follicle. When the follicular cells are inactive, their shape is low cuboidal to squamous, but under the influence of thyroid stimulating hormone (TSH) they become active in secretion and range from cuboidal to low columnar in shape. The follicular cells produce two hormones: thyroxine, which is also called tetraiodothyronine (T4) because it contains four atoms of iodine and triiodothyronine (T3), which contains three atoms of iodine. T3 and T4 together are also known as thyroid hormones.

A few cells called parafollicular cells or C cells lie between follicles. They produce the hormone calcitonin, which helps regulate calcium homeostasis.

Like other endocrine glands, the thyroid releases these hormones directly into the bloodstream. Each follicle is surrounded by a basket like network of capillaries, the globular clusters of blood vessels. These are supplied by the superior and inferior thyroid arteries. The thyroid receives one of the body’s highest rates of blood flow per gram of tissue and consequently has a dark reddish brown color.

Thyroid hormone is secreted or inhibited in response to fluctuations in metabolic rate. The brain monitors the body’s metabolic rate and stimulates thyroid hormone (TH) secretion through the action of thyrotropin-releasing hormone (TRH) and thyroid stimulating hormone (TSH) as depicted in figure 3.

The primary effect of thyroid hormone (TH) is to increase one’s metabolic rate. As a result, it raises oxygen consumption and has a calorigenic effect—it increases heat production. To ensure an adequate blood and oxygen supply to meet this increased metabolic demand, thyroid hormone also raises the respiratory rate, heart rate, and strength of the heartbeat. It stimulates the appetite and accelerates the breakdown of carbohydrates, fats, and protein for fuel. Thyroid hormone also promotes alertness and quicker reflexes; growth hormone secretion; growth of the bones, skin, hair, nails, and teeth; and development of the fetal nervous system.

The thyroid gland also contains nests of parafollicular cells, also called clear (C) cells, at the periphery of the follicles. They respond to rising levels of blood calcium by secreting the hormone calcitonin. Calcitonin antagonizes parathyroid hormone and stimulates osteoblast activity, thus promoting calcium deposition and bone formation. It is important mainly in children, having relatively little effect in adults.

Figure 1. Thyroid gland location

Figure 2. Thyroid gland location

Thyroid gland function

Formation, Storage, and Release of Thyroid Hormones

The thyroid gland is the only endocrine gland that stores its secretory product in large quantities—normally about a 100-day supply. Synthesis and secretion of triiodothyronine (T3) and tetraiodothyronine (T4) occurs as follows:

1. Iodide trapping. Thyroid follicular cells trap iodide ions (I ⁻) by actively transporting them from the blood into the cytosol. As a result, the thyroid gland normally contains most of the iodide in the body.
2. Synthesis of thyroglobulin. While the follicular cells are trapping I ⁻, they are also synthesizing thyroglobulin (TGB), a large glycoprotein that is produced in the rough endoplasmic reticulum, modified in the Golgi complex, and packaged into secretory vesicles. The vesicles then undergo exocytosis, which releases thyroglobulin into the lumen of the follicle.
3. Oxidation of iodide. Some of the amino acids in thyroglobulin are tyrosines that will become iodinated. However, negatively charged iodide  (I ⁻) ions cannot bind to tyrosine until they undergo oxidation (removal of electrons) to iodine: I ⁻→ I. As the iodide ions are being oxidized, they pass through the membrane into the lumen of the follicle.
4. Iodination of tyrosine. As iodine atoms (I) form, they react with tyrosines that are part of thyroglobulin molecules. Binding of one iodine atom yields monoiodotyrosine (T1), and a second iodination produces diiodotyrosine (T2). The thyroglobulin with attached iodine atoms, a sticky material that accumulates and is stored in the lumen of the thyroid follicle, is termed colloid.
5. Coupling of monoiodotyrosine (T1) and diiodotyrosine (T2). During the last step in the synthesis of thyroid hormone, two diiodotyrosine (T2) molecules join to form tetraiodothyronine (T4) or one T1 and one T2 join to form triiodothyronine (T3).
6. Pinocytosis and digestion of colloid. Droplets of colloid reenter follicular cells by pinocytosis and merge with lysosomes. Digestive enzymes in the lysosomes break down thyroglobulin, cleaving off molecules of T3 and T4.
7. Secretion of thyroid hormones. Because T3 and T4 are lipid soluble, they diffuse through the plasma membrane into interstitial fluid and then into the blood. T4 normally is secreted in greater quantity than T3, but T3 is several times more potent. Moreover, after T4 enters a body cell, most of it is converted to T3 by removal of one iodine.
8. Transport in the blood. More than 99% of both the T3 and the T4 combine with transport proteins in the blood, mainly thyroxine binding globulin (TBG).

Figure 3. Thyroid gland anatomy

Footnote: (a) Gross anatomy, anterior view. (b) Histology, showing the saccular thyroid follicles (the source of thyroid hormone) and nests of C cells (the source of calcitonin).

Hyperthyroidism complications

Several complications can occur with an overactive thyroid (hyperthyroidism), particularly if the condition isn’t treated.

Eye problems

Eye problems, known as thyroid eye disease or Graves’ ophthalmopathy, affect around one in three people with an overactive thyroid caused by Graves’ disease.

These can include:

• the eyes feeling dry and gritty
• sensitivity to light
• watering eyes
• blurred or double vision
• red eyes
• red, swollen or pulled back eyelids
• bulging eyes

Many cases are mild and get better as your overactive thyroid is treated, but in around one in every 20 to 30 cases there’s a risk of vision loss.

If you experience eye problems, you will probably be referred to an eye specialist (ophthalmologist) for treatment, such as eye drops, steroid medication or possibly surgery.

Pregnancy problems

If you have an overactive thyroid during pregnancy and your condition isn’t well controlled, it can increase the risk of:

• pre-eclampsia
• miscarriage
• giving birth prematurely (before the 37th week of pregnancy)
• your baby having a low birthweight

Tell your doctor if you’re planning a pregnancy or think you might be pregnant.

They will want to check whether your condition is under control and they may recommend switching to a treatment that won’t affect the baby, such as the medication propylthiouracil.

If you’re not planning a pregnancy, it’s important to use contraception because some treatments for an overactive thyroid can harm an unborn baby.

Thyroid storm

In rare cases, an undiagnosed or poorly controlled overactive thyroid can lead to a serious, life-threatening reaction called a thyroid storm.

This is a sudden flare-up of symptoms that can be triggered by:

• an infection
• pregnancy
• not taking your medication correctly
• damage to the thyroid gland, such as a punch to the throat

Symptoms of a thyroid storm include:

• a rapid heartbeat
• a high temperature (fever) over 38 °C (100.4 °F)
• diarrhea and vomiting
• yellowing of the skin and eyes (jaundice)
• severe agitation and confusion
• loss of consciousness

A thyroid storm is a medical emergency. If you think you or someone in your care is experiencing it, call your local emergency services number for an ambulance immediately.

Other problems

An overactive thyroid can also increase your chances of developing:

• atrial fibrillation – a heart condition that causes an irregular and often abnormally fast heart rate
• weakened bones (osteoporosis) – this can make your bones fragile and more likely to break
• heart failure – where the heart is unable to pump blood around the body properly

Hyperthyroidism in Pregnancy

Thyroid hormone levels that are just a little high are usually not a problem in pregnancy. However, more severe hyperthyroidism that isn’t treated can affect both the mother and the baby. If you have hyperthyroidism, be sure your disease is under control before becoming pregnant.

What are the symptoms of hyperthyroidism in pregnancy?

Some signs and symptoms of hyperthyroidism often occur in normal pregnancies, including faster heart rate, trouble dealing with heat, and tiredness.

Other signs and symptoms can suggest hyperthyroidism:

• fast and irregular heartbeat
• shaky hands
• unexplained weight loss or failure to have normal pregnancy weight gain

What causes hyperthyroidism in pregnancy?

Hyperthyroidism in pregnancy is usually caused by Graves’ disease and occurs in 1 to 4 of every 1,000 pregnancies in the United States ³. Graves’ disease is an autoimmune disorder. With this disease, your immune system makes antibodies that cause the thyroid to make too much thyroid hormone. This antibody is called thyroid stimulating immunoglobulin.

Graves’ disease may first appear during pregnancy. However, if you already have Graves’ disease, your symptoms could improve in your second and third trimesters. Some parts of your immune system are less active later in pregnancy so your immune system makes less thyroid stimulating immunoglobulin. This may be why symptoms improve. Graves’ disease often gets worse again in the first few months after your baby is born, when thyroid stimulating immunoglobulin levels go up again. If you have Graves’ disease, your doctor will most likely test your thyroid function monthly throughout your pregnancy and may need to treat your hyperthyroidism ³. Thyroid hormone levels that are too high can harm your health and your baby’s.

Rarely, hyperthyroidism in pregnancy is linked to hyperemesis gravidarum —severe nausea and vomiting that can lead to weight loss and dehydration. Experts believe this severe nausea and vomiting is caused by high levels of hCG (human chorionic gonadotrophin) early in pregnancy. High hCG (human chorionic gonadotrophin) levels can cause the thyroid to make too much thyroid hormone. This type of hyperthyroidism usually goes away during the second half of pregnancy.

Less often, one or more nodules, or lumps in your thyroid, make too much thyroid hormone.

How can hyperthyroidism affect you and your baby?

Untreated hyperthyroidism during pregnancy can lead to:

• miscarriage
• premature birth
• low birthweight
• preeclampsia—a dangerous rise in blood pressure in late pregnancy
• thyroid storm—a sudden, severe worsening of symptoms
• congestive heart failure

Rarely, Graves’ disease may also affect a baby’s thyroid, causing it to make too much thyroid hormone. Even if your hyperthyroidism was cured by radioactive iodine treatment to destroy thyroid cells or surgery to remove your thyroid, your body still makes the thyroid stimulating immunoglobulin antibody. When levels of this antibody are high, thyroid stimulating immunoglobulin may travel to your baby’s bloodstream. Just as thyroid stimulating immunoglobulin caused your own thyroid to make too much thyroid hormone, it can also cause your baby’s thyroid to make too much.

Tell your doctor if you’ve had surgery or radioactive iodine treatment for Graves’ disease so he or she can check your thyroid stimulating immunoglobulin levels. If they are very high, your doctor will monitor your baby for thyroid-related problems later in your pregnancy.

An overactive thyroid in a newborn can lead to:

• a fast heart rate, which can lead to heart failure
• early closing of the soft spot in the baby’s skull
• poor weight gain
• irritability

Sometimes an enlarged thyroid can press against your baby’s windpipe and make it hard for your baby to breathe. If you have Graves’ disease, your health care team should closely monitor you and your newborn.

Hyperthyroidism in pregnancy diagnosis

Your doctor will review your symptoms and do some blood tests to measure your thyroid hormone levels. Your doctor may also look for antibodies in your blood to see if Graves’ disease is causing your hyperthyroidism.

Hyperthyroidism during pregnancy treatment

If you have mild hyperthyroidism during pregnancy, you probably won’t need treatment. If your hyperthyroidism is linked to hyperemesis gravidarum, you only need treatment for vomiting and dehydration.

If your hyperthyroidism is more severe, your doctor may prescribe antithyroid medicines, which cause your thyroid to make less thyroid hormone. This treatment prevents too much of your thyroid hormone from getting into your baby’s bloodstream. You may want to see a specialist, such as an endocrinologist or expert in maternal-fetal medicine, who can carefully monitor your baby to make sure you’re getting the right dose.

Doctors most often treat pregnant women with the antithyroid medicine propylthiouracil (PTU) during the first 3 months of pregnancy. Another type of antithyroid medicine, methimazole , is easier to take and has fewer side effects, but is slightly more likely to cause serious birth defects than propylthiouracil. Birth defects with either type of medicine are rare. Sometimes doctors switch to methimazole after the first trimester of pregnancy. Some women no longer need antithyroid medicine in the third trimester.

Small amounts of antithyroid medicine move into the baby’s bloodstream and lower the amount of thyroid hormone the baby makes. If you take antithyroid medicine, your doctor will prescribe the lowest possible dose to avoid hypothyroidism in your baby but enough to treat the high thyroid hormone levels that can also affect your baby.

Antithyroid medicines can cause side effects in some people, including:

• allergic reactions such as rashes and itching
• rarely, a decrease in the number of white blood cells in the body, which can make it harder for your body to fight infection
• liver failure, in rare cases

Stop your antithyroid medicine and see your doctor right away if you develop any of these symptoms while taking antithyroid medicines:

• yellowing of your skin or the whites of your eyes, called jaundice
• dull pain in your abdomen
• constant sore throat
• fever

If you can’t see your doctor the same day, you should go to the nearest emergency room.

You should also contact your doctor if any of these symptoms develop for the first time while you’re taking antithyroid medicines:

• increased tiredness or weakness
• loss of appetite
• skin rash or itching
• easy bruising

If you are allergic to or have severe side effects from antithyroid medicines, your doctor may consider surgery to remove part or most of your thyroid gland. The best time for thyroid surgery during pregnancy is in the second trimester.

Radioactive iodine treatment is not an option for pregnant women because it can damage the baby’s thyroid gland.

Is it safe to breastfeed while taking beta-blockers, thyroid hormone, or antithyroid medicines?

Certain beta-blockers are safe to use while you’re breastfeeding because only a small amount shows up in breast milk. The lowest possible dose to relieve your symptoms is best. Only a small amount of thyroid hormone medicine reaches your baby through breast milk, so it’s safe to take while you’re breastfeeding. However, in the case of antithyroid drugs, your doctor will most likely limit your dose to no more than 20 milligrams (mg) of methimazole or, less commonly, 400 mg of propylthiouracil.

Hyperthyroidism signs and symptoms

Symptoms of hyperthyroidism can vary from person to person and may include:

• changes in menstrual patterns, such as lighter flow or less frequent periods, in women.
• nervousness, anxiety, touchiness or irritability
• fatigue or muscle weakness
• increased sensitivity to heat
• difficulty sleeping
• shaky hands or tremor
• rapid and irregular heartbeat
• frequent bowel movements or diarrhea
• weight loss
• mood swings
• goiter (enlarged thyroid), which can appear as swelling at the base of the neck
• breathlessness
• eye problems
• increased appetite
• increased sweating
• changes in bowel habits or menstrual patterns
• thin skin
• fine, brittle hair

In people over age 60, hyperthyroidism is sometimes mistaken for depression or dementia. Older adults may have different symptoms, such as loss of appetite or withdrawal from people, than younger adults with hyperthyroidism.

People who have Graves’ disease may have additional symptoms. One of the most common symptoms is swollen or bulging eyes. This can cause your eyes to be dry and red. You may have pain, tearing, blurry or double vision, or sensitivity to light.

You may want to ask your health care provider about hyperthyroidism if you or your loved one show these symptoms.

Hyperthyroidism causes

Hyperthyroidism has several causes, including Graves’ disease, thyroid nodules, and thyroiditis—inflammation of the thyroid. Rarely, hyperthyroidism is caused by a noncancerous tumor of the pituitary gland located at the base of the brain. Consuming too much iodine or taking too much thyroid hormone medicine also may raise your thyroid hormone levels.

Graves’ disease

Graves’ disease is the most common cause of hyperthyroidism (more than 70% of cases). Graves’ disease is an autoimmune disorder. With Graves’ disease, your immune system attacks the thyroid and causes it to make too much thyroid hormone.

Normally, the immune system helps protect your body against viruses, bacteria, and other substances. An autoimmune disease causes it to attack your body’s tissues and/or organs. Doctors think Graves’ disease may run in families. It is most common among young women.

People who have Graves’ disease may develop red, swollen skin on their shins and feet. Try using over-the-counter creams with hydrocortisone for relief. You also may have eye problems due to Graves’ opthalmopathy. To relieve these symptoms:

• Apply a cool compress to your eyes.
• Wear sunglasses.
• Use lubricating eye drops.
• Elevate the head of your bed to reduce blood flow to your head.

Overactive thyroid nodules

Thyroid nodules are lumps in your thyroid. Thyroid nodules are common and usually benign, meaning they are not cancerous. However, one or more nodules may become overactive and produce too much thyroid hormone. The presence of many overactive nodules occurs most often in older adults.

Thyroiditis

Thyroiditis is inflammation of your thyroid that causes stored thyroid hormone to leak out of your thyroid gland. The hyperthyroidism may last for up to 3 months, after which your thyroid may become underactive, a condition called hypothyroidism. The hypothyroidism usually lasts 12 to 18 months, but sometimes is permanent.

Several types of thyroiditis can cause hyperthyroidism and then cause hypothyroidism:

• Subacute thyroiditis: This condition involves a painfully inflamed and enlarged thyroid. Experts are not sure what causes subacute thyroiditis, but it may be related to an infection caused by a virus or bacteria.
• Postpartum thyroiditis: This type of thyroiditis develops after a woman gives birth.
• Silent thyroiditis: This type of thyroiditis is called “silent” because it is painless, even though your thyroid may be enlarged. Experts think silent thyroiditis is probably an autoimmune condition.

Too much iodine

Your thyroid uses iodine to make thyroid hormone. The amount of iodine you consume affects the amount of thyroid hormone your thyroid makes. In some people, consuming large amounts of iodine may cause the thyroid to make too much thyroid hormone.

Some medicines and cough syrups may contain a lot of iodine. One example is the heart medicine amiodarone. Seaweed and seaweed-based supplements also contain a lot of iodine.

Too much thyroid hormone medicine

Some people who take thyroid hormone medicine for hypothyroidism may take too much. If you take thyroid hormone medicine, you should see your doctor at least once a year to have your thyroid hormone levels checked. You may need to adjust your dose if your thyroid hormone level is too high.

Some other medicines may also interact with thyroid hormone medicine to raise hormone levels. If you take thyroid hormone medicine, ask your doctor about interactions when starting new medicines.

Hyperthyroidism be prevention

You cannot prevent hyperthyroidism. However, some people are more at risk for overactive thyroid. This includes people who:

• Were born female.
• Have a family history of thyroid disease.
• Are younger than 40 years old or older than 60 years old.
• Have certain problems, such as type 1 diabetes, pernicious anemia, or an immune system disorder.
• Consume large amounts of iodine, either through food or medicine.

Hyperthyroidism diagnosis

Your doctor will take a medical history and do a physical exam, but also will need to do some tests to confirm a diagnosis of hyperthyroidism. Many symptoms of hyperthyroidism are the same as those of other diseases, so doctors usually can’t diagnose hyperthyroidism based on symptoms alone.

Because hypothyroidism can cause fertility problems, women who have trouble getting pregnant often get tested for thyroid problems.

Your doctor may use several blood tests to confirm a diagnosis of hyperthyroidism and find its cause. Imaging tests, such as a thyroid scan, can also help diagnose and find the cause of hyperthyroidism.

Blood tests to check thyroid function

Doctors may order one or more blood tests to check your thyroid function. Tests may include thyroid stimulating hormone (TSH), T4, T3, and thyroid antibody tests.

For these tests, a health care professional will draw blood from your arm and send it to a lab for testing. Your doctor will talk to you about your test results.

TSH test

Health care professionals usually check the amount of thyroid stimulating hormone (TSH) in your blood first. TSH is a hormone made in the pituitary gland that tells the thyroid how much T4 and T3 to make.

• A high TSH level most often means you have hypothyroidism, or an underactive thyroid. This means that your thyroid isn’t making enough hormone. As a result, the pituitary keeps making and releasing TSH into your blood.
• A low TSH level usually means you have hyperthyroidism, or an overactive thyroid. This means that your thyroid is making too much hormone, so the pituitary stops making and releasing TSH into your blood.

If the TSH test results are not normal, you will need at least one other test to help find the cause of the problem.

T4 tests

A high blood level of T4 may mean you have hyperthyroidism. A low level of T4 may mean you have hypothyroidism.

In some cases, high or low T4 levels may not mean you have thyroid problems. If you are pregnant or are taking oral contraceptives, your thyroid hormone levels will be higher. Severe illness or using corticosteroids—medicines to treat asthma, arthritis, skin conditions, and other health problems—can lower T4 levels. These conditions and medicines change the amount of proteins in your blood that “bind,” or attach, to T4. Bound T4 is kept in reserve in the blood until it’s needed. “Free” T4 is not bound to these proteins and is available to enter body tissues. Because changes in binding protein levels don’t affect free T4 levels, many healthcare professionals prefer to measure free T4.

T3 test

If your health care professional thinks you may have hyperthyroidism even though your T4 level is normal, you may have a T3 test to confirm the diagnosis. Sometimes T4 is normal yet T3 is high, so measuring both T4 and T3 levels can be useful in diagnosing hyperthyroidism.

Thyroid antibody tests

Measuring levels of thyroid antibodies may help diagnose an autoimmune thyroid disorder such as Graves’ disease—the most common cause of hyperthyroidism—and Hashimoto’s disease—the most common cause of hypothyroidism. Thyroid antibodies are made when your immune system attacks the thyroid gland by mistake. Your health care professional may order thyroid antibody tests if the results of other blood tests suggest thyroid disease.

Imaging tests

Your health care professional may order one or more imaging tests to diagnose and find the cause of thyroid disease. A trained technician usually does these tests in your doctor’s office, outpatient center, or hospital. A radiologist, a doctor who specializes in medical imaging, reviews the images and sends a report for your health care professional to discuss with you.

Ultrasound

Ultrasound of the thyroid is most often used to look for, or more closely at, thyroid nodules. Thyroid nodules are lumps in your neck. Ultrasound can help your doctor tell if the nodules are more likely to be cancerous.

For an ultrasound, you will lie on an exam table and a technician will run a device called a transducer over your neck. The transducer bounces safe, painless sound waves off your neck to make pictures of your thyroid. The ultrasound usually takes around 30 minutes.

Thyroid scan

Health care professionals use a thyroid scan to look at the size, shape, and position of the thyroid gland. This test uses a small amount of radioactive iodine to help find the cause of hyperthyroidism and check for thyroid nodules. Your health care professional may ask you to avoid foods high in iodine, such as kelp, or medicines containing iodine for a week before the test.

For the scan, a technician injects a small amount of radioactive iodine or a similar substance into your vein. You also may swallow the substance in liquid or capsule form. The scan takes place 30 minutes after an injection, or up to 24 hours after you swallow the substance, so your thyroid has enough time to absorb it.

During the scan, you will lie on an exam table while a special camera takes pictures of your thyroid. The scan usually takes 30 minutes or less.

Thyroid nodules that make too much thyroid hormone show up clearly in the pictures. Radioactive iodine that shows up over the whole thyroid could mean you have Graves’ disease.

Even though only a small amount of radiation is needed for a thyroid scan and it is thought to be safe, you should not have this test if you are pregnant or breastfeeding.

Radioactive iodine uptake test

A radioactive iodine uptake test, also called a thyroid uptake test, can help check thyroid function and find the cause of hyperthyroidism. The thyroid “takes up” iodine from the blood to make thyroid hormones, which is why this is called an uptake test. Your health care professional may ask you to avoid foods high in iodine, such as kelp, or medicines containing iodine for a week before the test.

For this test, you will swallow a small amount of radioactive iodine in liquid or capsule form. During the test, you will sit in a chair while a technician places a device called a gamma probe in front of your neck, near your thyroid gland. The probe measures how much radioactive iodine your thyroid takes up from your blood. Measurements are often taken 4 to 6 hours after you swallow the radioactive iodine and again at 24 hours. The test takes only a few minutes.

If your thyroid collects a large amount of radioactive iodine, you may have Graves’ disease, or one or more nodules that make too much thyroid hormone. You may have this test at the same time as a thyroid scan.

Even though the test uses a small amount of radiation and is thought to be safe, you should not have this test if you are pregnant or breastfeeding.

If you have a thyroid nodule

If your health care professional finds a nodule or lump in your neck during a physical exam or on thyroid imaging tests, you may have a fine needle aspiration biopsy to see if the lump is cancerous or noncancerous.

For this test, you will lie on an exam table and slightly bend your neck backward. A technician will clean your neck with an antiseptic and may use medicine to numb the area. An endocrinologist who treats people with endocrine gland problems like thyroid disease, or a specially trained radiologist, will place a needle through the skin and use ultrasound to guide the needle to the nodule. Small samples of tissue from the nodule will be sent to a lab for testing. This procedure usually takes less than 30 minutes. Your health care professional will talk with you about the test result when it is available.

Hyperthyroidism treatment

If you are diagnosed with hyperthyroidism, there are a few different treatments that can be given. The best one depends on your age, health, cause, and how severe your condition is. The goal is to control your thyroid levels and make them normal. Doing this relieves symptoms and prevents future health problems.

Medication can reduce the amount of hormone your thyroid produces, or you could be given radioactive iodine therapy, taken as a single dose to shrink the thyroid. If neither of these treatments is suitable, the thyroid could be removed by surgery although this carries a risk of damaging surrounding glands and nerves.

You could also be prescribed medication to control a fast heart rate and palpitations.

You’ll normally be referred to an endocrinologist (specialist in hormone conditions) to plan your treatment.

The main treatments are:

• Anti-thyroid medicine. These drugs tell your thyroid to produce fewer hormones. Symptoms begin to improve in 6 to 12 weeks as your hormone levels adjust. Treatment can last for at least a year. This is a better option for women who are pregnant or breastfeeding. Talk to your doctor about possible side effects.
• Radioactive iodine. You take a pill or liquid by mouth. It gets into your blood stream and destroys the overactive thyroid cells. This causes the level of thyroid hormone in your body to decrease. Symptoms often lessen in 3 to 6 months. The final result is permanent low thyroid activity (hypothyroidism). This condition can be treated with thyroid supplements. Despite concerns about radioactive material, the treatment has been used for more than 60 years without any problems. Most adults in the United States who have hyperthyroidism are treated with radioactive iodine. This option is not suitable for women who are pregnant or breastfeeding.
• Surgery. A thyroidectomy is when the doctor removes most of your thyroid gland. After surgery, you likely will develop hypothyroidism. You can take thyroid supplements to restore your hormone levels to normal.
• Beta blockers. These drugs slow your heart rate and reduce tremors and anxiety. They can be used with other forms of treatment. You should be able to stop taking them once your thyroid levels return to normal.

Hyperthyroidism medication

Antithyroid therapy is the simplest way to treat hyperthyroidism. Antithyroid medicines cause the thyroid to make less thyroid hormone. These medicines usually don’t provide a permanent cure. Medicines called thionamides are a common treatment for an overactive thyroid. These stop your thyroid producing excess hormones. Health care providers most often use the antithyroid medicine methimazole, carbimazole and propylthiouracil. Health care providers more often treat pregnant women with propylthiouracil during the first 3 months of pregnancy, because methimazole can harm the fetus, although this happens rarely.

You’ll usually need to take the medicine for a month or two before you notice any benefit. You may be given another medication called a beta-blocker to quickly relieve your symptoms in the meantime.

Once treatment with antithyroid medicine begins, your thyroid hormone levels may not move into the normal range for several weeks or months. The total average treatment time is about 1 to 2 years, but treatment can continue for many years. Antithyroid medicines are not used to treat hyperthyroidism caused by thyroiditis.

Once your thyroid hormone level is under control, your dose may be gradually reduced and then stopped. But some people need to continue taking medication for several years or possibly for life.

Antithyroid medicines can cause side effects in some people.

During the first couple of months, some people experience the following side effects:

• feeling sick
• headaches
• aching joints
• an upset stomach
• allergic reactions such as rashes and itching

These should pass as your body gets used to the medication.

A less common but more serious side effect is a sudden drop in your white blood cell level (agranulocytosis), which can mean you’re very vulnerable to infections. Contact your doctor immediately if you get symptoms of agranulocytosis, such as a fever, sore throat or persistent cough so a blood test can be carried out to check your white blood cell level.

Another rare side effects of anti-thyroid medicine is liver failure.

Call your doctor right away if you have any of the following symptoms:

• fatigue
• weakness
• dull pain in your abdomen
• loss of appetite
• skin rash or itching
• easy bruising
• yellowing of your skin or whites of your eyes, called jaundice
• constant sore throat
• fever

Doctors usually treat pregnant and breastfeeding women with antithyroid medicine, since this treatment may be safer for the baby than other treatments.

Underactive thyroid

Treatment for hyperthyroidism often results in hormone levels that are too low – known as an underactive thyroid (hypothyroidism).

Symptoms of an underactive thyroid can include:

• sensitivity to cold
• tiredness
• weight gain
• constipation
• depression

An underactive thyroid (hypothyroidism) is sometimes only temporary, but often it’s permanent and requires long-term treatment with thyroid hormone medication.

Radioiodine treatment

Radioiodine treatment is where radioactive iodine is used to damage your thyroid, reducing the amount of hormones it can produce. It’s a common and highly effective treatment that can cure hyperthyroidism.

You’re given a drink or capsule that contains a low dose of radioactive iodine-131, which is then absorbed by your thyroid. The radioactive iodine slowly destroys the cells of the thyroid gland that produce thyroid hormone. Radioactive iodine does not affect other body tissues.

You may need more than one radioiodine treatment to bring your thyroid hormone levels into the normal range. However, most people only require a single treatment. It can take a few weeks or months for the full benefits to be felt, so you may need to take beta blockers for a short time to control your symptoms.

Almost everyone who has radioactive iodine treatment later develops hypothyroidism because the thyroid hormone-producing cells have been destroyed. However, hypothyroidism is easier to treat and causes fewer long-term health problems than hyperthyroidism. People with hypothyroidism can completely control the condition with daily thyroid hormone medicine.

Doctors don’t use radioiodine therapy in pregnant women or in women who are breastfeeding. Radioactive iodine can harm the fetus’ thyroid and can be passed from mother to child in breast milk.

Radioiodine treatment is also not suitable if your overactive thyroid is causing severe eye problems.

The dose of radiation you’re given is very low, but there are some precautions you’ll need to take after treatment:

• avoid prolonged close contact with children and pregnant women for a few days or weeks
• women should avoid getting pregnant for at least six months
• men shouldn’t father a child for at least four months.

Thyroid surgery

The least-used treatment for hyperthyroidism is surgery to remove part or most of the thyroid gland. Sometimes doctors use surgery to treat people with large goiters or pregnant women who cannot take antithyroid medicines.

This may be the best option if:

• your thyroid gland is severely swollen (a large goiter)
• you have severe eye problems resulting from an overactive thyroid
• you can’t have the other treatments mentioned above
• your symptoms come back after trying the treatments mentioned above

Removing the entire thyroid gland is normally recommended, as this cures an overactive thyroid and means there’s no chance of the symptoms coming back.

Before surgery, your doctor may prescribe antithyroid medicines to bring your thyroid hormone levels into the normal range. This treatment prevents a condition called thyroid storm—a sudden, severe worsening of symptoms—that can occur when people with hyperthyroidism have general anesthesia.

When part of your thyroid is removed, your thyroid hormone levels may return to normal. You may still develop hypothyroidism after surgery and need to take thyroid hormone medicine. If your whole thyroid is removed, you will need to take thyroid hormone medicine for life. After surgery, your doctor will continue to check your thyroid hormone levels.

Hyperthyroidism diet

People with Graves’ disease or other type of autoimmune thyroid disorder may be sensitive to harmful side effects from iodine. Eating foods that have large amounts of iodine—such as kelp, dulse, or other kinds of seaweed—may cause or worsen hyperthyroidism. Taking iodine supplements can have the same effect. Talk with members of your health care team about what foods you should limit or avoid, and let them know if you take iodine supplements. Also, share information about any cough syrups or multivitamins that you take because they may contain iodine.

1. Bahn RS, Burch HB, Cooper DS, et al. Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. Endocrine Practice. 2011;17(3):456–520.[↩]
2. Golden SH, Robinson KA, Saldanha I, Anton B, Ladenson PW. Clinical review: prevalence and incidence of endocrine and metabolic disorders in the United States: a comprehensive review. Journal of Clinical Endocrinology and Metabolism. 2009;94(6):1853–1878.[↩]
3. Alexander EK, Pearce EN, Brent GA, et al. 2017 guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and the postpartum. Thyroid. 2017;27(3):315–389.[↩][↩]