Hyperthyroidism, also called thyrotoxicosis, is a condition resulting from an overactive thyroid gland. It leads to an oversupply of thyroid hormones that help to control metabolism in the body. Hyperthyroidism is 4-5 times more likely to occur in women than men, affecting up to 2% of women at some point in their lives. [1]
The thyroid gland plays a key role in the endocrine system, which produces hormones that control bodily functions such as metabolism. If hormone levels are not within a normal range, this can affect the whole body, causing a wide range of symptoms and health problems.
The thyroid gland is located at the front of the throat, just above the hollow between the upper ends of the collarbones and below the Adam's apple (the larynx). It has two lobes that sit on either side of the windpipe. It is controlled by the pituitary gland, which sits at the base of the brain and secretes thyroid-stimulating hormone (TSH).
The thyroid produces two hormones:
Stimulation of the thyroid gland by thyroid-stimulating hormone (TSH) to produce thyroid hormones (T3 and T4).
The thyroid hormones circulate throughout the bloodstream, regulating metabolism. The higher the levels of T3 and T4 are, the faster metabolism will be.
The nutrient iodine is very important in the production of T3 and T4. It is found in a range of foods including iodized salt, dairy products, seafood and bread made with iodized salt. Not having enough iodine in the diet can lead to an underactive thyroid as well as other health problems. Consuming too much iodine can lead to an overactive thyroid.
A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.
The sum of all chemical changes that take place within an organism to maintain growth and development and convert food into energy and building blocks.
Murtagh J. MD. (2011) John Murtagh’s General Practice (5th revised edition). North Ryde N.S.W.: McGraw-Hill Education (Australia) Pty Ltd.
There are many causes of hyperthyroidism. Some of the more common ones include:
More rare causes of hyperthyroidism include:
A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralize them or target them for destruction.
A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.
Graves' disease is the most common cause of hyperthyroidism. It is an autoimmune disorder in which antibodies produced by the immune system mimic the action of TSH and stimulate the thyroid gland to produce an excessive amount of thyroid hormones.
It is 5-10 times more common in women than men. [2] Smoking and stress can increase the risk of developing Graves' disease and the risk is also increased for women following a pregnancy. Graves' disease tends to run in families. Consuming excessive levels of iodine or taking the drug amiodarone can also increase the risk of developing this condition.
People with Graves' disease are also at an increased risk of a range of other autoimmune conditions including type 1 diabetes, pernicious anemia, Addison's disease, coeliac disease and vitiligo.
People with Graves' disease may develop symptoms affecting their eyes (see potential complications).
Growths of the thyroid such as toxic multinodular goiter and thyroid adenomas can produce excess hormones. These growths are usually not cancerous.
A toxic multinodular goiter is a growth on the thyroid that grows out of a simple goiter and overproduces thyroid hormones. When there is one growth it is called a toxic nodule, when there is more than one growth it is a multinodular goiter. It is most common in older people, particularly women over 60 years of age.
Inflammation of the thyroid (thyroiditis) can cause the release of hormones stored in the gland. This causes a temporary form of hyperthyroidism. Because of the damage done to the thyroid, some people may go on to develop an underactive thyroid (hypothyroidism), for which they may require treatment.
Thyroiditis can be triggered by:
The recommended daily intake of iodine for adults who are not pregnant is 150 micrograms. Consistently consuming more than this can lead to hyperthyroidism.
The most common causes of taking in too much iodine include:
Human chorionic gonadotropin (hCG) is a hormone that is produced in high amounts in the first four months of pregnancy. Like the antibodies in Graves' disease, hCG can mimic the action of thyroid-stimulating hormone (TSH) and stimulate the thyroid gland to produce too much T3 and T4 hormones.
Some men can develop hCG-related hyperthyroidism due to hCG being produced by testicular cancer.
A chronic condition in which the adrenal glands are damaged, leading to a reduction of the hormones cortisol and/or aldosterone. These hormones are important for daily bodily functions and their deficiency can lead to a wide variety of symptoms.
A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralize them or target them for destruction.
A medical condition in which the body's immune system abnormally targets substances that are normally found within the body.
A medication-based treatment, usually used in the treatment of cancers. There are numerous, different types of chemotherapy drugs that can be prescribed by a specialist. These can commonly be used alongside other cancer treatments such as surgery and radiotherapy.
A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.
A metal element that is used in medications that treat psychiatric illnesses.
Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.
There are many symptoms that can occur with hyperthyroidism and they can vary a lot from person to person.
Symptoms can include:
A goiter is an enlargement of the thyroid gland and can appear as a lump or swelling on the front of the throat.
While enlargement of the thyroid gland (goiter) can occur in hyperthyroidism, it can also occur for other reasons, including underactive thyroid (hypothyroidism) and thyroid cancer.
A goiter is an enlargement of the thyroid gland.
A feeling of tension, nervousness and dread about future events. It can trigger physical symptoms such as a rapid pulse or breathing difficulties.
The periodic shedding of the lining of a woman's uterus. Typically occurring about every four weeks between puberty and menopause (except during pregnancy). The menstrual period varies between individuals, but typically lasts 3-5 days.
There can be many reasons why thyroid hormone levels are elevated and not all are due to hyperthyroidism. The doctor will consider your symptoms and health history.
A physical examination can help identify signs of hyperthyroidism. The exam can include:
A blood test can measure the levels of TSH, T3 and T4 hormones. In hyperthyroidism the TSH levels are usually low and either or both of the T3 and T4 hormones levels are high. A blood test can also detect thyroid antibodies that can cause Graves' disease and thyroiditis.
A blood test can be used to measure thyroid hormones.
During a nuclear thyroid scan, iodine is marked with a radioactive label called a tracer and absorbed by the thyroid from the bloodstream. Measuring the amount of iodine the thyroid takes up can help to determine what is causing the hyperthyroidism. It is particularly useful for detecting toxic nodules and areas of the gland that are overactive.
A picture of the thyroid is obtained using ultrasound and can show enlargement of the gland and indicate some changes in the gland tissue.
A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralize them or target them for destruction.
The pressure the blood places on the walls of the arteries, largely mirroring the contraction of the heart, and consisting of two readings. The higher reading is systolic blood pressure, when the heart contracts, and the lower is diastolic blood pressure, when the heart is relaxed.
A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.
Treatment of hyperthyroidism will vary depending on the cause, the symptoms and other aspects of general health, for example, whether or not a woman is pregnant.
Beta-blocker drugs such as propranolol can be prescribed to help relieve symptoms such as shaking, a racing heartbeat, sweating and anxiety until antithyroid medications can take effect.
Antithyroid drugs such as carbimazole and propylthiouracil work by reducing the amount of hormone the thyroid produces. They are usually taken for around 12-18 months.
Taken by mouth, radioactive iodine is taken up by cells in the thyroid, where the radiation destroys the cells over the following weeks or months. This reduces the amount of hormone the thyroid can produce. Some people may require more than one dose.
Thyroid surgery usually involves the removal of all or part of the thyroid gland. This operation is performed under a general anesthetic in a hospital. It will often require you to stay in hospital for 1-2 days.
A feeling of tension, nervousness and dread about future events. It can trigger physical symptoms such as a rapid pulse or breathing difficulties.
An anesthetic given to a person to put them to sleep while having an operation or medical procedure. Afterwards, the person regains consciousness and usually has no memory of the procedure. A general anesthetic is given in hospital by a specialist called an anesthetist.
A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.
Complications with hyperthyroidism can depend on what type of the condition it is and the treatment.
They can include:
People with Graves' disease may develop symptoms affecting their eyes. In this condition inflammatory cells accumulate in the soft tissues around the eyes, causing swelling, particularly of the eyelids and the muscles that move the eyes.
This can:
Treatment for Graves' ophthalmopathy includes corticosteroids to help reduce the inflammation, tear supplements to help keep eyes moist and comfortable and surgery if necessary. Smoking increases the risk of developing symptoms.
Graves' ophthalmopathy results in bulging of the eyes.
Also called a thyroid storm, this is an extreme form of hyperthyroidism that is a medical emergency and requires intensive treatment. It can be triggered by thyroid surgery or radioactive iodine treatment.
Hyperthyroidism can lead to a fast heart rate, abnormal heart rhythm (atrial fibrillation) and in severe cases, heart failure, which can be life-threatening.
Prolonged hyperthyroidism can promote bone loss leading to osteoporosis.
Treatments, including antithyroid medications, radioactive iodine and thyroid surgery can lead to an underactive thyroid, which is also known as hypothyroidism. This is treated by taking replacement thyroid hormone daily. This medication will usually need to be taken permanently.
Antithyroid medications can cause a range of side effects including nausea, vomiting and rash.
Agranulocytosis, which a severe reduction in white blood cells, is a rare but serious complication (0.2-0.5% of cases [2] ) that can be life-threatening. Symptoms include fever, mouth ulcers and sore throat.
Complications that can occur with surgery include:
A medication that resembles the cortisol hormone produced in the brain. It is used as an anti-inflammatory medication.
A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.
An open sore in the skin or mucous membranes such as those of the stomach lining, intestine or mouth.
The nerve that controls the function of the voice box to produce speech, allow breathing and supply sensation to the voice box.
Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.
Prognosis depends on the type of hyperthyroidism, the severity of the symptoms and treatment. It is not uncommon for people to develop hypothyroidism after treatment, although it may take years to develop.
Most forms of hyperthyroidism cannot be prevented. Avoiding excess iodine intake may prevent iodine-related forms of hyperthyroidism, however, it is important to consume adequate amounts of iodine to prevent hypothyroidism, particularly during pregnancy.