What is hyperthyroidism?

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:

  • Tri-iodothyronine (T3), and;
  • Thyroxine (T4).

Cross-section of the head and throat showing the brain, the pituitary gland, the thyroid gland and the production of thyroid-stimulating hormone and thyroid 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 iodised salt, dairy products, seafood and bread made with iodised 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.

Hormones

A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.

Metabolism

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.

1. Murtagh J. MD. (2011) John Murtagh’s General Practice (5th revised edition). North Ryde N.S.W.: McGraw-Hill Education (Australia) Pty Ltd.

Causes

There are many causes of hyperthyroidism. Some of the more common ones include:

  • A condition of the immune system that leads to antibodies overstimulating the thyroid to produce ecxessive thyroid hormones (Graves' disease); 
  • Abnormal growths of the thyroid gland (such as multinodular goitre and toxic adenoma);
  • Inflammation of the thyroid gland that causes the release of thyroid hormones (thyroiditis);
  • Consuming too much iodine via foods or undergoing medical imaging tests that use dyes containing iodine, and;
  • Taking the medication amiodarone, which contains a large amount of iodine.

More rare causes of hyperthyroidism include:

  • Consuming large amounts of thyroid hormone (thyrotoxicosis factitia);
  • Some tumours of the ovaries, which can produce thyroid hormones;
  • High blood levels of human chorionic gonadotropin, a hormone that can stimulate the thyroid to produce extra hormone;
  • Oversecretion of thyroid-stimulating hormone due to a tumour in the pituitary gland, and;
  • Thyroid cancer.

Antibodies

A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralise them or target them for destruction.

Hormones

A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.

1. Murtagh J. MD. (2011) John Murtagh’s General Practice (5th revised edition). North Ryde N.S.W.: McGraw-Hill Education (Australia) Pty Ltd.

Types

Graves' disease

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 anaemia, Addison's diseasecoeliac disease and vitiligo.

People with Graves' disease may develop symptoms affecting their eyes (see potential complications).

Benign growths of the thyroid

Growths of the thyroid such as toxic multinodular goitre and thyroid adenomas can produce excess hormones. These growths are usually not cancerous.

A toxic multinodular goitre is a growth on the thyroid that grows out of a simple goitre 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 goitre. It is most common in older people, particularly women over 60 years of age.

Thyroiditis

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:

  • Viral infections;
  • Pregnancy (symptoms usually occur after the pregnancy), and;
  • Some medications including lithium and medications used in chemotherapy.

Iodine-induced hyperthyroidism

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:

  • Dyes containing iodine used for medical imaging tests;
  • Overconsumption of foods very high in iodine such as kelp and nori, and;
  • Medications high in iodine such as amiodarone (commonly used to treat heart arrhythmias).

Human chorionic gonadotropin-related hyperthyroidism

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.

Addison's disease

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.

Antibodies

A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralise them or target them for destruction.

Autoimmune disorder

A medical condition in which the body's immune system abnormally targets substances that are normally found within the body.

Chemotherapy

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.

Hormones

A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.

Lithium

A metal element that is used in medications that treat psychiatric illnesses.

2. Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.

Signs and symptoms

There are many symptoms that can occur with hyperthyroidism and they can vary a lot from person to person.

Symptoms can include:

  • Rapid pulse;
  • Rapid or irregular heartbeat (palpitations);
  • Shaking of the hands;
  • Finding the heat extremely uncomfortable (heat intolerance) and increased sweating;
  • Problems sleeping and fatigue;
  • Nervousness, restlessness, agitation and anxiety;
  • Frequent bowel movements and diarrhoea;
  • Reduced or irregular menstruation in women;
  • An enlarged thyroid gland, sometimes called a goitre (see below);
  • Increased appetite;
  • Weight loss despite eating more (weight gain in rare cases);
  • Protruding, staring eyes;
  • Flushed skin;
  • Hair loss or fine hair, and;
  • Itching.

Goitre

A goitre 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 (goitre) can occur in hyperthyroidism, it can also occur for other reasons, including underactive thyroid (hypothyroidism) and thyroid cancer.

A person with a goitre.A goitre is an enlargement of the thyroid gland. 

Anxiety

A feeling of tension, nervousness and dread about future events. It can trigger physical symptoms such as a rapid pulse or breathing difficulties.

Menstruation

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.

2. Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.

Methods for diagnosis

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.

Physical examination

A physical examination can help identify signs of hyperthyroidism. The exam can include:

  • Measuring heart rate;
  • Checking the hands for trembling;
  • Checking the neck for signs of an enlarged thyroid gland;
  • Measuring blood pressure, and;
  • Examining the eyes for signs of swelling and inflammation.

Blood test

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: a syringe drawing blood from an arm.A blood test can be used to measure thyroid hormones. 

Nuclear thyroid scan

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.

Thyroid ultrasound

A picture of the thyroid is obtained using ultrasound and can show enlargement of the gland and indicate some changes in the gland tissue.

Antibodies

A protein molecule produced by the immune system. Antibodies bind specifically to foreign substances to neutralise them or target them for destruction.

Blood pressure

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.

Hormone

A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.

Ultrasound

A scan that uses high-frequency soundwaves to produce images of the body’s internal structures.

2. Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.

Types of treatment

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-blockers

Beta-blocker drugs such as propranol can be prescribed to help relieve symptoms such as shaking, a racing heartbeat, sweating and anxiety until antithyroid medications can take effect.

Antithyroid medications

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.

Radioactive iodine treatment

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 (thyroidectomy)

Thyroid surgery usually involves the removal of all or part of the thyroid gland. This operation is performed under a general anaesthetic in a hospital. It will often require you to stay in hospital for 1-2 days.

Anxiety

A feeling of tension, nervousness and dread about future events. It can trigger physical symptoms such as a rapid pulse or breathing difficulties.

General anaesthetic

An anaesthetic 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 anaesthetic is given in hospital by a specialist called an anaesthetist.

Hormone

A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.

2. Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.

Potential complications

Complications with hyperthyroidism can depend on what type of the condition it is and the treatment.

They can include:

Graves' ophthalmopathy

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:

  • Push the eyes forward, making it difficult to shut the eyelids completely;
  • Restrict eye movements, which in severe cases can cause double vision, and;
  • Cause damage to the optic nerves because of pressure created by the swelling.

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.

A young woman showing signs of Graves ophthalmopathy (thyroid eye disease) including bulging eyes and inflamed eye muscles.Graves' ophthalmopathy results in bulging of the eyes. 

Thyroid crisis

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.

Heart damage

Hyperthyroidism can lead to a fast heart rate, abnormal heart rhythm (atrial fibrillation) and in severe cases, heart failure, which can be life-threatening.

Osteoporosis

Prolonged hyperthyroidism can promote bone loss leading to osteoporosis.

Hypothyroidism

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.

Side effects of antithyroid medications

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 due to surgery

Complications that can occur with surgery include:

  • Scarring of the neck;
  • Speech problems due to damage to the laryngeal nerve, and;
  • Damage to the parathyroid glands attached to the thyroid that control calcium levels in the blood.

Corticosteroids

A medication that resembles the cortisol hormone produced in the brain. It is used as an anti-inflammatory medication.

Hormone

A chemical substance secreted in one part of an organism and transported to another part of that organism, where it has a specific effect.

Ulcers

An open sore in the skin or mucous membranes such as those of the stomach lining, intestine or mouth.

Laryngeal nerve

The nerve that controls the function of the voice box to produce speech, allow breathing and supply sensation to the voice box.

2. Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.

Prognosis

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.

2. Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.

Prevention

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.

2. Campbell K. and Dogue M. (2012) Evaluating and managing patients with thyrotoxicosis. Australian Family Physician. 41:564-572.