Hyperthyroidism

Hyperthyroidism occurs when the thyroid gland makes too much thyroid hormone, causing the body’s metabolism to speed up. This can lead to a wide range of symptoms affecting the heart, weight, energy levels, and emotions. The condition is treatable with medications, radioactive iodine, or surgery.

Table of contents

• What is hyperthyroidism?
• Associated anatomy
• How common is hyperthyroidism?
• Symptoms of hyperthyroidism
• Causes of hyperthyroidism
• Risk factors
• Possible complications
• How is hyperthyroidism diagnosed?
• Treatment options

What is hyperthyroidism?

Hyperthyroidism, also called overactive thyroid, happens when the thyroid gland makes too much thyroid hormone. The thyroid is a small gland in the front of the neck that makes hormones controlling how the body uses energy. These hormones affect nearly every organ in the body and control many of the body’s most important functions, including breathing, heart rate, weight, digestion, and moods.^[1][2]

When there is too much thyroid hormone in the body, many functions speed up. This excessive concentration of thyroid hormones in tissues causes a characteristic clinical state with noticeable symptoms that can affect overall well-being.^[3][8]

The condition is also sometimes referred to as thyrotoxicosis, which means there is too much thyroid hormone in the body.^[5]

Overactive thyroid, Thyrotoxicosis

Associated anatomy

• Thyroid gland
• Neck

The thyroid gland is a butterfly-shaped gland located in the lower front of the neck, just in front of the windpipe. It produces thyroid hormones that are released into the blood and carried to every tissue in the body. These hormones help the body use energy, stay warm, and keep the brain, heart, muscles, and other organs working properly.^[5][7]

How common is hyperthyroidism?

Hyperthyroidism is relatively rare. In the United States, the overall prevalence is 1.2%, with approximately 1.3% of people affected. The prevalence of overt hyperthyroidism is 0.5%, and subclinical hyperthyroidism is 0.7%.^[2][8]

Hyperthyroidism is more common in women than in men. It affects approximately 2% of women and 0.2% of men. The condition is about 10 times more common in women than men and typically happens between 20 and 40 years of age.^[7][14]

Symptoms of hyperthyroidism

Hyperthyroidism can impact the entire body, causing many different symptoms. These symptoms can start suddenly or develop slowly over time. Not everyone experiences all symptoms, and some people may have many symptoms at the same time.^[1][2]

When there is too much thyroid hormone, the body speeds up, which can cause the following symptoms:

• Rapid heartbeat, a condition called tachycardia, or irregular heartbeat, also called arrhythmia
• Pounding of the heart, sometimes called heart palpitations
• Increased blood pressure
• Nervousness, anxiety, and irritability
• Tremor, usually a small trembling in the hands and fingers
• Weight loss despite normal or even increased appetite
• Increased hunger
• Frequent bowel movements or diarrhea
• Increased sweating and feeling hot
• Increased sensitivity to heat
• Tiredness and muscle weakness
• Difficulty sleeping (insomnia)
• Hair loss or brittle, thinning hair
• Warm, moist skin or thinning skin
• Changes in menstrual cycles, often lighter or less frequent periods
• Trouble swallowing or fullness in the neck
• Enlarged thyroid gland, sometimes called a goiter, which may appear as a swelling at the base of the neck
• Mood swings
• Pain behind the eyes or swelling or bulging of the eyes (for autoimmune thyroid dysfunction only)

The thyroid gland, located at the front of the neck, often becomes noticeably larger, causing a goiter. The whole gland is not always swollen; sometimes a lump, called a nodule, may be felt or seen instead. However, some people have an overactive thyroid without a goiter or thyroid nodules.^[1][3][5]

Older adults, particularly those over age 60, are more likely to have symptoms that are hard to notice. These symptoms may include an irregular heartbeat, weight loss, depression, and withdrawal from other people. Sometimes this can be mistaken for depression or dementia.^[1][4]

Causes of hyperthyroidism

Several medical conditions and situations can cause hyperthyroidism. The most common causes involve excessive production of thyroid hormones:^[2][8]

Graves’ disease is the most common cause of hyperthyroidism in the United States. It is an autoimmune disorder in which the body’s immune system produces antibodies that stimulate the thyroid-stimulating hormone (TSH) receptors, triggering the thyroid gland to make too much thyroid hormone. It tends to happen more often in younger women, and autoimmune thyroid conditions like Graves’ disease can run in families.^[2][5][8]

Thyroid nodules are lumps or growths of cells in the thyroid gland. They can sometimes produce excess thyroid hormone. Healthcare providers may call this toxic multinodular goiter or toxic adenoma. Thyroid nodules are more common in older adults and are rarely cancerous.^[2][4]

Thyroiditis is inflammation of the thyroid gland. It can cause hyperthyroidism temporarily by triggering a release of stored thyroid hormone from the gland. The most common cause of excessive passive release of thyroid hormones is painless (silent) thyroiditis. After this phase, called the thyrotoxic phase, it may cause hypothyroidism (underactive thyroid). When the inflammation goes away, hormone levels may stabilize.^[2][8]

Consuming excess iodine through foods or medications can cause the thyroid to produce more thyroid hormone. Iodine is a mineral that the thyroid uses to create thyroid hormone. Receiving intravenous iodinated contrast (iodine “dye”) or taking certain medications like amiodarone may cause hyperthyroidism.^[2][4]

Too much thyroid medicine can happen if people who take thyroid hormone medicine for hypothyroidism (underactive thyroid) take too much of it.^[4]

TSH-releasing pituitary adenoma (thyrotropinoma) is a growth in the pituitary gland that releases excess thyroid-stimulating hormone (TSH). The pituitary gland normally releases TSH to trigger the thyroid to release thyroid hormone. Excess TSH can lead to excess thyroid hormone. This is a very rare cause of hyperthyroidism.^[2]

Risk factors

Several factors can increase the risk of developing hyperthyroidism:^[4][6]

• Being a woman
• Being older than age 60
• Having been pregnant or having had a baby within the past 6 months
• Having had thyroid surgery or a thyroid problem, such as goiter
• Having a family history of thyroid disease
• Having a personal or family history of an autoimmune disorder
• Having pernicious anemia, in which the body cannot make enough healthy red blood cells because it does not have enough vitamin B12
• Having type 1 or type 2 diabetes
• Having primary adrenal insufficiency, a hormonal disorder
• Getting too much iodine, from eating large amounts of foods containing iodine or using iodine-containing medicines or supplements
• Using nicotine products

Possible complications

If hyperthyroidism is not treated, it can cause some serious health problems:^[4][6][7]

An irregular heartbeat can lead to blood clots, stroke, heart failure, and other heart problems. Hyperthyroidism increases the risk of cardiovascular disease, which includes problems affecting the heart and blood vessels.^[3][4]

An eye disease called Graves’ ophthalmopathy or thyroid eye disease can develop. It can cause double vision, light sensitivity, eye pain, and swelling or bulging of the eyes. In rare cases, it can lead to vision loss.^[4]

Hyperthyroidism can lead to thinning bones and osteoporosis.^[4]

For women, hyperthyroidism can cause fertility problems. Complications in pregnancy can occur, such as premature birth, low birth weight, high blood pressure in pregnancy, and miscarriage.^[4][6]

A rare but serious complication is thyroid storm, a sudden and life-threatening flare-up of symptoms. This can cause nausea, vomiting, diarrhea, severe sweating, extreme restlessness and confusion, high fever, and a fast heartbeat.^[7][16]

How is hyperthyroidism diagnosed?

Hyperthyroidism is diagnosed with a medical history, physical exam, and blood tests. Healthcare providers may use many tools to make a diagnosis.^[4][9]

During the physical exam, the healthcare provider may check for slight tremor in the fingers and hands, overactive reflexes, rapid or irregular pulse, eye changes, and warm, moist skin. The provider also examines the thyroid gland as you swallow to see if it is larger than usual, bumpy, or tender.^[9]

Blood tests that measure thyroid hormones can confirm a diagnosis. The tests measure the hormones T-4 (thyroxine) and T-3 (triiodothyronine) and thyroid-stimulating hormone (TSH). A high level of T-4 and a low level of TSH is common in people with hyperthyroidism. Blood tests are particularly important for older adults because they may not have classic symptoms of hyperthyroidism.^[8][9]

If blood tests show high levels of free thyroxine (FT4) or free triiodothyronine (FT3) above the reference range and low TSH levels below the reference range (usually lower than 0.1 mU/L), this indicates hyperthyroidism. If TSH-receptor antibodies (TRAb) are positive, this confirms a diagnosis of Graves’ disease.^[23]

If blood test results show hyperthyroidism, the healthcare provider may suggest additional tests to help find out why the thyroid is overactive:^[9]

A radioiodine scan and uptake test involves taking a small dose of radioactive iodine to see how much of it collects in the thyroid gland and where it collects. If the thyroid gland takes in a high amount of radioiodine, that means the thyroid gland is making too much thyroid hormone. The most likely cause is either Graves’ disease or overactive thyroid nodules.^[9]

Imaging tests such as a thyroid scan, ultrasound, or radioactive iodine uptake test may be used to determine the cause of hyperthyroidism.^[4]

Treatment options

Hyperthyroidism is usually treatable. Several treatments are available, and all are effective, though no single method offers an absolute cure. The choice of treatment depends on the underlying diagnosis, the presence of contraindications to a particular treatment, the severity of hyperthyroidism, the patient’s age, symptoms, comorbidities, and preference.^[7][8][14]

The three main treatments are medicines, radioactive iodine treatment, and surgery.^[7][11]

Antithyroid medicines

Medicines called thionamides are commonly used to treat an overactive thyroid. They stop the thyroid from producing excess hormones. The main types used are carbimazole and propylthiouracil. Methimazole is the preferred antithyroid medication in most cases, except in the first trimester of pregnancy and in patients with an adverse reaction to the medication.^[8][11]

Patients usually need to take the medicine for 12 to 18 months, and it may be a few months after starting before they notice any benefit. Once thyroid hormone levels are under control, the dose may be gradually reduced and then stopped. However, some people need to continue taking medicine for several years or possibly for life.^[11]

Beta-blocker medicines may be prescribed to slow the pulse and help with symptoms like rapid heartbeat, palpitations, tremor, heat intolerance, and anxiety in the meantime. However, this is not a treatment for hyperthyroidism itself but is given to manage symptoms.^[11][16]

Radioactive iodine treatment

Radioactive iodine treatment is a type of radiotherapy used to destroy the cells in the thyroid gland, reducing the amount of hormones it can produce. It is a highly effective treatment that can cure an overactive thyroid. Radioactive iodine ablation is the most widely used treatment in the United States.^[8][11]

Patients are given a drink or capsule that contains iodine and a low dose of radiation, which is absorbed by the thyroid. Most people only need a single treatment. It can take a few weeks or months for the full benefits to be felt, so patients may need to take medicine, such as carbimazole or propylthiouracil, for a short time.^[11]

The dose of radiation used during radioactive iodine treatment is very low, but there are some precautions patients need to take after treatment. These include avoiding prolonged close contact with children and pregnant women for about 3 weeks, and women should avoid getting pregnant for at least 6 months while men should not father a child for at least 4 months. Radioactive iodine treatment is not suitable for women who are pregnant or breastfeeding. It is also not suitable if the overactive thyroid is causing severe eye problems.^[11]

Surgery

Occasionally, surgery to remove all or part of the thyroid may be recommended. This may be the best option if the thyroid gland is severely swollen because of a large goiter, if there are severe eye problems caused by an overactive thyroid, if other less invasive treatments cannot be used, or if symptoms return after trying other treatments.^[7][11]

Removing all of the thyroid gland is usually recommended because it stops the symptoms of hyperthyroidism from coming back. However, removing the thyroid means the body will be unable to produce thyroid hormones, so patients will need to take medicine, such as levothyroxine, for the rest of their life.^[11]

In some cases, depending on what is causing it, hyperthyroidism may improve without medication or other treatment.^[1]