Hyperthyroidism or overactive thyroid, also known as hyperthyroidism or thyrotoxicosis is a medical condition. It is caused by a thyroid gland that is too active.[1]
| Hyperthyroidism | |
|---|---|
| Other names | Overactive thyroid, hyperthyreosis |
 | |
| Triiodothyronine (T3, pictured) and thyroxine (T4) are both forms of thyroid hormone. | |
| Medical specialty | Endocrinology |
| Symptoms | Irritability, muscle weakness, sleeping problems, fast heartbeat, heat intolerance, diarrhea, enlargement of the thyroid, weight loss[2] |
| Complications | Thyroid storm[3] |
| Usual onset | 20–50 years old[3] |
| Causes | Graves' disease, multinodular goiter, toxic adenoma, inflammation of the thyroid, eating too much iodine, too much synthetic thyroid hormone[2][3] |
| Diagnostic method | Based on symptoms and confirmed by blood tests[2] |
| Treatment | Radioiodine therapy, medications, thyroid surgery[2] |
| Medication | Beta blockers, methimazole[2] |
| Frequency | 1.2% (US)[4] |
| Deaths | Rare directly, unless thyroid storm occurs; associated with increased mortality if untreated (1.23 HR)[5] |
The thyroid gland makes hormones. It is a small butterfly-shaped gland in the neck, just in front of the windpipe (trachea).[1] It produces hormones that affect things such as heart rate and body temperature,[1] and metabolism. An example of one of these hormones is thyroxine.
Hyperthyroidism can affect anyone, but it's about 10 times more common in women than men, and typically happens between 20 and 40 years of age.
Synthesis
- Thyroglobulin is synthesized in the rough endoplasmic reticulum and follows the secretory pathway to enter the colloid in the lumen of the thyroid follicle by exocytosis.
- Meanwhile, a sodium-iodide (Na/I) symporter pumps iodide (I−) actively into the cell, which previously has crossed the endothelium by largely unknown mechanisms.
- This iodide enters the follicular lumen from the cytoplasm by the transporter pendrin, in a purportedly passive manner.
- In the colloid, iodide (I−) is oxidized to iodine (I0) by an enzyme called thyroid peroxidase.
- Iodine (I0) is very reactive and iodinates the thyroglobulin at tyrosyl residues in its protein chain (in total containing approximately 120 tyrosyl residues).
- In conjugation, adjacent tyrosyl residues are paired together.
- The entire complex re-enters the follicular cell by endocytosis.
- Proteolysis by various proteases liberates thyroxine and triiodothyronine molecules, which enters the blood by largely unknown mechanisms.
The thyroid-stimulating hormone starts the making of thyroxine. The thyroid-stimulating hormone is also called “TSH.”
TSH is made in the pituitary gland. Hyperthyroidism is determined by a doctor by blood tests that show a decreased thyroid-stimulating hormone (TSH) level.[7]
Causes
The thyroid gland producing too much of the thyroid hormones results in high levels of the 2 main thyroid hormones, triiodothyronine (also called T3) and thyroxine (also called T4) in the body. There are a number of conditions that can cause the thyroid to become overactive.[1]
Grave's disease
"Graves’ disease"[1] is the most common cause of this disorder. About 4 in every 5 people with an overactive thyroid gland have Graves' disease.[1] It is a condition in which the thyroid gland becomes overactive. Antibodies[1]from the immune system in the bloodstream attack itself (this is called an autoimmune disease). This causes the thyroid gland to grow, as well as produce more thyroid hormones.[8]
The cause of Graves' disease is unknown, but it mostly affects young or middle-aged women and often runs in families. Smoking can also increase the risk of getting it.[1]
Thyroid nodules
Less commonly, The thyroid can become overactive if lumps (nodules) develop on the thyroid. Nodules are usually non-cancerous (benign), but they may contain thyroid tissue, which can result in the production of excess thyroid hormones.[1]
It's not known why some people develop thyroid nodules, but they usually affect people over 60 years of age.[1]
Medicine[1]
An increased level of iodine in the body can cause the thyroid to produce excess thyroid hormones. This can occasionally happen if medicine that contains iodine, such as amiodarone is taken. Sometimes it is used to control an irregular heartbeat (arrhythmia).
An overactive thyroid that's caused by a medicine will usually improve once the person taking that medicine stops, although it may take several months for thyroid hormone levels to return to normal[1] and to taper off the drug.
Other causes
Other possible causes of an overactive thyroid include:[1]
- high levels of a substance called human chorionic gonadotrophin in the body – this can happen in early pregnancy, a multiple pregnancy or a molar pregnancy (where a lump of abnormal cells grows in the womb instead of a healthy foetus)
- a pituitary adenoma – a non-cancerous (benign) tumour in the pituitary gland (a gland at the base of the brain that can affect the level of hormones produced by the thyroid)
- thyroiditis – swelling (inflammation) of the thyroid, which can cause extra thyroid hormones to be produced
- thyroid cancer – rarely, a cancerous thyroid tumour can affect the production of thyroid hormones
Symptoms
Common
It can cause a wide range of signs and symptoms. Some symptoms of the disorder are swelling of the neck, weight loss.[1] In addition, a patient with hyperthyroidism could experience:
- hands trembling or twitching[1]
- blood pressure increasing
- sensitivity to heat
- nervousness and anxiety attacks[1][9]
- mood changes[1]
- difficulty sleeping[1]
- Sexual dysfunction[1]
An overactive thyroid can cause a wider range of symptoms than the list above, such as[1] persistent tiredness and weakness (and malaise), goitre, and an irregular and/or unusually fast heart rate (palpitations). Diarrhea, needing to pee more than often, persistent thirst, as well as physical signs beyond these.[1]
The symptoms may develop gradually or suddenly. For some people they're mild, but for others they can be severe and significantly affect their life.[1]
Physical (common)[1]
- warm skin and excessive sweating
- red palms of the hands (palamar erythema)
- loose nails (kilonychia)
- a raised, itchy rash. Known as hives (urticaria)
- patchy hair loss or thinning
- eye problems, such as redness, dryness or a vision problem
These symptoms and signs can have a number of causes. But a blood test can often help to determine whether they're caused by a thyroid problem.[1]
Treatment
- Medication can stop the effects of hyperthyroidism. However, hyperthyroidism cannot be fixed completely. Hyperthyroidism can occasionally cause death.[10]
An overactive thyroid (hyperthyroidism) is usually treatable. There are 3 common treatments. A specialist in hormonal conditions (endocrinologist) who will plan out treatment.[1]
Medication[1]
- Medicines called thionamides are commonly used to treat an overactive thyroid. The main types used are carbimazole and propylthiouracil.
- These work by not letting the thyroid produce more hormones. It will usually take the medicine 12 to 18 months, and may be a few months after first taking it, before visble or mental benefit
- There may be another medicine called a beta blocker given to help relieve some symptoms in the meantime
Once thyroid hormone levels are under control, the dose may be gradually reduced and then stopped. But some people need to continue taking medicine for several years or possibly for life.[1]
- Side effects
During the first couple of months, some people experience the following side effects:[1]
- feeling sick
- high temperature
- headaches
- aching joints
- altered taste
- upset stomach
- an itchy rash
These should pass as the body gets used to the medicine.[1]
- Make sure there is effective contraception while taking carbimazole. Taking carbimazole while pregnant can harm an unborn baby.
- A pregnanancy while taking the medication is something the prescribing doctor should be told about
- A less common but more serious side effect is a sudden drop in the white blood cell count (agranulocytosis), which can make the person very vulnerable to infections.
- radioactive iodine treatment[1]
It can take a few weeks or months for the full benefits to be felt, so there may be need to take medicine, such as carbimazole or propylthiouracil, for a short time
- 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's a highly effective treatment that can cure an overactive thyroid.
- Radioactive iodine treatment is not suitable for women who are pregnant or breastfeeding. It's also not suitable if the overactive thyroid is causing severe eye problems.
- surgery[1]
- Occasionally, surgery to remove all or part of the thyroid may be recommended.
This may be the best option if:[1]
- The thyroid gland is severely swollen because of a large goitre
- There are severe eye problems caused by an overactive thyroid
- Cannot have other, less invasive treatments
- symptoms return after trying other treatments
Removing all of the thyroid gland is usually recommended because it stops the symptoms of hyperthyroidism coming back. But removing the thyroid means that the body will be unable to produce thyroid hormones. So medicine, such as levothyroxine, will have to be taken for the rest of the patient's life. Levothyroxine is often used to treat an underactive thyroid.[1]
Related pages
References
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