![]() ![]() ![]() ![]() Acta Chir Scand. Active and inactive thyroid hormone levels in elective and acute surgery. Hagenfeldt I, Melander A, Thorell J, Tibblin S. An underactive thyroid in dogs could make Fido lose his spark and could be a sign of canine hypothyroidism. Explore these FAQs on canine thyroid troubles. The toning of the vowel chant K-A-Y-E-E not only stimulates the thyroid and parathyroids, it activates the throat chakra to open more fully. If you simply wish to activate or open the throat chakra, the intonation of K-A-Y-E-E once or twice will work effectively. If you have an underactive thyroid, toning with this important chant. [] Hyperthyroidism is the condition that occurs due to excessive production of by the. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidism. Some, however, use the terms interchangeably. Signs and symptoms vary between people and may include irritability, muscle weakness, sleeping problems, a,,,, and. Symptoms are typically less in the old and during. An uncommon complication is in which an event such as an results in worsening symptoms such as confusion and a and often results in death. The opposite is, when the thyroid gland does not make enough thyroid hormone. Is the cause of about 50% to 80% of the cases of hyperthyroidism in the United States. Other causes include,,, eating too much, and too much. A less common cause is a. The diagnosis may be suspected based on signs and symptoms and then confirmed with blood tests. Typically blood tests show a low (TSH) and raised. Uptake by the thyroid,, and may help determine the cause. Treatment depends partly on the cause and severity of disease. There are three main treatment options:, medications, and thyroid surgery. Radioiodine therapy involves taking by mouth which is then concentrated in and destroys the thyroid over weeks to months. The resulting hypothyroidism is treated with synthetic thyroid hormone. Medications such as may control the symptoms, and such as may temporarily help people while other treatments are having effect. Surgery to remove the thyroid is another option. This may be used in those with very large thyroids or when cancer is a concern. In the United States hyperthyroidism affects about 1.2% of the population. It occurs between two and ten times more often in women. Onset is commonly between 20 and 50 years of age. Overall the disease is more common in those over the age of 60 years. Illustration depicting enlarged thyroid that may be associated with hyperthyroidism Hyperthyroidism may be asymptomatic or present with significant symptoms. Some of the symptoms of hyperthyroidism include nervousness, irritability, increased perspiration, heart racing, hand tremors, anxiety, difficulty sleeping, thinning of the skin, fine brittle hair, and muscular weakness—especially in the upper arms and thighs. More frequent bowel movements may occur, and diarrhea is common. Weight loss, sometimes significant, may occur despite a good appetite (though 10% of people with a hyperactive thyroid experience weight gain), vomiting may occur, and, for women, menstrual flow may lighten and menstrual periods may occur less often, or with longer cycles than usual. Thyroid hormone is critical to normal function of cells. In excess, it both overstimulates metabolism and exacerbates the effect of the, causing 'speeding up' of various body systems and symptoms resembling an overdose of (adrenaline). These include fast heart beat and symptoms of, nervous system such as of the hands and symptoms, digestive system, unintended weight loss, and (in 'lipid panel' blood tests) a lower and sometimes unusually low serum. Major clinical signs include (often accompanied by an increased ), anxiety,, hair loss (especially of the outer third of the eyebrows), muscle aches, weakness, fatigue, hyperactivity, irritability,, [ ],,,, (in ),, and sweating., inability to concentrate, and problems may also occur. And, common during, are rare with milder hyperthyroidism. Many persons will experience complete remission of symptoms 1 to 2 months after a state is obtained, with a marked reduction in anxiety, sense of exhaustion, irritability, and depression. Some individuals may have an increased rate of anxiety or persistence of and cognitive symptoms for several months to up to 10 years after a euthyroid state is established. In addition, those with hyperthyroidism may present with a variety of physical symptoms such as and (the notable ones being ), shortness of breath (), loss of,,,,, and. Long term untreated hyperthyroidism can lead to. These classical symptoms may not be present often in the elderly. [ ] Neurological manifestations can include,,, and in some susceptible individuals (in particular of Asian descent). An association between thyroid disease and has been recognized. The thyroid disease, in this condition, is autoimmune in nature and approximately 5% of patients with myasthenia gravis also have hyperthyroidism. Myasthenia gravis rarely improves after thyroid treatment and the relationship between the two entities is not well understood. [ ] In, may cause the eyes to look enlarged because the eye muscles swell and push the eye forward. Sometimes, one or both eyes may bulge. Some have swelling of the front of the neck from an enlarged thyroid gland (a goiter). Minor ocular (eye) signs, which may be present in any type of hyperthyroidism, are eyelid retraction ('stare'), weakness, and lid-lag. [ ] In hyperthyroid stare () the eyelids are retracted upward more than normal (the normal position is at the superior, where the 'white' of the eye begins at the upper border of the iris). Extraocular muscle weakness may present with double vision. In lid-lag (), when the patient tracks an object downward with their eyes, the eyelid fails to follow the downward moving iris, and the same type of upper globe exposure which is seen with lid retraction occurs, temporarily. These signs disappear with treatment of the hyperthyroidism. [ ] Neither of these ocular signs should be confused with (protrusion of the eyeball), which occurs specifically and uniquely in hyperthyroidism caused by Graves' disease (note that not all exophthalmos is caused by Graves' disease, but when present with hyperthyroidism is diagnostic of Graves' disease). This forward protrusion of the eyes is due to immune-mediated inflammation in the retro-orbital (eye socket) fat. Exophthalmos, when present, may exacerbate hyperthyroid lid-lag and stare. Thyroid storm [ ]. Main article: Thyroid storm is a severe form of thyrotoxicosis characterized by rapid and often, high temperature, vomiting, diarrhea, and mental agitation. Symptoms may be unusual in the young, old, or pregnant. It is a and requires hospital care to control the symptoms rapidly. Even with treatment, death occurs in 20% to 50%. Hypothyroidism [ ] Hyperthyroidism due to certain types of can eventually lead to (a lack of thyroid hormone), as the thyroid gland is damaged. Also, treatment of Graves' disease often eventually leads to hypothyroidism. Such hypothyroidism may be treated by regular thyroid hormone testing and oral thyroid hormone supplementation. Causes [ ] There are several causes of hyperthyroidism. Most often, the entire gland is overproducing thyroid hormone. Less commonly, a single nodule is responsible for the excess hormone secretion, called a 'hot' nodule. Thyroiditis (inflammation of the thyroid) can also cause hyperthyroidism. Functional thyroid tissue producing an excess of thyroid hormone occurs in a number of clinical conditions. The major causes in humans are: •. An autoimmune disease (usually, the most common etiology with 50-80% worldwide, although this varies substantially with location- i.e., 47% in Switzerland (Horst et al., 1987) to 90% in the USA (Hamburger et al. Thought to be due to varying levels of iodine in the diet. It is eight times more common in females than males and often occurs in young females, around 20 – 40 years of age. • (the most common etiology in Switzerland, 53%, thought to be atypical due to a low level of dietary iodine in this country) • High blood levels of thyroid hormones (most accurately termed ) can occur for a number of other reasons: • of the thyroid is called. There are several different kinds of thyroiditis including (Hypothyroidism immune-mediated), and (de Quervain's). These may be initially associated with secretion of excess thyroid hormone but usually progress to gland dysfunction and, thus, to hormone deficiency and hypothyroidism. • Oral consumption of excess thyroid hormone tablets is possible (surreptitious use of thyroid hormone), as is the rare event of consumption of ground beef contaminated with thyroid tissue, and thus thyroid hormone (termed 'hamburger hyperthyroidism'). •, an, is structurally similar to thyroxine and may cause either under- or overactivity of the thyroid. • (PPT) occurs in about 7% of women during the year after they give birth. PPT typically has several phases, the first of which is hyperthyroidism. This form of hyperthyroidism usually corrects itself within weeks or months without the need for treatment. • A is a rare form of monodermal that contains mostly thyroid tissue, which leads to hyperthyroidism. • Excess iodine consumption notably from algae such as. Thyrotoxicosis can also occur after taking too much thyroid hormone in the form of supplements, such as (a phenomenon known as exogenous thyrotoxicosis, thyrotoxicosis, or factitial thyrotoxicosis). Hypersecretion of (TSH), which in turn is almost always caused by a, accounts for much less than 1 percent of hyperthyroidism cases. Diagnosis [ ] Measuring the level of (TSH), produced by the pituitary gland (which in turn is also regulated by the hypothalamus's TSH Releasing Hormone) in the blood is typically the initial test for suspected hyperthyroidism. A low TSH level typically indicates that the pituitary gland is being inhibited or 'instructed' by the brain to cut back on stimulating the thyroid gland, having sensed increased levels of T 4 and/or T 3 in the blood. In rare circumstances, a low TSH indicates primary failure of the pituitary, or temporary inhibition of the pituitary due to another illness () and so checking the T 4 and T 3 is still clinically useful. Measuring specific, such as anti-TSH-receptor antibodies in Graves' disease, or anti-thyroid peroxidase in — a common cause of — may also contribute to the diagnosis. The diagnosis of hyperthyroidism is confirmed by blood tests that show a decreased thyroid-stimulating hormone (TSH) level and elevated T 4 and T 3 levels. TSH is a hormone made by the pituitary gland in the brain that tells the thyroid gland how much hormone to make. When there is too much thyroid hormone, the TSH will be low. A radioactive iodine uptake test and thyroid scan together characterizes or enables radiologists and doctors to determine the cause of hyperthyroidism. The uptake test uses radioactive iodine injected or taken orally on an empty stomach to measure the amount of iodine absorbed by the thyroid gland. Persons with hyperthyroidism absorb much more iodine than healthy persons which includes the radioactive iodine which is easy to measure. A thyroid scan producing images is typically conducted in connection with the uptake test to allow visual examination of the over-functioning gland. Thyroid is a useful test to characterize (distinguish between causes of) hyperthyroidism, and this entity from thyroiditis. This test procedure typically involves two tests performed in connection with each other: an and a scan (imaging) with a. The uptake test involves administering a dose of radioactive iodine (radioiodine), traditionally ( 131I), and more recently ( 123I). May be the preferred radionuclide in some clinics due to its more favorable radiation (i.e. Less radiation dose to the patient per unit administered radioactivity) and a gamma photon energy more amenable to imaging with the. For the imaging scan, I-123 is considered an almost ideal isotope of iodine for imaging thyroid tissue and thyroid cancer metastasis. Typical administration involves a pill or liquid containing sodium iodide (NaI) taken orally, which contains a small amount of, amounting to perhaps less than a grain of salt. A 2-hour fast of no food prior to and for 1 hour after ingesting the pill is required. This low dose of radioiodine is typically tolerated by individuals otherwise allergic to iodine (such as those unable to tolerate contrast mediums containing larger doses of iodine such as used in, (IVP), and similar imaging diagnostic procedures). Excess radioiodine that does not get absorbed into the thyroid gland is eliminated by the body in urine. Some patients may experience a slight allergic reaction to the diagnostic radioiodine and may be given an. The patient returns 24 hours later to have the level of radioiodine 'uptake' (absorbed by the thyroid gland) measured by a device with a metal bar placed against the neck, which measures the radioactivity emitting from the thyroid. This test takes about 4 minutes while the uptake% is accumulated (calculated) by the machine software. A scan is also performed, wherein images (typically a center, left and right angle) are taken of the contrasted thyroid gland with a; a will read and prepare a report indicating the uptake% and comments after examining the images. Hyperthyroid patients will typically 'take up' higher than normal levels of radioiodine. Normal ranges for RAI uptake are from 10-30%. In addition to testing the TSH levels, many doctors test for T 3, Free T 3, T 4, and/or Free T 4 for more detailed results. Typical adult limits for these hormones are: TSH (units): 0.45 - 4.50 uIU/mL; T 4 Free/Direct (nanograms): 0.82 - 1.77 ng/dl; and T 3 (nanograms): 71 - 180 ng/dl. Persons with hyperthyroidism can easily exhibit levels many times these upper limits for T 4 and/or T 3. See a complete table of normal range limits for thyroid function at the article. In hyperthyroidism CK-MB () is usually elevated. See also: In overt primary hyperthyroidism, TSH levels are low and T 4 and T 3 levels are high. Subclinical hyperthyroidism is a milder form of hyperthyroidism characterized by low or undetectable serum TSH level, but with a normal serum free thyroxine level. Although the evidence for doing so is not definitive, treatment of elderly persons having subclinical hyperthyroidism could reduce the incidence of. There is also an increased risk of (by 42%) in people with subclinical hyperthyroidism; there is insufficient evidence to say whether treatment with antithyroid medications would reduce that risk. Screening [ ] In those without symptoms who are not pregnant there is little evidence for or against screening. Treatment [ ] Antithyroid drugs [ ] Thyrostatics (antithyroid drugs) are drugs that inhibit the production of thyroid hormones, such as (used in the UK) and (used in the US), and. Thyrostatics are believed to work by inhibiting the of by and, thus, the formation of tetraiodothyronine (T 4). Propylthiouracil also works outside the thyroid gland, preventing the conversion of (mostly inactive) T 4 to the active form T 3. Because thyroid tissue usually contains a substantial reserve of thyroid hormone, thyrostatics can take weeks to become effective and the dose often needs to be carefully titrated over a period of months, with regular doctor visits and blood tests to monitor results. A very high dose is often needed early in treatment, but, if too high a dose is used persistently, patients can develop symptoms of hypothyroidism. This titrating of the dose is difficult to do accurately, and so sometimes a 'block and replace' attitude is taken. In block and replace treatments thyrostatics are taken in sufficient quantities to completely block thyroid hormones, and the patient treated as though they have complete hypothyroidism. Beta-blockers [ ] Many of the common symptoms of hyperthyroidism such as palpitations, trembling, and anxiety are mediated by increases in beta-adrenergic receptors on cell surfaces., typically used to treat high blood pressure, are a class of drugs that offset this effect, reducing rapid pulse associated with the sensation of palpitations, and decreasing tremor and anxiety. Thus, a patient suffering from hyperthyroidism can often obtain immediate temporary relief until the hyperthyroidism can be characterized with the Radioiodine test noted above and more permanent treatment take place. Note that these drugs do not treat hyperthyroidism or any of its long-term effects if left untreated, but, rather, they treat or reduce only symptoms of the condition. Some minimal effect on thyroid hormone production however also comes with - which has two roles in the treatment of hyperthyroidism, determined by the different isomers of propranolol. L-propranolol causes beta-blockade, thus treating the symptoms associated with hyperthyroidism such as tremor, palpitations, anxiety, and. D-propranolol inhibits thyroxine deiodinase, thereby blocking the conversion of T 4 to T 3, providing some though minimal therapeutic effect. Other beta-blockers are used to treat only the symptoms associated with hyperthyroidism. In the UK, and in the US, are most frequently used to augment treatment for hyperthyroid patients. Diet [ ] People with autoimmune hyperthyroidism should not eat foods high in iodine, such as and kelps. From a public health perspective, the general introduction of iodized salt in the United States in 1924 resulted in lower disease, goiters, as well as improving the lives of children whose mothers would not have eaten enough iodine during pregnancy which would have lowered the IQs of their children. Surgery [ ] ( to remove the whole thyroid or a part of it) is not extensively used because most common forms of hyperthyroidism are quite effectively treated by the radioactive iodine method, and because there is a risk of also removing the, and of cutting the, making swallowing difficult, and even simply generalized infection as with any major surgery. Some people with Graves' may opt for surgical intervention. This includes those that cannot tolerate medicines for one reason or another, people that are allergic to iodine, or people that refuse radioiodine. If people have toxic nodules treatments typically include either removal or injection of the nodule with alcohol. Radioiodine [ ] In (radioiodine), which was first pioneered by Dr., radioactive iodine-131 is given orally (either by pill or liquid) on a one-time basis, to severely restrict, or altogether destroy the function of a hyperactive thyroid gland. This isotope of radioactive iodine used for ablative treatment is more potent than diagnostic radioiodine (usually iodine-123 or a very low amount of iodine-131), which has a biological half-life from 8–13 hours. Iodine-131, which also emits beta particles that are far more damaging to tissues at short range, has a half-life of approximately 8 days. Patients not responding sufficiently to the first dose are sometimes given an additional radioiodine treatment, at a larger dose. Iodine-131 in this treatment is picked up by the active cells in the thyroid and destroys them, rendering the thyroid gland mostly or completely inactive. Since iodine is picked up more readily (though not exclusively) by thyroid cells, and (more important) is picked up even more readily by over-active thyroid cells, the destruction is local, and there are no widespread side effects with this therapy. Radioiodine ablation has been used for over 50 years, and the only major reasons for not using it are pregnancy and breastfeeding (breast tissue also picks up and concentrates iodine). Once the thyroid function is reduced, replacement hormone therapy taken orally each day may easily provide the required amount of thyroid hormone the body needs. There is extensive experience, over many years, of the use of radioiodine in the treatment of thyroid overactivity and this experience does not indicate any increased risk of thyroid cancer following treatment. However, a study from 2007 has reported an increased cancer incidence after radioiodine treatment for hyperthyroidism. The principal advantage of radioiodine treatment for hyperthyroidism is that it tends to have a much higher success rate than medications. Depending on the dose of radioiodine chosen, and the disease under treatment (Graves' vs. Toxic goiter, vs. Hot nodule etc.), the success rate in achieving definitive resolution of the hyperthyroidism may vary from 75-100%. A major expected side-effect of radioiodine in patients with Graves' disease is the development of lifelong hypothyroidism, requiring daily treatment with thyroid hormone. On occasion, some patients may require more than one radioactive treatment, depending on the type of disease present, the size of the thyroid, and the initial dose administered. Graves' disease patients manifesting moderate or severe are cautioned against radioactive iodine-131 treatment, since it has been shown to exacerbate existing thyroid eye disease. Patients with mild or no ophthalmic symptoms can mitigate their risk with a concurrent six-week course of. The mechanisms proposed for this side effect involve a TSH receptor common to both and retro-orbital tissue. As radioactive iodine treatment results in the destruction of thyroid tissue, there is often a transient period of several days to weeks when the symptoms of hyperthyroidism may actually worsen following radioactive iodine therapy. In general, this happens as a result of thyroid hormones being released into the blood following the radioactive iodine-mediated destruction of thyroid cells that contain thyroid hormone. In some patients, treatment with medications such as beta blockers (,, etc.) may be useful during this period of time. Most patients do not experience any difficulty after the radioactive iodine treatment, usually given as a small pill. On occasion, neck tenderness or a sore throat may become apparent after a few days, if moderate inflammation in the thyroid develops and produces discomfort in the neck or throat area. This is usually transient, and not associated with a fever, etc. Women breastfeeding should discontinue breastfeeding for at least a week, and likely longer, following radioactive iodine treatment, as small amounts of radioactive iodine may be found in breast milk even several weeks after the radioactive iodine treatment. A common outcome following radioiodine is a swing from hyperthyroidism to the easily treatable hypothyroidism, which occurs in 78% of those treated for Graves' thyrotoxicosis and in 40% of those with toxic multinodular goiter or solitary toxic adenoma. Use of higher doses of radioiodine reduces the incidence of treatment failure, with penalty for higher response to treatment consisting mostly of higher rates of eventual hypothyroidism which requires hormone treatment for life. There is increased sensitivity to radioiodine therapy in thyroids appearing on as more uniform (hypoechogenic), due to densely packed large cells, with 81% later becoming hypothyroid, compared to just 37% in those with more normal scan appearances (normoechogenic). Thyroid storm [ ] presents with extreme symptoms of hyperthyroidism. It is treated aggressively with measures along with a combination of the above modalities including: an intravenous beta blockers such as, followed by a such as, an iodinated radiocontrast agent or an iodine solution if the radiocontrast agent is not available, and an intravenous such as. Epidemiology [ ] In the United States hyperthyroidism affects about 1.2% of the population. About half of these cases have obvious symptoms while the other half do not. It occurs between two and ten times more often in women. The disease is more common in those over the age of 60 years. Modestly increases the risk of cognitive impairment and dementia. History [ ] first made the association between the goiter and protrusion of the eyes in 1786, however, did not publish his findings until 1825. In 1835, Irish doctor discovered a link between the protrusion of the eyes and goiter, giving his name to the autoimmune disease now known as Graves' Disease. Pregnancy [ ]. See also: Recognizing and evaluating hyperthyroidism in pregnancy is a diagnostic challenge. Thyroid hormones are naturally elevated during pregnancy and hyperthyroidism must also be distinguished from gestational transient thyrotoxicosis. Nonetheless, high maternal FT4 levels during pregnancy have been associated with impaired brain developmental outcomes of the offspring and this was independent of for example hCG levels. Other animals [ ] Cats [ ] Hyperthyroidism is one of the most common endocrine conditions affecting older domesticated. Some estimate that it occurs in up to 2% of cats over the age of 10. The disease has become significantly more common since the first reports of feline hyperthyroidism in the 1970s. One cause of hyperthyroidism in cats is the presence of, but the reason these cats develop such tumors continues to be studied. However, recent research published in Environmental Science & Technology, a publication of the American Chemical Society, suggests that many cases of feline hyperthyroidism are associated with exposure to environmental contaminants called (PBDEs), which are present in in many household products, in particular, furniture and some electronics. The study on which the report was based was conducted jointly by researchers at the EPA's National Health and Environmental Effects Laboratory and Indiana University. In the study, which involved 23 pet cats with feline hyperthyroidism, PBDE blood levels were three times as high as those in younger, non-hyperthyroid cats. In ideal circumstances, PBDE and related endocrine disruptors that seriously damage health would not be present in the blood of any animals, including humans. Several studies indicate canned fish, liver and giblet prepared cat food may increase risk whereas fertilizers, herbicides, or plant pesticides had no effect. Another study suggests cat litter could be a problem. Mutations of the thyroid-stimulating hormone receptor that cause a constitutive activation of the thyroid gland cells have been discovered recently. Many other factors may play a role in the of the disease such as ( such as,, and ) as well as the and content of the cat's diet. The most common presenting symptoms are: rapid, (rapid heart rate),,, increased consumption of fluids () and food, and increased urine production (). Other symptoms include hyperactivity, possible aggression,, a, an unkempt appearance, and large, thick. About 70% of afflicted cats also have enlarged thyroid glands (). The same three treatments used with humans are also options in treating feline hyperthyroidism (surgery, radioiodine treatment, and anti-thyroid drugs). The drug that is used to help reduce the hyperthyroidism is methimazole. Where drug therapy is used it must be given to cats for the remainder of their lives but this may be the least expensive option, especially for very old cats. Anti-thyroid drugs for cats are available in both pill form and in a, that is applied using a to the hairless skin inside a cat's ear. Many cat owners find this gel a good option for cats that don't like being given pills. Radioiodine treatment and surgery often cure hyperthyroidism but some veterinarians prefer radioiodine treatment over surgery because it doesn't carry the risks associated with. Radioiodine treatment, however, is not available in all areas for cats as this treatment requires nuclear radiological expertise and facilities as the cat's urine, sweat, saliva, and stool are radioactive for several days after the treatment requiring special inpatient handling and facilities usually for a total of 3 weeks (first week in total isolation and the next two weeks in close confinement). In the United States, the guidelines for radiation levels vary from state to state; some states such as Massachusetts allow hospitalization for as little as two days before the animal is sent home with care instructions. Surgery tends to be done only when just one of the thyroid glands is affected (unilateral disease); however, following surgery, the remaining gland may become overactive. As in people, one of the most common complications of the surgery is. Dogs [ ] Hyperthyroidism is very rare in, occurring in less than 1% of dogs. [ ] Hyperthyroidism may be caused by a thyroid tumor. This may be a thyroid. About 90% of carcinomas are a very aggressive; they invade the surrounding tissues and (spread), to other tissues, particularly the lungs. This has a poor. Surgery to remove the tumor a carcinoma is often very difficult, due to the spread of the tumor to the surrounding tissue, for example, into, the, or the. It may be possible to reduce the size of the tumor, thus relieving symptoms and allowing time for other treatments to work. [ ] About 10% of thyroid tumors are benign; these often cause few symptoms. [ ] In dogs treated for (lack of thyroid hormone), hyperthyroidism may occur as a result of an overdose of the thyroid hormone replacement medication,; in this case treatment involves reducing the dose of levothyroxine. Dogs which display, that is, which often eat feces, and which live in a household with a dog receiving levothyroxine treatment, may develop hyperthryoidism if they frequently eat the feces from the dog receiving levothyroxine treatment. Hyperthyroidism may occur if a dog eats an excessive amount of thyroid gland tissue. This has occurred in dogs fed commercial dog food. See also [ ] • • References [ ]. If you have an underactive thyroid gland, the condition is called hypothyroidism. In hypothyroidism, there is a reduced level of thyroid hormone (thyroxine) in the body. This can cause various symptoms, the most common being tiredness, weight gain, constipation, aches, dry skin, lifeless hair and feeling cold. Treatment usually involves taking a daily tablet of thyroid hormone to replace the missing thyroxine. Treatment works very well for most people with hypothyroidism but is required for life. Thyroxine is a hormone made by the thyroid gland in the neck. It is carried round the body in the bloodstream. It helps to keep the body's functions (the metabolism) working at the correct pace. Many cells and tissues in the body need thyroxine to keep them going correctly. Underactive thyroid gland (hypothyroidism) results from the thyroid gland being unable to make enough thyroxine, which causes many of the body's functions to slow down. Hypothyroidism may also occur if there is not enough thyroid gland left to make thyroxine - for example, after surgical removal or injury. (In contrast, if you have hyperthyroidism, you make too much thyroxine. This causes many of the body's functions to speed up.). What are the symptoms of hypothyroidism? Many symptoms of having an underactive thyroid gland (hypothyroidism) can be caused by a low level of thyroxine. Basically, many body functions slow down. Not all symptoms develop in all cases. • Symptoms that commonly occur include: • Tiredness • Weight gain • Constipation • Aches • Feeling cold • Dry skin • Lifeless hair • Fluid retention • Mental slowing • Depression • Less common symptoms include: • A hoarse voice. • Irregular or heavy menstrual periods in women. • Infertility. • Loss of sex drive. • Carpal tunnel syndrome (which causes pains and numbness in the hand). • Memory loss or confusion in the elderly. However, all these symptoms can be caused by other conditions and sometimes the diagnosis is not obvious. Symptoms usually develop slowly and gradually become worse over months or years as the level of thyroxine in the body gradually falls. What are the possible complications of hypothyroidism? If you have an untreated underactive thyroid gland (hypothyroidism): • You have an increased risk of developing heart disease. This is because a low thyroxine level causes the blood fats (lipids) - cholesterol, etc - to rise. • If you are pregnant, you have an increased risk of developing some pregnancy complications - for example: • Pre-eclampsia. • Premature labour. • Low birth weight. • Stillbirth. • Serious bleeding after the birth. • Hypothyroid coma (myxoedema coma) is a very rare complication. However, with treatment, the outlook is excellent. With treatment, symptoms usually go and you are very unlikely to develop any complications. Who develops hypothyroidism? About 1 in 50 women and about 1 in 1,000 men develop an underactive thyroid gland (hypothyroidism) at some time in their lives. It most commonly develops in adult women and becomes more common with increasing age. However, it can occur at any age and can affect anyone. What causes hypothyroidism? Autoimmune thyroiditis - the common cause in the UK The most common cause of having an underactive thyroid gland (hypothyroidism) is an autoimmune disease called autoimmune thyroiditis. The immune system normally makes antibodies to attack bacteria, viruses and other germs. If you have an autoimmune disease, the immune system makes antibodies against certain tissues of your body. With autoimmune thyroiditis, you make antibodies that attach to your own thyroid gland, which affect the gland's function. The thyroid gland is then not able to make enough thyroxine and hypothyroidism gradually develops. It is thought that something triggers the immune system to make antibodies against the thyroid. The trigger is not known. Autoimmune thyroiditis is more common than usual in people with: • A family history of hypothyroidism caused by autoimmune thyroiditis. Hypothyroidism develops in 1 in 3 people with Down's syndrome before the age of 25 years. Symptoms of hypothyroidism may be missed more easily in people with Down's syndrome. Therefore, some doctors recommend that all people with Down's syndrome should have an annual blood test to screen for hypothyroidism. Again, an annual blood test to screen for hypothyroidism is usually advised for people with this condition. • A past history of or thyroiditis following childbirth. • A personal or family history of other autoimmune disorders - for example: • • • • • Premature ovarian failure • • Some people with autoimmune thyroiditis also develop a swollen thyroid gland (goitre). Autoimmune thyroiditis with a goitre is called Hashimoto's disease. Also, people with autoimmune thyroiditis have a small increased risk of developing other autoimmune conditions such as vitiligo, pernicious anaemia, etc. Surgery or radioactive treatment to the thyroid gland These are common causes of hypothyroidism in the UK, due to increasing use of these treatments for other thyroid conditions. Other causes Other causes of hypothyroidism include: • Worldwide, iodine deficiency is the most common cause of hypothyroidism. (Your body needs iodine to make thyroxine.) This affects some countries more commonly than others, depending on the level of iodine in the diet. • A side-effect to some medicines - for example, amiodarone and lithium. • Other types of thyroid inflammation (thyroiditis) caused by various rare conditions. • A pituitary gland problem is a rare cause. The pituitary gland that lies just under the brain makes a hormone called thyroid-stimulating hormone (TSH). This stimulates the thyroid gland to make thyroxine. If the pituitary does not make TSH then the thyroid cannot make enough thyroxine. • Some children are born with an underactive thyroid gland (congenital hypothyroidism). How is hypothyroidism diagnosed?. A normal blood test will also rule it out if symptoms suggest that it may be a possible diagnosis. One or both of the following may be measured: • TSH. This hormone is made in the pituitary gland. It is released into the bloodstream. It stimulates the thyroid gland to make thyroxine. If the level of thyroxine in the blood is low, then the pituitary releases more TSH to try to stimulate the thyroid gland to make more thyroxine. Therefore, a raised level of TSH means the thyroid gland is underactive and is not making enough thyroxine. A low level of thyroxine confirms hypothyroidism. Other tests are not usually necessary unless a rare cause of hypothyroidism is suspected. For example, tests of the pituitary gland may be done if both the TSH and thyroxine levels are low. Subclinical hypothyroidism Some people have a raised TSH level but have a normal thyroxine level. This means that you are making enough thyroxine but the thyroid gland is needing extra stimulation from TSH to make the required amount of thyroxine. In this situation you have an increased risk of developing hypothyroidism in the future. Your doctor may advise a repeat blood test every so often to see if you do eventually develop hypothyroidism. How is hypothyroidism treated? The treatment of underactive thyroid gland (hypothyroidism) is to take tablets each day. This replaces the thyroxine which your thyroid gland is not making. Most people feel much better soon after starting treatment. Ideally, take the tablet on an empty stomach (before breakfast). This is because some foods rich in calcium or iron may interfere with the absorption of levothyroxine from the gut. (For the same reason, don't take levothyroxine tablets at the same time of day as calcium or iron tablets.) What is the dose of levothyroxine? Most adults need between 100 and 150 micrograms daily. A low dose is prescribed at first, especially in those aged over 60 or with heart problems. The dose is then gradually increased over a period of time. Blood tests are usually taken regularly and the dose may be adjusted accordingly. The blood test measures TSH (see above). Once the blood TSH level is normal it usually means you are taking the correct amount of levothyroxine. It is then common practice to check the TSH blood level once a year. The dose may need adjustment in the early stages of pregnancy. Also, as you get into late middle age and older, you may need a reduced dose of levothyroxine. Missed a tablet? Everyone forgets to take their tablets from time to time. Don't worry as it is not dangerous to miss the odd forgotten levothyroxine tablet. If you forget to take a dose, take it as soon as you remember if this is within two or three hours of your usual time. If you do not remember until after this time, skip the forgotten dose and take the next dose at the usual time. Do not take two doses together to make up for a missed dose. However, you should try to take levothyroxine regularly each morning for maximum benefit. How long is the treatment for? For most people, treatment is for life. Occasionally, the disease process reverses. This is uncommon, apart from the following: • Children. Sometimes hypothyroidism is a temporary condition in older children. (This is not so for children who are born with an underactive thyroid.) • Pregnancy. Some women develop thyroid imbalance after having a baby. If it occurs, it typically happens about three to six months after the birth. Often this lasts just a few months and corrects itself. Treatment is needed only in a small number of cases. However, afterwards it is wise to have a yearly blood test, as there is an increased risk of developing autoimmune thyroiditis and long-term hypothyroidism in the future. Are there any side-effects or problems from treatment? Levothyroxine tablets replace the body's natural hormone, so side-effects are uncommon. However, if you have angina, you may find that your angina pains become worse when you first start levothyroxine. Tell a doctor if this happens. If you take too much levothyroxine it can lead to symptoms and problems of an overactive thyroid gland (hyperthyroidism) - for example: • The sensation of a 'thumping heart' (palpitations). • Irritability. • An increased risk of developing 'thinning' of the bones (osteoporosis). This is why you need blood tests to check that you are taking the correct dose. Other medicines may interfere with the action of levothyroxine - for example, carbamazepine, iron tablets, phenytoin, and rifampicin. If you start any of these medicines, or change the dose, you may need to alter the dose of the levothyroxine. Your doctor will advise. Also, if you take warfarin, the dose may need to be altered if you have a change in your dose of levothyroxine. Free prescriptions If you have hypothyroidism, you are entitled to. This is for all your medicines, whether related to the hypothyroidism or not. Ask at your GP surgery for a form to fill in (form FP92A) to claim this benefit.
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January 2018
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