Hypothyroidism - Knowledge (XXG)

1979:. Worldwide about one billion people are estimated to be iodine deficient; however, it is unknown how often this results in hypothyroidism. In large population-based studies in Western countries with sufficient dietary iodine, 0.3–0.4% of the population have overt hypothyroidism. A larger proportion, 4.3–8.5%, have subclinical hypothyroidism. Undiagnosed hypothyroidism is estimated to affect about 4–7% of community-derived populations in the US and Europe. Of people with subclinical hypothyroidism, 80% have a TSH level below the 10 mIU/L mark regarded as the threshold for treatment. Children with subclinical hypothyroidism often return to normal thyroid function, and a small proportion develops overt hypothyroidism (as predicted by evolving antibody and TSH levels, the presence of celiac disease, and the presence of a goitre). 1959:

stronger in pregnant women with subclinical hypothyroidism (defined as TSH 2.5–10 mIU/L) who are anti-TPO positive, in view of the risk of overt hypothyroidism. If a decision is made not to treat, close monitoring of the thyroid function (every 4 weeks in the first 20 weeks of pregnancy) is recommended. If anti-TPO is not positive, treatment for subclinical hypothyroidism is not currently recommended. It has been suggested that many of the aforementioned recommendations could lead to unnecessary treatment, in the sense that the TSH cutoff levels may be too restrictive in some ethnic groups; there may be little benefit from treatment of subclinical hypothyroidism in certain cases.

1603:. The presentation of subclinical hypothyroidism is variable and classic signs and symptoms of hypothyroidism may not be observed. Of people with subclinical hypothyroidism, a proportion will develop overt hypothyroidism each year. In those with detectable antibodies against thyroid peroxidase (TPO), this occurs in 4.3%, while in those with no detectable antibodies, this occurs in 2.6%. In addition to detectable anti-TPO antibodies, other risk factors for conversion from subclinical hypothyroidism to overt hypothyroidism include female sex or in those with higher TSH levels or lower level of normal free T 2092:

gland, and idiopathic atrophy, which leads to the gradual replacement of the gland by fatty tissue. There is often lethargy, cold intolerance, exercise intolerance, and weight gain. Furthermore, skin changes and fertility problems are seen in dogs with hypothyroidism, as well as a number of other symptoms. The signs of myxedema can be seen in dogs, with prominence of skin folds on the forehead, and cases of myxedema coma are encountered. The diagnosis can be confirmed by blood test, as the clinical impression alone may lead to overdiagnosis. Lymphocytic thyroiditis is associated with detectable

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further recommend universal treatment (independent of risk factors) in those with TSH levels that are markedly elevated; above 10 mIU/L because of an increased risk of heart failure or death due to cardiovascular disease. NICE recommends that those with a TSH above 10 mIU/L should be treated in the same way as overt hypothyroidism. Those with an elevated TSH but below 10 mIU/L who have symptoms suggestive of hypothyroidism should have a trial of treatment but with the aim to stopping this if the symptoms persist despite normalisation of the TSH.

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century when people and animals who had had their thyroid removed showed improvement in symptoms with transplantation of animal thyroid tissue. The severity of myxedema, and its associated risk of mortality and complications, created interest in discovering effective treatments for hypothyroidism. Transplantation of thyroid tissue demonstrated some efficacy, but recurrences of hypothyroidism was relatively common, and sometimes required multiple repeat transplantations of thyroid tissue.

62: 1763:-thyroxine). In young and otherwise healthy people with overt hypothyroidism, a full replacement dose (adjusted by weight) can be started immediately; in the elderly and people with heart disease a lower starting dose is recommended to prevent over supplementation and risk of complications. Lower doses may be sufficient in those with subclinical hypothyroidism, while people with central hypothyroidism may require a higher than average dose. 665: 653: 1943:, it is recommended that serum TSH levels are closely monitored. Levothyroxine should be used to keep TSH levels within the normal range for that trimester. The first trimester normal range is below 2.5 mIU/L and the second and third trimesters normal range is below 3.0 mIU/L. Treatment should be guided by total (rather than free) thyroxine or by the 1951:. Similarly to TSH, the thyroxine results should be interpreted according to the appropriate reference range for that stage of pregnancy. The levothyroxine dose often needs to be increased after pregnancy is confirmed, although this is based on limited evidence and some recommend that it is not always required; decisions may need to based on TSH levels. 2953: 2053:, this was used as a marker to guide adjustments in therapy in the early 20th century (around 1915). However, a low basal metabolic rate was known to be non-specific, also present in malnutrition. The first laboratory test to be helpful in assessing thyroid status was the serum protein-bound iodine, which came into use around the 1950s. 1816:

causes of the symptoms should be excluded. Addition of liothyronine should be regarded as experimental, initially only for a trial period of 3 months, and in a set ratio to the current dose of levothyroxine. The guideline explicitly aims to enhance the safety of this approach and to counter its indiscriminate use.

919:(E2), and estriol (E3), with estradiol being the most potent of the three Women with estrogen dominance have estradiol levels of 115 pg/ml on day 3 of their cycle. However, estrogen dominance is not just about an over abundance of estradiol, but is more likely correlated with an imbalance between estradiol and 1649: 425:

levels and an elevated TSH level, is thought to occur in 4.3–8.5% of people in the United States. Hypothyroidism is more common in women than in men. People over the age of 60 are more commonly affected. Dogs are also known to develop hypothyroidism, as are cats and horses, albeit more rarely. The word

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for hypothyroidism is performed in the newborn period in many countries, generally using TSH. This has led to the early identification of many cases and thus the prevention of developmental delay. It is the most widely used newborn screening test worldwide. While TSH-based screening will identify the

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In 1971, the thyroid stimulating hormone (TSH) radioimmunoassay was developed, which was the most specific marker for assessing thyroid status in patients. Many people who were being treated based on basal metabolic rate, minimizing hypothyroid symptoms, or based on serum protein-bound iodine, were

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American guidelines recommend that treatment should be considered in people with symptoms of hypothyroidism, detectable antibodies against thyroid peroxidase, a history of heart disease or are at an increased risk for heart disease, if the TSH is elevated but below 10 mIU/L. American guidelines

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Subclinical hypothyroidism is a biochemical diagnosis characterized by an elevated serum TSH level, but with a normal serum free thyroxine level. The incidence of subclinical hypothyroidism is estimated to be 3-15% and a higher incidence is seen in elderly people, females and those with lower iodine

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Laboratory testing of thyroid stimulating hormone levels in the blood is considered the best initial test for hypothyroidism; a second TSH level is often obtained several weeks later for confirmation. Levels may be abnormal in the context of other illnesses, and TSH testing in hospitalized people is

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introduced subcutaneously injected sheep thyroid extract, followed shortly after by an oral formulation. Purified thyroxine was introduced in 1914 and in the 1930s synthetic thyroxine became available, although desiccated animal thyroid extract remained widely used. Liothyronine was identified in

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means) may require thyroid hormone supplementation even if the TSH level is normal. This is particularly true if they have had previous miscarriages or have been hypothyroid in the past. Supplementary levothyroxine may reduce the risk of preterm birth and possibly miscarriage. The recommendation is

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Diagram of the hypothalamic–pituitary–thyroid axis. The hypothalamus secretes TRH (green), which stimulates the production of TSH (red) by the pituitary gland. This, in turn, stimulates the production of thyroxine by the thyroid (blue). Thyroxine levels decrease TRH and TSH production by a negative

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In veterinary practice, dogs are the species most commonly affected by hypothyroidism. The majority of cases occur as a result of primary hypothyroidism, of which two types are recognized: lymphocytic thyroiditis, which is probably immune-driven and leads to destruction and fibrosis of the thyroid

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when the TSH is over 10 mIU/L. There may be an increased risk for cardiovascular death. A 2007 review found no benefit of thyroid hormone replacement except for "some parameters of lipid profiles and left ventricular function". There is no association between subclinical hypothyroidism and an

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People with hypothyroidism who do not feel well despite optimal levothyroxine dosing may request adjunctive treatment with liothyronine. A 2012 guideline from the European Thyroid Association recommends that support should be offered with regards to the chronic nature of the disease and that other

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Pregnant and breastfeeding women, who require 66% more daily iodine than non-pregnant women, may still not be getting enough iodine. The World Health Organization recommends a daily intake of 250 μg for pregnant and breastfeeding women. As many women will not achieve this from dietary sources

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Worldwide about one billion people are estimated to be iodine-deficient; however, it is unknown how often this results in hypothyroidism. In the United States, hypothyroidism occurs in 0.3–0.4% of people. Subclinical hypothyroidism, a milder form of hypothyroidism characterized by normal thyroxine

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Pregnancy leads to marked changes in thyroid hormone physiology. The gland is increased in size by 10%, thyroxine production is increased by 50%, and iodine requirements are increased. Many women have normal thyroid function but have immunological evidence of thyroid autoimmunity (as evidenced by

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Blood free thyroxine and TSH levels are monitored to help determine whether the dose is adequate. This is done 4–8 weeks after the start of treatment or a change in levothyroxine dose. Once the adequate replacement dose has been established, the tests can be repeated after 6 and then 12 months,

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The first cases of myxedema were recognized in the mid-19th century (the 1870s), but its connection to the thyroid was not discovered until the 1880s when myxedema was observed in people following the removal of the thyroid gland (thyroidectomy). The link was further confirmed in the late 19th

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Women are more likely to develop hypothyroidism than men. In population-based studies, women were seven times more likely than men to have TSH levels above 10 mU/L. 2–4% of people with subclinical hypothyroidism will progress to overt hypothyroidism each year. The risk is higher in those with

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Hypothyroidism may be prevented in a population by adding iodine to commonly used foods. This public health measure has eliminated endemic childhood hypothyroidism in countries where it was once common. In addition to promoting the consumption of iodine-rich foods such as dairy and fish, many

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Other species that are less commonly affected include cats and horses, as well as other large domestic animals. In cats, hypothyroidism is usually the result of other medical treatment such as surgery or radiation. In young horses, congenital hypothyroidism has been reported predominantly in

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In pregnancy, subclinical hypothyroidism is defined as a TSH between 2.5 and 10 mIU/L with a normal thyroxine level, while those with TSH above 10 mIU/L are considered to be overtly hypothyroid even if the thyroxine level is normal. Antibodies against TPO may be important in making

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Blum MR, Bauer DC, Collet TH, Fink HA, Cappola AR, da Costa BR, Wirth CD, Peeters RP, Åsvold BO, den Elzen WP, Luben RN, Imaizumi M, Bremner AP, Gogakos A, Eastell R, Kearney PM, Strotmeyer ES, Wallace ER, Hoff M, Ceresini G, Rivadeneira F, Uitterlinden AG, Stott DJ, Westendorp RG, Khaw KT,

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Garber JR, Cobin RH, Gharib H, Hennessey JV, Klein I, Mechanick JI, Pessah-Pollack R, Singer PA, Woeber KA (December 2012). "Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association".

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treats hypothyroidism. Medical professionals adjust the dose according to symptoms and normalization of the thyroxine and TSH levels. Thyroid medication is safe in pregnancy. Although an adequate amount of dietary iodine is important, too much may worsen specific forms of hypothyroidism.

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Becker DV, Braverman LE, Delange F, Dunn JT, Franklyn JA, Hollowell JG, Lamm SH, Mitchell ML, Pearce E, Robbins J, Rovet JF (October 2006). "Iodine supplementation for pregnancy and lactation-United States and Canada: recommendations of the American Thyroid Association".

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level. Levothyroxine is best taken 30–60 minutes before breakfast, or four hours after food, as certain substances such as food and calcium can inhibit the absorption of levothyroxine. There is no direct way of increasing thyroid hormone secretion by the thyroid gland.

1742:, and suggests testing in those with depression or unexplained anxiety (all ages), in children with abnormal growth, or unexplained change in behaviour or school performance. On diagnosis of autoimmune thyroid disease, NICE also recommends screening for celiac disease. 5135:

Bekkering GE, Agoritsas T, Lytvyn L, Heen AF, Feller M, Moutzouri E, Abdulazeem H, Aertgeerts B, Beecher D, Brito JP, Farhoumand PD, Singh Ospina N, Rodondi N, van Driel M, Wallace E, Snel M, Okwen PM, Siemieniuk R, Vandvik PO, Kuijpers T, Vermandere M (14 May 2019).

871:(tertiary hypothyroidism). Primary hypothyroidism is about a thousandfold more common than central hypothyroidism. Central hypothyroidism is the name used for secondary and tertiary, since hypothalamus and pituitary gland are at the center of thyroid hormone control. 1851:; these are not present in synthetic hormone medication. This extract was once a mainstream hypothyroidism treatment, but its use today is unsupported by evidence; British Thyroid Association and American professional guidelines discourage its use, as does NICE. 684:

is a rare but life-threatening state of extreme hypothyroidism. It may occur in those with established hypothyroidism when they develop an acute illness. Myxedema coma can be the first presentation of hypothyroidism. People with myxedema coma typically have a

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alone. Similarly, American guidelines discourage combination therapy due to a lack of evidence, although they acknowledge that some people feel better when receiving combination treatment. Guidelines by NICE for England and Wales discourage liothyronine.

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During pregnancy, the thyroid gland must produce 50% more thyroid hormone to provide enough thyroid hormone for the developing fetus and the expectant mother. In pregnancy, free thyroxine levels may be lower than anticipated due to increased binding to

1673:, 70% of the world's population across 130 countries are receiving iodized salt. In some countries, iodized salt is added to bread. Despite this, iodine deficiency has reappeared in some Western countries as a result of attempts to reduce salt intake. 6048: 6033: 1725:

of thyroid disease, those who have received radioiodine or other radiation therapy to the neck, those who have previously undergone thyroid surgery, those with an abnormal thyroid examination, those with psychiatric disorders, people taking

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levels. Those with subclinical hypothyroidism and detectable anti-TPO antibodies who do not require treatment should have repeat thyroid function tested more frequently (e.g. every 6 months) compared with those who do not have antibodies.

851:; clinical research has shown there is a high rate of thyroid dysfunction in mood disorders and schizophrenia-spectrum disorders, concluding that there is a case for screening for the former among people with those psychiatric disorders. 1419:

testing in both adults and children if central hypothyroidism is suspected and the TSH is low. There are a number of symptom rating scales for hypothyroidism; they provide a degree of objectivity but have limited use for diagnosis.

1738:, as they are at higher risk of thyroid disease. Guidelines for England and Wales from the National Institute for Health and Care Excellence (NICE) recommend testing for thyroid disease in people with type 1 diabetes and new-onset 923:. Women who have too much unopposed estrogen, which is estrogen that does not have enough counterbalancing progesterone in their bodies, commonly have unbalanced thyroid levels, in addition to excess growths within their uteri. 795:. Normal growth and development may be delayed, and not treating infants may lead to an intellectual impairment (IQ 6–15 points lower in severe cases). Other problems include the following: difficulty with large scale and fine 822:

In older children and adolescents, the symptoms of hypothyroidism may include fatigue, cold intolerance, sleepiness, muscle weakness, constipation, a delay in growth, overweight for height, pallor, coarse and thick skin,

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Very severe hypothyroidism and myxedema coma are rare, with it estimated to occur in 0.22 per million people a year. The majority of cases occur in women over 60 years of age, although it may happen in all age groups.

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determination is included in the screening done at birth, this will identify cases of congenital hypothyroidism of central origin in 1:16,000 to 1:160,000 children. Considering that these children usually have other

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Rieben C, Segna D, da Costa BR, Collet TH, Chaker L, Aubert CE, Baumgartner C, Almeida OP, Hogervorst E, Trompet S, Masaki K, Mooijaart SP, Gussekloo J, Peeters RP, Bauer DC, Aujesky D, Rodondi N (December 2016).

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Adding liothyronine to levothyroxine has been suggested as a measure to provide better symptom control, but this has not been confirmed by studies. In 2007, the British Thyroid Association stated that combined

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discouraged unless thyroid dysfunction is strongly suspected as the cause of the acute illness. An elevated TSH level indicates that the thyroid gland is not producing enough thyroid hormone, and free T

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antibodies against thyroid peroxidase. Subclinical hypothyroidism is estimated to affect approximately 2% of children; in adults, subclinical hypothyroidism is more common in the elderly, and in

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are abnormal in both primary overt hypothyroidism and subclinical hypothyroidism. T3 and TSH are essential for regulation of cardiac electrical activity. Prolonged ventricular repolarization and

1717:) recommend either intermittent testing above a certain age in all sexes or only in women. Targeted screening may be appropriate in a number of situations where hypothyroidism is common: other 5925: 1625:. They should either be corrected for the stage of pregnancy, or total thyroxine levels should be used instead for diagnosis. TSH values may also be lower than normal (particularly in the 3058:"Attention Deficit and Hyperactivity Disorders in the Offspring of Mothers Exposed to Mild-Moderate Iodine Deficiency: A Possible Novel Iodine Deficiency Disorder in Developed Countries" 2002:

Most hypothyroidism is primary in nature. Central/secondary hypothyroidism affects 1:20,000 to 1:80,000 of the population, or about one out of every thousand people with hypothyroidism.

2211: 5605:"Endocrine disorders in childhood and adolescence. Natural history of subclinical hypothyroidism in children and adolescents and potential effects of replacement therapy: a review" 1640:, as subtle thyroid dysfunction can be associated with pregnancy loss, but this recommendation is not universal, and presence of thyroid antibodies may not predict future outcome. 1586:

levels are low. Overt hypothyroidism may also be diagnosed in those who have a TSH on multiple occasions of greater than 5mIU/L, appropriate symptoms, and only a borderline low T

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within the thyroid gland does not require thyroid imaging; however, if the thyroid feels abnormal, diagnostic imaging is then recommended. The presence of antibodies against

915:. It is one of the most common hormone imbalance problems in women, but is not always linked with hypothyroidism There are three different types of estrogens: estrone (E1), 4583: 1241: 1408: 1404: 2938: 1265:

Thyroid hormone is required for the normal functioning of numerous tissues in the body. In healthy individuals, the thyroid gland predominantly secretes thyroxine (T

3239:"Maternal Thyroid Function in the First Twenty Weeks of Pregnancy and Subsequent Fetal and Infant Development: A Prospective Population-Based Cohort Study in China" 2652: 1795:) alone has not received enough study to make a recommendation as to its use; due to its shorter half-life it would need to be taken more often than levothyroxine. 1767:

unless there is a change in symptoms. Normalization of TSH does not mean that other abnormalities associated with hypothyroidism improve entirely, such as elevated

3959:"Deciphering the roles of triiodothyronine (T3) and thyroid-stimulating hormone (TSH) on cardiac electrical remodeling in clinical and experimental hypothyroidism" 4663:

Rose SR, Brown RS, Foley T, Kaplowitz PB, Kaye CI, Sundararajan S, Varma SK (June 2006). "Update of newborn screening and therapy for congenital hypothyroidism".

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Hypothyroidism is caused by inadequate function of the gland itself (primary hypothyroidism), inadequate stimulation by thyroid-stimulating hormone from the

5100: 5015: 1734:, and those with a number of health conditions (such as certain heart and skin conditions). Yearly thyroid function tests are recommended in people with 1368:

plays a key role in maintaining thyroid hormone levels within normal limits. Production of TSH by the anterior pituitary gland is stimulated in turn by

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Alexander EK, Pearce EN, Brent GA, Brown RS, Chen H, Dosiou C, Grobman WA, Laurberg P, Lazarus JH, Mandel SJ, Peeters RP, Sullivan S (March 2017).

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In people with central/secondary hypothyroidism, TSH is not a reliable marker of hormone replacement and decisions are based mainly on the free T

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Most people with hypothyroidism symptoms and confirmed thyroxine deficiency are treated with a synthetic long-acting form of thyroxine, known as

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Stagnaro-Green A, Abalovich M, Alexander E, Azizi F, Mestman J, Negro R, Nixon A, Pearce EN, Soldin OP, Sullivan S, Wiersinga W (October 2011).

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Vermiglio F, Lo Presti VP, Moleti M, Sidoti M, Tortorella G, Scaffidi G, Castagna MG, Mattina F, Violi MA, Crisà A, Artemisia A (2004-12-01).

6388: 5975:"2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease During Pregnancy and the Postpartum" 2141: 885:(chronic autoimmune thyroiditis). Hashimoto's may be associated with a goitre. It is characterized by infiltration of the thyroid gland with 364: 2203: 1859:

There is no evidence of a benefit from treating subclinical hypothyroidism in those who are not pregnant, and there are potential risks of

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is the most common cause of hypothyroidism in countries with sufficient dietary iodine. Less common causes include previous treatment with

2619: 839:. A goiter may be present with a completely enlarged thyroid gland; sometimes only part of the thyroid is enlarged and it can be knobby. 457:

are associated with hypothyroidism and can be related to the underlying cause, or a direct effect of having not enough thyroid hormones.

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Transiently: due to maternal iodine deficiency or excess, anti-TSH receptor antibodies, certain congenital disorders, neonatal illness

1040: 6604: 4533: 4178: 4025:"Guidelines of the American Thyroid Association for the diagnosis and management of thyroid disease during pregnancy and postpartum" 3814:"Optimising outcome in congenital hypothyroidism; current opinions on best practice in initial assessment and subsequent management" 2683: 2265: 985: 755:

Newborn children with hypothyroidism may have normal birth weight and height (although the head may be larger than expected and the

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Estradiol disrupts thyroid hormone production because high blood levels of estrogen signal the liver to increase the production of

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Malt EA, Dahl RC, Haugsand TM, Ulvestad IH, Emilsen NM, Hansen B, Cardenas YE, Skøld RO, Thorsen AT, Davidsen EM (February 2013).

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worldwide. In areas of the world with sufficient dietary iodine, hypothyroidism is most commonly caused by the autoimmune disease

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Ferri's differential diagnosis : a practical guide to the differential diagnosis of symptoms, signs, and clinical disorders

1927:, particularly if the level of consciousness is too low to be able to safely swallow medication. While administration through a 5930: 1920: 5220:"Minor perturbations of thyroid homeostasis and major cardiovascular endpoints-Physiological mechanisms and clinical evidence" 1310: 3003:"Oral and intestinal microbial features in pregnant women with hypothyroidism and their correlations with pregnancy outcomes" 1376:

process. Not enough TRH, which is uncommon, can lead to not enough TSH and thereby to not enough thyroid hormone production.

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LeFevre ML (May 2015). "Screening for thyroid dysfunction: U.S. Preventive Services Task Force recommendation statement".

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Early attempts at titrating therapy for hypothyroidism proved difficult. After hypothyroidism was found to cause a lower

1369: 1165: 864: 2644: 1895:, close observation and treatment of abnormalities in breathing, temperature control, blood pressure, and sodium levels. 6823: 6813: 6702: 6692: 1940: 1714: 1678: 1056: 981: 736: 4864:"Systemic Thyroid Hormone Status During Levothyroxine Therapy In Hypothyroidism: A Systematic Review and Meta-Analysis" 6808: 6405: 2093: 1489:

and liver enzymes in the blood. They typically return to normal when hypothyroidism has been fully treated. Levels of

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Wiles KS, Jarvis S, Nelson-Piercy C (October 2015). "Are we overtreating subclinical hypothyroidism in pregnancy?".

1987:. There is a much higher rate of thyroid disorders, the most common of which is hypothyroidism, in individuals with 6725: 6577: 6209: 5107: 1824: 1600: 1530:(TPO) makes it more likely that thyroid nodules are caused by autoimmune thyroiditis, but if there is any doubt, a 1322: 1228: 1064: 927: 882: 458: 375: 219: 5371:"Subclinical Thyroid Dysfunction and the Risk of Cognitive Decline: a Meta-Analysis of Prospective Cohort Studies" 2096:, although they typically become undetectable in advanced disease. Treatment is with thyroid hormone replacement. 6768: 6670: 6526: 6479: 4508: 3336:

Negro R, Stagnaro-Green A (October 2014). "Diagnosis and management of subclinical hypothyroidism in pregnancy".

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In adults, widespread screening of the general population is a matter of debate. Some organizations (such as the

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Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J (2011). "341: disorders of the thyroid gland".

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decisions about treatment, and should, therefore, be determined in women with abnormal thyroid function tests.

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Man with myxedema or severe hypothyroidism showing an expressionless face, puffiness around the eyes and pallor

264: 3859:"Deiodinases: the balance of thyroid hormone: type 1 iodothyronine deiodinase in human physiology and disease" 1380:

autoantibodies) or are iodine deficient, and develop evidence of hypothyroidism before or after giving birth.

5961:. The Association for Clinical Biochemistry, British Thyroid Association and British Thyroid Foundation. 2006 3196:

Vissenberg R, van den Boogaard E, van Wely M, van der Post JA, Fliers E, Bisschop PH, Goddijn M (July 2012).

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and vision changes. Central hypothyroidism should be investigated further to determine the underlying cause.

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which can occur together with hypothyroidism). Careful correction of low sodium levels may be achieved with

1864: 1860: 1494: 1145: 1133: 186: 5764:"Note on the Treatment of Myxoedema by Hypodermic Injections of an Extract of the Thyroid Gland of a Sheep" 2233: 6730: 6719: 3662: 2145: 2074: 2042: 2027: 1944: 1928: 1896: 1531: 1389: 1117: 1048: 950: 828: 591: 476: 462: 247: 3156:"Maternal thyroid deficiency during pregnancy and subsequent neuropsychological development of the child" 1550:(not enough TSH or TRH secretion by the pituitary gland or hypothalamus). There may be other features of 6712: 6338: 4080: 2023: 1912: 1904: 1637: 1559: 1236: 1129: 5319:

Langhammer A, Ferrucci L, Gussekloo J, Williams GR, Walsh JP, Jüni P, Aujesky D, Rodondi N (May 2015).

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is a characteristic sign of hypothyroidism and is associated with the severity of the hormone deficit.

5179:"Meta-analysis: subclinical thyroid dysfunction and the risk for coronary heart disease and mortality" 3002: 1599:

levels. Subclinical hypothyroidism is most commonly caused by autoimmune thyroid diseases, especially

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Khandelwal D, Tandon N (January 2012). "Overt and subclinical hypothyroidism: who to treat and how".

2608:(10th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins Health. p. 552. 2050: 1967:

The effectiveness and safety of using Chinese herbal medicines to treat hypothyroidism is not known.

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can be elevated; the impact of subclinical hypothyroidism on lipid parameters is less well-defined.

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Escobar-Morreale HF, Botella-Carretero JI, Escobar del Rey F, Morreale de Escobar G (August 2005).

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is rare, although it may develop later in children who have a thyroid gland that does not produce

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due to a number of causes. In most causes, however, it is unclear if the relationship is causal.

1201: 1190: 1137: 912: 897: 812: 520: 387: 161: 6653: 6643: 6617: 1372:(TRH), released from the hypothalamus. Production of TSH and TRH is decreased by thyroxine by a 1361:. Not enough iodine, or not enough TSH, can result in decreased production of thyroid hormones. 1019: 727:. Hypothyroidism in early pregnancy, even with limited or no symptoms, may increase the risk of 2257:

Comprehensive Handbook of Iodine Nutritional, Biochemical, Pathological and Therapeutic Aspects

1923:. For rapid treatment of the hypothyroidism, levothyroxine or liothyronine may be administered 1863:. Untreated subclinical hypothyroidism may be associated with a modest increase in the risk of 960:

Autoimmune thyroiditis (Hashimoto's) is associated with other immune-mediated diseases such as

930:(TBG). This is an inhibitor protein that binds to the thyroid hormone, reducing the amount of T 6572: 6544: 6531: 6469: 6219: 6103: 6074: 6004: 5884: 5842: 5793: 5744: 5680: 5626: 5577: 5536: 5487: 5466:"Interventions for clinical and subclinical hypothyroidism pre-pregnancy and during pregnancy" 5438: 5400: 5350: 5300: 5251: 5200: 5159: 5081: 4993: 4942: 4893: 4818: 4766: 4723: 4680: 4637: 4529: 4482: 4465:

Charlton K, Skeaff S (November 2011). "Iodine fortification: why, when, what, how, and who?".

4414: 4373: 4332: 4278: 4220: 4174: 4146: 4095: 4054: 3988: 3932: 3880: 3839: 3794: 3769: 3720: 3641: 3603: 3562: 3514: 3463: 3411: 3353: 3315: 3307: 3268: 3260: 3219: 3198:"Treatment of thyroid disorders before conception and in early pregnancy: a systematic review" 3175: 3167: 3136: 3087: 3079: 3030: 3022: 2913: 2857: 2771: 2717: 2679: 2673: 2609: 2603: 2581: 2525: 2459: 2326: 2286: 2261: 2255: 1976: 1916: 1900: 1713:) state that evidence is insufficient to support routine screening, while others (such as the 1662: 1563: 1373: 1105: 1101: 969: 965: 874: 792: 780: 636: 627: 495: 371: 360: 344: 316: 252: 226: 215: 171: 149: 5195: 5178: 4168: 2560:"Clinical review: Central hypothyroidism: pathogenic, diagnostic, and therapeutic challenges" 6633: 6509: 6309: 6301: 6255: 6250: 6245: 5994: 5986: 5876: 5832: 5824: 5783: 5775: 5734: 5726: 5670: 5660: 5616: 5567: 5526: 5518: 5477: 5430: 5390: 5382: 5340: 5332: 5290: 5282: 5241: 5231: 5190: 5149: 5071: 5063: 5016:"Armour Thyroid(USP) and combinedthyroxine/tri-iodothyronine as thyroid hormone replacement" 4983: 4973: 4932: 4924: 4883: 4875: 4808: 4758: 4715: 4672: 4629: 4474: 4404: 4363: 4322: 4314: 4268: 4260: 4212: 4136: 4126: 4044: 4036: 3978: 3970: 3922: 3914: 3870: 3829: 3821: 3759: 3593: 3552: 3544: 3504: 3494: 3453: 3403: 3345: 3299: 3287: 3250: 3209: 3126: 3118: 3069: 3014: 2905: 2849: 2763: 2571: 2515: 2505: 2451: 2318: 2011: 1270: 1161: 1157: 1141: 1082: 848: 768: 603: 328: 82: 2937:. Office on Women's Health, U.S. Department of Health and Human Services. 1 February 2017. 739:

in 0.3–0.5% of pregnancies. Subclinical hypothyroidism during pregnancy is associated with

6818: 6564: 6453: 6370: 6292: 6181: 5920: 5138:"Thyroid hormones treatment for subclinical hypothyroidism: a clinical practice guideline" 4962:"REVIEW: Treatment of hypothyroidism with combinations of levothyroxine plus liothyronine" 1992: 1703: 1666: 1626: 1555: 1551: 1486: 1358: 1338:

The thyroid gland is the only source of thyroid hormone in the body; the process requires

1153: 1074: 954: 860: 832: 698: 469:(enlarged thyroid gland). In middle-aged women, the symptoms may be mistaken for those of 340: 324: 33: 4706:

Pollitt RJ (June 2009). "Newborn blood spot screening: new opportunities, old problems".

1843:(a hormone produced in the thyroid gland involved in the regulation of calcium levels), T 953:

which can occur up to nine months afterwards. This is characterized by a short period of

5531: 5506: 4561: 3983: 3958: 1697:

testing is required to pick up the rarer central causes of neonatal hypothyroidism. If T

17: 6780: 6775: 6758: 6658: 6589: 6399: 6365: 6314: 5999: 5974: 5837: 5812: 5788: 5763: 5739: 5714: 5675: 5648: 5395: 5370: 5345: 5320: 5295: 5270: 5246: 5219: 5076: 5051: 4937: 4912: 4888: 4863: 4327: 4302: 4273: 4252: 4141: 4114: 4049: 4024: 3927: 3902: 3834: 3813: 3598: 3581: 3557: 3536: 3509: 3482: 3131: 3122: 3106: 3001:

Wang B, Xu Y, Zhang M, Zhang J, Hou X, Li J, Cai Y, Sun Z, Ban Y, Wang W (2020-12-01).

2520: 2493: 2126: 2101: 1908: 1888: 1722: 1520: 1498: 1302: 1213: 1011: 1007: 973: 878: 824: 816: 808: 585: 6057: 4584:"Reaching Optimal Iodine Nutrition in Pregnant and Lactating Women and Young Children" 4391:

Practice Committee of the American Society for Reproductive Medicine (November 2012).

453:

People with hypothyroidism often have no or only mild symptoms. Numerous symptoms and

61: 6797: 6599: 6491: 6344: 6189: 5915: 5589: 4778: 4409: 4392: 3286:

Abalovich M, Gutierrez S, Alcaraz G, Maccallini G, Garcia A, Levalle O (2004-07-09).

3042: 2957: 2783: 2767: 2142:"hypothyroidism - definition of hypothyroidism in English from the Oxford dictionary" 2031: 2030:

proposed in 1852 that endemic goitre was the result of not enough iodine intake, and

1988: 1884: 1869: 1756: 1735: 1350: 1321:. In blood, almost all thyroid hormone (99.97%) are bound to plasma proteins such as 1306: 1052: 1003: 901: 744: 728: 681: 573: 417: 395: 320: 284: 260: 154: 5896: 5867:

Mooney CT (May 2011). "Canine hypothyroidism: a review of aetiology and diagnosis".

5450: 4735: 4649: 4494: 4426: 4232: 3423: 3365: 3107:"Influence of maternal thyroid hormones during gestation on fetal brain development" 2869: 2338: 1504:

Very severe hypothyroidism and myxedema coma are characteristically associated with

701:. There may be physical signs suggestive of hypothyroidism, such as skin changes or 6514: 6194: 6172: 6114: 5522: 5482: 5465: 5286: 5177:

Ochs N, Auer R, Bauer DC, Nanchen D, Gussekloo J, Cornuz J, Rodondi N (June 2008).

4692: 4591:

Joint Statement by the World Health Organization and United Nations Children's Fund

2494:"Treatment for primary hypothyroidism: current approaches and future possibilities" 2121: 1984: 1788: 1505: 1314: 1290: 1169: 999: 920: 890: 868: 764: 702: 618: 528: 454: 416:

has prevented hypothyroidism in many populations. Thyroid hormone replacement with

413: 383: 336: 274: 179: 167: 5572: 5555: 1954:

Women with anti-TPO antibodies who are trying to become pregnant (naturally or by

847:

Thyroid hormone abnormalities are common in major psychiatric disorders including

763:, poor weight gain, a hoarse-sounding cry, feeding difficulties, constipation, an 6068: 5880: 5603:

Monzani A, Prodam F, Rapa A, Moia S, Agarla V, Bellone S, Bona G (January 2013).

5464:

Reid SM, Middleton P, Cossich MC, Crowther CA, Bain E (May 2013). Reid SM (ed.).

4478: 2853: 6684: 6334: 6279: 6274: 6098: 5052:"2012 ETA Guidelines: The Use of L-T4 + L-T3 in the Treatment of Hypothyroidism" 3788: 3629: 1768: 1509: 1490: 1318: 1015: 836: 796: 776: 724: 720: 694: 686: 664: 598: 581: 547: 348: 3974: 3712: 3582:"Thyroid dysfunction in major psychiatric disorders in a hospital based sample" 3303: 3018: 2909: 1636:

Determination of TPO antibodies may be considered as part of the assessment of

957:

followed by a period of hypothyroidism; 20–40% remain permanently hypothyroid.

6204: 6120: 6079: 6042: 4928: 4719: 1840: 1727: 1343: 1121: 1109: 1078: 1060: 804: 399: 379: 231: 6125: 5236: 3311: 3264: 3171: 3083: 3026: 1136:), surgery or radiation to the pituitary, drugs, injury, vascular disorders ( 166:

extreme fatigue, Poor ability to tolerate cold, feeling tired, muscle aches,

6474: 6297: 6268: 6233: 6109: 4813: 4796: 4633: 3499: 3214: 3197: 1523: 1301:

and the production of specific proteins. Additionally, the hormone binds to

1256: 1090: 916: 772: 760: 567: 532: 470: 407: 356: 239: 196: 192: 6008: 5888: 5846: 5828: 5797: 5779: 5748: 5684: 5630: 5581: 5540: 5491: 5442: 5404: 5354: 5336: 5304: 5255: 5204: 5163: 5085: 4997: 4946: 4897: 4822: 4770: 4727: 4684: 4676: 4641: 4486: 4418: 4393:"Evaluation and treatment of recurrent pregnancy loss: a committee opinion" 4377: 4368: 4351: 4336: 4282: 4253:"Subclinical hypothyroidism in children: natural history and when to treat" 4224: 4150: 4099: 4058: 3992: 3936: 3884: 3843: 3798: 3773: 3724: 3645: 3607: 3566: 3518: 3467: 3415: 3357: 3319: 3272: 3223: 3179: 3155: 3140: 3091: 3034: 2917: 2861: 2775: 2585: 2529: 2463: 2330: 2322: 1349:. Iodine in the bloodstream is taken up by the gland and incorporated into 652: 5990: 4879: 4522:

Assessment of iodine deficiency disorders and monitoring their elimination

4216: 4040: 2455: 2057:

found to have excessive thyroid hormone. The following year, in 1972, a T

351:. Occasionally there may be swelling of the front part of the neck due to 6486: 5940: 5386: 5050:

Wiersinga WM, Duntas L, Fadeyev V, Nygaard B, Vanderpump MP (July 2012).

4978: 4961: 3918: 3764: 3747: 3458: 3441: 3407: 3255: 3238: 3237:

Su PY, Huang K, Hao JH, Xu YQ, Yan SQ, Li T, Xu YH, Tao FB (2011-10-01).

3074: 3057: 2814: 2576: 2559: 1567: 1346: 1278: 1177: 537: 516: 398:. The diagnosis of hypothyroidism, when suspected, can be confirmed with 256: 6137: 5621: 5604: 4836: 3875: 3858: 3105:

Moog N, Entringer S, Heim C, Wadhwa P, Kathmann N, Buss C (2017-02-07).

2605:

Werner & Ingbar's the thyroid : a fundamental and clinical text

2510: 1590:. It may also be diagnosed in those with a TSH of greater than 10mIU/L. 1152:, polyglandular disorders), infiltrative diseases (iron overload due to 6199: 6168: 5813:"A Case of Myxoedema Treated by Taking Extract of Thyroid by the Mouth" 4988: 4131: 2896:

Klubo-Gwiezdzinska J, Wartofsky L (March 2012). "Thyroid emergencies".

2309:

Syed S (April 2015). "Iodine and the "near" eradication of cretinism".

2015: 1622: 1173: 671: 607: 554: 442: 332: 175: 5665: 5434: 5154: 5137: 5067: 4264: 3825: 3548: 3349: 1629:) and the normal range should be adjusted for the stage of pregnancy. 69:

Molecular structure of thyroxine, which is deficient in hypothyroidism

6753: 6264: 6037: 5934: 5730: 4843:. National Institute for Health and Care Excellence. 2 September 2015 4762: 4516: 4512: 2821:. National Institute for Health and Care Excellence. 20 November 2019 2285:(2nd ed.). Philadelphia, PA: Elsevier/Mosby. p. Chapter H. 2019: 1339: 1113: 886: 800: 784: 466: 352: 6025: 5321:"Subclinical thyroid dysfunction and fracture risk: a meta-analysis" 4318: 3580:

Radhakrishnan R, Calvin S, Singh JK, Thomas B, Srinivasan K (2013).

1485:

Many cases of hypothyroidism are associated with mild elevations in

4913:"Drug interactions--principles, examples and clinical consequences" 4303:"Subclinical hypothyroidism: an update for primary care physicians" 1807:

therapy carried a higher rate of side effects and no benefit over T

6519: 6422: 2078: 1648: 1647: 1255: 1219: 1039:

Iodine deficiency (developing countries), autoimmune thyroiditis,

559: 5101:"ESA Position Statement on Desiccated Thyroid or Thyroid Extract" 5014:

British Thyroid Association Executive Committee (November 2007).

2956:

This article incorporates text from this source, which is in the

1706:, early identification of these cases may prevent complications. 1407:

in the assessment for hypothyroidism. In England and Wales, the

835:. Signs may include delayed relaxation of the ankle reflex and a 791:. A goitre may also develop in children growing up in areas with 3687:"Friends or Foes? Estrogen, Progesterone & Thyroid Hormones" 2208:

National Institute of Diabetes and Digestive and Kidney Diseases

1325:; only the free unbound thyroid hormone is biologically active. 1298: 1207: 27:

Insufficient production of thyroid hormones by the thyroid gland

6426: 6141: 4862:

McAninch EA, Rajan KB, Miller CH, Bianco AC (1 December 2018).

4441:"Recurrent Miscarriage, Investigation and Treatment of Couples" 3394:

Counts D, Varma SK (July 2009). "Hypothyroidism in children".

1828: 1168:), particular inherited congenital disorders, and infections ( 670:

Additional symptoms include swelling of the arms and legs and

112: 4170:

Endocrine and metabolic disorders clinical lab testing manual

3483:"Oral manifestations of thyroid disorders and its management" 3288:"Overt and Subclinical Hypothyroidism Complicating Pregnancy" 1827:

is an animal-based thyroid gland extract, most commonly from

124: 5271:"Thyroid hormone replacement for subclinical hypothyroidism" 4556:

e-Library of Evidence for Nutrition Actions (eLENA) (2014).

3007:

American Journal of Physiology. Endocrinology and Metabolism

1656:

showing myxedematous facies, a big tongue, and skin mottling

103: 3442:"Update in lipid alterations in subclinical hypothyroidism" 2678:(9 ed.). Elsevier Health Sciences. 2013. p. 887. 133: 106: 97: 91: 5649:"History of U.S. iodine fortification and supplementation" 5269:

Villar HC, Saconato H, Valente O, Atallah AN (July 2007).

2996: 2994: 1578:

In overt primary hypothyroidism, TSH levels are high and T

719:

Even mild or subclinical hypothyroidism leads to possible

4837:"Coeliac disease: recognition, assessment and management" 4352:"Subclinical hypothyroidism: summary of evidence in 2014" 4203:

Peeters RP (29 June 2017). "Subclinical Hypothyroidism".

4115:"Hyponatremia and the Thyroid: Causality or Association?" 118: 4467:

Current Opinion in Clinical Nutrition and Metabolic Care

374:

in the diet is the most common cause of hypothyroidism.

5715:"The History and Future of Treatment of Hypothyroidism" 4257:

Journal of Clinical Research in Pediatric Endocrinology

3818:

Journal of Clinical Research in Pediatric Endocrinology

3541:

Journal of Clinical Research in Pediatric Endocrinology

877:

is the most common cause of primary hypothyroidism and

4868:

The Journal of Clinical Endocrinology & Metabolism

3857:

Maia AL, Goemann IM, Meyer EL, Wajner SM (June 2011).

3663:"Hormonal Imbalance: Causes, Symptoms & Treatment" 3243:

The Journal of Clinical Endocrinology & Metabolism

3062:

The Journal of Clinical Endocrinology & Metabolism

2649:

Merck Veterinary Manual, 10th edition (online version)

5956:"UK Guidelines for the use of thyroid function tests" 5556:"Low awareness and under-diagnosis of hypothyroidism" 3748:"Approach to the patient with postpartum thyroiditis" 863:(secondary hypothyroidism), or inadequate release of 731:, offspring with lower intelligence, and the risk of 121: 85: 6015: 5375: