{"id":6534,"date":"2023-09-25T11:37:45","date_gmt":"2023-09-25T06:07:45","guid":{"rendered":"https:\/\/www.diabetesasia.org\/magazine\/?p=6534"},"modified":"2024-11-21T11:47:17","modified_gmt":"2024-11-21T06:17:17","slug":"hypothyroidism","status":"publish","type":"post","link":"https:\/\/www.diabetesasia.org\/magazine\/hypothyroidism\/","title":{"rendered":"Hypothyroidism"},"content":{"rendered":"

Background Hypothyroidism is a common endocrine disorder resulting from a deficiency of thyroid hormone. It is usually a primary process in which the thyroid gland cannot produce sufficient amounts of thyroid hormone. Hypothyroidism can also be secondary\u2014that is, the thyroid gland itself is normal. Still, it receives insufficient stimulation because of the pituitary gland’s low secretion of thyrotropin (i.e., thyroid-stimulating hormone [TSH]). This generally occurs in the presence of other pituitary hormone deficiencies. In tertiary hypothyroidism, inadequate secretion of thyrotropin-releasing hormone (TRH) from the hypothalamus leads to insufficient release of TSH, which in turn causes inadequate thyroid stimulation. But<\/b>\u00a0this\u00a0rarely<\/b>\u00a0happens.<\/b>\u00a0Worldwide, iodine deficiency remains the\u00a0leading<\/b> cause of hypothyroidism.<\/p>\n

In the United States and other areas where<\/b>\u00a0iodine\u00a0intake<\/b>\u00a0is<\/b>\u00a0adequate,<\/b>\u00a0the<\/b>\u00a0most<\/b>\u00a0common<\/b>\u00a0cause<\/b>\u00a0is<\/b>\u00a0autoimmune thyroid disease\u00a0Hashimoto’s<\/b>\u00a0disease).<\/b>\u00a0Drugs<\/strong>\u00a0or\u00a0other<\/strong>\u00a0iatrogenic<\/strong>\u00a0factors can also cause hypothyroidism<\/strong><\/span>.<\/b>\u00a0(see<\/b>\u00a0Etiology)<\/b>\u00a0Some, but not all, studies\u00a0suggest<\/b>\u00a0that low vitamin D levels\u00a0may<\/b>\u00a0be linked to autoimmune thyroid\u00a0diseases<\/b>\u00a0such\u00a0as Hashimoto’s<\/strong><\/span>\u00a0thyroiditis\u00a0and Graves<\/strong><\/span>‘<\/strong><\/span>‘<\/b>\u00a0disease. However, intervention studies\u00a0to<\/b>\u00a0date<\/b>\u00a0have not demonstrated\u00a0the<\/b>\u00a0benefits<\/b>\u00a0of supplementation. No association\u00a0was<\/b>\u00a0found between vitamin D levels and thyroid cancer. This\u00a0is<\/b>\u00a0still<\/b>\u00a0an area of investigation.<\/b><\/p>\n

The patient’s<\/strong>\u00a0condition<\/b>\u00a0ranges<\/b>\u00a0from asymptomatic to myxedema coma with multisystem organ failure. Because\u00a0thyroid<\/b>\u00a0hormones<\/b>\u00a0are<\/b>\u00a0required<\/b>\u00a0for<\/b>\u00a0almost<\/b>\u00a0all metabolically active\u00a0cells,<\/b>\u00a0a<\/b>\u00a0deficiency\u00a0in<\/b>\u00a0these<\/b>\u00a0hormones<\/b>\u00a0can<\/b>\u00a0have<\/b>\u00a0vari<\/strong>ous<\/span>\u00a0consequences.<\/b>\u00a0(See\u00a0presentation.)<\/b>\u00a0Third-generation TSH assays are readily available and are generally the most sensitive screening\u00a0tools<\/b>\u00a0for primary hypothyroidism. The generally accepted reference range for<\/p>\n

normal serum TSH\u00a0levels<\/b>\u00a0is\u00a00.40<\/b>\u00a0to<\/b>\u00a04.2<\/b>\u00a0mIU\/L. If\u00a0your<\/b>\u00a0TSH levels are above the reference range, the next step\u00a0is<\/b>\u00a0to measure free thyroxine (T4). Subclinical hypothyroidism, also\u00a0called<\/b>\u00a0mild hypothyroidism, is defined\u00a0by<\/b> normal serum-free T4 and triiodothyronine (T3)\u00a0levels<\/b>\u00a0and<\/b>\u00a0mildly<\/b>\u00a0elevated<\/b>\u00a0serum TSH\u00a0concentrations.<\/b>\u00a0Like<\/b> clinical hypothyroidism,\u00a0Hashimoto’s<\/strong><\/span>s<\/b> thyroiditis is the most common cause of subclinical hypothyroidism in the United States.<\/p>\n

In<\/b>\u00a0hypothyroidism, thyroid\u00a0hormones<\/b>\u00a0are<\/b>\u00a0prescribed<\/b>\u00a0to supplement or replace endogenous production. In general, hypothyroidism can be adequately treated with\u00a0regular<\/b>\u00a0daily\u00a0administration<\/b>\u00a0of levothyroxine (LT4). (See Treatment and\u00a0Medicines)<\/b>\u00a0Congenital hypothyroidism, which affects 1\u00a0in<\/b>\u00a04,000<\/b>\u00a0newborns, is\u00a0caused<\/b>\u00a0by<\/b>\u00a0a<\/b>\u00a0congenital\u00a0malformation<\/b>\u00a0of the thyroid\u00a0gland<\/b>\u00a0(see Pediatric Hypothyroidism). This disorder is included in newborn screening\u00a0programs<\/b>\u00a0in the United States and many other\u00a0countries<\/b>\u00a0and is\u00a0easily<\/b>\u00a0treatable once detected. Cretinism refers to severe hypothyroidism in\u00a0infants<\/b>\u00a0and<\/b>\u00a0young<\/b>\u00a0children.<\/b>\u00a0This is\u00a0usually<\/b>\u00a0caused<\/b>\u00a0by<\/b>\u00a0maternal iodine deficiency,\u00a0but<\/b>\u00a0fortunately,<\/b>\u00a0this<\/b>\u00a0is\u00a0becoming<\/b>\u00a0less<\/b>\u00a0common.<\/b><\/p>\n

Hypothyroidism<\/b> (underactive thyroid<\/i>,\u00a0low thyroid,<\/i>\u00a0or\u00a0hypothyreosis<\/i>) is a\u00a0disorder of the endocrine system\u00a0in which the\u00a0thyroid gland<\/a>\u00a0does not produce enough\u00a0thyroid hormone.<\/sup> It can cause several symptoms, such as\u00a0poor ability to tolerate colds, a\u00a0feeling of tiredness,\u00a0constipation,\u00a0slow heart rate,\u00a0depression<\/a>, and\u00a0weight gain.<\/sup> Occasionally, the front part of the neck may be swelling due to goiter.<\/sup>\u00a0Untreated cases of hypothyroidism during\u00a0pregnancy<\/a>\u00a0can lead to delays in\u00a0growth and intellectual development\u00a0in the baby or\u00a0congenital iodine deficiency syndrome.<\/sup><\/p>\n

Worldwide,\u00a0too little iodine in the diet is the most common cause of hypothyroidism. Hashimoto’s thyroiditis is the most common cause in countries with sufficient dietary iodine.<\/sup>\u00a0Less common causes include previous treatment with\u00a0radioactive iodine, injury to the\u00a0hypothalamus\u00a0or the\u00a0anterior pituitary\u00a0gland, certain medications,\u00a0a lack of a functioning thyroid at birth, or previous\u00a0thyroid surgery.<\/sup><\/sup>\u00a0The diagnosis of hypothyroidism, when suspected, can be confirmed with\u00a0blood tests<\/a>\u00a0measuring\u00a0thyroid-stimulating hormone\u00a0(TSH) and\u00a0thyroxine\u00a0levels.<\/sup><\/p>\n

Salt iodization\u00a0has prevented hypothyroidism in many populations.<\/sup>\u00a0Thyroid hormone replacement with\u00a0levothyroxine<\/a>\u00a0treats hypothyroidism.<\/sup>\u00a0Medical professionals adjust the dose according to symptoms and normalization of the thyroxine and TSH levels.<\/sup>\u00a0Thyroid medication is safe in pregnancy.<\/sup>\u00a0Although an adequate amount of dietary iodine is important, too much may worsen specific forms of hypothyroidism.<\/sup><\/p>\n

Worldwide, about one billion people are estimated to be iodine-deficient; however, it is unknown how often this results in hypothyroidism. <\/sup>In the United States, hypothyroidism occurs in 0.3\u20130.4% of people.<\/sup>\u00a0Subclinical hypothyroidism, a milder form of hypothyroidism characterized by normal thyroxine levels and an elevated TSH level, is thought to occur in 4.3\u20138.5% of people in the United States.<\/sup>\u00a0Hypothyroidism is more common in women than in men.<\/sup>\u00a0People over the age of 60 are more commonly affected.<\/sup>\u00a0Dogs are also known to develop hypothyroidism, as are cats and horses, albeit more rarely.<\/sup>\u00a0The word\u00a0hypothyroidism<\/i> is from the Greek\u00a0hypo-<\/em>‘reduce<\/span>”, there’s<\/i>\u00a0<\/span>‘shiel”,\u00a0and eidos’<\/em><\/span>\u00a0<\/span>‘for”.<\/sup><\/p>\n

<\/div>\n

Signs and symptoms<\/span><\/h2>\n

People with hypothyroidism often have no or only mild symptoms. Numerous symptoms and\u00a0signs<\/a> are associated with hypothyroidism and can be related to the underlying cause, or a direct effect of having not enough thyroid hormones. Hashimoto’ss thyroiditis\u00a0may present with the\u00a0mass effect\u00a0of a\u00a0goiter<\/a>\u00a0(enlarged thyroid gland).<\/sup>\u00a0In middle-aged women, the symptoms may be mistaken for those of\u00a0menopause<\/a>.<\/sup><\/p>\n

<\/a>
Symptoms and signs of hypothyroidism<\/sup><\/figcaption><\/figure>\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Symptoms<\/sup><\/th>\nSigns<\/sup><\/th>\n<\/tr>\n
Fatigue<\/a><\/td>\nDry, coarse skin<\/td>\n<\/tr>\n
Feeling cold<\/td>\nCool extremities<\/td>\n<\/tr>\n
Poor memory and concentration<\/td>\nMyxedema<\/a>\u00a0(mucopolysaccharide\u00a0deposits in the skin)<\/td>\n<\/tr>\n
Constipation<\/a>,\u00a0dyspepsia<\/sup><\/td>\nHair loss<\/a><\/td>\n<\/tr>\n
Weight gain with poor appetite<\/td>\nSlow pulse rate<\/td>\n<\/tr>\n
Shortness of breath<\/td>\nSwelling<\/a>\u00a0of the limbs<\/td>\n<\/tr>\n
Hoarse voice<\/td>\nDelayed relaxation of\u00a0tendon reflexes<\/a><\/td>\n<\/tr>\n
In females,\u00a0heavy menstrual periods\u00a0(and later\u00a0light periods<\/a>)<\/td>\nCarpal tunnel syndrome<\/td>\n<\/tr>\n
Abnormal sensation<\/td>\nPleural effusion,\u00a0ascites,\u00a0pericardial effusion<\/a><\/td>\n<\/tr>\n
Poor hearing<\/td>\n<\/td>\n<\/tr>\n
Muscle weakness<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\"\"<\/a><\/p>\n

Delayed relaxation after testing the\u00a0ankle jerk reflex<\/a>\u00a0is a characteristic sign of hypothyroidism and is associated with the severity of the hormone deficit.<\/sup><\/p>\n

Myxedema coma<\/span><\/h3>\n
\n
\n
\n
\n
<\/div>\n
Man with myxedema or severe hypothyroidism showing an expressionless face, puffiness around the eyes, and pallor.<\/div>\n<\/div>\n
\n
\"\"<\/a><\/div>\n
Additional symptoms include swelling of the arms and legs and\u00a0ascites<\/a>.<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

Myxedema coma is a rare but life-threatening state of extreme hypothyroidism. It may occur in those with established hypothyroidism when they develop an acute illness, and it can be the first presentation of hypothyroidism. People with myxedema coma typically have a\u00a0low body temperature\u00a0without shivering,\u00a0confusion, a\u00a0slow heart rate<\/a>,\u00a0and\u00a0reduced breathing effort. There may be physical signs suggestive of hypothyroidism, such as skin changes or\u00a0enlargement of the tongue.<\/sup><\/p>\n

Pregnancy<\/span><\/h3>\n
Main article:\u00a0Thyroid disease in women<\/div>\n

Even mild or subclinical hypothyroidism leads to possible\u00a0infertility\u00a0and an increased risk of\u00a0miscarriage<\/a>.<\/sup><\/sup>\u00a0Hypothyroidism in early pregnancy, even with limited or no symptoms, may increase the risk of\u00a0pre-eclampsia<\/a>, offspring with lower intelligence,<\/sup><\/sup><\/sup><\/sup>\u00a0and the risk of\u00a0infant death around the time of birth. <\/sup><\/sup><\/sup>Women are affected by hypothyroidism in 0.3\u20130.5% of pregnancies.<\/sup>\u00a0Subclinical hypothyroidism during pregnancy is associated with\u00a0gestational diabetes<\/a>, low birth weight, placental abruption, and the birth of the baby before 37 weeks of pregnancy.<\/sup><\/sup><\/sup><\/sup><\/p>\n

Pathophysiology<\/h2>\n
\n

The hypothalamic-pituitary-thyroid axis governs thyroid hormone secretion (see the image below).<\/p>\n

<\/div>\n
\"The<\/a><\/div>\n
The hypothalamic-pituitary-thyroid axis. A complex feedback system involving the hypothalamus and pituitary gland regulates circulating thyroid hormone levels.<\/span><\/div>\n
<\/div>\n

Although hypothalamic or pituitary disorders can affect thyroid function, localized disease of the thyroid gland that results in decreased thyroid hormone production is the most common cause of hypothyroidism. Under normal circumstances, the thyroid releases 100-125 nmol of T4 daily and small amounts of T3. The ratio of T4:T3 production varies between about 14:1 and 4:1, depending on iodine sufficiency and TSH stimulation. The half-life of T4 is approximately 7-10 days, whereas the half-life of T3 is about 24 hours. T4, a prohormone, is converted via deiodinases to T3, the active thyroid hormone.<\/p>\n

Early in the disease process, compensatory mechanisms maintain T3 levels. Decreased production of T4 causes an increase in the pituitary gland’s secretion of TSH. TSH stimulates hypertrophy and hyperplasia of the thyroid gland and 5\u2019-deiodinase activity, thereby increasing T3 production.<\/p>\n

Thyroid hormone deficiency has a wide range of effects. Systemic effects result from either derangemderangementbolic processes or direct effects by myxedematous infiltration (i.e., accumulation of glycosaminoglycans in the tissues).<\/p>\n

The hypothyroid changes in the heart result in decreased contractility, cardiac enlargement, pericardial effusion, pulse, and cardiac output.<\/p>\n

In the gastrointestinal (GI) tract, achlorhydria and prolonged intestinal transit time with gastric stasis can occur in hypothyroidism. Non-alcoholic fatty liver disease (NAFLD) may also be significantly associated with hypothyroidism, as shown in a meta-analysis of 44,140 individuals with diagnosed hypothyroidism.\u00a0<\/sup><\/p>\n

Delayed puberty, anovulation, menstrual irregularities, and infertility are common. TSH screening should be a routine part of any menstrual irregularities or infertility investigation.<\/p>\n

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Patient Education<\/h2>\n
\n

Emphasize proper compliance at each visit. Discuss the lifelong nature of hypothyroidism, the need for lifelong levothyroxine therapy, the appropriate way to take medicine, and the need for TSH testing at least annually.<\/p>\n

Patients should take thyroid hormone as a single daily dose. Thyroid hormone is better absorbed in the small bowel; therefore, absorption can be affected by malabsorptive states, small bowel disease (e.g., celiac sprue), and the patient’s age. Many drugs (e.g., iron, calcium carbonate, calcium acetate aluminum hydroxide, sucralfate, raloxifene, and proton pump inhibitors) can interfere with absorption and, therefore, should not be taken within 2-4 hours of LT4 administration. \u00a0<\/sup>\u00a0Continuous tube feedings interfere with thyroid hormone absorption; the tube feedings should be interrupted for at least 30-60 minutes before and after hormone administration.<\/p>\n

For patients with malabsorption issues, such as those with celiac disease,\u00a0Helicobacter pylori\u00a0<\/em>infection, lactose intolerance, inflammatory bowel disease, atrophic gastritis, or status post bariatric surgery, liquid LT4 formulations may be more efficient than tablet form for replacement and suppressive therapy. For those without malabsorption, either form is sufficient.\u00a0<\/sup><\/p>\n

The effects of using soft gel LT4 may also prove beneficial in malabsorptive states, and its effects have been found to be consistent with those of the liquid formulation. For both liquid and soft gel LT4 formulations, cost is often a limiting factor for use.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"

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