Hypothyroidism
| Hypothyroidism | |
|---|---|
| Other names | Underactive thyroid, low thyroid, hypothyreosis |
| Molecular structure of thyroxine, which is deficient in hypothyroidism | |
| Pronunciation |
|
| Specialty | Endocrinology |
| Symptoms | Fatigue (feeling tired), poor ability to tolerate cold, muscle aches, constipation, weight gain, depression, anxiety, irritability |
| Complications | During pregnancy can result in cretinism in the baby |
| Usual onset | > 60 years old |
| Causes | Hashimoto's thyroiditis, thyroiditis, surgical removal of thyroid gland, iodine deficiency, lithium treatment |
| Diagnostic method | Blood tests (thyroid-stimulating hormone, thyroxine) |
| Differential diagnosis | Depression, dementia, heart failure, chronic fatigue syndrome |
| Prevention | Salt iodization |
| Treatment | Levothyroxine |
| Frequency | 0.3–0.4% |
Hypothyroidism is an endocrine disease in which the thyroid gland does not produce enough thyroid hormones. It can cause a number of symptoms, such as poor ability to tolerate cold, extreme fatigue, muscle aches, constipation, slow heart rate, depression, and weight gain. Occasionally there may be swelling of the front part of the neck due to goiter. Untreated cases of hypothyroidism during pregnancy can lead to delays in growth and intellectual development in the baby or congenital iodine deficiency syndrome.
Worldwide, too little iodine in the diet is the most common cause of hypothyroidism. Hashimoto's thyroiditis, an autoimmune disease where the body's immune system reacts to the thyroid gland, is the most common cause of hypothyroidism in countries with sufficient dietary iodine. Less common causes include previous treatment with radioactive iodine, injury to the hypothalamus or the anterior pituitary gland, certain medications, a lack of a functioning thyroid at birth, or previous thyroid surgery. The diagnosis of hypothyroidism, when suspected, can be confirmed with blood tests measuring thyroid-stimulating hormone (TSH) and thyroxine (T4) levels.
Salt iodization has prevented hypothyroidism in many populations. Thyroid hormone replacement with levothyroxine treats hypothyroidism. Medical professionals adjust the dose according to symptoms and normalization of the 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.
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, overt hypothyroidism occurs in approximately 0.3–0.4% of people. Subclinical hypothyroidism, a milder form of hypothyroidism characterized by normal thyroxine 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 hypothyroidism is from Greek hypo- 'reduced', thyreos 'shield', and eidos 'form', where the two latter parts refer to the thyroid gland.