Hypothyroidism means your thyroid gland cannot produce the normal amount of thyroid hormone. Your thyroid gland is under active. The thyroid gland is located in the lower, front of the neck.
Thyroid hormones regulate the body's energy. When levels of thyroid hormones are abnormally low, the body burns energy more slowly, and vital functions, such as heartbeat and temperature regulation, slow down. Causes of hypothyroidism include:
- Thyroid surgery or radioiodine ablation treatments to treat thyroid cancer or hyperthyroidism (abnormally high levels of thyroid hormones)
- An autoimmune disorder, in which the body's own immune system attacks the thyroid
- An inborn (congenital) thyroid defect
Short-term hypothyroidism can be caused by certain types of thyroid inflammation or thyroid infections with a virus. In less than 5% of cases, hypothyroidism is caused by a problem with the hypothalamus or a pituitary gland rather than the thyroid gland. The hypothalamus is a brain structure that normally signals the pituitary gland to make thyroid stimulating hormone (TSH), which causes the thyroid to make thyroid hormones. Some medical problems can affect either the hypothalamus or the pituitary gland, and interrupt the chain of signals from the brain to the thyroid. If this happens, the thyroid gland doesn't get the message to make thyroid hormones, even though it is able to function perfectly. This is called secondary hypothyroidism, which usually occurs when the pituitary gland is damaged by a tumor, infection, sarcoidosis, or cancer that has spread from somewhere else in the body. Less often, hypothyroidism is the result of an injury to the hypothalamus.
Hypothyroidism is more common in women than men. Babies can be born with hypothyroidism.
In adults, hypothyroidism can cause the following symptoms:
- Lack of energy
- A constant tired feeling
- Abnormal sensitivity to cold temperatures, which can develop gradually
- Muscle cramps and stiffness
- Weight gain (often in spite of a poor appetite)
- Dry skin and hair
- Hair loss
- Hoarseness or husky voice
- Slowed heart rate
If severe hypothyroidism is not treated, a cluster of symptoms called myxedema may appear. These symptoms include an expressionless face, thin hair, puffiness around the eyes, enlarged tongue, and thick skin that feels cool and doughy.
In babies born with hypothyroidism, there may be a hoarse cry, slow growth, unusual sleepiness, constipation and feeding problems. If hypothyroidism is not treated, the child may be unusually short and have dry skin, thin hair, an unusual facial appearance, a protruding abdomen, delayed eruption of teeth and problems with mental development. When hypothyroidism occurs in an older child, it may delay puberty and cause other symptoms similar to those seen in adults.
Your doctor will examine you and will inspect your thyroid gland, which may be enlarged. Your doctor also will check for characteristic signs of hypothyroidism, such as looking for dry skin, thinning hair, and a slow heart rate. Your doctor will check your knee and ankle reflexes to see if they respond more slowly than expected.
Your doctor will diagnose hypothyroidism based on the results of blood tests for levels of thyroid hormones and serum TSH. The TSH test is the most sensitive test for hypothyroidism caused by problem with the thyroid gland. Your doctor also may order blood tests for cholesterol and other blood components, which are often abnormal in people with hypothyroidism.
In people with short-term hypothyroidism caused by certain types of thyroid inflammation or viral thyroid infections, levels of thyroid hormones often return to normal after several months. In other people with hypothyroidism, the disorder is a lifelong problem.
The thyroid needs iodine (in tiny amounts) to make thyroid hormone. Today, so many foods contain iodine that hypothyroidism secondary to iodine deficiency has become extremely rare. However, ingesting extra iodine does not prevent hypothyroidism. So in reality, there is no way to prevent hypothyroidism.
Hypothyroidism is treated with replacement doses of thyroid hormones. Synthetic forms of these hormones are used, including levothyroxine (Synthroid, Levoxyl and other brand names), liothyronine (Cytomel) or liotrix (Thyrolar).
Anyone taking thyroid medication has to have a blood test periodically to make sure the dose he or she is taking is maintaining the right levels of thyroid hormones in the body. It is especially important for people with hypothyroidism to be monitored during pregnancy, because the need for thyroid hormone may go up. Also some foods and medications can lower the amount of active thyroid hormone available to the body's cells. For example, iron can interfere with the absorption of thyroid medication inside the intestine, and oral estrogen tends to make more circulating thyroid bind to proteins in the blood, so less free thyroid hormone is available to the body's cells.
Call your doctor if you have the symptoms of hypothyroidism, especially if you constantly feel tired, notice that you are losing hair, and develop an abnormal sensitivity to cold. If your infant or child has symptoms of hypothyroidism, call your pediatrician immediately.
In adults, treatment with thyroid hormones usually relieves symptoms of hypothyroidism within weeks, although it can take months. However, in some elderly patients, dosages may need to be increased very slowly over six to eight weeks to prevent strain on the heart. In infants and children with hypothyroidism, immediate and consistent treatment with thyroid hormones usually can prevent problems with growth or intellectual development.
American Thyroid Association, Inc.
6066 Leesburg Pike
Falls Church, VA 22041