Hypothyroidism

What Is It?

Hypothyroidism means you do not have enough thyroid hormones, which are made by the thyroid gland 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.

In 95 percent of cases of hypothyroidism, the thyroid is not making enough thyroid hormones. Causes of this include:

• Complications of either thyroid surgery or radioiodine ablation treatments for 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 about 5 percent 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), and that 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.

Currently, about 1 percent of adults in the United States have some form of hypothyroidism, although it may affect up to 10 percent of the elderly. About one in every 5,000 babies is born with hypothyroidism.

Symptoms

In adults, hypothyroidism can cause the following symptoms:

• Lack of energy
• A constant tired feeling
• Constipation
• 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
• Psychiatric symptoms, including depression

If 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.