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Hypothyroidism

 

Definition

Hypothyroidism means your thyroid is not making enough thyroid hormone. The thyroid is a butterfly-shaped gland in the front of your neck. It makes hormones that control the way your body uses energy.

Having a low level of thyroid hormone affects your whole body. It can make you feel tired and weak. If hypothyroidism is not treated, it can raise your cholesterol levels and make you more likely to have a heart attack or stroke. During pregnancy, untreated hypothyroidism can harm your baby. Luckily, hypothyroidism is easy to treat.

People of any age can get hypothyroidism, but older adults are more likely to get it. Women age 60 and older have the highest risk. You are more likely to get the disease if it runs in your family.


Causes

In the United States, the most common cause of hypothyroidism is Hashimoto's thyroiditis, a condition that causes the body's defenses—the immune system—to produce antibodies that over time destroy thyroid tissue. As a result, the thyroid gland cannot make enough thyroid hormone.

Worldwide, iodine deficiency is the number one cause of hypothyroidism. Iodine added to salt, food, and water has eliminated this problem in the United States and other Western countries.

Other common causes of hypothyroidism include:

Less common causes include:

Mild (subclinical) hypothyroidism is most often caused by inadequate treatment of hypothyroidism, Hashimoto's thyroiditis, or radioactive iodine therapy.2 But it may be caused by anything that causes hypothyroidism.

Pregnancy, which requires an increased production of thyroid hormone, can cause hypothyroidism. About 2% of pregnant women in the United States get hypothyroidism.


Symptoms

Symptoms of hypothyroidism usually appear slowly over months or years. Symptoms and signs may include:

Other, less common symptoms may include:

In general, how bad your symptoms are depends on your age, how long you have had hypothyroidism, and the seriousness of the condition. The symptoms may be so mild and happen so slowly that they go unnoticed for years. The older you are, the more likely you are to notice symptoms.

Mild (subclinical) hypothyroidism often causes no symptoms or vague symptoms that may be attributed to aging, such as memory problems, dry skin, and fatigue.

Symptoms of hypothyroidism during and after pregnancy include fatigue, weight loss, dizziness, depression, and memory and concentration problems. Some women develop a goiter.

Because of the variety of symptoms, hypothyroidism can be mistaken for depression, especially during and after pregnancy. In older people, it may be confused with Alzheimer's disease, dementia, and other conditions that cause memory problems.


Symptoms of hypothyroidism in infants, children, and teens

Although rare, hypothyroidism can occur in infants, children, and teens. In infants, symptoms of a goiter include a poor appetite and choking on food. Symptoms of hypothyroidism may include dry, scaly skin. In children and teens, symptoms include behavior problems and changes in school performance. Children and teens may gain weight and yet have a slowed growth rate. Teens may have delayed puberty and look much younger than their age.


Diagnosis

A thorough medical history and physical exam are the first steps in diagnosing hypothyroidism or mild (subclinical) hypothyroidism. If the results lead your doctor to suspect you have hypothyroidism or subclinical hypothyroidism, you will have tests to confirm the diagnosis.

Blood tests are always used to confirm a diagnosis of hypothyroidism or mild hypothyroidism. The tests used most often are:

If the above tests are not normal, the antithyroid antibody test may determine whether you have the autoimmune disease Hashimoto's thyroiditis, in which the body's defense system attacks the thyroid gland.

On rare occasions, the following imaging tests may be used to evaluate a thyroid gland that appears to be abnormal during physical examination:

A computed tomography (CT) scan or magnetic resonance imaging (MRI) of the hypothalamus or pituitary gland may be done to look for any changes in these areas of the brain.


Early Detection

Because of the possibility of mental retardation in infants with hypothyroidism, every state in the United States tests newborns for hypothyroidism. If your baby was not born in a hospital, or if you believe your baby may not have been tested, talk to your health professional. Screening tests for hypothyroidism are not always accurate. Watch your child for symptoms of hypothyroidism, even if test results are negative.

Some health professionals now recommend routine testing for people at risk for hypothyroidism, including:

Not all experts agree on whether to recommend widespread screening for hypothyroidism. Some groups say there is not enough evidence of benefit to recommend screening for everyone. But people who are at high risk—women older than 60 and anyone with a family history of thyroid disease or who has other autoimmune diseases—may want to be screened.


Treatment

Hypothyroidism can be easily treated using thyroid hormone medicine. The most effective and reliable thyroid replacement hormone is man-made (synthetic). After starting treatment, you will have regular visits with your doctor to make sure you have the right dose of medicine.

In most cases, symptoms of hypothyroidism start to improve within the first week after you start treatment. All symptoms usually disappear within a few months. Infants and children with hypothyroidism should always be treated. Older adults and people who are in poor health may take longer to respond to the medicine.


Initial treatment

Your doctor will treat your hypothyroidism with the thyroid medicine levothyroxine sodium (for example, Synthroid, Levoxyl, or Levothroid). Take your medicine as directed. Your doctor will want to see you 6 to 8 weeks later to make sure the dose is right for you.

If you take too little medicine, you may have symptoms of hypothyroidism, such as constipation, feeling cold or sluggish, and gaining weight. Too much medicine can cause nervousness, difficulty sleeping, and shaking (tremors). If you have heart disease, too much medicine can cause irregular heartbeats and chest pain. People with heart disease often start on a low dose of levothyroxine, which is increased gradually.

If you have severe hypothyroidism by the time you are diagnosed, you will need immediate treatment. Severe, untreated hypothyroidism can cause myxedema coma, a rare, life-threatening condition. Treatment for myxedema coma involves care in an intensive care unit (ICU). Thyroid hormone is given intravenously (IV). If you have trouble breathing, a ventilator may be used. You will also be monitored for heart problems, including heart attack, and treated if necessary.

Treatment during pregnancy is especially important because hypothyroidism can harm the developing fetus.


Ongoing treatment

You are likely to need treatment for hypothyroidism for the rest of your life. As a result, you need to take your medicine as directed. For some people, hypothyroidism is a progressive disease and the dosage of thyroid medicine may have to be increased gradually as the thyroid continues to slow down.

Most people treated with thyroid hormone develop symptoms again if their medicine is stopped. If this occurs, medicine needs to be restarted.

If a serious illness or infection triggers your hypothyroidism, your thyroid function most likely will return to normal when you recover. To determine whether thyroid function has returned to normal, thyroid hormone medicine may be stopped for a short time. In most people, a brief period of hypothyroidism occurs after thyroid medicine is stopped; there is often a delay in the body's signals that tell the thyroid to start working again. If the thyroid can produce enough hormone on its own, treatment is no longer needed. But if hormone levels remain too low, you need to restart thyroid medicine.

While taking thyroid hormone medicine, you need to see your doctor once a year for checkups. You will have a blood test (thyroid-stimulating hormone [TSH] assay) to make sure you have a normal hormone level.


Treatment if the condition gets worse

Sometimes symptoms of hypothyroidism continue, such as sluggishness, constipation, confusion, and feeling cold. This may occur if you are not taking enough thyroid hormone or if your medicine is not absorbed from your gastrointestinal tract. Having a bowel disease or taking certain other medicines may block thyroid hormone. Your doctor may increase your dose of thyroid medicine if you are taking estrogen or phenytoin (Dilantin). Take calcium supplements at least 4 hours before or after taking thyroid hormone.

Your doctor may suggest you try the combination therapy of T3/T4 medicine if T4 medicine is not controlling your symptoms.

If your dose of thyroid hormone is too high, you may develop complications such as irregular heartbeats and, over time, osteoporosis. If you have heart disease, too much medicine can cause pain (angina) and irregular heartbeats. Your doctor will monitor your thyroid levels using a thyroid-stimulating hormone (TSH) assay. If necessary, your doctor will lower your dose.

 

This infomation was taken from the University of Michigan Health System's Health Library.