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:
- Thyroid surgery. Part or all of the thyroid gland may be removed to treat disorders such as having too much thyroid hormone (hyperthyroidism), an enlarged thyroid gland (goiter) that makes swallowing difficult, thyroid cancer, or thyroid nodules that may be overactive or cancerous. Hypothyroidism results when the thyroid gland is removed or when remaining thyroid tissue does not function properly.
- Radioactive iodine therapy, which is often used to treat hyperthyroidism. Radioactive iodine therapy can destroy the thyroid gland, leading to hypothyroidism.
- External beam radiation, which is used to treat some cancers, such as Hodgkin's lymphoma. This radiation treatment can destroy the thyroid gland.
Less common causes include:
- Infections. Viral and bacterial infections can temporarily damage the thyroid gland, causing a short-term form of the condition. Hypothyroidism caused by infection usually does not result in permanent hypothyroidism.
- Medicines. Some medicines can interfere with normal production of thyroid hormone. Lithium carbonate is one of the most common medicines that causes hypothyroidism. Others include amiodarone (such as Amiodarone, Cordarone, and Pacerone) and interferon alfa (such as Infergen, Rebetron, and Wellferon).
- In rare instances, disorders of the pituitary gland or the hypothalamus (secondary and tertiary forms of hypothyroidism). The pituitary gland and hypothalamus produce hormones that control the thyroid and, as a result, affect its ability to produce thyroid hormone.
- Excessive iodine, which, in food or medicines, can reduce the function of the thyroid gland. This is usually temporary.
- Congenital hypothyroidism. About 1 in 4,000 infants is born without a properly functioning thyroid gland. All children born in a hospital in the United States are tested at birth for hypothyroidism.
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:
- Coarse and thinning hair.
- Dry skin.
- Brittle nails.
- A yellowish tint to the skin.
- Slow body movements.
- Cold skin.
- Inability to tolerate cold.
- Feeling tired, sluggish, or weak.
- Memory problems, depression, or difficulty concentrating.
- Constipation.
- Heavy or irregular menstrual periods that may last longer than 5 to 7 days.
Other, less common symptoms may include:
- An enlarged thyroid gland (goiter).
- Modest weight gain, often 10 lb (4.5 kg) or less.
- Swelling of the arms, hands, legs, and feet, and facial puffiness, particularly around the eyes.
- Hoarseness.
- Muscle aches and cramps.
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:
- Thyroid-stimulating hormone (TSH) assay.
- Thyroxine (T4) measurement.
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:
- Thyroid ultrasound
- Thyroid scan and radioactive iodine uptake (RAIU) test
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:
- People age 35 and older. The American Thyroid Association guidelines recommend that screening begin at age 35 and continue every 5 years thereafter.
- People with one or more close relatives who have or had hypothyroidism.
- People with conditions associated with Hashimoto's thyroiditis, including Addison's Disease, rheumatoid arthritis, pernicious anemia, and type 1 diabetes.
- Pregnant women. In pregnant women known to have hypothyroidism, tests should be done at regular intervals to determine whether the dosage of thyroid hormone medicine is adequate.
- Women who are having symptoms of hypothyroidism after pregnancy (postpartum hypothyroidism), such as depression, memory and concentration problems, or thyroid enlargement (goiter). Women who have had hypothyroidism during or after pregnancy should be retested if they become pregnant again.
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.
- If you have had radiation therapy and have hypothyroidism, or if your thyroid gland has been removed, you will most likely need treatment for the rest of your life. If your hypothyroidism is caused by Hashimoto's thyroiditis, you might also need treatment for the rest of your life. Occasionally, thyroid gland function returns on its own in Hashimoto's thyroiditis.
- If a serious illness or infection triggered your hypothyroidism, your thyroid function most likely will return to normal when you recover.
- Some medicines may cause hypothyroidism. Your thyroid function will return to normal when you stop the medicines.
- If you have mild (subclinical) hypothyroidism, you may not need treatment but should be watched for signs of hypothyroidism getting worse. Current research does not provide clear evidence to support treatment, and many health professionals disagree about whether mild hypothyroidism should be treated. When making the decision to treat mild hypothyroidism, you and your doctor will talk about the possible benefits of improved symptoms compared to potential risks and the costs of medicine and monitoring symptoms. The dose of thyroid medicine must be monitored carefully in people with heart disease because too much medicine increases the risk of chest pain (angina) and irregular heartbeats (atrial fibrillation).
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.
- If you develop hypothyroidism during pregnancy, treatment should be started immediately. If you have hypothyroidism before you become pregnant, your thyroid hormone levels need to be monitored to determine whether the dosage of thyroid medicine is correct. During pregnancy, your dose of medicine may need to be increased by 25% to 50%.
- You also may need treatment if you develop hypothyroidism after pregnancy (postpartum hypothyroidism). You will be retested for hypothyroidism if you become pregnant again. In some cases, hypothyroidism will go away on its own; in other cases, it is permanent and requires lifelong treatment.
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.
