Hypothyroidism: MedlinePlus Mobile Medical Encyclopedia

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Causes
The thyroid gland is located in the front of the neck just below the voice box (larynx). It releases hormones that control metabolism.

Hypothyroidism, or underactive thyroid, is more common in women and people over age 50.

The most common cause of hypothyroidism is thyroiditis. Swelling and inflammation damage the thyroid gland's cells. Causes of this problem include:

An attack of the thyroid gland by the immune system
Cold or other respiratory infection
Pregnancy (often called "postpartum thyroiditis")

Other causes of hypothyroidism include:

Certain drugs, such as lithium and amiodarone
Congenital (birth) defects
Radiation treatments to the neck or brain to treat different cancers
Radioactive iodine used to treat an overactive thyroid gland
Surgical removal of part or all of the thyroid gland
Sheehan syndrome, a condition that may occur in a woman who bleeds severely during pregnancy or childbirth and causes the destruction of the pituitary gland

Symptoms
Early symptoms:

Hard stools or constipation
Increased sensitivity to cold
Fatigue or feeling slowed down
Heavier menstrual periods
Joint or muscle pain
Paleness or dry skin
Sadness or depression
Thin, brittle hair or fingernails
Weakness
Weight gain without trying

Late symptoms, if left untreated:

Decreased taste and smell
Hoarseness
Puffy face, hands, and feet
Slow speech
Thickening of the skin
Thinning of eyebrows

Exams and Tests
A physical examination may reveal a smaller-than-normal thyroid gland, although sometimes the gland is normal size or even enlarged (goiter). The examination may also reveal:

Brittle nails
Coarse features of the face
Pale or dry skin, which may be cool to the touch
Swelling of the arms and legs
Thin and brittle hair

Lab tests to determine thyroid function include:

Other tests that may be done:

Cholesterol levels
Complete blood count (CBC)
Liver enzymes
Prolactin
Sodium

Treatment
The purpose of treatment is to replace the thyroid hormone that is lacking. Levothyroxine is the most commonly used medication.

Doctors will prescribe the lowest dose possible that relieves your symptoms and brings your blood hormone levels back to normal.
If you have heart disease or you are older, your doctor may start you on a very small dose.
Most people with an underactive thyroid will need lifelong therapy.

When starting your medication, your doctor may check your hormone levels every 2 - 3 months. After that, your thyroid hormone levels should be monitored at least every year.

Important things to remember when you are taking thyroid hormone:

Do NOT stop taking the medication when you feel better. Continue taking them exactly as your doctor prescribed.
If you change brands of thyroid medicine, let your doctor know. Your levels may need to be checked.
What you eat can change the way your body absorbs the thyroid medicine. Talk with your doctor if you are eating a lot of soy products or are on a high-fiber diet.
Thyroid medicine works best on an empty stomach and when taken 1 hour before any other medications.
Do NOT take thyroid hormone with fiber supplements, calcium, iron, multivitamins, aluminum hydroxide antacids, colestipol, or medicines that bind bile acids.

While you are taking thyroid replacement therapy, tell your doctor if you have any symptoms that suggest your dose is too high, such as:

Palpitations
Rapid weight loss
Restlessness or shakiness
Sweating

Myxedema coma is a medical emergency that occurs when the body's level of thyroid hormones becomes very low. It is treated with intravenous thyroid hormone replacement and steroid medications. Some patients may need supportive therapy (oxygen, breathing assistance, fluid replacement) and intensive-care nursing.

Outlook (Prognosis)
In most cases, thyroid levels return to normal with proper treatment. However, you must take thyroid hormone replacement for the rest of your life.

Myxedema coma can result in death.

Possible Complications
Myxedema coma, the most severe form of hypothyroidism, is rare. It may be caused by an infection, illness, exposure to cold, or certain medications in people with untreated hypothyroidism.

Symptoms and signs of myxedema coma include:

Below normal temperature
Decreased breathing
Low blood pressure
Low blood sugar
Unresponsiveness

Other complications are:

Heart disease
Increased risk of infection
Infertility
Miscarriage

People with untreated hypothyroidism are at increased risk for:

Giving birth to a baby with birth defects
Heart disease because of higher levels of LDL ("bad") cholesterol
Heart failure

People treated with too much thyroid hormone are at risk for angina or heart attack, as well as osteoporosis (thinning of the bones).

When to Contact a Medical Professional
Call your health care provider if you have symptoms of hypothyroidism (or myxedema).

If you are being treated for hypothyroidism, call your doctor if:

You develop chest pain or rapid heartbeat
You have an infection
Your symptoms get worse or do not improve with treatment
You develop new symptoms

Prevention
There is no prevention for hypothyroidism.

Screening tests in newborns can detect hypothyroidism that is present from birth (congenital hypothyroidism).

Alternative Names
Myxedema; Adult hypothyroidism

References
Brent GA, Davies TF. Hypothyroidism and thyroiditis. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, et al. Williams Textbook of Endocrinology . 12th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 13.

Kim M, Ladenson P. Thyroid. In: Goldman L, Schafer AI, eds. Cecil Medicine . 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 233.

Update Date: 6/4/2012
David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by Shehzad Topiwala, MD, Chief Consultant Endocrinologist, Premier Medical Associates, The Villages, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.