Hypothyroidism

Also known as: Myxedema and Adult hypothyroidism

Definition

Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone. This condition is often called underactive thyroid.

Causes

The thyroid gland is an important organ of the endocrine system. It is located at the front of the neck, just above where your collarbones meet. The thyroid makes hormones that control the way every cell in the body uses energy. This process is called metabolism.

Hypothyroidism 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:

  • The immune system attacking the thyroid gland
  • Viral infections (common cold) or other respiratory infections
  • Pregnancy (often called postpartum thyroiditis)

Other causes of hypothyroidism include:

  • Certain medicines, 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
  • Pituitary tumor or pituitary surgery

Symptoms

Early symptoms:

Late symptoms, if untreated:

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

Exams and Tests

The health care provider will do a physical exam and find that your thyroid gland is enlarged. Sometimes, the gland is normal size or smaller-than-normal. The exam may also reveal:

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

Blood tests are also ordered to measure your thyroid hormones TSH and T4.   

You may also have tests to check:

Treatment

Treatment is aimed at replacing the thyroid hormone you are lacking.

Levothyroxine is the most commonly used medicine:

  • You will be prescribed 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 to take this medicine for life.

When starting you on your medicine, your doctor may check your hormone levels every 2 to 3 months. After that, your thyroid hormone levels should be monitored at least once every year.

When you are taking thyroid medicine, be aware of the following:

  • Do not stop taking the medicine even when you feel better. Continue taking it 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 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. Ask your doctor if you should take your medicine at bedtime. Studies have found that taking it at bedtime may allow your body to absorb the medicine better than taking it in the daytime.
  • Wait at least 4 hours after taking thyroid hormone before you take 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:

  • Rapid weight loss
  • Restlessness or shakiness
  • Sweating

Outlook (Prognosis)

In most cases, thyroid hormone levels become normal with proper treatment. You will likely take a thyroid hormone medicine for the rest of your life.

Possible Complications

Myxedema coma, the most severe form of hypothyroidism, is rare. It occurs when thyroid hormone levels get very low. It can be caused by an infection, illness, exposure to cold, or certain medicines in people with untreated hypothyroidism.

Myxedema coma is a medical emergency that must be treated in the hospital. Some patients may need oxygen, breathing assistance (ventilator), fluid replacement, and intensive-care nursing.

Symptoms and signs of myxedema coma include:

People with untreated hypothyroidism are at increased risk of:

  • Infection
  • Infertility, miscarriage, giving birth to a baby with birth defects
  • Heart disease because of higher levels of LDL ("bad") cholesterol
  • Heart failure

When to Contact a Medical Professional

Call your health care provider if you have symptoms of hypothyroidism.

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

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: Elsevier Saunders; 2011:chap 13.

Garber JR, Cobin RH, Gharib H, et al. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Thyroid. 22;12:1200-1235.

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

Review date:
October 5, 2014
Reviewed by:
Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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