Underactive Thyroid
Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone, which regulates metabolism, to meet the body’s needs. Without enough thyroid hormone, many of the body’s functions slow down.

Thyroid hormone production is regulated by thyroid-stimulating hormone (TSH), which is made by the pituitary gland. The pituitary gland is located in the brain, and is the “master gland” of the endocrine system.

Women are much more likely to develop hypothyroidism than men. Hypothyroidism disease is also more common among people older than age 60. The American Thyroid Association recommends that adults, particularly women, have a blood test to detect thyroid problems every 5 years starting at age 35.

Causes of Hypothyroidism

Hashimoto’s Disease
Hashimoto’s disease, an autoimmune disorder, is also called chronic lymphocytic thyroiditis. Hashimoto’s disease is the most common cause of hypothyroidism in the United States.

Hashimoto’s disease is an autoimmune disorder, which means the body’s immune system, which normally protects the body by attacking foreign organisms, acts against its own healthy cells and tissues. In Hashimoto’s disease, the immune system makes antibodies that attack cells in the thyroid and interfere with their ability to produce thyroid hormone.

Thyroiditis, or Inflammation of the Thyroid gland
Thyroiditis causes stored thyroid hormone to leak out of the inflamed thyroid gland. At first, the leakage raises hormone levels in the blood, leading to hyperthyroidism that lasts for a month or two. Most people then develop hypothyroidism before the thyroid is completely healed. Several types of thyroiditis can lead to hypothyroidism:

  • Subacute thyroiditis is a condition that involves painful inflammation and enlargement of the thyroid. Doctors aren’t sure what causes subacute thyroiditis, but it may be related to a viral or bacterial infection. The condition usually goes away on its own in a few months.
  • Postpartum thyroiditis – About 8 percent of women who have been pregnant develop postpartum thyroiditis within a few months of giving birth.2 In some women, the thyroid does not heal and their hypothyroidism is permanent. Postpartum thyroiditis is believed to be an autoimmune condition.
  • Silent thyroiditis is called “silent” because it is painless, as is postpartum thyroiditis, even though the thyroid may be enlarged. Silent thyroiditis is probably an autoimmune condition and sometimes develops into permanent hypothyroidism.

Congenital Hypothyroidism
Congenital hypothyroidism is hypothyroidism that is present at birth. Some babies are born with a thyroid that is not fully developed or does not function properly. If untreated, congenital hypothyroidism can lead to mental retardation and growth failure. Most newborns in the United States are screened for hypothyroidism, and early treatment can prevent these complications.

Surgical Removal of the Thyroid
Part or all of the thyroid gland may be surgically removed as a treatment for:

  • Hyperthyroidism – when the thyroid makes too much thyroid hormone.
  • A large goiter, which is an enlarged thyroid gland that may cause the neck to appear swollen and can interfere with normal breathing and swallowing.
  • Thyroid nodules, which are lumps in the thyroid that can produce excess thyroid hormone.
  • Thyroid cancer.
  • When part of the thyroid is removed, the remaining part may produce normal amounts of thyroid hormone, but some people who have this surgery develop hypothyroidism. Removal of the entire thyroid always results in hypothyroidism.

    Radiation Treatment of the Thyroid
    Radioactive iodine, a common treatment for hyperthyroidism, gradually destroys the cells of the thyroid. Almost everyone who receives radioactive iodine treatment eventually develops hypothyroidism. People with Hodgkin’s disease, other lymphomas, and head or neck cancers are treated with radiation, which can also damage the thyroid.

    Some drugs can interfere with thyroid hormone production and lead to hypothyroidism. These drugs include:

    • Amiodarone, a heart medication
    • Interferon alpha, a cancer medication
    • Lithium, a bipolar disorder medication
    • Interleukin-2, a kidney cancer medication

    Symptoms of Hypothyroidism

    Hypothyroidism has many symptoms that can vary from person to person. Some common symptoms of hypothyroidism are:

    • Fatigue – feeling very tired.
    • Weight gain, even though you are not eating more food.
    • Puffy face.
    • Pale dry skin.
    • Cold intolerance – Increased sensitivity to cold.
    • Joint and muscle pain – muscle weakness.
    • Constipation.
    • Hoarse voice.
    • Dry, thinning hair.
    • Decreased sweating
    • Heavy or irregular menstrual periods and impaired fertility.
    • Depression.
    • Slowed heart rate.

    Symptoms more specific to Hashimoto’s disease are goiter and a feeling of fullness in the throat.

    Hypothyroidism can contribute to high cholesterol. People with high cholesterol should be tested for hypothyroidism. Rarely, severe untreated hypothyroidism may lead to myxedema coma, an extreme form of hypothyroidism in which the body slows to the point that it becomes life-threatening. Myxedema requires immediate medical treatment.

    Pregnancy and Hypothyroidism

    Women with hypothyroidism should discuss their condition with their doctor before becoming pregnant.

    Uncontrolled hypothyroidism raises the chance of miscarriage, preterm delivery, and preeclampsia, which is a potentially serious complication that increases blood pressure.

    Untreated hypothyroidism during pregnancy may also affect the baby’s growth and brain development. Thyroid medications can help prevent these problems and are safe to take during pregnancy.

    Postpartum thyroiditis sometimes goes undiagnosed because the symptoms are mistaken for postpartum blues – the exhaustion and moodiness that sometimes follow delivery. Women whose symptoms do not go away within 6 months should talk with their doctor.

    Treatment of Hypothyroidism

    Hypothyroidism is treated with synthetic thyroxine, which is identical to the T4 made by the thyroid. The exact dose will depend on the person’s age and weight, the severity of the hypothyroidism, the presence of other health problems, and whether the person is taking other drugs that might interfere with how well the body uses thyroid hormone.

    Doctors test TSH (thyroid-stimulating hormone) levels about 6 to 8 weeks after a person begins taking thyroid hormone and make any necessary adjustments to the dose. Each time the dose is adjusted, the blood is tested again. Once a stable dose is reached, blood tests are normally repeated in 6 months and then once a year after that.

    Hypothyroidism can almost always be completely controlled with synthetic thyroxine, as long as the recommended dose is taken every day as instructed.

    Source: www.endocrine.niddk.nih.gov – May 2008

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