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Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.

See also:

• Chronic thryoiditis (Hashimoto's disease)
• Subacute thyroiditis
• Silent thyroiditis
• Neonatal hypothyroidism

Myxedema; Adult hypothyroidism

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

The most common cause of hypothyroidism is inflammation of the thyroid gland, which damages the gland's cells. Autoimmune or Hashimoto's thyroiditis, in which the immune system attacks the thyroid gland, is the most common example of this. Some women develop hypothyroidism after pregancy (often referred to as "postpartum throiditis").

Other common causes of hypothyroidism include:

• Congenital (birth) defects
• Radiation treatments to the neck to treat different cancers, which may also damage the thyroid gland
• Radioactive iodine used to treat an overactive thyroid (hyperthyroidism)
• Surgical removal of part or all of the thyroid gland, done to treat other thyroid problems
• Viral thyroiditis, which may case hyperthyroidism and is often followed by temporary or permanent hypothyroidism

Certain drugs can cause hyperthyroidism, including:

• Amiodarone
• Drugs used for hyperthyroidism (overactive thyroid), such as propylthiouracil (PTU) and methimazole
• Lithium
• Radiation to the brain
• Sheehan syndrome, a condition that may occur in a woman who bleeds severely during pregnancy or childbirth and causes destruction of the pituitary gland

Risk factors include:

• Age over 50 years
• Being female

Early symptoms:

• Being more sensitive to cold
• Constipation
• Depression
• Fatigue or feeling slowed down
• Heavier menstrual periods
• Joint or muscle pain
• Paleness or dry skin
• Thin, brittle hair or fingernails
• Weakness
• Weight gain (unintentional)

Late symptoms, if left untreated:

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

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 facial features
• Pale or dry skin, which may be cool to the touch
• Swelling of the arms and legs
• Thin and brittle hair

A chest x-ray may show an enlarged heart.

Laboratory tests to determine thyroid function include:

• Serum TSH
• T4 test

Lab tests may also reveal:

• Anemia on a complete blood count (CBC)
• Increased cholesterol levels
• Increased liver enzymes
• Increased prolactin
• Low sodium

In most cases, thyroid levels return to with proper treatment. However, thyroid hormone replacement must be taken for the rest of your life.

Myxedema coma can result in death.

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).

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

There is no prevention for hypothyroidism.

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

Fatourechi V. Subclinical hypothyroidism: an update for primary care physicians. Mayo Clin Proc. 2009;84(1):65-71.

Ladenson P, Kim M. Thyroid. In: Goldman L and Ausiello D, eds. Goldman: Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders; 2007:chap 244.

Vaidya B, Pearce SH. Management opf hypothyroidism in adults. BMJ. 2008;28;337:a801.