Hyprthyrodism

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

Causes, incidence, and risk factors

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

Signs 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:

• TSH test
• T4 test

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.

Expectations (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.

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