What Is Hypothyroidism? What Causes Hypothyroidism?

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Main Category: Endocrinology
Article Date: 11 Sep 2009 - 8:00 PDT

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Hypothyroidism, also known as underactive thyroid, is a condition in which the thyroid gland, which supplies hormones to keep the metabolism in working order, is not functioning properly. This results in lower-than-required levels of essential hormones that are distributed to the rest of the body - undermining the body's ability to function efficiently. Hypothyroidism generally affects adults, but can affect children too. Often, the term "hypothyroidism" is used incorrectly for either myxedema or congenital hypothyroidism. Hypothyroidism refers to an underactive thyroid gland while hyperthyroidism refers to an overactive thyroid gland.

Myxedema, commonly referred to as advanced hypothyroidism, is a rare, life-threatening condition that can result from long-term undiagnosed hypothyroidism. Women are six times more likely than men to develop this form of hypothyroidism. Myxedema most commonly occurs in adults, while Congenital hypothyroidism is present from birth.

The modern English word "hypothyroidism" is derived from the ancient Greek prefix hypo, meaning "under" and the Greek words thyreos, meaning "shield" and eidos, meaning "shape or form"; hence, the shield-like shape of the thyroid gland, which protects the glottis (in the throat, where the vocal cords are located).

According to Medilexicon's medical dictionary, hypothyroidism means "Diminished production of thyroid hormone, leading to clinical manifestations of thyroid insufficiency, including low metabolic rate, tendency to gain weight, somnolence, and sometimes myxedema."

The thyroid gland produces three main hormones:


• Thyroxine (T-4)
• Triiodothyronine (T-3)
• Calcitonin

T-3 and T-4 maintain the rate at which our bodies utilize carbohydrates and fats. They also have an impact on our heart rates, and play an important role in protein synthesis. Calcitonin is a hormone that regulates the production of calcium in the blood.

The hypothalamus, a part of the brain that is in charge of hunger, thirst, body temperature, and the pituitary gland (located at the base of the hypothalamus), work together to control the release of T-3 and T-4. The hypothalamus regulates the pituitary gland's production of the thyroid-stimulating hormone (TSH); depending on the levels of T-3 and T-4 found in your bloodstream, the corresponding amount of this hormone is then released into your blood. The thyroid gland then regulates its production of hormones based on how much TSH it receives.

What causes hypothyroidism?

• Causes of Myxedema (the adult form of this condition):
  
  
  • Thyroiditis - an autoimmune inflammation of the thyroid gland
  • Overtreatment for hyperthyroidism (overactive thyroid gland) - radiation or surgery
  • Severe iodine deficiency - resulting in a reduction in the production of thyroid hormones
  • Pituitary gland disorder
  • Lithium
  • Pregnancy - during or after, may seriously affect the fetus


• Causes of congenital hypothyroidism (present from birth):
  
  
  • Iodine deficiency in the mother's diet during pregnancy and in that of the child after birth
  • Defective or absent thyroid gland - for unknown reasons, it doesn't develop normally

What are the risk factors for hypothyroidism?

A risk factor is something that raises the risk of developing a disease or condition. For example, smoking is a risk factor for lung cancer - it raises the risk of developing lung cancer. Old age is a risk factor for many cancers - the older you are, the higher the risk.

The most common risk factors for hypothyroidism are:

• Being female and over 50 years of age; however anyone can develop hypothyroidism
• Being treated with radioactive iodine (or other anti-thyroid drugs)
• Age, people over 60 years of age have a higher risk of developing hypothyroidism
• A close relative having an autoimmune disease
• Radiation exposure
• Thyroidectomy - partial surgical removal of the thyroid

What are the signs and symptoms of hypothyroidism?

The main symptoms of hypothyroidism are fatigue and lethargy. However, most symptoms take years to develop. The slower your metabolism gets, the more obvious the signs and symptoms will become. If hypothyroidism goes untreated, the signs and symptoms could become severe, such as an inflamed thyroid (goiter), slow thought processes, or depression.

• More common symptoms include:
  
  
  • Weight gain
  • Bloated face
  • Dry, pallid, flaky skin
  • Hoarse voice
  • Amplified sensitivity to cold
  • Frail fingernails and hair (eyebrows may become thinned)
  • Constipation
  • Muscle weakness
  • Heavier than usual, or loss of, menstrual period
  • Swollen or stiff joints
  • Stiff, weak, painful muscle aches
  • Higher than usual blood cholesterol level


• Babies born with congenital hypothyroidism often do not display any signs or symptoms. However, if present, they may include:
  
  
  • Jaundice (yellow skin)
  • Swollen face
  • Recurrent choking
  • Bulging tongue
  • Under-development - muscle tone, adult teeth
  • Fatigue
  • Constipation


• A person with myxedema (advanced hypothyroidism) will experience:
  
  
  • Decreased breathing
  • Lower body temperature
  • Hypotension (low blood pressure)
  • Unresponsiveness (can be life-threatening)

How is hypothyroidism diagnosed?

Doctors recommend that pregnant women be tested for hypothyroidism so that if they do have it, they can take iron supplements to prevent the baby from being born with the same condition. Older women are also encouraged to be screened for the disorder annually.

Some doctors will ask the patient if they have experienced any of the symptoms of hypothyroidism or have had any previous issues with the thyroid gland.

Doctors will usually take a blood sample to detect levels of TSH and follow up with a test of thyroxine (T-4) levels. If the level of TSH is above average and the level of T-4 is below average, it means that the hypothalamus and pituitary gland are attempting to compensate for the underactivity of the thyroid by stimulating it with more TSH.

Some patients who do not experience symptoms may still have a mild form of the condition (subclinical hypothyroidism) and thus are encouraged to be screened periodically. If the patient has hypothyroidism, levels of TSH will be high, even if T-4 levels are normal.

In the case of a fetus, the blood samples can be acquired from the umbilical cord.

When a baby is born with congenital hypothyroidism, they must be diagnosed and begin treatment within the first few days. The difference from one day to the next could be the difference between a baby with a reasonably normal upbringing and one with a severe mental handicap.

What are the treatment options for hypothyroidism?

A slow or inactive thyroid gland does not produce enough T-4 (thyroxine). To restore normal body function the patient will need to take a supplement. The supplement is a synthetic thyroid hormone called levothyroxin (levoxyl, synthroid).

After a few weeks on levothyroxin, symptoms are reduced and even reversed in the case of weight gain. However, because hypothyroidism cannot be cured, doctors will urge patients to continue treatment throughout the course of their lives, incrementing the dosage as indicated by periodic checks of TSH levels, which will also help the body adjust to the increase in metabolism.

The good thing about levothyroxin is that it is relatively inexpensive and has practically no side effects. As different brands of levothyroxin have varying dosages it is important to let the doctor know if you change brands. If the patient stops taking levothyroxin at any time, signs and symptoms will return when the body has used up the last dosage of the medication.

Some medications and foods may interfere with the absorption of levothyroxine, so be sure to review this with your doctor.

If diagnosed with subclinical hypothyroidism, that is, your thyroid stimulating hormone (TSH) levels are only slightly elevated, hormone replacement therapy or supplements may do more harm than good. Review treatment options with your doctor.

How can hypothyroidism be prevented?

Hypothyroidism can only be prevented if it is caused by a lack of iodine in the diet, in which case people need to ensure their diet contains sufficient levels of iodine. Below is a list of some foods and their iodine content:

• Iodized salt - 3,000 micrograms per 100 grams
• Seafood - 66 micrograms per 100 grams
• Meat - 32 micrograms per 100 grams
• Eggs - 26 micrograms per 100 grams
• Dairy - 13 micrograms per 100 grams
• Bread/cereals - 10 micrograms per 100 grams
• Fruits - 4 micrograms per 100 grams

Written by Caroline Gillott


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