Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone. This causes body processes (metabolism) to slow down, resulting in symptoms such as fatigue, intolerance to cold and dry skin.

Causes of hypothyroidism include autoimmune diseases, certain medications, pregnancy, damage to the pituitary gland, radiation therapy, surgery and treatment of hyperthyroidism. Potential complications of hypothyroidism include heart disease, muscle injury, cholesterol problems, infertility, birth defects or an enlarged thyroid (goiter).

Hypothyroidism can be difficult to diagnose because its symptoms vary considerably and may be found in other diseases. This illness is most common in women over the age of 50. As a result, physicians often screen for this disease during routine physical examinations of women in this age group. In other cases, a physician may check for hypothyroidism in patients who display symptoms. Thyroid blood tests aid in diagnosis.

Thyroid hormone replacement treatment can control hypothyroidism. These medications help return the body's metabolism to a normal state.

Hypothyroidism is a condition that occurs when a patient's thyroid gland cannot produce enough thyroid hormone to keep the body's metabolism functioning normally. This lack of hormone causes the body processes to slow down, leading patients to experience symptoms such as fatigue, intolerance to cold, weight gain and dry skin.

About 10 percent of women and 3 percent of men have hypothyroidism, according to the American Association of Clinical Endocrinologists.

The thyroid gland sits just below the Adam's apple in the neck. It secretes hormones that regulate a person's metabolism, the physical and chemical processes necessary for the maintenance of life. Thyroid hormones help to:

• Control the rate at which the body uses fats and carbohydrates
  
• Maintain body temperature
  
• Influence heart rate
  
• Regulate the production of protein
  
• Regulate the amount of calcium in the blood

The thyroid gland is one link in the complex chain that regulates metabolism. This process begins in the brain, where a gland called the hypothalamus signals the pituitary gland to make and release a hormone called thyroid-stimulating hormone (TSH). TSH then causes the release of the thyroid's two major hormones: thyroxine (T4) and triiodothyronine (T3). When disorders affect the thyroid function, they may disturb the release of these thyroid hormones, which may affect many aspects of the metabolism and lead to major health problems.

Hypothyroidism can be associated with an enlarged thyroid gland (goiter), which can be felt or even seen as a swelling at the base of the neck. It results from constant stimulation of the thyroid by the pituitary in an effort to have the thyroid produce more hormones. An autoimmune condition known as Hashimoto's thyroiditis is among the most common causes of hypothyroidism and goiter.

Other health problems that can result from thyroid underactivity include:

• Heart disease. People with hypothyroidism are more vulnerable to developing high levels of low-density lipoprotein (LDL) cholesterol. This is the so-called "bad" cholesterol. Enlarged heart (cardiomegaly) and heart failure are other potential complications of underactive thyroid.
  
  
• Infertility and birth defects. Untreated hypothyroidism can complicate pregnancy. Children born to these mothers also are at increased risk of intellectual, neurological and developmental problems.
  
  
• Joint pain.
  
  
• Mental health problems. Depression and reduced mental functioning may be associated with hypothyroidism.
  
  
• Obesity.
  
  
• Dwarfism. Hypothyroidism results in growth hormone deficiency and in children can cause short stature.

According to recent research, hypothyroidism may also increase the risk of glaucoma, a leading cause of vision loss and blindness.

Left untreated, hypothyroidism can progress to a rare and severe form of the disease known as myxedema, which may include skin changes, swelling and lethargy, and eventually lead to coma. This is a potentially life-threatening condition.

Hypothyroidism occurs when the thyroid gland releases too little thyroid hormone.. Numerous disorders and conditions may cause hypothyroidism. These include:

• Thyroiditis. Inflammation of the thyroid gland destroys thyroid cells and allows excess hormones to leak into the bloodstream. At first, the excess hormones may produce hyperthyroidism, but as the thyroid cells are destroyed by inflammation, they are unable to produce hormones and hypothyroidism sets in. In some cases, thyroiditis is caused by an autoimmune disease, which occurs when antibodies (protective proteins) mistakenly attack the gland, damaging thyroid cells. Examples include Hashimoto's thyroiditis and atrophic thyroiditis, the disorders most commonly associated with hypothyroidism. People who have an autoimmune disease, such as type 1 diabetes, are at increased risk of developing other autoimmune disorders. Thyroiditis also can result from pregnancy (see below) or a viral infection.
  
  
• Hyperthyroidism treatments. Patients who produce too much thyroid hormone (hyperthyroidism) may be treated with medications designed to reduce such hormone production. In some cases, production may be curbed too much, leading to hypothyroidism. After treatment of an overactive thyroid with radioactive iodine, enough thyroid tissue may be lost as to result in hypothyroidism. Likewise, patients who require surgical removal of part or all of the thyroid often require thyroid hormone supplements post-operatively to prevent hypothyroidism.
  
  
• Iodine deficiency. Lack of dietary iodine, a trace mineral, can lead to hypothyroidism, although this rarely occurs in the United States. Iodine is found primarily in iodized salt, seafood, seaweed and plants grown in iodine-rich soil. Excessive levels of iodine paradoxically can also lead to hypothyroidism.
  
  
• Medications. Various medications can contribute to hypothyroidism, including amiodarone (antiarrhythmic heart drug), lithium (bipolar disorder drug), interferon alpha (cancer drug), interleukin-2 (biological response modifier). Growth hormone, a treatment for some causes of dwarfism in children, can cause temporary hypothyroidism.
  
  
• Pituitary disorder. In some cases, a patient's pituitary gland may fail to produce adequate levels of thyroid-stimulating hormone (TSH). This rare condition can lead to hypothyroidism and is usually the result of a benign tumor. Radiation therapy and surgery also can cause this type of disorder.
  
  
• Pregnancy. Women who are pregnant may produce antibodies to their own thyroid gland, leading to hypothyroidism that increases the risk of miscarriage, premature delivery and preeclampsia. In addition, some women will have a bout of hyperthyroidism followed by hypothyroidism shortly after giving birth. This is known as postpartum thyroiditis and is usually temporary.
  
  
• Radiation therapy. Radiation treatments used to treat cancers of the head and neck can damage the thyroid gland, leading to hypothyroidism.
  
  
• Genetic disorders. Turner syndrome, which affects only females, typically involves short stature and dysfunctional ovaries and can lead to hypothyroidism or other thyroid problems, diabetes, cardiovascular conditions, high blood pressure and osteoporosis. Children with Down syndrome, a chromosomal disorder that causes mental retardation, also have a greater risk of hypothyroidism or other thyroid problems.

• Other conditions. Some illnesses can leave substances in the thyroid that impair the functioning of this gland. These illnesses include infections, amyloidosis (abnormal buildup of proteins in organs, sometimes resulting from kidney dialysis), sarcoidosis (disease marked by inflammatory lumps in the lungs and other organs) and hemochromatosis. Head injury or other trauma can also impair thyroid function.

Although hypothyroidism can affect anyone, women (especially those over 50) are at greater risk than men. The risk increases with age. However, in some cases, children are born with no thyroid gland, a defective thyroid or a thyroid in the wrong place (ectopic thyroid). All of these conditions can lead to hypothyroidism.

Other risk factors for hypothyroidism include:

• Family history of autoimmune disease.
  
  
• Individual history of treatment with radioactive iodine, antithyroid medications or radiation therapy to the neck and upper chest.
  
  
• Individual history of surgery on the thyroid.
  
  
• Obesity.
  
  
• Exposure to chemicals. Women exposed to perchlorate, a common industrial chemical that has been found in U.S. drinking water, produce and milk, may be at risk for reduced thyroid function, the Centers for Disease Control and Prevention (CDC) reported in 2006.

Most patients who are diagnosed with hypothyroidism will have the condition for life, although underactive thyroid associated with pregnancy or viral illness is more likely to disappear over time.

Signs and symptoms of hypothyroidism vary significantly from patient to patient and often develop slowly. It can take years before symptoms become obvious. In some cases, symptoms may progress over time.

Initially, many patients report fatigue and sluggishness. Over time, more obvious symptoms may emerge, including puffiness of the face, increased sensitivity to cold and unexplained weight gain.

Other symptoms may include:

• Constipation
• Puffiness around the eyes and ankles (edema)
• Depression or changes in personality
• Forgetfulness, impaired concentration or confusion
• Dry, pale, scaly or thick skin
• Dry hair or loss of hair
• Heavy menstrual periods
• Enlarged thyroid (goiter)
• Hoarseness or slow speech
• Muscle aches, weakness, stiffness and tenderness
• Muscle cramps
• Pain, stiffness or swelling in the joints
• Rise in blood cholesterol levels

  

• Dull facial expression
• Burning mouth syndrome

Hypothyroidism is more likely to affect adults than children. However, babies sometimes are born without a thyroid gland or with a gland that does not function properly. Symptoms of hypothyroidism in young children may include:

• Constipation
• Excessive sleepiness
• Frequent choking
• Large and protruding tongue
• Poor muscle tone
• Muscle swelling (hypertrophy)
• Yellowing of the skin and whites of the eyes (jaundice)
• Growth retardation

Left untreated, hypothyroidism in young children can lead to severe physical disabilities and mental retardation. Children may experience poor growth and delayed development of permanent teeth. Poor mental development and delayed onset of puberty also may occur in these children.

Patients of any age whose hypothyroidism goes untreated are at risk for developing an advanced form of the illness known as myxedema. This rare condition is potentially life-threatening and requires prompt medical attention. Symptoms associated with myxedema include:

• Drowsiness that can progress to profound lethargy and coma
• Decreased body temperature
• Decreased breathing
• Intense intolerance to cold
• Low blood pressure (hypotension), which may cause dizziness or fainting

Hypothyroidism can be difficult to diagnose because its symptoms vary considerably and may be found in other diseases. This illness is most common in women over the age of 50. As a result, physicians often screen for this disease during routine examinations of women in this age group. Screenings also may be performed on women who are pregnant or who are thinking of becoming pregnant.

Screenings also may be performed on women who are pregnant or who are thinking of becoming pregnant. The American Academy of Clinical Endocrinologists recommends thyroid blood testing before pregnancy or during the first trimester, although the American College of Obstetricians and Gynecologists now advises against this routine screening.

Infants are routinely checked with a blood test shortly after birth for congenital hypothyroidism. People with a family history of hypothyroidism also may be good candidates for regular screenings.

In other cases, a physician may check for hypothyroidism in patients who display symptoms of this illness. Diagnosis typically begins with the physician reviewing the patient's medical history and performing a physical examination. The physician will look for signs such as changes in the thyroid gland, dry skin, swelling, slowed reflexes and slowed heart rate.

With hypothyroidism, thyroid blood tests usually show high levels of thyroid-stimulating hormone (TSH) and low measures of thyroxine (T4). The physician may also check the blood for the antibodies that are associated with Hashimoto’s thyroiditis. Patients with a condition called subclinical hypothyroidism, which does not cause prominent symptoms but can still cause health problems, typically have high levels of TSH and normal levels of thyroxine.

When blood testing reveals hypothyroidism, the physician will probably suggest a follow-up test that measures the level of a thyroid hormone in a patient’s system. Tests also may be performed to look for complications associated with hypothyroidism. For example, a chest x-ray may show an enlarged heart, and a cholesterol blood test may show unhealthy levels of cholesterol.

There is no cure for hypothyroidism. However, this illness can be effectively treated with hormone medications. These medications can be synthetic or natural and are identical to the hormones produced by a healthy thyroid gland. These medications help return the body's metabolism back to a normal state. They also help improve cholesterol levels and may reduce depression. Patients who use these drugs may also lose the excess weight they gained as a result of hypothyroidism. In most cases, patients must remain on these medications throughout their lifetimes.

Rarely, patients experience side effects when they take these medications in large amounts or while the dosage is being adjusted when treatment begins. Such side effects may include heart palpitations, increased appetite (polyphagia), insomnia, intolerance to heat and shakiness. A physician usually can adjust the dosage level of these drugs to help reduce or eliminate such side effects.

Diets high in soy products and fiber, and supplements of iron or calcium, may interfere with the absorption of these drugs into the body. Medications and supplements that can reduce the absorption of thyroid medications include iron supplements, calcium supplements, some cholesterol-lowering drugs and aluminum hydroxide (found in some antacids).

Patients who take thyroid hormone medications require regular monitoring to ensure that they are getting proper dosage levels.

There is no known way of preventing hypothyroidism. Screening at-risk adults or testing infants for congenital hypothyroidism may lead to diagnosis and treatment that can avert complications.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about hypothyroidism:

1. What are the first signs that I may have hypothyroidism?
   
   
2. How will you diagnose my hypothyroidism?
   
   
3. Do I need to do anything to prepare for blood tests?
   
   
4. What is the likely source of my hypothyroidism?
   
   
5. Do I have any of the complications related to hypothyroidism?
   
   
6. What are my treatment options? What are the pros and cons of these treatments?
   
   
7. How often will I need to be monitored to ensure that I am receiving the right dose of medication?
   
   
8. Will I need to change my diet while on this medication?
   
   
9. What is my long-term prognosis?
   
   
10. Are there any other diseases or conditions associated with the type of hypothyroidism I have?
    
    
11. How can I tell if my infant may have hypothyroidism? What do I need to tell my family members about getting screened for thyroid disease?