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Updated 14 May 2013

Hypothyroidism

Hypothyroidism is a condition in which the thyroid gland does not produce enough of the thyroid hormone, thyroxine.

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Summary

  • Hypothyroidism is a condition in which the thyroid gland does not produce enough of the thyroid hormone, thyroxine.  
  • The symptoms vary widely, depending on the person’s age and the severity of the hormone deficiency.  
  • Reliable testing and synthetic hormones are available for the diagnosis and treatment of hypothyroidism.  
  • Treatment usually relieves most symptoms within a week, although it takes some months for all the symptoms to disappear.

Description

Hypothyroidism is a condition in which the thyroid gland does not produce enough thyroid hormones. Insufficient amounts of hormones slow down all the chemical reactions in the body, causing mental and physical changes.

The thyroid is a small gland that is wrapped around the windpipe (trachea) below the Adam’s apple. It has the shape of a butterfly, with two "wings" attached by a middle part. The thyroid takes iodine from the food you eat to make iodine-containing hormones, of which thyroxine (T4, which has four iodine molecules attached to its structure) and triiodothyroxine (T3, with three iodine molecules) are the most important. These hormones regulate the rate at which you burn kilojoules for energy. They regulate growth and the rate of chemical reactions (metabolism) in the body. The amount of T3 and T4 can be determined by a blood test.

Iodine is found in seafood, bread, salt and seaweed.

Normally the rate of thyroid hormone production is controlled by the pituitary gland located at the base of the brain. When the supply of thyroid hormones is insufficient, the pituitary gland releases thyroid-stimulating hormone (TSH) to trigger the production of thyroid hormones in the thyroid gland. If the thyroid gland is unable to produce the thyroid hormones, the pituitary releases more and more TSH. By measuring the amount of TSH, it is possible to test for the cause of hypothyroidism.

Cause

  • Hashimoto’s disease (also called Hashimoto’s thyroiditis or chronic lymphocytic thyroiditis), or inflammation of the thyroid gland – this condition is a disorder of the immune system, which usually protects you from infection, but in this case destroys thyroid tissue and/or inhibits the action of thyroid hormones. The thyroid gland is initially enlarged (goitre) and cannot produce the required thyroid hormones. Later the gland becomes small and hard.
  • Radiation treatment for an overactive thyroid gland (hyperthyroidism) or cancers of the head and neck – this may have shrunk or destroyed the gland.
  • Surgical removal of the thyroid gland as treatment for thyroid cancer, hyperthyroidism, goitre or cancerous thyroid nodules
  • Inflammation of the thyroid gland (thyroiditis) after a viral illness – this may lead to temporary hypothyroidism
  • Failure of the pituitary gland to release sufficient TSH to stimulate production of the thyroid hormones (rare)
  • Congenital hypothyroidism, a rare condition in infants who are born without thyroid glands or with glands that cannot produce thyroid hormones
  • Pregnancy – may cause a mild hypothyroidism in some women
  • Iodine deficiency in the diet, or an excessive amount of iodine from foods such as seaweed
  • Medications, such as propylthiouracil (PTU) or methimazole, used for treating an overactive thyroid; lithium carbonate, used in the treatment of psychiatric illness; or amiodarone, used for controlling abnormal heart rhythms
  • Inadequate production of thyroid hormones by the thyroid gland, called primary hypothyroidism

Symptoms

The symptoms of hypothyroidism are related to the speed of development and the severity of the condition. People with mild hypothyroidism usually have no symptoms.

Symptoms in adults

The onset of symptoms in adults may be so gradual that it is ascribed to the normal ageing process. These symptoms affect almost all body systems:

  • Physical changes, such as thickened facial features
  • Thick, dry skin, yellowish skin colour
  • Inability to tolerate cold temperatures
  • Husky voice
  • Dry, coarse hair, loss of hair from outer third of eyebrows, loss of hair from scalp
  • Premature greying of hair in young adults
  • Brittle nails
  • Decreased sweating
  • Swelling of arms, legs and feet, and facial puffiness, particularly around the eyes
  • Numb and tingling hands
  • Swelling in the throat (goitre), caused by an enlarged thyroid
  • Changes in the central nervous system
  • Sluggishness or drowsiness
  • Fatigue, sleepiness and weakness
  • Decreased body temperature
  • Depression
  • Memory problems, diminished concentration
  • Hearing problems
  • Slow speech
  • Heart (cardiovascular) changes
  • Increased cholesterol level
  • Slowed heart rate
  • High blood pressure (hypertension)
  • Changes in the digestive system
  • Modest weight gain (3 to 4 kg)
  • Constipation
  • Changes in bone, muscles and joints
  • Weakness
  • Muscle aches and cramps
  • Changes in the reproductive system
  • Heavy or irregular menstrual periods
  • Infertility

 

Symptoms in infants

Severe hypothyroidism in infants causes slow growth and slow mental development. If left untreated, it results in cretinism. The age at which symptoms become apparent and their severity depend on how poorly the baby’s thyroid functions. Symptoms include the following:

  • Poor appetite and choking while nursing
  • Failure to gain weight and slow growth
  • Constipation
  • Breathing difficulties
  • Hoarse cry
  • Sluggishness
  • Enlarged abdomen
  • Cold and mottled skin
  • Swollen genitals, hands and feet

Reviewed by Dr P.H.S. van Zijl, MB.Ch B. MMed(Int).

 
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