In hypothyroidism, also known as myxoedema, the thyroid gland does not produce enough thyroid hormones. These hormones are important in regulating the body’s metabolism. A deficiency causes a slowing down of many of the body’s functions.

Hypothyroidism is more common in women, particularly over age 40, and runs in families.

Causes of Hypothyroidism

  1. A common cause of hypothyroidism is thyroiditis. The most common type of thyroiditis leading to hypothyroidism is an autoimmune disorder known as Hashimoto’s thyroiditis, in which the body produces antibodies that attack the thyroid gland, damaging it permanendy. Other forms of thyroiditis may lead to temporary or permanent hypothyroidism. Thyroiditis occurs in women after the birth of a baby in about 10 percent of cases, but is usually a temporary condition.
  2. Treatments for an overactive thyroid gland that involve radioactive iodine or surgery can also lead to permanent hypothyroidism. These treat¬ments destroy part of the gland, and the tissue that remains may not produce sufficient hormones.
  3. Insufficient dietary iodine, which is essential for the production of thyroid hormones, can cause hypothyroidism but is rare in developed countries.
  4. In rare cases, hypothyroidism is due to the pituitary gland releasing insufficient amounts of thyroid-stimulating hormone (TSH), which stimulates the thyroid gland to secrete its own hormones. The underproduction of TSH is often due to a pituitary tumour.

Symptoms of Hypothyroidism

The symptoms of hypothyroidism vary in severity, usually develop slowly over months or years and may initially go unnoticed. Symptoms include:

  • fatigue, which may make even minimal physical activity difficult
  • weight gain
  • constipation
  • hoarseness of the voice
  • intolerance to cold
  • swelling of the face and puffy eyes
  • generalized hair thinning
  • in women, heavy menstrual periods.

Some people with hypothyroidism develop a swelling in the neck (a goitre) due to an enlarged thyroid.

Measures of Hypothyroidism

Your doctor may arrange for you to have blood tests to measure the levels of thyroid hormones and to check for antibodies that act against the thyroid gland.

Treatment of Hypothyroidism

Treatment is aimed at the underlying cause. Permanent hypothyroidism may be treated with replacement synthetic thyroid hormones, which you will need to take for life. The symptoms should begin to improve about three weeks after drug treatment starts. Hormone treatment must be monitored regularly to ensure that the correct dosage is maintained.

If a pituitary tumour is the cause, further tests will be done and the tumour may be removed surgically or treated with radiotherapy. Temporary hypothyroidism does not usually need to be treated, but short-term hormone replacement may be given in some cases, for instance if thyroiditis occurs after birth. A deficiency in dietary iodine can be treated with supplements or an improved diet.