Hyperthyroidism

Definition

Hyperthyroidism, also known as overactive thyroid, is defined as a condition in which the thyroid gland produces and releases abnormally high amounts of thyroid hormones. The thyroid gland produces two important hormones – T3 (triiodothyronine) and T4 (thyroxine). The pituitary gland in the brain stimulates the production of thyroid hormones by releasing a hormone known as the thyroid stimulating hormone (TSH). In this way the levels of the thyroid hormones are kept within a normal range.

Thyroid hormones play an important role in the overall regulation of metabolism (chemical processes by which cells use substances in food to produce energy and compounds useful to the body). Therefore, too little or too much of thyroid hormones disrupt the normal balance of metabolic processes in the body. Hyperthyroidism results in an overactive metabolism which has far reaching consequences on almost every organ and system in the body. If severe and untreated, it can even have life threatening consequences.

Symptoms

Regardless of the cause of hyperthyroidism, the symptoms of hyperthyroidism remain the same. The following are the common symptoms of hyperthyroidism:

  • Warm and moist skin
  • Fast and irregular heartbeats
  • Forceful thumping of the heart that is felt by the patient
  • Fatigue
  • Weight loss despite increased appetite
  • Nervousness, restlessness and increased activity
  • Tremors
  • Enlargement of thyroid gland in the neck (goiter)
  • Inability to tolerate heat
  • Increased sweating
  • Inability to sleep (insomnia)
  • Diarrhea
  • Lack of menstruation in women
  • Depression or dementia-like symptoms in elderly patients
  • Large staring eyes due to bulging eyeballs and eyelid retraction

The exact diagnosis of hyperthyroidism requires measurement of the levels of thyroid hormones (T3 and T4) and thyroid stimulating hormone (TSH) in the blood.

Causes

Many factors can cause hyperthyroidism by stimulating excessive production of thyroid hormones. The following are some of the causative factors:

  • Graves disease is an autoimmune disorder that leads to an overactive thyroid gland. It is the most common cause of hyperthyroidism.
  • Thyroiditis or inflammation of thyroid gland can result in excessive release of stored thyroid hormones.
  • Mutations in the gene for TSH receptor could lead to continuous stimulation of the thyroid gland and excessive production of thyroid hormones.
  • A tumor of the pituitary gland could result in excessive production of TSH, which then stimulates the thyroid gland to synthesize excessive thyroid hormones.
  • Iodine is an important component of the thyroid hormones. Therefore, too much iodine in the body (e.g., from iodine containing drugs) could lead to hyperthyroidism.
  • A molar pregnancy (abnormal growth of placental tissue during pregnancy) produces an abnormal hCG hormone that could over stimulate the thyroid gland.
  • Some drugs (amiodarone, interferon alpha) may cause inflammation of thyroid gland and hyperthyroidism.
  • Tumors of the thyroid gland could also result in overproduction of thyroid hormones.

Treatment

Treatment of hyperthyroidism is aimed at treating the cause of the condition. Following are the treatment options:

  • Anti-thyroid medications (methimazole, carbimazole, propylthiouracil, dexamethasone) are given to prevent either the formation of thyroid hormones or the conversion of inactive thyroid hormones into active forms.
  • Beta-blockers (propanolol, atenolol, metoprolol) are used to normalize heart functions.
  • Iodine can be given to stop the release of thyroid hormones.
  • Radioactive iodine can be given to destroy the thyroid gland (e.g, in Graves disease).
  • Surgical removal of thyroid gland is the last option in case the other treatments do not work.

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