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Hyperthyroidism

What Causes Hyperthyroidism?

Last modified: 
21/04/2013 - 17:33

Contributing Author: Guy Slowik FRCS

These are two major causes of hyperthyroidism.

  • About 95 percent of persons diagnosed with hyperthyroidism are found to have a condition called Graves' disease.
  • Most of the remaining persons have a condition called nodular thyroid disease.
  • A less frequent cause is inflammation of the thyroid gland, called thyroiditis
  • Uncommon causes include hormone producing tumors of the pituitary gland or ovary and iodine-induced hyperthyroidism from iodine-containing drugs

What Is Graves' disease?

Graves' disease is a condition resulting from a problem in the body's immune system.

The immune system is a complex network that normally defends the body against "invading" organisms and other foreign substances. When the immune system detects a foreign substance in the body, it responds to this by producing antibodies against the invaders. These antibodies will recognize and attack this foreign substance when they next encounter it.

In Graves' disease the immune system mistakenly directs an immune "attack" against its own healthy cells. Antibodies are manufactured and misdirected against the thyroid gland, mimicking the action of the hormone from the brain (thyroid stimulating hormone) that normally controls the thyroid function. These antibodies act like a switch put into a permanent "on" position. Thyroid cells are continually stimulated to produce and release thyroid hormone, even after blood levels are already high.

Any condition in which the body's immune system attacks its own cells is called an autoimmune disease.

Graves' disease is more frequent in women than in men. The symptoms of Graves' disease may begin at any age but those between the ages of 20 and 40 are more likely to develop this condition.

What Happens With Graves' Disease?

With time, the over stimulated thyroid becomes generally enlarged and may eventually become noticeable to the affected person or others as a swelling in the front of the neck. In addition, in some people Graves' disease may be associated with particular eye and skin changes.

The eye changes are called hyperthyroid eye disease and occur in about 30 percent of people with Graves' disease. These changes are visible as protruding eyes. There is no relationship between the appearance of eye changes and the severity of the hyperthyroidism. There is increased risk for infection and visual problems in persons with severe hyperthyroid eye disease.

Eye disease is most likely to progress in people who fit a certain profile. This includes those:

  • Whose hyperthyroidism is not promptly corrected and controlled
  • Whose thyroid hormone level is not within normal limits
  • Who smoke cigarettes

The autoimmune process that causes hyperthyroid eye disease is poorly understood. Doctors do understand what causes the swelling of tissues behind the eyeball, decreased range of motion of the muscles around the eyeball, and retraction (a pulling back) of the eyelids.

Common symptoms include pain, excessive tearing, increased sensitivity to light, blurred vision, double vision, or protrusion of the eyes from the face.

The most common skin problem associated with Graves' disease is called pretibial myxedema, which is characterized by swollen patches of skin on the front of the lower legs. This skin change is found in about five percent of persons with Graves' disease. These patches itch and become bothersome; usually no other symptoms or problems are associated with them. Doctors evaluating a patient with possible hyperthyroidism check for pretibial myxedema because it is almost never found in persons who do not have Graves' disease.

What Is Nodular Thyroid Disease?

Nodular thyroid disease is unlike Graves' disease in five important ways:

  • Nodular disease is much less common.
  • The cause is not known.
  • It tends to develop in persons older than those who develop Graves' disease.
  • The disease process is not found throughout the thyroid gland.
  • No particular problems outside the thyroid, such as eye or skin disease, are seen with nodular thyroid disease.

When a physical exam is done, the thyroid is usually enlarged and painless. As untreated disease progresses, distinct nodules (lumps) may be felt with the fingertips. Within the thyroid gland, nodules of abnormal thyroid cells are visible among areas of normal cells. This patter of nodular disease is seen as spots of over activity on radioactive iodine uptake scanning.

Is Hyperthyroidism Genetic?

Certain genetic factors may make someone more likely to develop an autoimmune disorder. It is not uncommon for individuals with Graves' disease to develop other autoimmune conditions including:

  • Hashimoto's thyroiditis, a thyroid condition that results in an unusually low thyroid hormone level
  • Pernicious anemia

Nice To Know:

The fact that there is a genetic basis for Graves' disease means that more than one member of a family may develop it. When one person is diagnosed with Graves' disease, other family members should have their thyroid function checked by their doctors.

 

 
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Hyperthyroidism

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From Andrew Maynard - Chair of the University of Michigan Department of Environmental Health Sciences, with help from David Faulkner - 2013 Master of Public Health graduate.