Health Illustrated Encyclopedia

Hypothyroidism

Definition

Hypothyroidism is a condition in which the thyroid gland fails to produce enough thyroid hormone.

Alternative Names

Myxedema; Adult hypothyroidism

Causes

The thyroid gland is located in the front of the neck just below the voice box (larynx). It releases hormones that control metabolism. These hormones are thyroxine (T4) and triiodothyronine (T3).

The release of T3 and T4 is controlled by the pituitary gland and the hypothalamus in the brain. Thyroid disorders may be caused by defects in the thyroid gland itself. They may also be caused by abnormalities of the pituitary or hypothalamus.

An underactive thyroid gland (hypothyroidism) may affect all body functions. The most severe form, called myxedema coma, is a medical emergency.

The most common cause of hypothyroidism is Hashimoto's thyroiditis, in which the immune system attacks the thyroid gland. A less common cause of hypothyroidism is when the pituitary gland does not release a hormone to stimulate the thyroid gland (secondary hypothyroidism).

Other causes include:

  • Congenital (birth) defects
  • Inflammatory conditions
  • Radiation to the gland
  • Surgical removal of the thyroid gland

Risk factors include:

  • Age over 50 years
  • Exposure of the neck to x-ray or radiation treatments
  • Female gender
  • Obesity
  • Thyroid surgery

Symptoms

Early symptoms:

Late symptoms:

Other symptoms that can occur with this disease:

Exams and Tests

A physical examination will show:

A chest x-ray may show an enlarged heart.

Laboratory tests to determine thyroid function include:

Other findings on lab tests may include:

Treatment

The purpose of treatment is to replace the thyroid hormone that is lacking. Levothyroxine is the most commonly used medication. Doctors will prescribe the lowest dose that effectively relieves symptoms and brings the TSH level to a normal range.

Patients will need lifelong therapy. You must continue taking your medication even when your symptoms go away. After the medication dose is determined, your thyroid hormone levels should be monitored every year.

After you have begun taking replacement therapy, report to your health care provider any symptoms of increased thyroid activity (hyperthyroidism) such as:

  • Rapid weight loss
  • Restlessness
  • Sweating

Myxedema coma is a medical emergency that occurs when the body's level of thyroid hormones becomes extremely low. It is treated with intravenous thyroid hormone replacement and steroid medications. Some patients may need supportive therapy (oxygen, breathing assistance, fluid replacement) and intensive-care nursing.

Outlook (Prognosis)

With treatment, most people will return to normal. However, you will need to take medication for the rest of your life.

Myxedema coma can result in death.

Possible Complications

Myxedema coma, the most severe form of hypothyroidism, is rare. It may be caused by an infection, illness, exposure to cold, or certain medications in people with untreated hypothyroidism.

Symptoms and signs of myxedema coma include:

Other complications are:

When to Contact a Medical Professional

Call your health care provider if:

  • You have symptoms of hypothyroidism (or myxedema)
  • You develop chest pain or rapid heartbeat
  • You have an infection
  • Your symptoms get worse or do not improve with treatment
  • You develop new symptoms

Prevention

There is no prevention for hypothyroidism. However, screening tests in newborns can detect congenital hypothyroidism.

References

AACE Thyroid Task Force. American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for the Evaluation and Treatment Of Hyperthyroidism and Hypothyroidism. Endocr Pract. 2002;8 (6).

Ladenson P, Kim M. Thyroid. In: Goldman L and Ausiello D, eds. Goldman: Cecil Medicine. 23rd ed. Philadelphia, Pa:Saunders; 2007:chap 244.


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Review Date: 6/17/2008
Reviewed By: Elizabeth H. Holt, MD, PhD, Assistant Professor of Medicine, Section of Endocrinology and Metabolism, Yale University. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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