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Hypothyroidism - Overview

Alternative Names

Myxedema; Adult hypothyroidism

Definition of Hypothyroidism:

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

Causes, incidence, and risk factors:

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

Reviewed last on: 6/17/2008
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.

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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