Hypothyroidism, or low thyroid activity, occurs when the thyroid, a gland in the neck that controls body growth and metabolism, produces insufficient amounts of thyroid hormone, thereby slowing all metabolic processes in the body.

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Symptoms depend on the degree of thyroid deficiency and may develop slowly over many years. (When full-blown symptoms do occur, the condition is known as myxedema.) Although hypothyroidism can occur at any age and in both sexes, it is most common in women over age 50.

The disorder can be completely controlled with proper treatment. In rare cases, however, severe untreated hypothyroidism may result in myxedema coma, a life-threatening condition that may be precipitated by illness, sedatives, cold weather, surgery, or injury. Untreated hypothyroidism occurring during infancy results in mental retardation and dwarfism (cretinism).

What Causes Hypothyroidism?

  • Hypothyroidism is frequently due to an autoimmune disorder (such as Hashimoto’s disease), wherein the body’s natural defenses against infection mistakenly attack healthy tissue (in this case, the thyroid).
  • Hypothyroidism may also occur when the pituitary gland, located at the base of the brain, fails to produce sufficient quantities of thyroid-stimulating hormone (TSH), a regulator of the thyroid gland. (Paradoxically, when hypothyroidism is caused by a defect in the thyroid gland itself, the pituitary releases increased quantities of TSH in an attempt to compensate for low levels of thyroid hormone.)
  • The disorder may occur following surgical removal of the thyroid gland to treat hyperthyroidism or thyroid cancer.
  • Medical treatments for hyperthyroidism may cause hypothyroidism. Radioactive iodine treatment results in permanent hypothyroidism in more than 50 percent of patients; hypothyroidism due to antithyroid drugs persists only for as long as the drugs are taken.
  • Certain drugs such as lithium can interfere with thyroid function.
  • In rare cases, an insufficient dietary intake of iodine may cause hypothyroidism.
  • Infants may be born with thyroid defects.
  • Rare disorders such as amyloidosis, sarcoidosis and hemochromatosis can deposit substances in the thyroid that results in hypothyroidism.
  • In women, hypothyroidism may develop during and after pregnancy.
  • Risk of hypothyroidism is greater in women age 50 and over.
  • Risk of hypothyroidism in greater in men age 60 and over.

Symptoms of Hypothyroidism

  • Fatigue, lethargy, and slowed movement
  • Intolerance to cold
  • Unusual weight gain
  • Constipation
  • Dry, thickened, flaky skin
  • Muscle cramps and weakness
  • Deepened voice
  • Lack of interest in sex
  • Possibly, goiter (swelling in the neck).
  • Unusually heavy, prolonged menstrual periods
  • Puffiness around the eyes
  • Dry, brittle hair or hair loss
  • Impaired mental faculties
  • High blood cholesterol
  • Weight gain
  • Depression

Hypothyroidism Prevention

  • There is no known way to prevent hypothyroidism, although diagnostic screening allows for early detection and treatment in those at risk for congenital hypothyroidism.
  • If you have hypothyroidism, it is advisable that you inform your family members. Hypothyroidism is a hereditary disease. You should encourage them to have a regular TSH test for early detection and treatment.

Hypothyroidism Diagnosis

  • Patient history and physical examination are needed. Slowed heart and pulse rates, low systolic blood pressure (the higher number), and low body temperature suggest hypothyroidism.
  • Blood tests are taken to determine levels of thyroid hormone and TSH. (Measuring TSH is the most sensitive test for hypothyroidism due to disease of the thyroid gland. TSH is not accurate when hypothyroidism is caused by disease of the pituitary gland.)

How Hypothyroidism Is Treated

  • Lifelong hormone replacement therapy with thyroid hormone (thyroxine) is usually necessary. The lowest effective dose is determined and then maintained. (In the elderly and those with coronary artery disease, hormone replacement is started with a small dose and gradually increased. It is controversial whether to initiate such therapy at all in those with slightly elevated TSH but no symptoms.)
  • If a large goiter causes breathing or swallowing difficulty, surgical removal may be required.
  • Hospitalization is necessary for treatment of myxedema coma. Intravenous thyroid hormone replacement, as well as steroid therapy, will usually be administered. In addition, oxygen, artificial respiration, fluid replacement, and other intensive care measures may be warranted.
  • Medications like the synthetic thyroid hormone pill can regulate your hormone levels and shift your metabolism back to normal.

When to Call a Doctor

  • If you experience the symptoms of hypothyroidism, consult a doctor as soon as possible.


Johns Hopkins Symptoms and Remedies: The Complete Home Medical Reference

Simeon Margolis, M.D., Ph.D., Medical Editor

Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 13 Oct 2011

Last Modified: 19 Feb 2015