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Hypothyroidism by Editorial Staff And Contributors

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Definition

Hypothyroidism happens when the thyroid gland does not produce enough thyroid hormone. The thyroid gland is a butterfly-shaped gland in the front of the neck. It produces hormones that control metabolism. The most common form is Hashimoto's thyroiditis.

Thyroid Gland

Causes

Hashimoto's thyroiditis occurs when:

Immune system produces antibodies that attack cells of the thyroid gland, causing chronic thyroid swelling and loss of function
Other causes:
- Idiopathic thyroid atrophy—destruction of thyroid tissue for unknown reasons
- Iodine deficiency—when a thyroid gland needs iodine to produce thyroid hormone (rare in the US)
- Subacute thyroiditis—following a viral upper respiratory tract infection
- Medical treatments— radiation to the head and neck or surgical removal of part of the thyroid gland (called subtotal thyroidectomy )
- Medications (eg, lithium , iodine, alpha-interferons, thiourea, amiodarone , interleukins)
- Certain diseases (eg, cancer or infection)
- Pituitary adenoma —benign tumor of the pituitary gland

Risk Factors

These factors increase your chance of developing hypothyroidism:

Risk factors include:

Age: risk increases with age, especially over 65 years old
Sex: more common in females
Genetics: multiglandular autoimmune syndrome
Ethnicity: Caucasian, Hispanic
History of family members with hypothyroidism
History of other autoimmune diseases:
- Pernicious anemia
- Type 1 diabetes
- Underactive adrenal or parathyroid glands
- Rheumatoid arthritis
- Lupus

Tell your doctor if you have any of these risk factors.

Symptoms

Years may pass before you notice symptoms.

Symptoms include:

Fatigue
Weakness
Coarse, brittle hair; hair loss
Facial puffiness
Dry skin
Swollen hands or feet
Cold intolerance
Weight gain
Constipation
Achy feeling all over
Depression and irritability
Memory loss
Difficulty with concentration
Blurred vision
Menstrual abnormalities or infertility

Symptoms of severe or prolonged cases include:

Stupor or coma
Slow heart rate
Depressed breathing
Hypothermia (low body temperature)
Hoarseness

Diagnosis

The doctor will ask about your symptoms and medical and family history, and perform a physical exam. To confirm the diagnosis, blood tests will be done, which include:

Thyroid stimulating hormone (TSH)
Free T4 and free T3
Antibodies that attack the thyroid gland

Treatment

In the early stages of Hashimoto's thyroiditis, there is no specific treatment. But, in most cases, you will end up developing hypothyroidism. Treatment includes:

Medication to replace the thyroid hormones (eg, levothyroxine , triiodothyronine)
High-fiber diet to reduce constipation
Low-fat , low-calorie diet if you are overweight or obese

Prevention

To help reduce your chance of getting hypothyroidism, take the following steps:

Get a screening test every five years if you are 50 years old or older.
Get regular screenings if you:
- Have Type 1 diabetes
- Have infertility (females)
- Take certain medications

RESOURCES:

The American Thyroid Association http://www.thyroid.org/
Women's Health.gov http://womenshealth.gov/

CANADIAN RESOURCES:

Canadian Institute for Health http://www.cihi.ca/
Thyroid Foundation of Canada http://www.thyroid.ca/

References:

American Association of Clinical Endocrinologists. AACE medical guidelines for clinical practice for the evaluation and treatment of hyperthyroidism and hypothyroidism. Endocrine Practice . 2002;8:457-469.
Braunwald E. Harrison's Principles of Internal Medicine. 15th ed. New York, NY: McGraw Hill; 2001.
Escobar-Morreale HF, Botella-Carretero JI, Escobar del Rey F, et al. Treatment of hypothyroidism with combinations of levothyroxine plus liothyronine. J Clin Endocrinol Metab . 2005;90:4946-4954.
Hypothyroidism. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/what.php . Updated June 2008. Accessed July 7, 2008
Roberts CG, Ladenson PW. Hypothyroidism. Lancet . 2004;363:793-803.
Surks MI, Ortiz E, Daniels GH, et al. Subclinical thyroid disease: scientific review and guidelines for diagnosis and management JAMA . 2004;291:228-238.

Last reviewed September 2009 by Bridget Sinnott, MD, FACE

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