Definition

Hypothyroidism is a disease in which 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. Hashimoto's thyroiditis is the most common cause of hypothyroidism.

	Thyroid Gland
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Causes

Hashimoto's thyroiditis is an autoimmune disease. Your own immune system creates antibodies that attack the cells of the thyroid gland. This causes chronic thyroid inflammation and loss of thyroid function. Other causes of hypothyroidism include:

• 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 neck or surgical removal of part of the thyroid gland (called subtotal thyroidectomy)
• Medications (lithium, iodine, alpha-interferons, thiourea, amiodarone, interleukins)
• Infiltrative disease (eg, cancer or infection)
• Pituitary adenoma —benign tumor of the pituitary gland

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition.

Risk factors include:

• Age: risk increases with age, especially over 65 years old
• Sex: female, with a female to male ratio of 5-10:1
• 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

Symptoms

Symptoms develop gradually and may go unnoticed for years.

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. Blood tests will be done to confirm the diagnosis, which include thyroid stimulating hormone (TSH), free T4 and free T3, and antibodies that attack the thyroid gland.

Treatment

In the early stages of Hashimoto's thyroiditis, there is no specific treatment. However, most people with this condition eventually develop hypothyroidism. At that point, you will need to start taking medication (levothyroxine and/or triiodothyronine) that replaces the thyroid hormones. You will have to take this medication indefinitely.

To reduce the discomfort from constipation, you will be asked to eat a high-fiber diet. If you are overweight or obese , you will be given a low-fat, low-calorie diet.

Prevention

If you are 50 years old or older, you should have a screening test (TSH) every five years.

You should be screened regularly if you have the following risk factors:

• Type 1 diabetes
• Infertility (females)
• Depression
• Treatment with 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/cihiweb/dispPage.jsp?cw_page=home_e

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.

Escobar-Morreale HF, Botella-Carretero JI, Escobar del Rey F, et al. Treatment of hypothyroidism with combinations of levothyroxine plus liothyronine. J Clin Endorinol Metab . 2005;90:4946-4954.

Harrison's Principles of Internal Medicine. 15th ed. McGraw Hill; 2001.

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.

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