When a person has an underactive thyroid, or hypothyroidism, her thyroid does not produce enough of the thyroid hormones — triiodothyronine (T-3) and thyroxine (T-4) — which are involved in metabolism. While both men and women can have an underactive thyroid, women who are over age 50 are more likely to have the condition, according to the MayoClinic.com.
Several conditions can cause an underactive thyroid. MedlinePlus noted that the most common cause is an inflammation of the thyroid gland. When the thyroid becomes inflamed, its cells become damaged.
The autoimmune disorder, known as Hashimoto’s disease, may cause hypothyroidism, as the immune system mistakes the patient’s thyroid gland as a foreign object and attacks it. About 0.1 to 5 percent of adults in Western countries have this form of chronic thyroiditis, according to MedlinePlus.
Some medications may cause hypothyroidism. Medications that treat hyperthyroidism, or an overactive thyroid, such as methimazole or propylthiouracil, may cause hypothyroidism.
Lithium, a psychiatric medication used to treat disorders such as bipolar disorder, may affect thyroid function. Patients who take amiodarone may develop hypothyroidism.
Other forms of treatment may cause an underactive thyroid, such as radiation therapy or thyroid surgery. Patients who suspect their medications have contributed to an underactive thyroid should talk to their doctors and should not alter their medication unless under the direction of a doctor.
After pregnancy, some women may develop hypothyroidism. If the symptoms of hypothyroidism occur after a women became pregnant, it is called postpartum thyroiditis. Sheehan syndrome may also cause an underactive thyroid, noted MedlinePlus.
With Sheehan syndrome, a woman bleeds severely either during her pregnancy or during childbirth. This severe bleeding damages the pituitary gland, affecting its normal functioning. The pituitary gland is involved in thyroid gland function, so damage to the pituitary gland affects thyroid function.
A congenital defect may affect normal thyroid function. The MayoClinic.com stated that about one in 3,000 babies in the United States are born with either no thyroid gland or a defective gland.
While rare, hypothyroidism may result from a pituitary gland disorder, in which the gland does not produce enough thyroid-stimulating hormone, or TSH. This type of pituitary gland disorder may occur if a patient has a benign tumor on her pituitary gland.
Other causes of an underactive thyroid include an iodine deficiency and viral thyroiditis, in which the patient has hyperthyroidism then temporary or permanent hypothyroidism.
References
MedlinePlus Medical Encyclopedia. Chronic Thyroiditis (Hashimoto’s Disease). Web. 2 January 2012
http://www.nlm.nih.gov/medlineplus/ency/article/000371.htm
MedlinePlus Medical Encyclopedia. Sheehan Syndrome. Web. 2 January 2012
http://www.nlm.nih.gov/medlineplus/ency/article/001175.htm
MedlinePlus Medical Encyclopedia. Hypothyroidism. Web. 2 January 2012
http://www.nlm.nih.gov/medlineplus/ency/article/000353.htm
MayoClinic.com. Hypothyroidism Web. 2 January 2012
http://www.mayoclinic.com/health/hypothyroidism/DS00353/METHOD=print&DSECTION=all
Reviewed January 2, 2012
by Michele Blacksberg RN
Edited by Jody Smith