Hypothyroidism
Signs & Symptoms
Hypothyroidism describes an underactive thyroid gland that is producing depressed levels of thyroid hormone ("hypo" means less than normal). Hypothyroidism affects nearly 2 percent of the population, but is much more commonly found among certain groups. For instance, women are more likely to exhibit hypothyroidism than men, and incidence increases as people age. Hypothyroid patients may experience a variety of symptoms, including weight gain, intolerance to cold, goiter (enlarged thyroid), dry coarse skin, fatigue, constipation, slowed heart rate, poor memory or depression.
The most common cause of hypothyroidism is Hashimoto's Thyroiditis, an autoimmune thyroid disease in which the body develops autoantibodies that attack and destroy thyroid tissue. The damaged thyroid is thus unable to produce adequate amounts of thyroid hormone and the individual becomes hypothyroid. Hypothyroidism is also the end result of treatments for hyperthyroidism (as in Grave's Disease or thyroid cancer) where therapy involves surgical removal or ablation of the thyroid with radioactive I131. Other causes include congenital hypothyroidism, in which a child is born without a thyroid gland; one out of every 4,000 children are affected. Also, a transient condition known as postpartum thyroiditis causes hypothyroidism in women within the 12 months following the birth of a child. An estimated 5 percent to percent of all pregnant women will develop postpartum thyroiditis. The state of depression often nicknamed "postpartum blues" may in fact be a result of abnormal thyroid function in these women.
Diagnosis of hypothyroidism involves testing a patient's TSH and T4 levels. Both overt and subclinical hypothyroid patients exhibit an elevated TSH concentration in the blood. Overt hypothyroid patients will additionally exhibit a low FT4 level, while normal FT4 values are characteristic of subclinical hypothyroid patients. While overt hypothyroidism affects 1 to 2 percent of the population, incidence of subclinical hypothyroidism are more common. It has been estimated that 10 percent of the general population and 20 percent of older women suffer from subclinical hypothyroidism. Often this condition goes undetected as the symptoms are often vague and nonspecific. Tests for the presence of autoantibodies may also be used to distinguish autoimmune disorders like Hashimoto's thyroiditis.
Hypothyroidism treatment involves thyroid hormone replacement therapy with levothyroxine for the life of the patient.
During development of hypothyroidism, serum TSH is the optimal test for diagnosing and assessing all phases of disease. A FT4E test can help quantitate the severity of the disease. Following initiation of T4 replacement therapy or a change in T4 dosage, normalization of serum T4 can be achieved within weeks. A FT4E test will most accurately reflect the efficacy of the T4 replacement therapy during the acute phase of treatment. Serum TSH is misleadingly high in this phase because of the lag in the pituitary reset of TSH secretion. Serum TSH again becomes the optimal test for reflecting the thyroid status when equilibrium returns (usually six to eight weeks after initiating T4 therapy).
For More Information
- American Thyroid Association
- Thyroid Foundation of Canada
- National Graves' Disease Foundation
- Gland Central
- American Association of Clinical Chemistry (Clinical Chemistry Journal)
- The Endocrine Society
- CLIANet (Clinical Laboratory Improvement Amendments)
- NCCLS (National Committee for Clinical Laboratory Standards)
