The thyroid is a butterfly-shaped gland at the base of the front of the neck. This gland is responsible for producing the hormones triiodothyronine (T3) and thyroxine (T4). When the thyroid gland doesn't produce enough of these hormones, it's known as hypothyroidism. Hypothyroidism can be caused by several drugs and medical conditions but can usually be treated with medications to relieve symptoms.
Causes
Hashimoto's thyroiditis is the most common cause of an underactive thyroid. This disease causes antibodies to attack the thyroid gland, which disrupts production of T3 and T4. People who are treated for hyperthyroidism (overactive thyroid gland) may experience hypothyroidism if they get too much medication or radiation. Radiation therapy for head and neck cancers can cause the thyroid gland to stop producing enough thyroid hormone. If part of the thyroid is removed or a large part is removed, hormone production can be reduced or stopped completely. Medications such as lithium are also one of the more common causes of this condition. Less common causes of hypothyroidism include iodine deficiency, birth defects, disorders of the pituitary gland and pregnancy.
Risk Factors
The presence of several risk factors can increase the likelihood that someone will develop hypothyroidism. Having a close relative with an autoimmune disease increases the risk of underactive thyroid. Having thyroid surgery or getting treatment with radioactive iodine, radiation therapy and anti-thyroid medications also increases the risk of developing hypothyroidism.
Signs & Symptoms
Signs and symptoms of hypothyroidism include decreased libido, memory loss, depression, muscle cramps, frequent muscle aches, hair loss, coarse hair, weakness, fatigue, weight gain, difficulty losing weight, dry skin, intolerance to cold temperatures, constipation, abnormal menstrual cycles and irritability.
Diagnosis
Hypothyroidism is diagnosed with blood tests that check the levels of thyroid-stimulating hormone (TSH), T3 and T4. If the TSH level is high and the T4 level is low, it means the thyroid gland is underactive. High levels of TSH indicate that the pituitary gland is producing more TSH to stimulate the thyroid gland into producing more T3 and T4. It's possible that someone can have normal levels of T- and T4 and elevated levels of TSH. This is known as subclinical hypothyroidism. It usually produces no outward signs or symptoms.
Treatment
Hypothyroidism can be treated with daily use of a drug known as levothyroxine. Levothyroxine is a synthetic thyroid hormone that reduces hormone levels and eliminates the symptoms of hypothyroidism. After two to three months of treatment, your thyroid hormone levels are checked to determine if your dose of levothyroxine should be adjusted. If the dose is too high, you may experience insomnia, heart palpitations, increased appetite and shakiness. After the correct dosage of levothyroxine has been determined, your thyroid hormone levels are checked annually. Do not take iron supplements, calcium supplements, aluminum hydroxide or cholestyramine without talking to your doctor, as these drugs can interfere with the absorption of levothyroxine.
Complications
If hypothyroidism remains untreated, it can lead to other health problems. When the thyroid gland is constantly stimulated, it can become larger, which is known as goiter. Though goiter doesn't usually cause pain, it can make it difficult to breathe or swallow normally and may also affect your appearance. Hypothyroidism also affects the heart. People with this condition may have high levels of low-density lipoprotein ("bad" cholesterol) or increased total cholesterol levels. Hypothyroidism can also impair the heart's ability to pump blood and cause heart failure or an enlarged heart. Myxedema, a life-threatening condition, can also occur with untreated hypothyroidism. This condition causes drowsiness and cold intolerance, followed by intense lethargy and unconsciousness. Untreated hypothyroidism can also lead to depression, infertility, slowed mental function and birth defects.
