Hypothyroidism, also referred to as an underactive thyroid, is the most common disorder of the thyroid gland. Having this condition means that you have too little thyroid hormone circulating in your blood stream, which may make you feel tired or sluggish because every function in your body is slowing down. You also have too much thyroid stimulating hormone, TSH, in your blood because the pituitary gland is releasing more TSH to “stimulate” your thyroid to produce more thyroid hormone
Hashimoto's thyroiditis is the most common cause of hypothyroidism. It is an autoimmune disease in which the body’s immune system, for reasons that are not clearly understood, attacks the thyroid gland and destroys the cells that make thyroid hormone. Your thyroid gland also may be enlarged (goiter) because it is working overtime to try to produce more thyroid hormone.
People with an autoimmune disease, such as Hashimoto's thyroiditis, have a higher risk of developing other autoimmune diseases such as type 1 diabetes or Addison’s disease.
Hypothyroidism also can occur for other reasons: it may develop if your pituitary gland is not working properly or if your body does not have enough iodine to make thyroid hormone. If you have had surgery to remove all or part of your thyroid gland you may become hypothyroid. Additionally, if you are being treated for hyperthyroidism, the treatment may make you hypothyroid.
Another condition, called subclinical hypothyroidism, may be diagnosed when you have elevated levels of thyroid stimulating hormone (TSH) but normal levels of thyroid hormone. The condition can eventually lead to hypothyroidism.
The incidence of hypothyroidism also increases as we age. Untreated, hypothyroidism can lead to serious medical conditions such as hardening of the arteries (atherosclerosis) from high levels of cholesterol. Atherosclerosis is a major cause of heart disease.
Mild hypothyroidism may not cause any symptoms to begin with. Symptoms associated with more severe cases include:
Hypothyroidism is treated with thyroid hormone replacement therapy, which is taken in pill form once a day. Most patients are treated with a form of thyroid hormone called T4 or levothyroxine. Synthroid, Levoxyl, Levothroid and Unithroid are the brands of T4. Some patients also require a different thyroid hormone called T3 or liothyronine. Cytomel is the brand name of T3. An older preparation called desiccated or Armour thyroid is still sometimes used and this contains both T4 and T3.
Once you begin treatment, you will take this therapy for the rest of your life, unless your hypothyroidism is in the setting of subacute thyroiditis. Your doctor will monitor your dosage over the course of your therapy by means of a blood test, and may re-adjust your dose periodically. The goal of treatment is to bring your levels of thyroid hormone (T4) and thyroid stimulating hormone (TSH) into balance.
There is controversy in the medical field about whether or not to treat mild hypothyroidism with daily intake of thyroid hormone, or to carefully monitor the condition by means of an annual blood test. At Virginia Mason Franciscan Health, your doctor may or may not choose to treat your condition but will check your levels of thyroid hormone (T4) and thyroid stimulating hormone (TSH) periodically with a blood test. This is done to ensure that your condition is not worsening.