Definition
Hypothyroidism is thyroid hormone deficiency. It can be due to primary disease of the thyroid gland itself or to the lack of stimulation of the thyroid gland by the pituitary gland via the hormone TSH (thyroid-stimulating hormone).
Hypothyroidism overwhelmingly afflicts women, (four times more often than men), especially those women between the ages of 35 and 60.
Description
The thyroid gland is located in the front of the neck, just below the larynx (voice box). It helps to maintain a healthy metabolism (the process by which foods are transformed into basic elements to be utilized by the body for energy or growth) by producing and releasing iodine-containing hormones called thyroxine (T4) and triiodothyronine (T3). They help regulate the body's growth, metabolism, digestion, body temperature and heartbeat.
In most people, hypothyroidism is neither chronic nor progressive. However, two conditions arise from untreated or undiagnosed hypothyroidism; myxedema coma and_cretinism_.
Myxedema coma usually develops slowly and may arise suddenly if provoked by sedatives, narcotics, illness, exposure to cold, an accident, injury or surgery. The symptoms and signs of myxedema coma include stupor, abnormally slow and shallow breathing, low levels of sodium and sugar in the blood, low blood pressure and a reduced body temperature.
Myxedema coma is an emergency situation and requires prompt medical treatment with hormone injections (to increase thyroid function, oxygen and respiratory support for the slow and shallow breathing), hydrocortisone (for the low blood pressure), fluid replacement, and antibiotics for infection.
Cretinism is caused by a decreased production of T4 and results in mental retardation, stunted growth and coarse facial features. The signs of cretinism are constant drooling, a swayback, a potbelly, short stature, and irregularly placed and poorly formed teeth. If this condition is diagnosed within the first several months of life (standard newborn tests should reveal low thyroid levels), the chances of normal development are excellent.
Causes
Insufficient thyroid hormone production can be caused by:
- thyroid gland dysfunction resulting from surgery (post-thyroidectomy)
- radiation therapy (particularly with radioactive iodine)
- inflammation
- autoimmune disease call Hashimoto's disease, in which the body's immune system develops antibodies against its own thyroid gland cells
- failure of the pituitary gland to produce thyroid-stimulating hormone (TSH). TSH is a product of the pituitary gland that stimulates the thyroid gland to produce its hormones (T3 and T4). The circulating levels of these hormones in turn control how much TSH the pituitary gland secretes.
- failure of the hypothalamus to produce thyrotropin-releasing hormone (TRH). TRH is the hormone that controls the production of TSH.
- congenital errors of thyroid hormone synthesis
- iodine deficiency
- use of anti-thyroid medications
A person may be susceptible or at risk for thyroid problems if they have the following risk factors:
- woman age 50 and over
- man age 60 and over
- family history of thyroid problems
- autoimmune disease such as diabetes, rheumatoid arthritis or lupus.
- thyroid surgery
- has had or is currently undergoing radiation therapy (particularly with radioactive iodine)
- taking medications containing iodine or lithium, or amiodarone (Cordarone)
- high cholesterol
Symptoms
Hypothyroidism usually comes on gradually, over several months or years. The early clues may be scarcely noticeable or may be attributed to other causes. Symptoms may include:
- low energy, constant tiredness
- depression
- dizziness
- weight gain, despite diminished appetite
- intolerance to cold
- inability to concentrate, memory lapses
- constipation
- slowed heart rate
- raised blood cholesterol
- muscle weakness, cramps
- goiter (enlarged thyroid)
- anemia
- menstrual irregularities
- ankle swelling
- hair loss (especially eyebrows)
- dry scaly skin and brittle nails
- hoarse voice
- puffy face, hands, and feet
- swelling around the eyes
- droopy eyelids
- swollen abdomen
- decreased sex drive
- infertility
- impaired coordination
Diagnosis
After a complete medical history and physical examination, the physician will probably order blood tests. A low T4 and a high TSH indicates hypothyroidism. Some patients beginning to experience thyroid failure may only show an increase in TSH. Other blood tests may be done as well.
Treatment
Since hypothyroidism develops from a shortage of thyroid hormone, the most effective treatment is generally thyroid hormone supplementation.
Supplements are either natural hormones extracted from the thyroid glands of animals or synthetic hormones (such as levothyroxine). Both types control the problem, but the newer, synthetic forms are much more efficient and their effects are more easily regulated.
Although treatment provides the necessary hormone control, hypothyroidism often continues throughout life, and the patient may require lifelong follow-up and medication to control the condition.
Although many people benefit from thyroid hormone therapy, not everyone with hypothyroidism needs therapy. Some elderly people are plagued by diseases that are made worse by this therapy. Additionally, postmenopausal women who take large doses of thyroid hormones may be at risk for accelerated bone loss.
If the thyroid hormone therapy is no longer sufficient, several possible explanations must be considered. One is that the degree of thyroid failure may have worsened. Or, it may be that another drug is blocking absorption of the thyroid hormone. Iron, for example, interferes with absorption even at doses found in multivitamins. Thyroid hormone may be broken down faster in the presence of drugs such as dilantin, tegretol and rifampin.