There are 3 categories of hypothyroidism – primary, secondary and tertiary. The categorization relates to how ‘far’ up the HPT (hypothalamic/pituitary/thyroid) axis the problem causing the under active thyroid is located.
- Primary hypothyroidism is when the issue is in the thyroid gland itself.
- Secondary hypothyroidism is when the problem lies in the pituitary gland and
- Tertiary hypothyroidism stems from the hypothalamus. Secondary and tertiary hypothyroidism are also referred to as central hypothyroidism and you’ll often see tertiary hypothyroidism referred to as secondary hypothyroidism too.
Causes Of Secondary Hypothyroidism
The pituitary gland is responsible for secreting a hormone called thyroid stimulating hormone (TSH). This hormone regulates thyroid hormone production. Secondary hypothyroidism occurs when the pituitary gland fails to produce enough TSH. The most common cause is a pituitary tumor or adenoma (benign tumor). However it can also be caused by:
- hemochromotosis – inherited iron disorder that causes the body, including the pituitary, to absorb too much iron
- other congenital or genetic defects in the pituitary that interfere with its function
- inflammation of the pituitary gland
- Sheehan’s syndrome
- some types of drugs
Risk Factors For Secondary Hypothyroidism
The predominant risk factors for secondary hypothyroidism include:
- gender – females are more likely to develop it
- age – people over the age of 50 are at higher risk
- medical history – people with a history of pituitary and/or hypothalamic problems are more prone to develop secondary hypothyroidism
However neither males nor females of any age are totally immune.
Interesting Questions about Thyroid:
The basic goal of treatment is to return thyroid hormone levels to normal.
Hyperthyroidism makes the body work too fast because there is too much thyroid hormone in the blood. Graves’ disease is the most common cause of hyperthyroidism. Graves’ disease occurs because of a problem in the body’s immune system: antibodies are produced that overstimulate the thyroid gland.
Patients who are hyperthyroid from taking too much thyroid hormone need only to have their dosage properly adjusted.
Patients whose hyperthyroidism is caused by transient thyroiditis usually do not require any of the treatments described below, since their condition gets better on its own.
Treatment for hyperthyroidism from Graves’ disease, toxic autonomously functioning thyroid nodule, or toxic multi-nodular goiter may include one or more of the following:
Radioactive iodine (I131)
Radioactive iodine shrinks an enlarged thyroid or toxic nodule or nodules that are making too much thyroid hormone. This treatment is safe and is widely used in adults with hyperthyroidism.
* Radioactive iodine (I131) is the treatment of choice for the majority of the endocrinologists in this country. It is an effective, simple, safe way to treat patients with Graves’ disease or other forms of hyperthyroidism. Patients often have fears and misconceptions about using radioactive iodine.
* Studies have been done since the 1940’s on patients receiving this treatment. Treated patients, their children, and their grandchildren do not have an increased incidence of cancer, leukemia, etc.
* There are no increased instances of birth defects in children born to mothers who have had this treatment and waited the recommended time before becoming pregnant. (Pregnancy should be avoided for at least six months after the treatment.) As a matter of fact, fertility is often restored to women whose infertility is due to hyperthyroidism. Treating the disease also lessens the chance of miscarriage.
* Pregnant women should not be given radioactive iodine for any reason. If a patient has any doubt as to whether she is pregnant, treatment (and testing) with radioactive iodine should be delayed.
* Hospitalization is not required in order to treat hyperthyroidism with radioactive iodine.
* Radioactive iodine treatment ablates the thyroid gland (turns it into something like a dried-up raisin). Patients wishing to avoid destruction of the gland should know that the thyroid gland frequently “burns out” within 15 years even without treatment.
* Radioactive iodine does not cause a person to gain weight. However, because Graves’ disease increases the metabolism, patients should keep in mind that they cannot continue to eat the way they did while hyperthyroid. Because of changes in the metabolism after hyperthyroidism is treated, many patients will gain weight . This weight can be lost through diet and exercise once the thyroid levels are normalized.
Antithyroid drugs, such as propylthiouracil (PTU) and methimazole (Tapozole®), are used in patients with Graves’ disease and, less commonly, in other hyperthyroid patients
In some cases beta-blocking drugs are prescribed to treat the symptoms of hyperthyroidism while waiting for one of the above treatments to work.
Your doctor will be able to discuss the benefits and risks of each treatment.
Many patients treated for hyperthyroidism become hypothyroid. They will need to take thyroid hormone pills for the rest of their lives. In addition, they will need to see their doctor at least once a year.
® Tapozole is a registered trademark of Jones Medical Industries.
If you or a blood relative has Hashimoto’s thyroiditis or Graves’ disease, there is a chance that your children will inherit the problem. These diseases are also linked to other autoimmune conditions, such as premature gray hair, diabetes mellitus, arthritis, and patchy loss of skin pigment (vitiligo). You should tell your child’s doctor, so that the appropriate examinations can be performed.
Also, one out of every 4,000 infants is born without a working thyroid gland. If the problem is not corrected, the child will become mentally and physically retarded. Therefore, all newborns in the United States are tested for the disease. Once the problem is discovered and corrected, the child can grow up normally.
The standard treatment for hypothyroidism is thyroid hormone pills. The pills provide the body with the right amount of thyroid hormone when the gland is not able to produce enough by itself. While the symptoms of hypothyroidism are usually corrected within a few months, most patients need to take the pills for the rest of their lives.
The preferred thyroid hormone for treatment is levothyroxine (T4). You should use only the brand-name that your doctor prescribes, since generic brands may not be as reliable. Name brand levothyroxine pills include Levothroid®, Synthroid®, Levoxyl®, and Eltroxin®.
Patients sometimes take more pills than they should, trying to speed up the treatment or lose weight. However, this can lead to hyperthyroidism, a disease in which there is too much thyroid hormone in the blood, and to long-term complications, such as osteoporosis. You should take the pills as your doctor prescribes.
At different times in your life, you may need to take different amounts of thyroid hormones. Therefore, you should see your doctor once a year to make sure everything is all right.
® Levothroid is a registered trademark of Forest Pharmaceuticals.
® Synthroid is a registered trademark of Knoll Pharmaceuticals.
® Levoxyl is a registered trademark of Jones Medical Industries.
® Eltroxin is a registered trademark of Roberts Pharmaceuticals.
Symptoms Of Secondary Hypothyroidism
Early symptoms of secondary hypothyroidism include:
- Brittle fingernails
- Coarseness, thinning of hair
- Cold intolerance
- Joint or muscle pain
- Weight gain
As the disease progresses, and if not treated, more symptoms develop, including:
- Decreased hearing
- Dry, flaky skin
- Menstrual disorders
- Puffy face, hands, and feet
- Slow speech
- Thickening of the skin
- Thinning of eyebrows
Diagnosing Secondary Hypothyroidism
Upon physical examination the patient’s thyroid is often abnormally small. There will usually be bradycardia present (slow heart rate) along with low blood pressure and a lower than normal basal temperature. An enlarged heart may also show up with chest x-rays.
The common tests for secondary hypothyroidism are blood tests that check levels of free T4, total T3 and serum levels of TSH. If the pituitary is malfunctioning, low TSH values are often seen but it’s also possible for a patient to have normal or high levels. Along with thyroid function tests, a patient may also be tested for other pituitary associated abnormalities as well as pituitary hormone levels in general:
- cholesterol levels (high)
- liver enzymes (high)
- serum prolactin (high)
- serum sodium (low)
- blood glucose (low)
- MRI scan to look for tumors
Treating Secondary Hypothyroidism
Treatment is by way of thyroid hormone replacement therapy because ultimately this is the hormone that is required throughout the body for normal function. Treatment needs to be continued even when symptoms disappear. It’s also important to keep an eye open for any symptoms of hyperthyroidism as this indicates too much thyroid hormone and your dose will need to be reduced.
It’s also likely that you’ll need to be on other medications for other disorders that are controlled by pituitary gland hormones. If you also have hypoadrenalism (Addison’s disease) you will need to start steroid replacement therapy before beginning your thyroid hormone replacement therapy.
A tumor may need to be removed, which may or may not improve pituitary function. If it doesn’t, you’ll require continuing thyroid hormone replacement therapy.