There are 3 types of hypothyroidism. Primary hypothyroidism is caused by disorders in the thyroid gland itself. Secondary hypothyroidism is caused by disorders in the pituitary gland and Tertiary hypothyroidism is caused by disorders in the hypothalamus.
Primary hypothyroidism is an umbrella name for a number of thyroid disorders that are all characterized by a thyroid that doesn’t produce enough thyroid hormone. The common causes are:
- iodine deficiency
- Hashimoto’s disease
- thyroid tumors
- thyroid surgery
- radiation treatment, including radioactive iodine
- some medications
- congenital thyroid agenesis
- genetic defects
- abnormal growths
Interesting Questions about Thyroid:
- means too much thyroid hormone
- affects 2.5 million people in the United States
- affects 2% of all women in the United States
- affects women 5 to 10 times more than men
- can cause infertility and miscarriage
- is the leading cause of hyperthyroidism
- is an autoimmune disease*
- means too little thyroid hormone
- affects 5 million Americans
- affects women 10 times more than men
- affects 1 out of every 4,000 infants born
- can cause infertility and miscarriage
- is the leading cause of hypothyroidism
- affects 1 out of 5 women over the age of 75
- is an autoimmune disease*
- is associated with a higher rate of miscarriage
- occurs in 5% – 9% of women after giving birth
- is usually temporary but can recur with future pregnancies
- affect 4% – 7% of the population
- are benign 90% of the time
- are less likely to be cancerous in women
*Autoimmune diseases run in families and are 5 times more common in women than men.
The leading cause of hyperthyroidism is an autoimmune disease called Graves’ Disease.
The leading cause of hypothyroidism is an autoimmune disease called Hashimoto’s thyroiditis.
Autoimmune diseases in general
Autoimmune diseases tend to run in families. In other words, there is a strong genetic predisposition to develop one or more autoimmune diseases. Females are affected five times more than men by autoimmune disease. Patients with other autoimmune diseases are more likely to develop autoimmune thyroid diseases.
Researchers are trying to unlock the mysteries of autoimmune diseases, but there are still many unanswered questions. Basically an autoimmune disease occurs when the immune system produces antibodies that attack healthy tissues. In Graves’ disease, the immune system produces anti-thyroid antibodies that cause the thyroid gland to make too much thyroid hormone. In Hashimoto’s thyroiditis, antithyroid antibodies damage the thyroid gland and prevent it from producing enough thyroid hormone.
Autoimmune diseases associated with a higher than normal rate of thyroid autoimmune diseases
- vitiligo (patchy loss of skin coloration)
- alopecia areata (sudden, circular hair loss)
- premature gray hair
- pernicious anemia (inability to absorb B12)
- rheumatoid arthritis
- myasthenia gravis (episodic muscle weakness that can affect vision, speech, swallowing, and breathing )
- Lupus erythematosus ( connective tissue disorder)
- insulin-dependent diabetes
- Addison’s disease (adrenal insufficiency)
- premature ovarian failure
Tests for antibodies present in autoimmune thyroid disease
- TPOab (thyroperoxidase antibodies)
- TGab (thyroglobulin antibodies)
One of these two types of antibodies is found in nearly all patients with Hashimoto’s thyroiditis and in approximately 50% of patients with Graves’ disease.
- TRab (thyrotropin receptor antibodies; also called thyroid stimulating immunoglobulins or thyroid stimulating antibodies.)
Thyroiditis is an inflammation of the thyroid gland. Thyroiditis can cause either hyperthyroidism or hypothyroidism, or one followed by the other. It can also cause a goiter, an abnormal swelling in the neck due to an enlarged thyroid. It affects about 12 million people in the United States.
Thyroiditis is the most common cause of hypothyroidism. When patients with thyroiditis have any symptoms, they are usually the symptoms of hypothyroidism. It is also common to have an enlarged thyroid that may shrink over time.
The type of thyroiditis seen most often is Hashimoto’s thyroiditis, a painless disease of the immune system that runs in families. Hashimoto’s thyroiditis affects about 5% of the adult population, increasing particularly in women as they age.
Another form of thyroiditis affects women of childbearing age. Postpartum thyroiditis occurs in 5%-9% of women soon after giving birth and is usually a temporary condition.
Viral and bacterial infections can also cause thyroiditis.
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Iodine deficiency: globally the main cause of primary hypothyroidism is still iodine deficiency but this cause is far more predominant in developing countries. Most developed countries have policies in place to ensure people get enough iodine in their diet so iodine deficiency is no longer an issue.
Hashimoto’s disease / thyroiditis: this is an autoimmune disease in which the immune system attacks the thyroid, reducing its ability to produce thyroid hormones. It’s the predominant cause of hypothyroidism in developed countries like the US.
Thyroid tumors/nodules: thyroid tumors and nodules can intefere with the thyroid’s ability to produce thryoid hormones. In many instances they have to be surgically removed or treated with radioactive therapy.
Thyroid surgery: quite often the entire thyroid gland or a significant portion of it has to be removed. If your thyroid has had to be removed you’ll definitely have hypothyroidism but your doctor will have put you onto replacement hormone treatment, probably before you develop any symptoms.
Radiation treatment: if you’ve had radiation treatment for other cancers of the upper body it may have adversely affected your thyroid, causing hypothyroidism. Another common type of therapy for hyperthyroidism, Graves disease and thyroid cancer is radioactive iodine therapy, which destroys the thyroid.
Congenital thyroid agenesis: this is a condition in which people are born without a thyroid.
Genetic defects: sometimes someone is born with genetic defects in the genes that regulate thyroid hormone productions. These are usually picked up at birth by newborn screening tests.
Medications: some types of medications can cause the thyroid to reduce thyroid hormone production. The common ones are:
- Lithium is used to treat depression and bipolar disorder and is a common cause of hypothyroidism – nearly a third of patients who are on it develop hypothyroidism because it slows down thyroid hormone production and release.
- Anti-thyroid drugs are used to treat hyperthyroidism. If dose rates are too high it can cause hypothyroidism.
- Amiodarone is a drug used for treating heart rhythm problems. It has a high iodine content, which for the thyroid can be just as bad as not enough iodine.
- Interferon-alpha is a drug used to treat some types of malignant tumors as well as hepatitis B and C. It can cause thyroid disorders, including hypothyroidism.
- Interleukin-2 (IL-2) is another cancer drug used to treat leukemia and some types of metastatic cancers. A small percentage of patients on this drug may develop thyroid problems.
Abnormal Growths: these can cause hypothyroidism if they invade the thyroid and displace healthy tissue. Sarcoidosis is an example of this type of growth.
Pregnancy: reproductive hormones can interfere with thyroid hormone production and with the production of the carrier proteins that transport thyroid hormone molecules around the body. Pregnancy can also escalate a cascade of health problems related to nutrition, hormones, immunity, stress, gut health and so on. If there are issues with any of these (poor nutrition or immune system imbalances for example) the demands that pregnancy places on the body can be overwhelming with serious consequences both for the mother and the growing fetus.