Hashimoto’s thyroiditis – also known as Hashimoto’s disease or chronic lymphocytic thyroiditis – is an autoimmune condition, meaning that antibodies from a person’s immune system attack a part of the body. In the case of Hashimoto’s, the target of the antibodies is the thyroid gland.
The thyroid is a butterfly-shaped gland in the neck that controls metabolism. Unlike Graves’ disease, in which antibodies stimulate the thyroid to overproduce thyroid hormones (a condition known as hyperthyroidism), Hashimoto’s disease begins with a brief period of hyperthyroidism and ends with low thyroid function. This is known as hypothyroidism or an underactive thyroid.
The number of people with Hashimoto’s disease in the United States is unknown, according to the National Institute of Diabetes and Digestive and Kidney Diseases (opens in new tab) (NIDDK), but is the most common cause of hypothyroidism affecting about 5 in 100 Americans. However, while Hashimoto’s disease is the most common cause of hypothyroidism, a person can be hypothyroid without Hashimoto’s etiology.
What causes Hashimoto’s disease?
The nature of the immune attack on the thyroid explains why Hashimoto’s can start with hyperthyroidism and end with hypothyroidism. Thyroid cells contain the hormones triiodothyronine (T3) and thyroxine (T4), which are waiting to be released into the blood as needed. However, when Hashimoto’s antibodies—such as thyroid peroxidase (TPO), thyroglobulin (TG), and thyroid-stimulating immunoglobulin (TSI)—hit the thyroid, a few things happen. If TSI is among the antibodies that hit the thyroid, the thyroid cells are stimulated to release their hormones. Whether or not TSI is among the antibodies that hit the thyroid, other antibodies such as TPO damage thyroid tissue, causing the hormones (T3 and T4) to leak into the blood quite quickly. The damage is generally permanent, so eventually the thyroid cells will not be able to produce more hormones.
Meanwhile, high levels of thyroid hormones are released, so over several days, blood levels of T3 and T4 rise. This causes hyperthyroidism (high concentrations of thyroid hormones) that usually lasts up to two weeks. However, because the gland is damaged, it cannot produce more hormones. After this brief increase, the amounts of T3 and T4 in the blood begin to fall. The person goes through a period when they have normal levels of thyroid hormones in the blood (this is called euthyroid).
Because the period of hyperthyroidism is so short and because the person passes from a euthyroid state on the way to becoming hypothyroid, temporary symptoms of hyperthyroidism are not always seen. Thyroid hormone levels continue to drop, so the person becomes more and more hypothyroid and stays that way.
It’s not clear what causes the immune system to attack thyroid cells, according to the Mayo Clinic (opens in new tab). Genetic factors, environmental factors (such as infection or stress), or a combination of the two may play a role.
Hashimoto’s risk factors
Hashimoto’s disease is four to ten times more common in women than men, according to the National Institute of Diabetes and Digestive and Kidney Diseases (opens in new tab) (NIDDK). It often develops between the ages of 30 and 50.
Having a first-degree relative with Hashimoto’s puts a person at increased risk for the condition, according to the NIDDK. Other risk factors include having other autoimmune diseases, such as celiac disease, rheumatoid arthritis, or type 1 diabetes.
What are the symptoms of Hashimoto’s disease?
According to the National Institute of Health (opens in new tab) (NIH), signs of Hashimoto’s disease may come from symptoms of hypothyroidism, including:
- Lethargy and fatigue
- Weight gain
- Constipation
- Muscular weakness
- Muscle aches and stiffness
- Pain and stiffness in the joints
- Dry, pale skin
- Face swollen
- Hair loss
- Brittle nails
In addition, people may have an enlarged tongue, feel depressed, have difficulty remembering, and feel very cold. Women may have prolonged or excessive menstruation.
However, a few weeks before symptoms of hypothyroidism, people may experience symptoms of hyperthyroidism. Such symptoms include palpitations (a feeling that the heart is pounding, pounding or skipping), nervousness, increased appetite, gastrointestinal disturbances, feeling too hot, tiredness or muscle weakness, and insomnia. The thyroid may also be enlarged or tender, according to the American Thyroid Foundation (opens in new tab)but only for the initial phase of hyperthyroidism.
How is Hashimoto’s disease diagnosed?
A diagnosis for Hashimoto’s begins with a blood test to measure the amount of a hormone called thyroid-stimulating hormone (TSH) in the blood. TSH is a hormone that comes from the pituitary gland at the base of the brain. In Hashimoto’s disease, when a person reaches the hypothyroid phase, TSH is elevated in the blood while thyroid hormone, specifically T4, is very low.
In addition, doctors test the blood for antibodies to an enzyme called thyroid peroxidase. The test for this antibody is not specific for Hashimoto’s disease, meaning that many people test positive for the antibodies without having symptoms or when they have another condition, such as Graves’ disease. Thus, doctors must interpret test results in the context of a person’s symptoms and signs that appear on physical examination.
Complications of Hashimoto’s disease
If left untreated, Hashimoto’s disease can worsen into an extreme form of hypothyroidism called myxedema, according to an article in the journal American Family Physician. (opens in new tab). This condition is characterized by abnormally low body temperature, impaired function of multiple organs, and impaired mental status, until the person falls into a coma.
Thyroid function in pregnancy
Pregnancy can lead to changes in thyroid function in multiple, complex ways. Specifically, the increase in levels of the hormones beta-human chorionic gonadotropin (beta-hCG) and estrogen stimulates the release of thyroid hormones T3 and T4, causing a corresponding drop in TSH levels.
However, the need for thyroid hormones also increases, particularly during the fetal and early fetal period, corresponding to the first trimester. This is because the baby cannot produce enough of its own thyroid hormones until the second trimester. Consequently, the thyroid-stimulating effect of beta-hCG and estrogen, causing higher than normal T3/T4 levels, is offset by the increased need for thyroid hormones. The balance can be different in different women, leading in some cases to relative hypothyroidism, meaning that the thyroid activity is not enough to keep up with the needs.
In addition, fetal growth and changing hormonal conditions further increase the need for thyroid hormones as pregnancy progresses into the second trimester. Because associated hypothyroidism is associated with an increased risk of miscarriage, it is recommended that TSH levels be monitored and maintained throughout pregnancy, according to the American Thyroid Association (opens in new tab). Maintaining TSH levels means taking thyroid hormone therapy (levothyroxine) when TSH levels are too high (meaning thyroid hormones are too low) and stopping levothyroxine when TSH levels are too low (meaning thyroid levels are too high).
At the same time, low thyroid function before or during pregnancy can lead to complications. In this case, the fetus or fetus is at increased risk of preterm delivery, low birth weight, small for gestational age, and intrauterine fetal death.
Hashimoto’s disease can occur before, during or after pregnancy. But when it appears immediately after childbirth, it must be distinguished from another phenomenon, called postpartum thyroiditis. In this case, thyroid function usually returns to normal after several months, although not always.
How is Hashimoto’s disease treated?
Hashimoto’s disease is usually diagnosed after the initial, hyperthyroid phase. If someone experiences an episode of hyperthyroidism, however, it can be treated with a type of medication called beta-blockers, which slow the heart rate.
Once someone becomes hypothyroid, they must take a synthetic thyroid hormone, levothyroxine (L-T4), every day. They are likely to need this treatment throughout their lives.
This article is for informational purposes only and is not intended to offer medical advice.