Hashimoto thyroiditis results when the body attacks the cells of the thyroid gland—an autoimmune reaction.
At first, the thyroid gland may function normally, be underactive (hypothyroidism) or, rarely, overactive (hyperthyroidism)
Most people eventually develop hypothyroidism.
People with hypothyroidism usually feel tired and cannot tolerate cold.
The diagnosis is based on results of a physical examination and blood tests.
People with hypothyroidism need to take thyroid hormone for the rest of their life.
(See also Overview of the Thyroid Gland.)
Thyroiditis refers to any inflammation of the thyroid gland. Inflammation of the thyroid may be caused by a viral infection or an autoimmune disorder.
Hashimoto thyroiditis is the most common type of thyroiditis and the most common cause of hypothyroidism. For unknown reasons, the body turns against itself (an autoimmune reaction). The thyroid is invaded by white blood cells, and antibodies are created that attack the thyroid gland (antithyroid antibodies).
In about 50% of people with Hashimoto thyroiditis, the thyroid is underactive initially. In most of the rest, the thyroid is normal at first (although in a small number of people, the gland initially becomes overactive), after which it usually becomes underactive.
Some people with Hashimoto thyroiditis have other endocrine disorders, such as diabetes, an underactive adrenal gland, or underactive parathyroid glands, and other autoimmune disorders, such as pernicious anemia, rheumatoid arthritis, Sjögren syndrome, or systemic lupus erythematosus (lupus).
Hashimoto thyroiditis is most common among women, particularly older women, and tends to run in families. The condition occurs more frequently among people with certain chromosomal abnormalities, including Down syndrome, Turner syndrome, and Klinefelter syndrome.
Hashimoto thyroiditis often begins with a painless, firm enlargement of the thyroid gland or a feeling of fullness in the neck. The gland usually has a rubbery texture and sometimes feels lumpy. If the thyroid is underactive, people may feel tired and intolerant of cold and have other symptoms of hypothyroidism. The few who have an overactive thyroid (hyperthyroidism) initially may have palpitations, nervousness, and intolerance of heat.
Doctors measure blood levels of thyroid hormones thyroxine (T4) and triiodothyronine (T3) and thyroid-stimulating hormone (TSH, a hormone produced by the pituitary gland to stimulate the thyroid gland to produce thyroid hormones) to determine how the gland is functioning (thyroid function tests). However, the diagnosis is based on a physical examination and the results of a blood test to determine whether the person has antithyroid antibodies.
No specific treatment is available for Hashimoto thyroiditis.
Most people eventually develop hypothyroidism and then must take thyroid hormone replacement therapy for the rest of their life. Thyroid hormone may also be useful in reducing the size of the enlarged thyroid gland.
People with Hashimoto thyroiditis who are not taking thyroid hormone replacement should avoid excess iodine (which can cause hypothyroidism) from natural sources, such as kelp tablets and seaweed.