Hashimoto thyroiditis results when antibodies in 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 Overview of the Thyroid Gland The thyroid is a small gland, measuring about 2 inches (5 centimeters) across, that lies just under the skin below the Adam’s apple in the neck. The two halves (lobes) of the gland are connected... read more .)
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 Hypothyroidism Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more 
. For unknown reasons, the body turns against itself (an autoimmune reaction Autoimmune Disorders An autoimmune disorder is a malfunction of the body's immune system that causes the body to attack its own tissues. What triggers an autoimmune disorder is not known. Symptoms vary depending... read more ). The thyroid is invaded by white blood cells White Blood Cells The main components of blood include Plasma Red blood cells White blood cells Platelets read more 
, 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 Diabetes Mellitus (DM) Diabetes mellitus is a disorder in which the body does not produce enough or respond normally to insulin, causing blood sugar (glucose) levels to be abnormally high. Urination and thirst are... read more , an underactive adrenal gland Adrenal Insufficiency In adrenal insufficiency, the adrenal glands do not produce enough adrenal hormones. Adrenal insufficiency may be caused by a disorder of the adrenal glands, a disorder of the pituitary gland... read more 
, or underactive parathyroid glands, and other autoimmune disorders, such as pernicious anemia, rheumatoid arthritis Rheumatoid Arthritis (RA) Rheumatoid arthritis is an inflammatory arthritis in which joints, usually including those of the hands and feet, are inflamed, resulting in swelling, pain, and often destruction of joints.... read more 
, Sjögren syndrome Sjögren Syndrome Sjögren syndrome is a common autoimmune connective tissue disorder and is characterized by excessive dryness of the eyes, mouth, and other mucous membranes. White blood cells can infiltrate... read more 
, or systemic lupus erythematosus Systemic Lupus Erythematosus (SLE) Systemic lupus erythematosus is a chronic autoimmune inflammatory connective tissue disorder that can involve joints, kidneys, skin, mucous membranes, and blood vessel walls. Problems in the... read more 
(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 Down Syndrome (Trisomy 21) Down syndrome is a chromosome disorder caused by an extra chromosome 21 that results in intellectual disability and physical abnormalities. Down syndrome is caused by an extra chromosome 21... read more 
, Turner syndrome Turner Syndrome Turner syndrome is a sex chromosome abnormality in which girls are born with one of their two X chromosomes partially or completely missing. Turner syndrome is caused by the deletion of part... read more 
, and Klinefelter syndrome Klinefelter Syndrome Klinefelter syndrome is a sex chromosome abnormality in which boys are born with two or more X chromosomes, instead of one, and one Y (XXY). Klinefelter syndrome occurs when a boy has one extra... read more 
.
Symptoms of Hashimoto Thyroiditis
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 Symptoms Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more . The few who have an overactive thyroid Hyperthyroidism Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions. Graves disease is the most common cause of hyperthyroidism... read more 
(hyperthyroidism) initially may have palpitations, nervousness, and intolerance of heat.
Diagnosis of Hashimoto Thyroiditis
Thyroid function tests (TSH and T4; T3 if hyperthyroidism is suspected)
Thyroid antibodies
Sometimes a thyroid ultrasound
Doctors do an examination of the thyroid. An ultrasound of the thyroid may be done if the thyroid feels like it has bump (nodules). They measure blood levels of the thyroid hormone thyroxine (T4) (and triiodothyronine (T3) if hyperthyroidism is suspected) 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 Thyroid function tests The thyroid is a small gland, measuring about 2 inches (5 centimeters) across, that lies just under the skin below the Adam’s apple in the neck. The two halves (lobes) of the gland are connected... read more ). They also do a blood test for antibodies that can attack the thyroid gland.
Treatment of Hashimoto Thyroiditis
Usually thyroid hormone replacement when the patient is clinically hypothyroid and the TSH level is elevated in the blood
Avoidance of excess iodine in food or nutritional supplements
Most people eventually develop hypothyroidism and then must take thyroid hormone replacement Treatment Hypothyroidism is underactivity of the thyroid gland that leads to inadequate production of thyroid hormones and a slowing of vital body functions. Facial expressions become dull, the voice... read more 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 high doses of iodine (which can cause hypothyroidism) from natural sources, such as kelp tablets and seaweed; however, iodized salt and iodine-fortified bread are allowed because they contain lower amounts of iodine.
