Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Hashimoto Thyroiditis

(Autoimmune Thyroiditis)


Laura Boucai

, MD, Weill Cornell Medical College

Reviewed/Revised Feb 2024
Topic Resources

Hashimoto thyroiditis is chronic, autoimmune inflammation of the thyroid gland.

  • Hashimoto thyroiditis results when antibodies in the body attack 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.

Thyroiditis refers to any inflammation of the thyroid gland. Inflammation of the thyroid may be caused by a viral infection or an autoimmune disorder.

The Thyroid

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. Symptoms of diabetes may... 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 Adrenal Insufficiency , or underactive parathyroid glands Hypoparathyroidism Hypoparathyroidism is a deficiency of parathyroid hormone (PTH) often caused by an autoimmune disorder, treatment-related damage to the parathyroid glands, or removal of the glands during surgery... read more , 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 Rheumatoid Arthritis (RA) , 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 Sjögren Syndrome , 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 Systemic Lupus Erythematosus (SLE) (lupus).

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 Symptoms . The few people 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 (hyperthyroidism) initially may be aware of their heartbeats (palpitations) or have nervousness and intolerance of heat.

Diagnosis of Hashimoto Thyroiditis

  • Thyroid function blood tests (measurement of thyroid-stimulating hormone and thyroxine and also measurement of triiodothyronine if hyperthyroidism is suspected)

  • Thyroid antibodies

  • Sometimes a thyroid ultrasound

Doctors do an examination of the thyroid gland. They feel the person's neck to see whether the thyroid gland is enlarged, is tender, or contains lumps (nodules).

An ultrasound of the thyroid may be done if the thyroid feels like it has bump (nodules).

Doctors measure blood levels of the thyroid hormone thyroxine (T4) ) 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 blood tests Thyroid function blood tests The thyroid is a small gland, measuring about 2 inches (5 centimeters) across, that is located just under the skin in the neck. The two halves (lobes) of the gland are connected in the middle... read more ). If doctors suspect the person has hyperthyroidism 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 , they measure the level of the hormone triiodothyronine (T3) in the blood. 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 has symptoms of hypothyroidism d and the TSH level is elevated in the blood

  • Avoidance of excess iodine in food or nutritional supplements

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.

quiz link

Test your knowledge

Take a Quiz!