Hashimoto's thyroiditis is chronic, autoimmune inflammation of the thyroid.
Hashimoto's 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—see Allergic Reactions and Other Hypersensitivity Disorders: Autoimmune Disorders). The thyroid is invaded by white blood cells, and antibodies are created that attack the thyroid gland. In about 50% of people with Hashimoto's 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's thyroiditis have other endocrine disorders, such as diabetes, an underactive adrenal gland, or underactive parathyroid glands, and other autoimmune diseases, such as pernicious anemia, rheumatoid arthritis, Sjögren's syndrome, or systemic lupus erythematosus (lupus).
Hashimoto's 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, Turner's, and Klinefelter's syndromes.
Hashimoto's 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 (see Thyroid Gland Disorders: Symptoms). The few who have an overactive thyroid (thyrotoxicosis) 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 to determine how the gland is functioning. However, the diagnosis is based on a physical examination and the results of a blood test to determine whether the person has antithyroid antibodies, which attack the thyroid gland.
No specific treatment is available for Hashimoto's 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's thyroiditis should avoid excess iodine (which can cause hypothyroidism) from natural sources, such as kelp tablets and seaweed.
Last full review/revision May 2012 by Jerome M. Hershman, MD