(See also Overview of Thyroid Function.)
Hashimoto thyroiditis is believed to be the most common cause of primary hypothyroidism in North America. It is several times more prevalent among women. Incidence increases with age and in patients with chromosomal disorders, including Down syndrome, Turner syndrome, and Klinefelter syndrome. A family history of thyroid disorders is common.
Hashimoto thyroiditis, like Graves disease, is sometimes associated with other autoimmune disorders, including Addison disease (adrenal insufficiency), type 1 diabetes mellitus, hypoparathyroidism, vitiligo, premature graying of hair, pernicious anemia, connective tissue disorders (eg, rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome), celiac disease, and type 2 polyglandular deficiency syndrome (Schmidt syndrome—a combination of Addison disease with hypothyroidism secondary to Hashimoto thyroiditis and/or type 1 diabetes mellitus). There may be an increased incidence of thyroid tumors, rarely thyroid lymphoma. Pathologically, there is extensive infiltration of lymphocytes with lymphoid follicles and scarring.
Patients complain of painless enlargement of the thyroid or fullness in the throat. Examination reveals a nontender goiter that is smooth or nodular, firm, and more rubbery than the normal thyroid. Many patients present with symptoms of hypothyroidism, but some present with hyperthyroidism that may be due to thyroiditis.
Testing consists of measuring T4, TSH, and thyroid autoantibodies. Early in the disease, T4 and TSH levels are normal and there are high levels of thyroid peroxidase antibodies and, less commonly, of antithyroglobulin antibodies.
Thyroid ultrasonography should be done if there are palpable nodules. Ultrasonography often reveals that the thyroid tissue has a heterogeneous, hypoechoic echotexture with septations that form hypoechoic micronodules.
Testing for other autoimmune disorders is warranted only when clinical manifestations are present.
Hashimoto thyroiditis is autoimmune inflammation of the thyroid.
Patients sometimes have other autoimmune disorders.
Thyroxine (T4) and thyroid-stimulating hormone (TSH) levels initially are normal, but later, T4 declines and TSH rises, and most patients become clinically hypothyroid.
There are high levels of thyroid peroxidase antibodies and, less commonly, of antithyroglobulin antibodies.
Lifelong thyroid hormone replacement is typically needed.