(Autoimmune Thyroiditis; Chronic Lymphocytic Thyroiditis; Hashimoto's Thyroiditis)
(See also Overview of Thyroid Function.)
Hashimoto thyroiditis is chronic autoimmune inflammation of the thyroid with lymphocytic infiltration. Findings include painless thyroid enlargement and symptoms of hypothyroidism. Diagnosis involves demonstration of high titers of thyroid peroxidase antibodies. Lifelong l-thyroxine replacement is typically required.
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, RA, SLE, Sjögren syndrome), celiac disease, and Schmidt syndrome (Addison disease, diabetes, and hypothyroidism secondary to Hashimoto thyroiditis). 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.
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 radioactive iodine uptake may be increased, perhaps because of defective iodide organification together with a gland that continues to trap iodine. Patients later develop hypothyroidism with decreased T4, decreased thyroid radioactive iodine uptake, and increased TSH.
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.
T4 and TSH levels initially are normal, but later, T4 declines and TSH rises, and 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.