Hashimoto's 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's thyroiditis is believed to be the most common cause of primary hypothyroidism in North America. It is twice as prevalent among women. Incidence increases with age and in patients with chromosomal disorders, including Down, Turner's, and Klinefelter's syndromes. A family history of thyroid disorders is common.

Hashimoto's thyroiditis, like Graves' disease, is sometimes associated with other autoimmune disorders, including Addison's disease (adrenal insufficiency), type 1 diabetes mellitus, hypoparathyroidism, vitiligo, premature graying of hair, pernicious anemia, connective tissue disorders (eg, RA, SLE, Sjögren's syndrome), celiac disease, and Schmidt's syndrome (Addison's disease, diabetes, and hypothyroidism secondary to Hashimoto's 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.

Symptoms and Signs

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.

Diagnosis

• Thyroxine (T₄)
• Thyroid-stimulating hormone (TSH)
• Thyroid autoantibodies

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.

Treatment

Occasionally, hypothyroidism is transient, but most patients require lifelong thyroid hormone replacement, typically l-thyroxine 75 to 150 μg po once/day.

Key Points

• Hashimoto's 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.
• Lifelong thyroid hormone replacement is typically needed.

Last full review/revision May 2012 by Jerome M. Hershman, MD