Description

• Hashimoto thyroiditis (HT), also called lymphocytic thyroiditis or chronic autoimmune thyroiditis, is characterized by autoimmune destruction of the thyroid gland that can result in progression to overt hypothyroidism or goiter formation.
• Lymphocytic infiltration of the thyroid gland and presence of antibodies to thyroid peroxidase (TPO) and thyroglobulin (Tg) are hallmark features.
• Clinical presentation can vary and includes asymptomatic disease, atrophic thyroid, transient hyperthyroidism (also known as hashitoxicosis), as well as transient conditions such as silent (or painless) thyroiditis and postpartum thyroiditis that may progress to thyroid failure years later.
• Hashimoto encephalopathy (HE) is a rare condition associated with high TPO titers. The neurologic manifestations are not related to the underlying thyroid status and are thought to be related to autoimmune vasculitis.

Epidemiology

• Most common etiology of hypothyroidism in iodine-sufficient areas. In the United States, prevalence of subclinical and overt hypothyroidism can be as high as 5% and 2%, respectively.
• 5 times more common in women than men
• 10% of the general population has antibodies to TPO and Tg.

Etiology and Pathophysiology

• Both genetic predisposition and environmental factors contribute to the development of HT.
• Characterized by lymphocytic infiltration of the thyroid tissue resulting in B- and T-cell–mediated destruction of the thyroid follicles and hypothyroidism
• Early in the course, disruption of the thyroid gland can result in thyroid hormone release and transient hyperthyroidism or hashitoxicosis.
• Extent of the infiltration, fibrosis, and TSH-mediated follicular cell hyperplasia determines a goitrous or atrophic presentation.
• Nearly all patients with HT have TPO and Tg antibodies. High titer in postpartum/silent thyroiditis or in subclinical disease indicates progression to overt hypothyroidism in later years.
• High TPO antibody titers can also be associated with autoimmune vasculitis and present as encephalopathy.

Risk Factors

• Presence of other autoimmune conditions
• Family history of autoimmune disorders
• Pregnancy
• High-iodine intake
• Radiation exposure
• Turner and Down syndrome
• Postpartum thyroiditis or painless thyroiditis

Commonly Associated Conditions

HT can be associated with other autoimmune diseases including type 1 diabetes mellitus, adrenal insufficiency, celiac disease, and pernicious anemia.