Hashimoto thyroiditis This autoimmune disorder occurs more often in women than in men. It is a common cause of hypothyroidism; may occasionally have anearly transient hypehyroid phase. Clinical characteristics include a slow, often inapparent course and a modestly enlarged and nontender thyroid; the patient is most often euthyroid at first, but transient hypehyroidism may occur; hypothyroidism develops latewhen the gland is shrunken and scarred. Histologic characteristics includemassive infiltrates of lymphocyteswithgerminal center formation; thyroid follicles are atrophic andHuhle cells(epithelial cells with eosinophilic granular cytoplasm) are prominent. Hashimoto thyroiditis is associated with various autoantibodies, most prominentlyantithyroglobulin, antithyroid peroxidase, anti-TSH receptor, and anti-iodine receptor antibodies. It may also be associated with an increased incidence of other autoimmune disorders such as pernicious anemia, diabetes mellitus, and Sjogren syndrome; incidence isincreased in HLA-DR5- and HLA-B5-positiveindividuals.