Hashimoto Thyroiditis: A Century LaterAhmed, Rania MD; Al-Shaikh, Safa MD; Akhtar, Mohammed MDAdvances in Anatomic Pathology: May 2012 - Volume 19 - Issue 3 - p 181–186 doi: 10.1097/PAP.0b013e3182534868 Review Articles Abstract Author Information More than a century has passed since the first description of Hashimoto thyroiditis (HT) as a clinicopathologic entity. HT is an autoimmune disease in which a breakdown of immune tolerance is caused by interplay of a variety of immunologic, genetic, and environmental factors. Thyrocyte injury resulting from environmental factors results in expression of new or hidden epitopes that leads to proliferation of autoreactive T and B cells. Infiltration of thyroid by these cells results in HT. In addition to the usual type of HT, several variants such as the fibrous type and Riedal thyroiditis are also recognized. The most recently recognized variant is immunoglobulin G4+ HT, which may occur as isolated thyroid limited disease or as part of a generalized Ig4-related sclerosing disease. The relationship between HT and Riedel thyroiditis remains unclear; however, recent evidence seems to suggest that it may also be part of the spectrum of Ig4-related sclerosing disease. HT is frequently associated with papillary thyroid carcinoma and may indeed be a risk factor for developing this type of cancer. The relationship between thyroid lymphoma and HT on the other hand appears well established. Department of Pathology and Laboratory Medicine, King Faisal Specialist Hospital and Research Centre, Riyadh, Kingdom of Saudi Arabia The authors have no funding or conflicts of interest to disclose. Reprints: Mohammad Akhtar, MD, Department of Pathology and Laboratory Medicine (MBC 10), King Faisal Specialist Hospital and Research Centre, P.O. Box 3354, Riyadh 11211, Kingdom of Saudi Arabia (e-mail: firstname.lastname@example.org). © 2012 Lippincott Williams & Wilkins, Inc.