title: Histopathologic and immunohistochemical features of Hashimoto thyroiditis.
abstract: BACKGROUND
  Intrathyroid lymphoid tissue is accrued in Hashimoto thyroiditis (HT). Histologically, this acquired lymphoid tissue bears a close resemblance to mucosa-associated lymphoid tissue (MALT) and can evolve to lymphoma.
  
  
  OBJECTIVE
  To demonstrate the morphological, and immunohistochemical profiles of Hashimoto thyroiditis and to ascertain the importance of light chain restriction in distinguishing HT with extensive lymphoplasmacytoid infiltrate from MALT lymphoma.
  
  
  METHODS
  We studied histopathologically and immunohistochemically (CD20, CD3, Igk, Igl and cytokeratin) 30 cases of HT for evaluation of the lymphoid infiltrate and the presence of lymphoepithelial lesions (LELs). Distinguishing between early thyroid lymphoma and HT was evaluated by light chain restriction. These findings were compared with two cases of primary thyroid lymphoma.
  
  
  RESULTS
  The histopathological findings were characteristic of HT. Immunohistochemistry confirmed inconspicuous, rare B-cell LELs as well as a prominent T-lymphocyte population. Testing for light chain restriction showed polyclonal population of plasma cells. The cases of MALT lymphoma had distinct destructive lymphoepithelial lesions, B-cell immunophenotyping and showed kappa light chain restriction in the plasmacytoid population.
  
  
  CONCLUSIONS
  Hashimoto thyroiditis differs both histopathologically and immunohistochemically from thyroid lymphoma. In suspicious cases, immunohistochemistry could be helpful in reaching a definitive diagnosis.
authors.affiliation: Department of Pathology, Medical Research Institute, Alexandria University, Egypt. amanikazem@hotmail.com
authors.forename: H Kazem
authors.initials: HK
authors.lastname: Amani
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D018951:Antigens, CD20 / Q000032:analysis; D017252:CD3 Complex / Q000032:analysis; D003937:Diagnosis, Differential; D005260:Female; D050031:Hashimoto Disease / Q000175:diagnosis* / Q000473:pathology*; D006651:Histocytochemistry; D006801:Humans; D007145:Immunoglobulin kappa-Chains / Q000032:analysis; D007146:Immunoglobulin lambda-Chains / Q000032:analysis; D007150:Immunohistochemistry; D007633:Keratins / Q000032:analysis; D008223:Lymphoma / Q000473:pathology; D008297:Male; D008853:Microscopy; D008875:Middle Aged; D013961:Thyroid Gland / Q000473:pathology*; D013964:Thyroid Neoplasms / Q000473:pathology; D055815:Young Adult
chemical_list: D018951:Antigens, CD20; D017252:CD3 Complex; D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains; D007633:Keratins