Pathologic and immunohistochemical characteristics of Hashimoto thyroiditis and MALT

Objective To describe the morphological and immunohistochemical characteristics of hashimoto thyroiditis (HT) and analyze the significance of light chain restriction in differential diagnosis of HT and MALT lymphoma. Methods HE-stained 30 HT paraffin samples and 2 MALT lymphoma samples were studied histopathologically. CD20, CD3, Igκ, Igλ and cytokeratin were detected with immunohistochemistry. Lymphoid infiltration and lymphoepithelial lesions (LEL) were assessed. Differential diagnosis of early thyroid lymphoma and HT was made by light chain restriction. Two patients with primary thyroid lymphoma were used as controls. Results The HT samples showed the histopathological characteristics of HT. Immunohistochemial staining revealed the LEL without significant morphological change, few B-cells and massive proliferation of T-lymphocytes. Light chain restriction test demonstrated polyclonal proliferation of plasma cells. Two MALT lymphoma samples displayed destructive lymphoepithelial lesions, immunophenotype of B-cells and lgκlight chain restriction in plasmacytoid population. Conclusion The histopathological and immunohistochemical characteristics of HT and thyroid lymphoma are significantly different. Imunohistochemistry contributes to their differential diagnosis.