Distinct Clinical, Serological, and Sonographic Characteristics of Hashimoto's Thyroiditis Based with and without IgG4-Positive Plasma Cells

Context: IgG4-related sclerosing disease is a new syndrome characterized by high serum IgG4 levels and increased IgG4-positive plasma cells in the involved organs. Recently the first description was made by our group of a subsection of Hashimoto's autoimmune thyroiditis (HT) patients showing indistinguishable histopathological features with IgG4-related sclerosing disease, which was termed as IgG4 thyroiditis. Objective: The objective of the study was analysis of the immunophenotypic features of IgG4 in 70 cases of HT patients and to clarify the histopathological and clinical characteristics of the patients with IgG4 thyroiditis. Design: Thyroid tissue samples were obtained from 70 patients with HT who were treated surgically. Quantitative analyses of the expression of IgG4 and IgG were performed. Statistical analyses of clinical and histopathological parameters were also conducted. Results: On the basis of immunohistochemistry of IgG4 and IgG4/IgG ratio, the 70 patients with HT were divided into two groups: IgG4 thyroiditis (19 cases) and non-IgG4 thyroiditis (51 cases). Histopathologically, IgG4 thyroiditis showed higher grade of stromal fibrosis, lymphoplasmacytic infiltration, and follicular cell degeneration than non-IgG4 thyroiditis. Moreover, these two groups were also demonstrated to be related with different clinical features, with IgG4 thyroiditis associated more with male gender, rapid progress, subclinical hypothyroidism, more diffuse low echogenicity, and higher level of circulating antibodies. Conclusions: From both clinical and histopathological aspects, IgG4 thyroiditis and non-IgG4 thyroiditis were demonstrated to be distinct entities. Measuring serum IgG4 concentration provides a useful method of distinguishing IgG4 thyroiditis from non-IgG4 thyroiditis. (J Clin Endocrinol Metab 95: 1309-1317, 2010)