Background: Hashimoto thyroiditis (HT) is the most commonest
form of autoimmune thyroiditis with heterogenous clinical
presentation. Recently a type of Hashimoto thyroiditis with dense
lymphoplasmacytic infiltration and marked fibrotic changes with
increased number of IgG4-positive plasma cells and serum IgG4
have been reported in the literature and they have a close relationship
to IgG4-related disease (IgG4-RD). On the basis of immunostaining
for IgG4, HT was divided into an IgG4 thyroiditis group and a
non-IgG4 thyroiditis group and their clinical and histopathological
features were studied. Aims and Objectives: To categorize Hashimoto
thyroiditis with reference to IgG4-positive plasma cell infiltration
and to study the histopathological characteristics of each group.
Materials and Methods: It was a retrospective cross sectional study for
a period of one and half year. Cases which were histopathologically
diagnosed as Hashimoto thyroiditis were included in the study.
Immunohistochemistry marker done for IgG4 and the foci with the
highest density of positive cells was evaluated. Results: Among the
13 cases of Hashimoto thyroiditis 8 cases were subtyped into IgG4
thyroiditis group and 5 cases into non IgG4 thyroiditis group based
on immunohistochemistry. All the cases were females in both the
groups and the age of presentation in IgG4 thyroiditis was younger
when compared to non IgG4 thyroiditis. Histopathologically,
IgG4 thyroiditis showed marked fibrosis and moderate to severe
lymphoplasmacytic infiltration with increased IgG4 positive plasma
cell infiltration when compared to non IgG4 thyroiditis. Conclusion:
Immunostaining of IgG4 can help in the subtyping of Hashimoto
thyroiditis and are closely related with IgG4 related diseases. IgG4
Hashimoto thyroiditis presents with a distinct histopathological
features when compared to non IgG4 thyroiditis.
Keywords: Hashimoto thyroiditis; IgG4; Immunohistochemistry;
Fibrosis; Histopathology.