IgG4 thyroiditis in the Asian population

Abstract

Immunoglobulin G4-related disease (IgG4-RD) is an immune-mediated fibro-inflammatory condition that often causes the formation of tumefactive lesions. The discovery of IgG4-RD linked many well-known isolated conditions as a distinct multi-organ disease, and started an era of promoting investigation and treatment in relevant fields. In the thyroid gland, a subcategory of Hashimoto thyroiditis (HT) with IgG4-rich inflammation was first discovered and named IgG4 thyroiditis by our group. This subtype of HT presents with rapidly progressive clinical manifestations and destructive histopathological features underlying thyroid dysfunction, which are significantly different from the common type of HT. Moreover, other IgG4-rich thyroid conditions in patients with Graves' disease and systemic IgG4-RD have been described. These observations are most frequently reported in the Asian population for unknown reasons. Although recent studies demonstrated that IgG4 thyroiditis is a specific entity independent from IgG4-RD, recognition of this unique subset of thyroid disease has yielded important insights into understanding its pathogenesis and the development of novel therapeutic approaches.

Keywords: Asian population; Thyroid; autoimmune thyroid disease; immunoglobulin G4 (IgG4); thyroiditis.

Figure 1

Histopathological features of IgG4 thyroiditis. (A) Dense stromal fibrosis, lymphoplasmacytic infiltration, and numerous microfollicles are noticed in the thyroid tissue (HE, ×40). (B) Atrophic thyroid follicles separated by the deposition of fibrous tissue with lymphoplasmacytic infiltration in the interfollicular area (HE, ×200).

Figure 2

A marked increase in IgG⁺ (A) and IgG4⁺ (B) plasma cells among the inflammatory infiltrates showing a high IgG4⁺/IgG⁺ ratio (IgG and IgG4; IHC, ×400).