Hashimoto's thyroiditis: old concepts and new insights

Area of Science:

• Endocrinology
• Immunology
• Pathology

Background:

• Hashimoto's thyroiditis is a well-established autoimmune thyroid disease.
• Understanding of Hashimoto's thyroiditis has seen limited evolution in recent decades.
• Its relationship with IgG4-related systemic disease (IgG4-RSD) is an emerging area of research.

Purpose of the Study:

• To review recent advancements in the understanding of Hashimoto's thyroiditis.
• To explore the intricate relationship between Hashimoto's thyroiditis and IgG4-RSD.

Main Methods:

• Literature review of studies published within the past year.
• Analysis of histopathological characteristics and clinical features of thyroiditis subtypes.
• Examination of serum IgG4 levels and circulating antibodies.

Main Results:

• Identification of a unique subtype: IgG4 thyroiditis, characterized by specific histopathological findings (lymphoplasmacytic infiltration, fibrosis, IgG4-positive plasma cells) and elevated serum IgG4 levels.
• IgG4 thyroiditis exhibits distinct clinical features compared to non-IgG4 thyroiditis, including rapid progression, subclinical hypothyroidism, higher antibody levels, and diffuse low echogenicity on ultrasound.
• Riedel's thyroiditis is recognized as a thyroid manifestation of systemic IgG4-RSD, necessitating an expanded definition of IgG4 thyroiditis.

Conclusions:

• New insights into Hashimoto's thyroiditis, particularly concerning IgG4-positive plasma cells, provide a novel perspective on this disease.
• IgG4-RSD in the thyroid gland presents as two distinct forms: organ-specific Hashimoto's thyroiditis and systemic Riedel's thyroiditis.
• Both thyroid manifestations share common IgG4-related sclerosing features, highlighting a unifying pathological mechanism.