- Hashimoto's thyroiditis is a common autoimmune thyroid disorder characterized by the presence of anti-thyroid peroxidase (anti-TPO) antibodies and lymphocytic infiltration of the thyroid gland, leading to gradual thyroid failure and hypothyroidism.
- It is the most frequent cause of chronic autoimmune thyroiditis and presents with a painless, diffusely enlarged thyroid.
- Unlike De Quervain and subacute granulomatous thyroiditis, which are typically post-viral and self-limiting, Hashimoto’s is a chronic condition marked by autoimmune destruction of thyroid tissue.
- Riedel thyroiditis involves fibrous replacement and is rare, not autoimmune-mediated.

Reference: Davidson’s Principles and Practice of Medicine, 24th Edition, Chapter: Disorders of the Thyroid Gland, Page 759.