Question
Hashimoto’s thyroiditis
Answer
Hashimoto thyroiditis is the most common cause of hypothyroidism in iodine-sufficient regions, resulting from autoimmune destruction of the thyroid gland.
Gross: Diffusely, symmetrically enlarged thyroid with an intact capsule; pale, grey-tan, firm, somewhat lobulated cut surface.
Microscopy: Dense lymphoplasmacytic infiltrate with well-formed germinal centres; atrophic thyroid follicles lined by Hürthle cells (oxyphil metaplasia — enlarged cells with abundant granular eosinophilic cytoplasm due to mitochondrial accumulation); variable interstitial fibrosis.
Immunology: Circulating anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin antibodies; a Type IV (and to a lesser extent Type II) hypersensitivity-mediated process involving CD8+ cytotoxic T cells and antibody-dependent mechanisms.
Clinical: Presents with painless goitre, progressing to hypothyroidism; associated with increased risk of thyroid lymphoma (rare) and slightly increased risk of papillary thyroid carcinoma.