Hashimoto thyroiditis
- Lesion
The immune system slowly destroys the thyroid. It is the commonest cause of an underactive thyroid where people get enough iodine.
What it is
Hashimoto thyroiditis is an autoimmune disease in which T cells and antibodies against thyroid antigens gradually replace the gland with lymphoid tissue and scar. It is far more common in women, peaks in middle age and clusters with other autoimmune diseases. It is the leading cause of hypothyroidism in iodine-sufficient regions and raises the risk of extranodal marginal zone (MALT) lymphoma of the thyroid.
Structure
- Gross: diffusely enlarged, firm, pale tan gland with intact capsule; late stages are small and fibrotic.
- Dense infiltrate of lymphocytes and plasma cells with well-formed germinal centres.
- Follicles are small and atrophic; the remaining epithelium turns into Hürthle cells (abundant granular eosinophilic cytoplasm full of mitochondria).
- Fibrous variant: dense fibrosis; IgG4-related variant: many IgG4 plasma cells and storiform fibrosis.
Step by step
- Genetic predisposition (CTLA4, PTPN22, HLA) weakens tolerance to thyroid antigens.
- Autoreactive CD4 T cells are activated and recruit cytotoxic CD8 T cells.
- CD8 cells and IFN-gamma-activated macrophages kill thyrocytes; Fas-mediated apoptosis adds to the loss.
- Anti-TPO and anti-thyroglobulin antibodies form and mediate antibody-dependent cytotoxicity.
- Follicles are progressively replaced by lymphoid tissue and fibrosis: hypothyroidism.
Markers
- Anti-TPO
- Anti-thyroglobulin
- CD20 (B cells)
- Light chain restriction (lymphoma)
Clinical notes
- Painless goitre in a middle-aged woman with slowly rising TSH.
- A rapidly enlarging thyroid in long-standing Hashimoto suggests lymphoma.
- Associated with type 1 diabetes, pernicious anaemia, adrenalitis, coeliac disease and Sjögren disease.
Test yourself
Think of the answer, then tap the question to see it.
What are Hürthle cells and why do they appear in Hashimoto thyroiditis?
Metaplastic follicular cells with abundant granular eosinophilic cytoplasm packed with mitochondria; they form in response to ongoing injury.
Which lymphoma is associated with Hashimoto thyroiditis?
Extranodal marginal zone (MALT) B-cell lymphoma of the thyroid.
Which antibody is most sensitive for Hashimoto thyroiditis?
Anti-thyroid peroxidase (anti-TPO) antibody.
Elsewhere in DurgiPedia
- Autoantibodies: the table to know
- HLA associations with disease
- Type IV hypersensitivity (delayed, T cells)
- Immune tolerance and how autoimmunity begins
- Thyroid follicles, C cells and parathyroid
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Hashimoto's disease (MedlinePlus, US National Library of Medicine, 2025); Hypothyroidism (StatPearls (NCBI Bookshelf), 2025).
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Representative model, for educational purposes only.