Thyroiditis - types, pathomorphology
Thyroiditis is inflammation of the thyroid. We will address each type in turn:
Hashimoto thyroiditis (chronic lymphocytic thyroiditis)
- Most common cause of hypothyroidism in the world where there is normal iodine
- It is gradual thyroid failure due to autoimmune destruction, common in women aged 45-60
- It is a loss of self tolerance to thyroid antigens, mechanisms of damage are via CD8+ cytotoxic T cells, cytokine-mediated cell death and antithyroid antibodies. Genetics is a significant predisposing factor.
- The thyroid is diffusely and symmetrically enlarged and microscopic examination shows mononuclear inflammatory infiltrate with well developed germinal centers. The thyroid follicles are atrophic and have Hurthle cells, characterised by high numbers of mitochondria.
- Clinical features of Hashimoto’s are those of hypothyroidism (see above)
H&E, Hashimoto thyroiditis: dense lymphocytic infiltrate with lymphoid follicles and germinal centres replacing the gland; the remaining thyroid follicles are small and atrophic.
Image: “Hashimoto thyroiditis -- low mag” by Librepath, CC BY-SA 3.0, via Wikimedia Commons.
Subacute granulomatous thyroiditis (de Quervain thyroiditis)
- Less common than Hashimoto's, found in women aged 30-50.
- Thought to be viral in etiology (most patients have an upper respiratory tract infection prior to onset) and can be thought of as being ‘immune related’
- Gland becomes firm, with an intact capsule, unilaterally or bilaterally enlarged. Histology will show disruption of follicles with polymorphonuclear infiltrate and extravasated colloid
- Clinical feature is pain in the neck, fever, malaise, enlargement of the thyroid and possibly transient hyperthyroidism. Condition is self limiting, most patients are euthyroid by 8 weeks.
Remember: de Quervain is the painful thyroiditis; Hashimoto and subacute lymphocytic (including postpartum) thyroiditis are painless. Its hallmark, after the early neutrophils, is granulomas with multinucleated giant cells engulfing fragments of colloid. Hashimoto, in contrast, carries a raised risk of B-cell (marginal zone) lymphoma of the thyroid.
Subacute lymphocytic thyroiditis
- Is a painless form of thyroiditis, in a subset of patients it is postpartum. Most likely to be autoimmune in etiology
- Presents with neck mass and features of hyperthyroidism
- Generally patients are euthyrotic within a few weeks