ETIOLOGY OF HASHIMOTO'S THYROIDITIS
ETIOLOGY OF HASHIMOTO'S THYROIDITIS
- It is an autoimmune disease -
- It is thought to be initiated by activation of CD4+T (helper) lymphocytes which further recruit cytotoxic CD8+T cells.
- Thyroid tissue is destroyed by cytotoxic T cells and autoantibodies
Autoantibodies are directed against following antigens.
- Thyroglobulin (Tg) 60%
- Thyroid peroxidase (TPO) 95%
- TSH-R, 60%
- Antibodies are directed less commonly against the sodium/iodine symporter (25%).
- Apoptosis (programmed cell death) is also implicated in the pathogenesis of Hashimoto's thyroiditis.
- Genetic association has been noted with
- HLA (B8, DR3, DR4 & DR5)
- CTLA-4 (a T cell regulating gene)
- Several chromosomal abnormalities have been associated with Hashimoto's thyroiditis
- Turner syndrome
- Down syndrome
PATHOLOGY OF HASHIMOTO'S THYROIDITIS1. Gross features
- Diffuse symmetrically enlarged thyroid.
- Capsule is intact
- Diffuse lymphocytic infiltration with germinal center formation and obliteration of thyroid follicles by widespread apoptosis.
- The thyroid follicles are atrophic, lined by Hurthle cells.
- Hurthle cells or Askanazy cells are metaplastic transformation of follicular cells.They have abundant eosinophilic granular cytoplasm (eosinophilic appearance is due to abundance of mitochondria in the cytoplasm).
- Hurthle cells are virtually pathognomonic] - scanty or no colloid within the follicle.
- There is mild to moderate: fibrosis (but not to the extent seen in Riedel's thyroiditis)
- Presence of Hurthle cells and lymphocytes on FNAC is characteristic of Hashimoto thyroiditis.
- Thyroid Bcell lymphoma is a rare but well recognized complication of Hashimoto's thyroiditis..
- Papillary thyroid carcinoma may also be occasionally associated.
CLINICAL PRESENTATION OF HASHIMOTO'S THYROIDITIS
- Like other autoimmune disease, more common in women (Male female ratio 1:10)
- Age :30-50 yrs. Most common presentation is that of a minimally or moderately enlarged firm gland with tenderness[20% of patients present with hypothyroidism, and 5% present with
- hyperthyroidism (hashitoxicosis)!
- On examiantion an enlarged pyramidal lobe is often palpable.
- Mild hyperthyroidism may be present initially (d/t destruction of thyroid tissue) but hypothyroidism is inevitable and usually permanent.
- Thyroid-associated ophthalmopathy is rare in patients with chronic autoimmune thyroiditis
INVESTIGATIONS IN A CASE OF HASHIMOTO'S THYROIDITIS
Laboratory findings are:
- Elevated TSH, reduced T4 & T3 levels.
- presence of thyroid autoantibodies (particularly TPO antibody)
- In cases of doubt, diagnosis is confirmed by FNA biopsy.
MANAGEMENT IN A CASE OF HASHIMOTO'S THYROIDITIS
- Thyroid hormone replacement therapy for overtly hypothyroid patients or in euthyroid patients to shrink large goiters.
- Surgery may occasionally be indicated for suspicion of malignancy or for goiters causing compressive symptoms or cosmetic deformity.
Exam Question of:
- Follicular destruction ,Increase in lymphocytes ,Oncocytic metaplasia is seen in Hashimoto's Thyroiditis.
- Orphan Annie eye nuclei is not seen in Hashimoto's Thyroiditis.
- Thyroid follicular infiltration by lymphocytes along with the presence of Hurthle cells is characteristic of Hashimoto's disease.
- Hashimoto's thyroiditis is an autoimmune disorder.
- In case of an Autoimmune disease,following is present: T cells recognise self antigen , Hashimoto's thyroiditis is an example, Polyclonal B cell activation.
- Higher incidence among females is present in an Autoimmune disease.
- In hashimoto's disease serum antibodies are mainly against Thyroid follicles and thyroglobulin.
- There is increased risk of developing B-cell lymphoma in Hashimoto's thyroiditis.
- 'Hurthle cells' are seen in Hashimoto's thyroiditis.
- Most common cause of Thyroiditis is Hashimoto's thyroiditis.
- Antithyroid nuclear antibodies are not seen in Hashimoto's thyroiditis.
- Antithyroid microsomal antibodies ,Anti TSH receptor antibodies and Increased level of thyroid hormones may be seen in Hashimoto's thyroiditis.
- Enlargement of thyroid gland with tenderness is most commonly seen in Hashimoto's thyroiditis.
- Anti-TPO antibodies are present in Hashimoto's thyroiditis.
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