Chronic Lymphocytic (Hashimoto) Thyroiditis

• Disease characterised by gradual thyroid failure, secondary to autoimmune destruction of the thyroid gland
• Pathogenesis:

  Breakdown in self tolerance to thyroid autoantigens, through immunologic mechanisms:

  1. CD8+ cytotoxic T cell-mediated cell death
  2. Cytokine-mediated cell death: Excessive T cell activation → Production of inflammatory cytokines (IFNγ) → Recruitment and activation of macros → Damage to follicles
  3. Binding of anti-thyroid Abs (antithyroglobulin, anti-thyroid peroxidase, antimicrosomal Abs, etc.) → Ab-dependent cellmediated cytotoxicity
  4. • Linkage to cytotoxic T-lymphocyte-associated Ag-4 gene (CTLA4)
• Macroscopic Features:

  •Diffusely, symmetrically enlarged thyroid (initially)

  • Symmetrically small [atrophic] thyroid (end-stage)

  • Cut surface:

  • Pale and grey - tan appearance
  • Firm and slightly friable tissue
• Microscopic Findings:

  • Inflammatory infiltrates (lymphocytes, plasma cells) + Germinal centers
  • Atrophic thyroid follicles, lined by Hürthle or Oxyphil cells (marked eosinophil., granular cytopl.)
• Clinical features:

  • Painless, symmetric and diffuse enlargement of the thyroid
  • Associated hypothyroidism (gradual development)
  • Co-existence with other autoimmune diseases (e.g. Addison’s disease, Pernicious Anaemia)
• Complications: • Increased risk for development of B - cell non Hodgkin lymphomas, within the thyroid gland