48-year-old female underwent subtotal thyroidectomy after treatment of hyperthyroidism with antithyroid drugs failed.
- Follicles are small to medium sized and irregularly formed. Colloid within the follicular lumen is scant with scalloped margins.
- The epithelium is tall and columnar. Crowding of cells leads to formation of papillae, which in contrast to papillary carcinoma lack a fibrovascular core.
- The inflammatory infiltrate consists of small lymphocytes, not staining for intracytoplasmic immunoglobulin. In addition, positively staining plasma cells infiltrate the septae, some aligned in chains in between follicles.
Pathogenesis: Type II hypersensitivity (antibody-mediated cellular dysfunction); agonistic antibodies targeting the TSH-receptor mimic TSH effects (TSI = thyroid stimulating immunoglobulins). Consequently, hyperplasia and hypertrophy of follicular cells ensues, leading to a usually diffuse enlargement of the thyroid (diffuse goiter). Unregulated stimulation of follicular cells to produce thyroxine (T4) and triiodthyronine (T3) leads to symptoms of hyperthyroidism.