Which histopathological feature best distinguishes Hashimoto thyroiditis from Graves disease?

Explanation

## Histopathological Distinction Between Hashimoto and Graves Disease ### Key Microscopic Features | Feature | Hashimoto Thyroiditis | Graves Disease | |---------|----------------------|----------------| | **Primary pathology** | Lymphocytic infiltration with germinal centers | Follicular hyperplasia | | **Hürthle cells** | Present (pathognomonic) | Absent | | **Fibrosis** | Progressive, can lead to fibrous variant | Minimal to absent | | **Follicular epithelium** | Atrophic, destroyed | Hyperplastic, tall columnar | | **Colloid** | Depleted or absent | Scalloped edges ("moth-eaten") | | **Vascularity** | Normal or reduced | Markedly increased | | **Germinal centers** | Present (B-cell aggregates) | Absent | **Key Point:** Hürthle cells (oncocytes with abundant mitochondria) are the hallmark of Hashimoto thyroiditis and are virtually absent in Graves disease. ### Pathological Basis **Hashimoto Thyroiditis:** - Autoimmune destruction of thyroid follicles - Lymphocytic infiltration with plasma cells - Germinal centers indicate active B-cell response - Progressive fibrosis in late stages - Results in hypothyroidism **Graves Disease:** - Stimulating TSH receptor antibodies (TRAb) - Follicular hyperplasia with increased height of epithelium - Increased vascularity and blood flow - No significant lymphocytic infiltration - Results in hyperthyroidism **High-Yield:** The presence of germinal centers + Hürthle cells = Hashimoto. Tall follicular epithelium + increased vascularity = Graves. **Clinical Pearl:** Hashimoto can progress to fibrous thyroiditis (Riedel thyroiditis-like appearance), but this is still distinguished by the prior history of lymphocytic infiltration and Hürthle cell change. [cite:Robbins 10e Ch 24]