Quantitative assessment of lymphocyte infiltration and fibrosis in Hashimoto’s thyroiditis and their clinical correlations

Background Hashimoto’s thyroiditis (HT) is characterized by lymphocytic infiltration and fibrosis of the thyroid gland. We quantitatively evaluated these histopathological changes and examined their associations with thyroid function, thyroid autoantibodies, and ultrasonographic findings. Methods We retrospectively analyzed 87 patients with histopathologically confirmed HT who underwent thyroid surgery. Lymphocytic infiltration and fibrosis in non-neoplastic thyroid tissue were quantified by image analysis. Patients were classified as mild (n=15), moderate (n=55), or severe (n=17) according to conventional histopathological severity. Continuous variables were analyzed using nonparametric methods. Results Thyroid function was significantly associated with histopathological severity (P=0.0025), and TSH differed significantly among the three groups (P=0.0004). Quantitative lymphocytic infiltration and fibrosis also differed significantly among the groups (P<0.0001 and P=0.0009, respectively). TgAb correlated with lymphocytic infiltration (ρ=0.4199, P=0.0006) and fibrosis (ρ=0.3701, P=0.0026), whereas TPOAb correlated with lymphocytic infiltration (ρ=0.3754, P=0.0021) but not with fibrosis. Quantitative ultrasonographic echogenicity showed weak inverse correlations with lymphocytic infiltration (ρ=−0.3095, P=0.0035) and fibrosis (ρ=−0.2387, P=0.0260). ROC analysis showed AUCs of 0.72 for lymphocytic infiltration and 0.75 for fibrosis in relation to the presence of hypothyroidism. Conclusions Quantitative histopathological assessment demonstrated significant associations between thyroid tissue degeneration and thyroid dysfunction, autoantibodies, and ultrasonographic echogenicity. This approach may provide an objective and reproducible method for characterizing histopathological changes in HT, although further studies are needed to establish its broader clinical applicability.