Increasing thyroid nodule size impacts cancer risk in a nonlinear fashion. A threshold is detected at 2.0 cm, beyond which cancer risk is unchanged. However, the risk of follicular carcinomas and other rare thyroid malignancies increases as nodules enlarge.

Context The impact of Hashimoto thyroiditis (HT) on the risk of thyroid cancer and its accurate detection remains unclear. The presence of a chronic lymphocytic infiltration imparts a logical mechanism potentially altering neoplastic transformation, while also influencing the accuracy of diagnostic evaluation. Methods We performed a prospective, cohort analysis of 9851 consecutive patients with 21,397 nodules ≥1 cm who underwent nodule evaluation between 1995 and 2017. The definition of HT included (i) elevated thyroid peroxidase antibody (TPOAb) level and/or (ii) findings of diffuse heterogeneity on ultrasound, and/or (iii) the finding of diffuse lymphocytic thyroiditis on histopathology. The impact of HT on the distribution of cytology and, ultimately, on malignancy risk was determined. Results A total of 2651 patients (27%) were diagnosed with HT, and 3895 HT nodules and 10,168 non-HT nodules were biopsied. The prevalence of indeterminate and malignant cytology was higher in the HT vs non-HT group (indeterminate: 26.3% vs 21.8%, respectively, P < 0.001; malignant: 10.0% vs 6.4%, respectively, P < 0.001). Ultimately, the risk of any nodule proving malignant was significantly elevated in the setting of HT (relative risk, 1.6; 95% CI, 1.44 to 1.79; P < 0.001), and was maintained when patients with solitary or multiple nodules were analyzed separately (HT vs non-HT: 24.5% vs 16.3% solitary; 22.1% vs 15.4% multinodular; P < 0.01). Conclusion HT increases the risk of thyroid malignancy in any patient presenting for nodule evaluation. Diffuse sonographic heterogeneity and/or TPOAb positivity should be used for risk assessment at time of evaluation.

Objective To investigate the concordance of serologic and sonographic evidence of Hashimoto’s thyroiditis with its gold standard histopathologic identification. Design We performed a retrospective analysis on a cohort of 825 consecutive patients in whom TPOAb and thyroid ultrasound were performed, and in whom thyroid nodule evaluation led to surgical and histopathologic analysis. The presence or absence of Hashimoto’s thyroiditis on histopathology was correlated with serologic and sonographic markers. We further assessed the impact of low versus high titers of TPOAb upon this concordance. Results Of 825 patients, 277 (33.5%) had histologic confirmation of Hashimoto’s thyroiditis, 235 patients (28.4%) had elevated serum levels of TPOAb, and 197 (23.8%) had sonographic evidence of diffuse heterogeneity. Of those with histopathologic evidence, only 64% had elevated TPOAb (sensitivity: 63.9%; specificity: 89.4%), while only 49% were sonographically diffusely heterogeneous (sensitivity: 49.1%; specificity: 88.9%). A subset of only 102 of 277 (37%) with histologically proven Hashimoto’s thyroiditis was positive for both TPOAb and diffusely heterogeneous. Concordance analysis demonstrated that TPOAb and histopathology had higher agreement (κ = 0.55) than did ultrasound and histopathology (κ = 0.40) for the diagnosis of Hashimoto’s thyroiditis. Higher titers of TPOAb correlated with a higher likelihood of Hashimoto’s thyroiditis, with a best cutoff of 2.11-fold the upper normal level of TPOAb. Conclusion Only moderate concordance exists between serological evidence of Hashimoto’s thyroiditis and histopathologic findings, though it increases with higher TPOAb concentration. Diffuse heterogeneity on ultrasound is a less-sensitive diagnostic tool than elevated TPOAb.