The Impact of Hashimoto’s Thyroiditis on Thyroid Nodule Cytology & Risk of Thyroid Cancer

Abstract

Purpose: The impact of Hashimoto’s thyroiditis (HT) upon the risk of thyroid cancer and its accurate detection remains unclear. Prior studies are limited by retrospective design, selection bias, or their narrow definitions of HT. Importantly, 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 studying 9,851 consecutive patients with 21,397 nodules >1cm who underwent nodule evaluation between 1995-2017. The definition of HT included a) elevated thyroid peroxidase antibody (TPOAb) and/or, b) findings of diffuse heterogeneity on ultrasound, and/or c) the finding of diffuse lymphocytic thyroiditis on histopathology. We then determined the impact of HT on the distribution of cytology, and ultimately upon malignancy risk. Results: 2,651 patients (27%) were diagnosed with HT. In total, 3,895 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%, p<0.001; Malignant: 10.0% vs. 6.4%, p<0.001). Ultimately, the risk of any nodule proving malignant was significantly elevated in the setting of HT (RR=1.6 95% CI: 1.44-1.79 p< 0.001). This increased prevalence 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). Conclusions: Hashimoto’s thyroiditis 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.