Chronic Lymphocytic Thyroiditis May Lower Accuracy of AUS/FLUS Cytopathology in Surgical Patients.

BACKGROUND: Chronic lymphocytic thyroiditis (CLT) increases cytologic atypia on fine-needle aspiration of thyroid nodules, and its effect on rate of malignancy in atypia of undetermined significance (AUS)/follicular lesions of undetermined significance (FLUS) thyroid nodules remains unclear. This study evaluates the effect of concomitant CLT on malignancy rates of AUS/FLUS thyroid nodules in surgical patients. METHODS: Retrospective review of 1061 patients who underwent thyroidectomy for a dominant thyroid nodule from a single institution was performed. Fine-needle aspiration was classified according to the Bethesda System for Reporting Thyroid Cytopathology. Patients with AUS/FLUS cytopathology were classified into two cohorts: AUS/FLUS with CLT and AUS/FLUS without CLT. Final pathology was reviewed, and the cohorts were further stratified into benign and malignant subgroups. When applicable, patients with gene expression classifier (GEC) testing were reviewed and the positive predictive value (PPV) was calculated. RESULTS: Of the entire surgical series, 293 (28%) patients had AUS/FLUS cytopathology with a rate of malignancy of 56% (163/293) on final pathology. Seventy-three (25%) patients had AUS/FLUS with CLT, of which 44% (n = 32) were malignant by final pathology. The remaining 75% (n = 220) had AUS/FLUS without CLT, 60% (n = 131) of which were malignant. GEC testing was performed in 36 of the AUS/FLUS with CLT patients, where of the 33 suspicious results, 17 were malignant on final pathology, yielding a PPV of 52%. CONCLUSIONS: The rate of malignancy for AUS/FLUS thyroid nodules is lower with coexisting CLT, and similar to previous studies, the PPV of GEC testing is approximately 50%. Cytologic atypia due to CLT may increase more AUS/FLUS results in thyroid nodules, which may lead to overestimation of malignancy rates in this patient population.