High prevalence of autoimmune thyroid disease in thyroids with oncocytic tumors.

We investigated 24 euthyroid patients with one prevalent nodule, “cold” at 99mTc-scintiscan, with Hürthle cells (HC) at fine needle aspiration cytology (FNAC). By FNAC, a diagnosis of oncocytic metaplasia (OM) or HC tumor (HCT) was suggested, when 10 – 75% HC or > 75% HC were observed, respectively. Echographic and serological evidence of Hashimoto’s thyroiditis (HT) was present in 5 cases (20.8%) and one patient (4.1%) had associated Graves’disease (GD). All patients were eventually submitted to total thyroidectomy. Histological examination displayed a malignant tumor in 14 cases, [7 HC follicular carcinoma (FC), 4 HC papillary thyroid carcinoma (PTC) and 3 PTC with OM]. Diffuse lymphocytic infitration was observed in 5 malignant HCT (2/5 FC and 3/5 PTC) and in the case with GD, which was associated to a HC-PTC. In ten cases (3 PTC and 7 benign lesions) OM was detected, and coexistent HT was observed in 2 PTC and in 1 follicular adenoma. Two occult PTC were detected in benign thyroid lesions (one follicular adenoma and one nodular HT). Taken together, istological evidence of autoimmune thyroid disease (ATD) was found in 10 (41.6%) cases, 9 of which associated to a malignant tumor. Although the presence of HC (as OM) in ATD is well known, the very high prevalence of ATD found in true HCT (6/10 cases) is surprising and suggests that HCT may often derive from pre-existent foci of OM in ATD. Moreover, an almost exclusive association of ATD with a malignant histotype was found. Whether and to what extent this supports the debated notion of a positive association between ATD and thyroid cancer is not clear, due to the selection bias of this study.