131I-SPECT/CT usefulness in patients with Hashimoto’s thyroiditis (HT) coexistence with papillary thyroid carcinoma (PC) without risk factors at surgery followed in a long-term follow-up after thyroidectomy and radioiodine ablation

Aim/Introduction: HT coexistence with PC has been reported, but it remains controversial that autoimmune infammatory disease may afect patient outcomes after thyroidectomy and radioiodine ablation. We further evaluated this problem in HT/PC patient group in long-term follow-up. Materials and Methods: Among a large HT/ PC patient group submitted to total thyroidectomy and radioiodine ablation, 64 patients without risk factors at surgery, such as extrathyroid tumor extension, multifocality, neck lymph node (LN), or distant metastases were retrospectively enrolled. Tumor size was ≤10 in 42 cases and >10 in 22 cases. Forty-two patients were at very low risk (VL) and 22 at low risk (L). We also evaluated 283 PC age/sex control patients without HT and risk factors. All patients underwent 131I-whole-body scans (WBS) and SPECT/CT during follow-up after 185 MBq radioiodine diagnostic dose. In all cases, thyroglobulin serum levels and AbTg were sequentially assayed. Results: During follow-up, 20/64 HT/PC patients, 9 with microcarcinoma, developed metastases (Group 1), while in 44/64 cases, 33 with microcarcinoma, no metastases were ascertained (Group 2). In particular, in Group 1 patients, 9 VL and 11 L, WBS detected 9 metastatic neck LN classifed as unclear in 9 patients, while SPECT/CT identifed 24 metastases characterizing the 9 unclear lesions and also 15 occult lesions (14 neck and 1 mediastinal LN) in 11 cases. Thyroglobulin was undetectable in 16 cases (12 with AbTg) and <2.5 ng/ml in four cases (1 with AbTg). In Group 2 patients, no metastases were ascertained at WBS and SPECT/CT. Among 283 control patients, 20 (7%), 10 VL and 10L, underwent metastases during follow-up. SPECT/ CT identifed 22 neck metastatic foci and 7 distant metastases (5 mediastinal, 1 lung, 1 spine), while WBS evidenced 5 neck and 3 distant metastases (2 mediastinal and 1 lung); however, except for lung lesion, the other neoplastic foci were classifed as unclear at WBS. Thyroglobulin was ≥2.5 ng/ml in 9 cases, undetectable in 11 (3 with AbTg). Conclusion: The HT/PC patients without risk factors at surgery showed an adverse tumor course during follow-up in 31.2 % of cases, many of these with microcarcinoma. Unlike other studies in the literature, the univariate analysis showed an increased risk of metastasis in patients with HT coexistence with PC, Odds ratio of 5.98 (95% CI 2.98-12.00) p<0.0001. Moreover, 131I-SPECT/CT proved an accurate diagnostic tool to identify metastases with signifcantly (p<0.0001) better performance than WBS also when thyroglobulin was undetectable or very low.