'Incidental' and 'non-incidental' thyroid papillary microcarcinomas are two different entities.

OBJECTIVE: Papillary thyroid microcarcinomas (microPTC) may be 'incidental' (Inc-microPTC), occasionally found at histology after surgery for benign disease or 'non-incidental' (Non-Inc-microPTC), diagnosed on clinical grounds. It is unclear whether these different microPTC reflect the same disease. The aim of the study was to compare Inc-microPTC and Non-Inc-microPTC for clinical and histological features as well as for serum TSH, a known factor involved in PTC development. DESIGN: We evaluated histology and serum TSH levels of consecutive patients submitted to thyroidectomy for goiter with compressive symptoms or for cytological diagnosis suspicious/indicative of PTC. METHODS: In total, 665 consecutive patients (259 with a single thyroid nodule, SN and 406 with a multinodular gland, MN) were included in the study. According to histology, patients were classified as: benign nodular goiter (Benign, n=291); Inc-microPTC (n=92); Non-Inc-microPTC (n=67) and PTC≥1cm (macroPTC, n=215). RESULTS: Inc-microPTC were significantly more frequent in MN than in SN (66/406, 16.2% vs 26/259, 10.0%, P=0.02). Patients with Inc-microPTC compared with Non-Inc-microPTC were older (mean age±s.d. 53.3±13.2 years vs 44.9±14.8 years, P=0.0002), had a smaller tumor size (median 4mm vs 9mm, P<0.0001), a higher frequency of multifocality (70/92, 76.1% vs 35/67, 52.2% P=0.001) and lower levels of TSH (median 0.6mIU/L, IR: 0.4-1.0mIU/L vs value 1. mIU/L, IR: 0.6-1.4mIU/L vs P=0.0001). CONCLUSION: Incidental and non-incidental papillary thyroid microcarcinomas appear to be two different entities.

Iodine contributes to thyroid autoimmunity in humans by unmasking a cryptic epitope on thyroglobulin.

CONTEXT: The mechanisms linking thyroid autoimmunity and iodine use in humans are unknown. OBJECTIVE: Our aim was to correlate iodine intake, thyroid autoimmunity, and recognition of thyroglobulin (Tg) epitopes after implementation of iodine prophylaxis. SETTING: The general community living in an Italian village was evaluated. MAIN OUTCOME MEASURES: Thyroglobulin autoantibodies (TgAb), thyroperoxidase autoantibodies (TPOAb), and urinary iodine excretion were assessed in 906 iodized salt users (IS-users) and 389 nonusers (IS-nonusers). Ultrasound (US) was performed to identify thyroid hypoechogenicity, suggestive of Hashimoto thyroiditis (HT). TgAb epitope pattern in 16 IS-users and 17 IS-nonusers was evaluated by an inhibition binding assay to Tg, using human monoclonal TgAb-Fab directed to A, B, C, and D epitopes on Tg. RESULTS: Median urinary iodine excretion was slightly higher in IS-users than in IS-nonusers (112.0 µg/L vs 86.5 µg/L; P < .01). TgAb, and not TPOAb, was more frequent in IS-users (18.9% vs 13.6%, P = .02). HT-US was found in 87 subjects, among whom both positive TgAb (58.4% vs 31.8%, P = .03) and TPOAb (61.5% vs 45.4%. P = .04) were more frequent in IS-users. In this group significantly higher serum levels of TgAb (median 108 U/mL vs 30 U/mL; P = .02), but not of TPOAb, were present. Iodized salt use had no effect on the 1208 non HT-US subjects. TgAb directed to the epitope B of Tg were more frequent in IS-users than in IS-nonusers (27.5% vs 3.0%, P = .047). CONCLUSIONS: Iodine-induced thyroid autoimmunity is related to TgAb and the unmasking of a cryptic epitope on Tg contributes to this relationship in humans.