Ectopic thyroid tissue in thyroglossal duct remnant is related to elevation of serum thyroglobulin after I-131 ablation therapy

Objectives Thyroglossal duct remnant (TGDR) is often visualized in post-ablative I-131 whole body scan (WBS). We investigated the correlation between the change of serum thyroglobulin (Tg) level after I-131 ablation therapy (IAT) and TGDR in differentiated thyroid cancer (DTC) patients.

Methods We included DTC patients after total or subtotal thyroidectomy who underwent the first IAT prepared with thyroid hormone withdrawal. We excluded patients with high level of serum anti-thyroglobulin antibody (≥ 100 U/mL), suspected regional or distant metastasis in pre- or post-ablation studies and negative iodine uptake of the anterior neck on WBS. Serum Tg was checked twice; one week after (scan Tg) as well as at the day of IAT (Tx Tg). TGDR defined as positive anterior midline uptake of the neck (above thyroidectomy bed) on WBS. Patients were divided into two groups according to the presence of TGDR (group 1; positive midline uptake, group 2; negative midline uptake). We analyzed the difference of serum Tg level or ΔTg (scan Tg - Tx Tg) between the two groups.

Results Finally, 156 patients were enrolled in this study. Ninety-one patients were included in group 1, and 65 patients in group 2. Based on univariate analysis, scan Tg level (25.86 ± 46.84 vs. 10.72 ± 19.17; P =0.006) and ΔTg (23.48 ± 45.62 vs. 8.82 ± 18.03; P = 0.006) were significantly higher in the group 1 than group 2 but age, sex, operation methods, T/N stage, overall stage and Tx Tg were not significantly different. In successive multivariate analysis, only scan Tg over 7.0 ng/ml was significant factor related with TGDR (OR = 2.879, 95% CI = 1.200-6.903; P = 0.018).

Conclusions TGDR is related to elevation of serum Tg level after IAT. Therefore, when TGDR is visualized on WBS and serum Tg is elevated after IAT, we should consider TGDR as one of the significant source of serum Tg as well as normal thyroidal parenchyma or metastatic lesions.