Is Very High Thyroid Stimulating Hormone Level Required in Differentiated Thyroid Cancer for Ablation Success?

Remnant ablation with radioactive iodine (I-131) is a successful form of treatment that aims to destroy the remaining residual tissue and/or metastatic tissue after total thyroidectomy in differentiated thyroid cancer (DTC) patients. High level of thyroid stimulating hormone (TSH) (≥30 mIU/L) is recommended for success of ablation treatment. In this retrospective study, our aim was to investigate whether the TSH levels at the time of ablation effect the success of radioactive iodine remnant ablation.

Patients who were diagnosed with DTC, treated with bilateral total/near total thyroidectomy and who were referred for I-131 remnant ablation were included in this study. Patients with undetectable TSH-stimulated serum thyroglobulin (Tg) level, normal physical examination, negative results on whole body scan with I-131, and no evidence of neck lymph node metastasis on ultrasound were defined as disease-free. The correlation between TSH level at the time of ablation and ablation success was assessed.

Two hundred sixty one consecutive patients were included in the present study. Mean TSH level was 19.47±6 mIU/L in the 34 patients with TSH <30 mIU/L, while mean TSH level was 73.65±27 mIU/L in the 227 patients with TSH ≥30 mIU/L during I-131 remnant ablation. Ablation was unsuccessful in only one patient with TSH <30 mIU/L who had lung metastasis. Ablation was unsuccessful in 5.1% of patients with TSH ≥30 mIU/L. The effect of TSH level was not significant on ablation success (p=0.472).

In conclusion, we think that a high TSH serum level alone is not a factor for the success of ablation. Age, presence of metastasis, extent of residual thyroid mass should also be considered. Especially, in the presence of metastatic tissue, obtaining adequate increase in TSH level is not always possible. The success of ablation at lower levels of TSH elevations may be sufficient for patients, and long-term hypothyroidism may not be required.