Response to Letter: “Postoperative Thyroglobulin and Neck Ultrasound in the Risk Restratification and Decision to Perform ¹³¹I Ablation”

We thank you for the opportunity to answer the letter by Giovanella et al. We also thank the authors for their interest in our study. However, we want to make some rebuttals to their comments.

First, we agree with Giovanella et al. that our study (1) demonstrates that preablation basal Tg and neck ultrasound (nUS) are able to predict the results of the postablation whole-body scan (ptWBS), and for this reason we strongly believe they are useful in deciding whether to perform ¹³¹I remnant ablation. In fact, if undetectable or low levels of preablation serum Tg accompanied by a negative nUS are predictive of a negative ptWBS, there is no rationale in treating this group of patients. Our study demonstrated that when serum postoperative Tg is <0.1 ng/mL (in the absence of detectable Tg antibodies), and the nUS is negative, we already reached the condition of excellent response (2) because none of these cases had an extrathyroidal uptake. Thus, there is no need to treat these cases until evidence this choice is wrong, and also because until now nobody has demonstrated that by treating these kind of patients with remnant ¹³¹I ablation the risk of recurrence is reduced (3).

We also observed that in one case, serum Tg was <0.1 ng/mL, but nUS was positive for lymph nodes metastases. This finding explains part of the title of our paper, which Giovanella et al. did not mention, in which we say that nUS, more than Tg, can impact risk restratification. In fact, this case, independent from its original risk level, can now be considered a structural persistent case (4).

Second, as far as the problem of the ptWBS, in our series, there were no big remnants (i.e., none were positive for thyroid tissue in the thyroid bed at nUS), and the level of uptake was very low, whereas it would be much higher if lesions other than the remnant were present. We agree that single-photon emission computed tomography/computed tomography would be more precise (5), but our ptWBS is performed after a period of time that is calculated to avoid the star effect that is the most important reason for equivocal imaging. Nevertheless, if some equivocal imaging is present, other cross-sectional images are taken to clarifying the case. Moreover, we very much rely on nUS that is nowadays able to detect small lymph nodes and small residual tissue in the thyroid bed. Thus, in our clinical practice, we feel comfortable performing planar whole-body scans at ablation treatment as screening whole-body scans and to reserve single-photon emission computed tomography/computed tomography to those cases with high levels of serum Tg or persistent disease after ablation treatment.

Third, for many years we have used low and fixed ¹³¹I activities (i.e., 30 mCi) for remnant ablation of low- and intermediate-risk cases, with ∼80% rate of successful ablation in a long-term follow-up (6). This technique is highly consolidated at the clinical level, and we do not need to perform a preblation diagnostic whole-body scan that might have a negative impact on thyroid uptake because of the stunning effect. The radioiodine neck uptake with very low activity of ¹³¹I (50 µCi) is done to calculate when to perform the ptWBS to avoid the star effect, which can happen if the scan is performed too early, and to improve the quality of the planar ptWBS.

Finally, we disagree with the last sentence of the letter of Giovanella et al. in which the authors say that the 2015 American Thyroid Association guidelines state that the use of imaging and Tg measurement should not be used to decide whether to ablate a differentiated thyroid cancer patient after surgery. In fact, in these guidelines, there are three figures (Figs. 5, 6, and 8) and two recommendations (50 A and 50 B) in which the authors of the guidelines clearly state that the postoperative disease status, as assessed with postoperative serum Tg measurement, neck ultrasound, and diagnostic WBS should be considered in “deciding whether additional treatment (e.g., RAI, surgery, or other treatment) may be needed” (7).

In conclusion, we think this study can add a small piece of knowledge both on the risk restratification of low- and intermediate-risk thyroid cancer patients after surgery and before ¹³¹I remnant ablation for which both Tg and nUS, but mainly nUS, can play an important role. We also think it can help decide whether to perform ¹³¹I normal thyroid remnant ablation, especially in those cases for which a selective use of ¹³¹I ablation is suggested.

Abbreviations:

 
• nUS

  neck ultrasound

 
• ptWBS

  postablation whole-body scan.

Acknowledgments

Disclosure Summary: The authors have nothing to disclose.

References

Author notes