Letter: Diagnostic Whole-Body Scan May Not Be Necessary for Intermediate-Risk Patients with Differentiated Thyroid Cancer after Low-Dose (30 mCi) Radioactive Iodide Ablation (Endocrinol Metab 2014;29:33-9, Eon Ju Jeon et al.)

The initial treatment of differentiated thyroid cancer (DTC) is thyroidectomy, followed by remnant ablation with radioiodine (I-131). However, substantial uncertainty persists over the indications and optimal dose for I-131. In addition, the usefulness of a follow-up diagnostic I-131 whole-body scan (WBS) performed within 6 to 12 months after initial therapy is controversial [1]. Although a diagnostic WBS is not recommended for low-risk patients, it may be of value in the follow-up of patients with high or intermediate risk [2]. Since incidence of DTC and patients who undergo remnant ablation has been increasing rapidly, these issues are interesting and important to clinicians. Jeon and Jung [3] demonstrated that a postablation diagnostic I-131 WBS in intermediate-risk patients with DTC may not be necessary. Although the authors suggested their study results carefully, in my opinion, below mentioned point need to be emphasized. According to this study, among 255 intermediate-risk patients, 233 had no I-131 uptake in the thyroid bed, and 22 had I-131 uptake on the thyroid bed. On diagnostic WBS, the group showing uptake had significantly higher lymph node metastasis and on average had stimulated thyroglobulin (TG) levels below 2 ng/mL in the absence of TG antibodies. Among the 22 patients showing uptake in the thyroid bed, only five revealed stimulated TG levels above 2 ng/mL. Stimulated TG levels alone did not represent thyroid uptake in a significant portion of patients, and alone was not sufficient to screen patients. Although the recurrence of thyroid cancer was not statistically different between the group with no uptake and the group with uptake in the thyroid bed, the duration of followup was short. Moreover, only one among four patients with recurrence showed stimulated TG levels above 2 ng/mL and diagnostic WBS showed no uptake in three patients with DTC recurrence. Prospective, long-term studies on whether patients with or without a thyroid remnant in diagnostic WBS show different prognoses and outcomes will provide important information about this issue. Long-term follow-up data from 17 patients with thyroid bed uptake in this study is expected to provide important information despite the small number of patients. In real practice, the recommended preparatory low-iodine diet before diagnostic WBS is very stressful and bothersome for patients. Therefore, these results by Jeon and Jung [3] will be very valuable data in establishing an evidence-based follow-up strategy for DTC.