Outcomes comparison of thyroxine withdrawal of 2 weeks and 3 weeks for radioiodine remnant ablation of differentiated thyroid carcinoma

Objectives: Thyroxine withdrawal (THW) for 3-4 weeks before radioiodine remnant ablation (RAA) is recommended for differentiated thyroid cancer (DTC) patients after total thyroidectomy. However, long time of THW may cause iatrogenic hypothyroidism which may influence quality of life (QoL). The objective of this study was to determine whether THW of 2 weeks is also an effective method to (1) meet the target level of TSH>30mIU/L, (2) obtain the success rate of RAA comparable with THW of 3 weeks, and (3) less impact on QoL and lipid metabolism.

Methods: After excluding those with distant metastases and incomplete tumor resection, a total of 261 patients with a history of DTC were retrospectively reviewed and underwent THW for 2 or 3 weeks before RAA. Patients were categorized by the length of THW grouping of 2-Week Group (n=136) and 3-Week Group (n=125). Serum TSH levels were measured before 131I treatment after THW. Successful ablation was defined as stimulated <1 ng/ml after at least 6 months follow-up, in the absence of interfering thyroglobulin antibodies, with or without confirmatory nuclear or other imaging studies. In addition, QoL scale (Modified Pilot Questions for Determining Effects of Hypothyroidism) was determined at the time of ablation. Changes in lipid profile were measured prior to surgery and after THW.

Results: Patients in the two groups did not differ significantly in baseline characteristics or tumor, node and metastasis (TNM) staging. The rate of reaching TSH≥30 mU/l was 94.1% (128/136) in 2-Week Group and 96.0% (120/125) in 3-Week Group, without significant differences (p=0.485). Except high density lipoprotein in 2-Week Group, there is a significant increase (p<0.05) on other lipids measured(cholesterol, triglycerides and low density lipoprotein) in pre-ablation both in 2-Week Group and in 3-Week Group compared to pre-operation. However, the two groups did differ (p<0.05) in the intra-individual percentage of increases. Patients in 2-Week Group have significantly higher (p<0.05) of cholesterol (CHOL), triglycerides (TG) and low density lipoprotein (LDL), whereas level of high density lipoprotein (HDL) did not differ (p=0.902) significantly compared with pre-operation. On the other hand, there was a significant increase (p<0.05) on all lipid indicators(CHOL, TG, HDL and LDL) in pre-ablation in 3-Week Group compared to pre-operation. However, increased rates of CHOL, HDL and LDL in 3-Week Group were significantly higher than that of in 2-Week Group. QoL was better preserved in 2-Week Group than 3-Week Group (p<0.05). Ablation was successful in 94 of 136 patients (69.1%) in 2-Week Group and in 91 of 125 patients (72.8%) in 3-Week Group, while the difference was not significant (p=0.428).

Conclusions: A preablative THW length of 2 weeks is an effective and alternative method for patients with DTC to stimulate TSH levels and may improve short-term alterations in the indicators of blood lipids and QoL during THW to a certain extent. Using of a short THW also affords an ablation success rate comparable to that seen after long THW.