Department of Nuclear Medicine, University of Würzburg, Würzburg, Germany.
Clin Endocrinol (Oxf). 2012 Apr;76(4):577-81. doi: 10.1111/j.1365-2265.2011.04262.x.
The effects of long-term TSH-suppressive levothyroxine (LT4) therapy on thyroid hormone metabolism in patients with differentiated thyroid carcinoma (DTC) are unknown. The aim of the study was to investigate the changes in thyroid hormone metabolism after long-term TSH-suppressive LT4 therapy in patients with DTC.
Sixty one patients with DTC were followed. For each patient, frozen remnant sera from two time points were selected: time1 (drawn within 1 year of I-131 ablation; TSH on file <0·3 mIU/l; recruitment period 1999-2002) and time2 (last available sample with TSH on file <0·3 mIU/l; minimum of 3 years of continuous TSH-suppressive LT4-therapy on record). TSH, reverse triiodothyronine (rT3), total triiodothyronine (TT3) and total thyroxine (TT4) levels were measured at both time1 and time2, and relationships between these parameters were analysed.
Total triiodothyronine, TT4 and TSH levels were significantly reduced at time2 (P < 0·001), whereas LT4 dose, bodyweight and rT3 levels remained constant between time1 and time2. There were no significant changes in the relationship between the dose of LT4/kg bodyweight and TT4 levels (P = 0·14). TT4/TT3 was increased at time2 (P < 0·001), whereas TT4/rT3 and TT3/rT3 were significantly decreased at time2. There appeared to be no relationship of the effects found and advancing age.
After long-term TSH-suppressive LT4 therapy for DTC, there are significant changes in thyroid hormone metabolism, which are best explained by a combined downregulation of deiodinases subtypes 1 and 2 and an upregulation of deiodinase subtype 3.
长期 TSH 抑制左旋甲状腺素（LT4）治疗对分化型甲状腺癌（DTC）患者甲状腺激素代谢的影响尚不清楚。本研究旨在探讨 DTC 患者长期 TSH 抑制 LT4 治疗后甲状腺激素代谢的变化。
对 61 例 DTC 患者进行随访。每位患者选择两个时间点的冷冻残余血清：时间 1（在 131I 消融后 1 年内抽取；档案中 TSH<0.3mIU/L；招募期为 1999-2002 年）和时间 2（档案中最后一个 TSH<0.3mIU/L 的可用样本；记录有至少 3 年的连续 TSH 抑制 LT4 治疗）。在时间 1 和时间 2 均测量 TSH、反三碘甲状腺原氨酸（rT3）、总三碘甲状腺原氨酸（TT3）和总甲状腺素（TT4）水平，并分析这些参数之间的关系。
时间 2 时 TT3、TT4 和 TSH 水平显著降低（P<0.001），而 LT4 剂量、体重和 rT3 水平在时间 1 和时间 2 之间保持不变。LT4/kg 体重与 TT4 水平之间的剂量关系无显著变化（P=0.14）。时间 2 时 TT4/TT3 升高（P<0.001），而 TT4/rT3 和 TT3/rT3 显著降低。发现的作用似乎与年龄增长无关。
在 DTC 的长期 TSH 抑制 LT4 治疗后，甲状腺激素代谢发生显著变化，这最好用脱碘酶亚型 1 和 2 的综合下调和脱碘酶亚型 3 的上调来解释。
