Nieckarz J A, Daniel G B
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville 37901-1071, USA.
Vet Radiol Ultrasound. 2001 Sep-Oct;42(5):448-57. doi: 10.1111/j.1740-8261.2001.tb00969.x.
Many hyperthyroid cats referred for thyroid imaging and 131I therapy are concurrently or recently receiving antithyroid medications. The effect of the antithyroid drug, methimazole, on thyroid uptake of 99mTcO4 and 123I was evaluated in 8 normal cats. Quantitative analysis was used to determine the normal percent dose uptake of 99mTcO4 and 123I, the change in thyroid:salivary ratios (T:S) of 99-TcO4 over time, and the duration of the methimazole effect on thyroid uptake of 123I. Methimazole was administered to 5 cats for 3 weeks in which a hypothyroid state was obtained; 3 cats served as non-treatment controls. 99mTcO4 and 8 and 24 hour 123I imaging was repeated after 3 weeks of methimazole therapy (time of maximum T4 suppression). Methimazole was then discontinued and 123I images and serum T4 concentrations were repeated at 1, 4, 9, 15, and 24 days post withdrawal. The percent dose uptake of 99mTcO4 increased throughout the acquisition period with maximum uptake occurring 4 hour post injection. The baseline 20 min. T:S ratio for controls and treatment cats were 0.79 +/- 0.08 and 0.81 +/- 0.05 respectively; with a peak value of 1.29 +/- 0.23 and 1.31 +/- 0.18 at 4 hours. The baseline T:S ratios were not significantly different from 20 minutes to 2 hours, however they were significantly elevated at 4 hours post injection. Baseline, 8 and 24 hour percent dose uptake of 123I were 2.1 +/- 0.42% and 7.04 +/- 1.24%, respectively. There was a significant increase in the T:S ratio in the treatment group at all time points. The 8 hour percent dose uptake of 123I at 1, 4, and 9 days post methimazole withdrawal were significantly increased and peaked at 4 days. The 24 hour uptake was significantly increased at 4 and 9 days, with peak uptake at 9 days post-methimazole withdrawal. The 123I percent dose uptake decreased to baseline values by day 15 post withdrawal. Radioiodine uptake is not inhibited by methimazole treatment in normal cats, and is significantly enhanced after recent withdrawal. This finding is supportive of a "short term rebund effect" with maximal enhanced uptake between 4 and 9 days after discontinuing antithyroid drugs. The increased uptake of 99mTcO4 may also affect the interpretation of 99mTcO4 thyroid scintigraphy for 2-3 weeks.
许多因甲状腺成像和¹³¹I治疗而转诊的甲亢猫同时或近期正在接受抗甲状腺药物治疗。在8只正常猫中评估了抗甲状腺药物甲巯咪唑对甲状腺摄取⁹⁹ᵐTcO₄和¹²³I的影响。采用定量分析来确定⁹⁹ᵐTcO₄和¹²³I的正常摄取剂量百分比、⁹⁹ᵐTcO₄的甲状腺与唾液比值（T:S）随时间的变化以及甲巯咪唑对¹²³I甲状腺摄取的作用持续时间。给5只猫服用甲巯咪唑3周以使其处于甲状腺功能减退状态；3只猫作为未治疗对照。在甲巯咪唑治疗3周后（T4抑制最大时）重复进行⁹⁹ᵐTcO₄以及8小时和24小时¹²³I成像。然后停用甲巯咪唑，并在停药后1、4、9、15和24天重复进行¹²³I成像和血清T4浓度检测。在整个采集期间，⁹⁹ᵐTcO₄的摄取剂量百分比增加，最大摄取发生在注射后4小时。对照组和治疗组猫的基线20分钟T:S比值分别为0.79±0.08和0.81±0.05；在4小时时峰值分别为1.29±0.23和1.31±0.18。从20分钟到2小时，基线T:S比值无显著差异，但在注射后4小时显著升高。¹²³I的基线、8小时和24小时摄取剂量百分比分别为2.1±0.42%和7.04±1.24%。治疗组在所有时间点的T:S比值均显著增加。甲巯咪唑停药后1、4和9天的¹²³I 8小时摄取剂量百分比显著增加，并在4天达到峰值。停药后4天和9天的24小时摄取显著增加，在停药后9天达到摄取峰值。¹²³I摄取剂量百分比在停药后15天降至基线值。在正常猫中，甲巯咪唑治疗不会抑制放射性碘摄取，且在近期停药后会显著增强。这一发现支持了“短期反弹效应”，即在停用抗甲状腺药物后4至9天摄取增强最大。⁹⁹ᵐTcO₄摄取增加也可能在2至3周内影响⁹⁹ᵐTcO₄甲状腺闪烁显像的解读。
