Effect of TSH stimulation protocols on adequacy of low-iodine diet for radioiodine administration

Low-iodine diet (LID) is a crucial preparation for radioactive iodine (RAI) treatment or scan in thyroid cancer. The aim of this study is to analyze the influence of thyroid stimulating hormone (TSH) stimulation protocols and other clinical factors on LID adequacy. Thyroid cancer patients who underwent LID for RAI scan or treatment were retrospectively analyzed. Patients were guided to have LID for 2 weeks before RAI administration and urine iodine/creatinine ratio (UICR, μg/g Cr) was measured. TSH stimulation was conducted using either thyroid hormone withdrawal (THW) or recombinant human TSH (rhTSH) injection. Adequacy of LID was classified by UICR as ‘excellent (< 50)’, ‘adequate (50–100)’, ‘inadequate (101–250)’ and ‘poor (> 250)’. A total of 1715 UICR measurements from 1054 patients were analyzed. UICR was significantly higher in case of rhTSH use than THW (72.4 ± 48.1 vs. 29.9 ± 45.8 μg/g Cr, P < 0.001). In patients who underwent LID twice using both TSH stimulation protocols alternately, UICR was higher in case of rhTSH than THW regardless of the order of method. Among clinical factors, female, old-age, and the first LID were significant factors to show higher UICR. Although the adequacy of LID was ‘adequate’ or ‘excellent’ in most patients, multivariate analysis demonstrated that THW method, male, young age, and prior LID-experience were significant determinants for achieving ‘excellent’ adequacy of LID. In conclusion, UICR was higher and the proportion of ‘excellent’ LID adequacy was lower with rhTSH than with THW. UICR was higher also in women, old-age, and LID-naïve patients. Further researches are required to suggest effective methods to reduce body iodine pool in case of rhTSH use and to validate the efficacy of such methods on outcomes of RAI treatment.

The Influences of TSH Stimulation Level, Stimulated Tg Level and Tg/TSH Ratio on the Therapeutic Effect of 131I Treatment in DTC Patients

PurposeTo study the influences of pre-ablation TSH stimulation level, sTg and sTg/TSH ratio on the therapeutic effect of the first 131I treatment in DTCs.MethodsAccording to the thyroid stimulating hormone (TSH) levels (mU/l), all the 479 differentiated thyroid cancer (DTC) patients were divided into two groups: TSH &lt; 30 and TSH ≥ 30. The TSH ≥ 30 group was divided into three subgroups: 30 ≤ TSH &lt; 60, 60 ≤ TSH &lt; 90 and TSH ≥ 90. The clinical features and the therapeutic effects of the first 131I treatment were analyzed. The cutoffs of stimulated thyroglobulin (sTg) and sTg/TSH ratio were calculated to predict the therapeutic effect of 131I treatment.ResultsAmong the three subgroups, the TSH ≥ 90 subgroup was younger and less likely to be associated with cervical lymph node metastasis (LNM). The postoperative levothyroxine (L-T4) dose in the 60 ≤ TSH &lt; 90 subgroup was the lowest. Between the two groups, patients in the TSH &lt; 30 group had higher postoperative L-T4 dose and longer thyroid hormone withdrawal (THW) time. The excellent response rates six months after the first 131I treatment among the three subgroups and between the two groups were not of statistical significance. The distribution of different TSH stimulation levels among each response group was similar. The cutoffs for the better therapeutic effect of the first 131I treatment in sTg and sTg/TSH were &lt; 9.51 ng/ml and &lt; 0.11, respectively. Both univariate and multivariate logistic regressions showed that cervical LNM, distant metastasis, higher sTg and higher sTg/TSH ratio predicted poorer therapeutic effect.ConclusionsThere was no significant influence of TSH stimulation levels before the first 131I treatment on the therapeutic effect of DTC. The sTg/TSH ratio can be considered as another predictor of 131I therapeutic effect.

Thyroid-Stimulating Hormone Stimulation Tests in the Bottlenose Dolphin (Tursiops truncatus)

Stimulation of the thyroid with thyroid-stimulating hormone (TSH) is a potentially useful diagnostic of thyroid dysfunction, but little is known about the response of the thyroid to TSH stimulation in bottlenose dolphins (Tursiops truncatus). To better characterize the response of the dolphin thyroid to TSH stimulation, five adult dolphins participated in a TSH stimulation study. Dolphins voluntarily beached onto a padded mat and were given a 1.5 mg intramuscular injection of human recombinant TSH. Blood samples collected the day prior, at multiple intervals the day of, and daily for three days after the injection were analyzed via radioimmunoassay for free and total triiodothyronine (fT3 and tT3), and free and total thyroxine (fT4 and tT4). Significant increases in circulating fT3, fT4, and tT4 were observed with peaks occurring for all hormones the day after the TSH injection; maximal increases were 44%, 47%, and 23% for each hormone, respectively. Temporal patterns in the hormones potentially reflected feedback mechanisms countering the surge in fT3 following stimulation. Though recombinant human TSH was effective at stimulating hormone release, it is likely that use of dolphin or dolphin-derived TSH would enhance the clinical utility of the stimulation test, as would the development of antibodies specific to dolphin TSH.

Iodide Metabolism and Effects

Iodine (I2) is essential in the synthesis of thyroid hormones T4 and T3 and functioning of the thyroid gland. Both T3 and T4 are metabolically active, but T3 is four times more potent than T4. Our body contains 20-30 mg of I2, which is mainly stored in the thyroid gland. Iodine is naturally present in some foods, added to others, and available as a dietary supplement. Serum thyroid stimulating hormone (TSH) level is a sensitive marker of thyroid function. Serum TSH is increased in hypothyroidism as in Hashimoto's thyroiditis. In addition to regulation of thyroid function, TSH promotes thyroid growth. If thyroid hormone synthesis is chronically impaired, TSH stimulation eventually may lead to the development of a goiter. This chapter explores the iodide metabolism and effects of Hashimoto's disease.

Diagnostic performance of 18F-FDG-PET/CT in DTC patients with thyroglobulin elevation and negative iodine scintigraphy: a meta-analysis

Purpose To evaluate the accuracy of 18F-FDG-PET/CT for the detection of recurrent and/or metastatic diseases in differentiated thyroid cancer (DTC) patients with thyroglobulin elevation and negative iodine scintigraphy. Whether PET/CT with TSH stimulation (sPET/CT) had better diagnostic performance than PET/CT without TSH stimulation (nsPET/CT) in this scenario was also evaluated. Methods PubMed and Embase databases were searched for eligible studies from January 2001 to December 2018. Only studies with clearly stated reference standard (histopathology confirmation and/or clinical/imaging follow-up) were included. Publication bias was assessed by Deeks funnel plot. The pooled sensitivity, specificity, diagnostic odds ratio (DOR) and the area under the summary receiver-operating characteristics curve (AUC) for PET/CT was determined by random-effect analysis, respectively. sPET/CT and nsPET/CT were compared pairwise for all diagnostic estimate indexes using Z-test. Results We included 17 studies with 1195 patients in this meta-analysis. The pooled sensitivity, specificity, DOR and AUC for PET/CT on patient-based data were 0.86 (95% CI: 0.79–0.91), 0.84 (95% CI: 0.72–0.91), 31.00 (95% CI: 12.00–80.00) and 0.91 (95% CI: 0.88–0.93), respectively. There was high heterogeneity (I 2 = 80% for sensitivity, I 2 = 82% for specificity) and possible publication bias (P = 0.01). Z test did not detect statistically significant difference between sPET/CT and nsPET/CT for all the diagnostic estimate indexes (all P > 0.05). Conclusions On patient-based analysis, 18F-FDG-PET/CT has high diagnostic accuracy for the detection of recurrent and/or metastatic diseases in DTC patients with thyroglobulin elevation and negative iodine scintigraphy, but existing studies were limited by high heterogeneity and possible publication bias. The diagnostic performance of sPET/CT may be not superior to nsPET/CT.