Influence of human body composition on serum peak thyrotropin (TSH) after recombinant human TSH administration in patients with differentiated thyroid carcinoma

Body composition changes in patients with differentiated thyroid cancer after iodine-131 treatment and short-term levothyroxine replacement and suppression therapy

PURPOSE

The purposes of this study were to assess the changes in body composition in patients who underwent thyroidectomy due to differentiated thyroid cancer (DTC) after radioactive iodine therapy (RAI) and short-term levothyroxine (LT4) supplementation and to explore the correlations between body composition distribution and corresponding blood indices.

METHODS

Fifty-seven thyroidectomized DTC patients were included. Serum was tested for several biochemical indices of thyroid function, lipids, and bone metabolism, and body composition parameters were measured via dual-energy X-ray absorptiometry before and 4-6 weeks after RAI and LT4 supplementation.

RESULTS

The body composition of DTC patients changed after RAI. Fat mass in all parts of the body decreased (range of relative change (RRC) -12.97--2.80%). Bone mineral content (BMC) increased throughout the body (relative change (RC) 12.12%), head (RC 36.23%), pelvis (RC 9.00%), and legs (RC 3.15%). Similarly, bone mineral density (BMD) increased in different regions (RRC 3.60-26.43%), except for the arms. Notably, lean mass in the arms (RC 4.30%) and legs (RC 3.67%) increased, while that in the head decreased (RC -2.75%), while total lean mass did not change at 4-6 weeks after LT4 supplementation. Furthermore, changes in fat distribution in the android region were related to the changes in total cholesterol (r = -0.390) and low-density lipoprotein cholesterol (r = -0.354), and changes in the BMC and BMD of the lumbar spine were positively associated with the changes in calcitonin (r = 0.302 and 0.325, respectively).

CONCLUSIONS

After RAI and short-term LT4 supplementation in DTC patients, body composition rapidly and positively changed and was characterized by decreased fat mass and increased BMC and BMD.

Influence of Obesity Parameters on Different Regional Patterns of Lymph Node Metastasis in Papillary Thyroid Cancer

OBJECTIVE

Obesity increases risk of thyroid cancer. However, the association between obesity and the progression of papillary thyroid cancer (PTC) remains controversial. This retrospective study aimed to explore the relationship between obesity and regional patterns of lymph node metastasis (LNM) in PTC.

METHODS

We retrospectively reviewed data from 1015 patients with PTC. We calculated obese parameters, such as body mass index (BMI), body fat percentage (BFP), and body surface area (BSA). Logistic regression models were used to assess associations between obese parameters and the rate of lymph node metastasis (LNM), number of LNM, pattern of LNM, and lymph node ratio (LNR).

RESULTS

Higher BMI was not associated with different regional patterns of LNM in PTC. In men with PTC, high BFP was an independent predictor of total LNM, central lymph node metastasis (CLNM), total lateral lymph node metastasis (LLNM), multiple lateral lymph node metastasis, and simultaneous metastasis in lateral compartment. In addition, male patients with high BFP had higher central LNR and higher number of CLNM. For women, high BSA was an independent predictor of LLNM and level IV metastasis. Female patients with high BSA had higher number of CLNM.

CONCLUSION

BFP and BSA, possibly influenced by gender, were positively associated with the number and risk of LNM in different regions of PTC patients. However, BMI was not the predictor for aggressiveness of PTC in terms of LNM. Clinical decision-making for regional LNM in PTC patients should consider the factor of obesity.

Clinical utility of an ultrasensitive thyroglobulin assay in the follow-up of patients with differentiated thyroid cancer: can the stimulation test be avoided in patients with an intermediate recurrence risk?

SUMMARY

Serum thyroglobulin (Tg) measurement during suppression with levothyroxine (LT4) using an ultrasensitive assay (OnT4-Tg) has been proposed as a replacement of TSH-stimulated Tg measurement (OffT4-Tg) in management of patients with differentiated thyroid cancer (DTC). The aim of this study is to evaluate the capacity of an ultrasensitive Tg assay in predicting an OffT4-Tg > 2.0 ng/mL based on the OnT4-Tg in patients with DTC and an intermediate recurrence risk. We analysed 101 patients with DTC and an intermediate (n = 92) or high risk of recurrence (n = 9) who were treated with total thyroidectomy and ablation with ¹³¹I, and followed for an average of 6 years. OnT4-Tg was undetectable in 64 of 101 patients; OffT4-Tg was #x003C; 2.0 ng/mL in 61 of these 64 patients, all with negative imaging results. Furthermore, 37 of 101 patients had detectable OnT4-Tg; 32 of these 37 patients also presented OffT4-Tg > 2.0 ng/mL, and only 3 of these 32 patients had metastases detected by neck ultrasound. Considering a cutoff point of 0.1 ng/mL for OnT4-Tg, the assay had a sensitivity of 91%, specificity of 92%, positive predictive value (PPV) of 86% and the negative predictive value (NPV) of 95% when predicting an OffT4-Tg > 2.0 ng/mL (biochemical disease). The use of an ultrasensitive Tg assay allows prediction of which patients will remain disease-free even if they are at an intermediate risk of recurrence, and to decrease the need for stimulated Tg assays in two-thirds of these patients.

Indirect Basal Metabolism Estimation in Tailoring Recombinant Human TSH Administration in Patients Affected by Differentiated Thyroid Cancer: A Hypothesis-Generating Study

PURPOSE

Recombinant human TSH (rhTSH) is currently used in follow-up of patients affected by differentiated thyroid cancer (DTC). Age, sex, weight, body mass index, body surface area (BSA) and renal function are known factors affecting serum TSH peak levels, but the proper rhTSH dose to deliver to single patient remains elusive. In this study, the correlations of basal metabolic rates with serum TSH peak following rhTSH administration were investigated.

METHODS

We evaluated 221 patients affected by thyroid cancer that received a standard dose rhTSH. Blood samples were collected at pre-established time points. Data on body weight, height, and BSA were collected. The Mifflin-St Jeor and Fleisch equations were used to assess basal metabolism.

RESULTS

The median value (range) of serum TSH peaks was 142 ± 53 μU/ml. Serum TSH peaks were significantly lower in males than in females (p = 0.04). TSH values also increased with age. Data showed a significant decrease of TSH peak levels at day 3 from the administration of rhTSH when basal metabolic rates increased (p = 0.002 and p = 0.009, respectively). Similar findings were observed at day 5 (p = 0.004 and p = 0.04, respectively). A multivariate analysis of several factors revealed that patients' basal metabolism (obtained using the Mifflin-St Jeor but not Fleisch equation) predicts serum TSH level peak at day 3 (p < 0.001). These results were used to generate a new formula based on Mifflin-StJeor equation which reveals as a promising tool in tailoring rhTSH dose.

CONCLUSION

Basal metabolism appears an improving factor in tailoring diagnostic rhTSH dose in patients affected by DTC.

Strong Neck Accumulation of 131I Is a Predictor of Incomplete Low-Dose Radioiodine Remnant Ablation Using Recombinant Human Thyroid-Stimulating Hormone

The purpose of this study was to identify the factors that predict incomplete low-dose radioiodine remnant ablation (RRA) with recombinant human thyroid-stimulating hormone (rhTSH) and to report the adverse events associated with this treatment. Between 2012 and 2014, 43 consecutive patients with thyroid cancer received low-dose RRA with rhTSH after total thyroidectomy. We retrospectively investigated the adverse events during low-dose RRA and during diagnostic whole body scan (DxWBS) using rhTSH, and analyzed the rate of RRA completion and the associations between RRA completion and various clinical/pathological factors. Complete RRA was seen in 33 (76.7%) patients, and incomplete RRA was observed in 10 (23.3%). Patients with incomplete RRA had stronger neck accumulation of 131I than those with complete RRA (P < 0.001). Adverse events at RRA and DxWBS were seen in 12 and 9 patients, respectively. All events at RRA were grade 1, with one exception (grade 2 vertigo after rhTSH administration). The rate of adverse events at DxWBS was significantly higher in patients with adverse events seen at RRA (risk ratio, 3.778, P = 0.008). Strong neck accumulation of 131I is significant independent predictor of incomplete low-dose RRA. The risk of adverse events at DxWBS was higher in patients who experienced adverse events at RRA than in those who did not.

Analysis of Clinical Factors for the Determination of Optimal Serum Level of Thyrotropin After Recombinant Human Thyroid-Stimulating Hormone Administration

PURPOSE

To determine the optimal levels of thyroid-stimulating hormone (TSH) levels after administration of recombinant human TSH (rhTSH) to patients with differentiated thyroid cancer (DTC), we have analyzed the clinical parameters that affected the degree of the increase in serum levels of TSH.

METHODS

We retrospectively analyzed 276 patients with differentiated thyroid cancer (DTC), post-thyroidectomy and remnant ablation. Pearson's correlation coefficient test was used to evaluate the correlation between serum levels of TSH after rhTSH stimulation and various clinical factors, including age, sex, height, weight, body mass index (BMI), body surface area (BSA), serum blood urea nitrogen, creatinine, and estimated glomerular filtration rate (GFR). Linear regression analysis was used to determine the predictors of the degree of increase in serum TSH level after rhTSH stimulation.

RESULTS

After the rhTSH injections, all subjects achieved TSH levels of >30 μU/mL, with a mean of 203.8 ± 83.4 μU/mL. On univariate analysis, age (r = 0.255) and serum creatinine (r = 0.169) level were positive predictors for higher levels of serum TSH after rhTSH stimulation, while weight (r = -0.239), BMI (r = -0.223), BSA (r = -0.217), and estimated GFR (r = -0.199) were negative predictors. Multiple linear regression analysis revealed that serum creatinine was the most powerful independent predictor for serum levels of TSH, followed by age, BSA, and BMI.

CONCLUSIONS

An increment in serum TSH after rhTSH stimulation was significantly affected by age, BSA, BMI, and creatinine, with creatinine being the most powerful predictor. By understanding the difference in the increased levels of TSH in various subjects, their dose of rhTSH can be adjusted during scheduling for radioiodine ablation, or during follow-up (recurrence surveillance) after surgery and ablation.

Age and body composition influence TSH concentrations after administration of rhTSH

AIM

Previous studies listed body surface area (BSA), lean body mass (LBM), and age as modifying factors on the TSH concentrations after administration of recombinant human thyrotropin (rhTSH). The purpose of this study was to identify the main modifying factors on serum TSH levels and to compare the stimulation via single rhTSH injection after a short thyroid hormone withdrawal (THW) with that of the standard stimulating protocol.

PATIENTS, METHODS

106 patients with differentiated thyroid cancer (DTC) undergoing radioiodine therapy (RIT) after rhTSH administration were obtained through chart review. Two groups were evaluated: Group I was treated with a single rhTSH administration after two weeks of T3 therapy followed by one week of THW. Group II was stimulated according to the international standard protocol via rhTSH injections for two consecutive days. Serum TSH concentrations were documented prior to rhTSH administration (day 1 TSH), one day after (day 3 TSH) and 3-6 days after (mean 4.2 days, day 6 TSH) the last rhTSH injection. The following data was collected: age, gender, weight, height, BMI, LBM, BSA, residual thyroid tissue, CRP, creatinine, GFR, liver enzymes, alkaline phosphatase, cholesterol, and triglycerides.

RESULTS

Group I: Age combined with anthropometric factors like BMI (TSH increase and day 6 TSH), BSA (TSH decrease), and gender (day 6 TSH) are the main modifying factors on serum TSH concentrations after rhTSH administration. Group II: Age and lean body mass (LBM) showed a significant impact on day 3 TSH, TSH increase (day 3-day 1), and TSH decrease (day 6-day 3). Day 6 TSH was found to be influenced by GFR (group II).

CONCLUSION

Age and anthropometric parameters have significant independent influence on TSH concentrations after rhTSH injection in both groups. Anthropometric parameters (BSA, LBM) and demographic parameters (female gender) show strong influence on TSH concentrations. Further research should be conducted to examine the influence of body compartments on TSH levels through measuring total body water.

Potential use of recombinant human thyrotropin in the treatment of distant metastases in patients with differentiated thyroid cancer

OBJECTIVE

In order to effectively treat differentiated thyroid cancer (DTC) with radioiodine (RAI) it is necessary to raise serum TSH levels either endogenously by thyroid hormone withdrawal (THW) or exogenously by administration of recombinant human TSH (rhTSH). The goal of this review is to present current data on the relative efficacy and side effects profile of rhTSH-aided versus THW-aided RAI therapy for the treatment of patients with distant metastases of DTC.

METHODS

We have searched the PubMed database for articles including the keywords "rhTSH", "thyroid cancer", and "distant metastases" published between January 1, 1996 and January 7, 2012. As references, we used clinical case series, case reports, review articles, and practical guidelines.

RESULTS

Exogenous stimulation of TSH is associated with better quality of life because it obviates signs and symptoms of hypothyroidism resulting from endogenous TSH stimulation. The rate of neurological complications after rhTSH and THW-aided RAI therapy for brain and spine metastases is similar. The rate of leukopenia, thrombocytopenia, xerostomia, and pulmonary fibrosis is similar after preparation for RAI treatment with rhTSH and THW. There is currently a controversy regarding RAI uptake in metastatic lesions after preparation with rhTSH versus THW, with some studies suggesting equal and some superior uptake after preparation with THW. Analysis of available retrospective studies comparing survival rates, progression free survival, and biochemical and structural response to a dosimetrically-determined dose of RAI shows similar efficacy after preparation for therapy with rhTSH and THW.

CONCLUSION

The rhTSH stimulation is not presently approved by the FDA as a method of preparation for adjunctive therapy with RAI in patients with metastatic DTC. Data on rhTSH compassionate use suggest that rhTSH stimulation is as equally effective as THW as a method of preparation for dosimetry-based RAI treatment in patients with RAI-avid metastatic DTC.

Impact of renal function and demographic/anthropomorphic variables on peak thyrotropin after recombinant human thyrotropin stimulation: a stepwise forward multiple-regression analysis

BACKGROUND

When applying the recommended standard doses of recombinant human thyrotropin (rhTSH) in the diagnostic/therapeutic management of patients with differentiated thyroid cancer (DTC), the resulting peak TSH levels vary extensively. Previous studies applying multivariate statistics identified patient-inherent variables influencing the rhTSH/peak TSH relation. However, those results were inconclusive and partly conflicting. Notably, no independent role of renal function was substantiated, despite the fact that the kidneys are known to play a prominent role in TSH clearance from blood. Therefore, the study's aim was to investigate the impact of renal function on the peak TSH concentration after the standard administration of rhTSH used in the management of thyroid cancer. The second objective was to calculate a ranking regarding the effect sizes of the selected variables on the peak TSH.

METHODS

There were 286 patients with DTC included in the study. Univariate and multivariate analyses were performed, testing the correlation of serum creatinine and glomerular filtration rate (GFR) as surrogate parameters of renal function, age, sex, weight, height, and body surface area (BSA) with the peak TSH level. In six additional patients, the subsequent TSH pharmacokinetics after the TSH peak were measured and qualitatively compared.

RESULTS

By univariate analyses, TSH correlated negatively with BSA, GFR, weight, and height, and positively with age, female sex, and serum creatinine (p<0.001). On the multivariate analysis, the stepwise forward multiple linear regression revealed BSA and renal function as the two most influential independent variables, followed by age, sex, and height. The pharmacokinetic datasets indicated that these identified parameters also influence the TSH decline over time.

CONCLUSION

Identifying those patients with a favorable combination of parameters predicting a high-peak TSH is the first step toward an individualization of rhTSH dosing. Additionally, the subsequent TSH decrease over time needs to be taken into account. A complete understanding of the interrelation of the identified key parameters and both the TSH peak and subsequent TSH pharmacokinetics might allow for a more personalized rhTSH dosage strategy to achieve sufficient TSH levels instead of the fixed dosing procedure used at present.

Sorafenib therapy decreases the clearance of thyrotropin

OBJECTIVE

Thyroid function abnormalities are common during treatment with tyrosine kinase inhibitors such as sorafenib. Suggested causes are direct effects on thyroid tissue and increased extrathyroidal metabolism of serum thyroxine and 3,5,3-triiodothyronine. We postulated that tyrosine kinase inhibitors may affect the peripheral metabolism of TSH as well. The effect of sorafenib on TSH clearance was studied.

DESIGN

In a study of athyreotic patients on TSH suppression therapy, TSH concentrations were measured after recombinant human TSH (rhTSH) injections before and after 26 weeks of sorafenib therapy.

METHODS

Before and after the last week of sorafenib therapy, 20 patients with progressive differentiated thyroid carcinoma received a standard dose regimen of two injections 0.9 mg rhTSH on two consecutive days. TSH concentrations were measured 48 h (TSH(48 h)) and 96 h (TSH(96 h)) after the first rhTSH injection. The area under the curve (TSH-AUC), reflecting TSH content between 48 and 96 h following rhTSH administration, was calculated.

RESULTS

TSH(48 h) levels (120.5 mU/l before vs 146.3 mU/l after; P=0.029), TSH(96 h) levels (22.0 mU/l before vs 35.5 mU/l after; P=0.001), and TSH-AUC (142.7 vs 186.8 mU/l; P=0.001) were significantly higher after sorafenib treatment. Higher sorafenib doses were associated with increased changes in TSH(96 h) and TSH-AUC. In two patients, TSH levels after sorafenib therapy exceeded 200 mU/l.

CONCLUSIONS

Sorafenib therapy is accompanied by higher rhTSH levels, probably due to a decreased TSH clearance. Further studies are recommended to clarify whether a decreased clearance of TSH is sorafenib specific.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

Age modifies the response to recombinant human thyrotropin

BACKGROUND

A standardized protocol is used to administer recombinant human thyrotropin (rhTSH) in preparation for diagnostic studies and treatment in patients with thyroid cancer. The expectation is that serum TSH concentrations will peak on the day after the second injection and will be sufficiently elevated to stimulate uptake of radioiodine. We wished to test the hypothesis that TSH concentrations achieved after rhTSH injection are influenced by age.

METHODS

Patients with thyroid cancer undergoing diagnostic radioiodine scanning were identified by chart review. Serum TSH concentrations were documented 24 and 72 hours after two rhTSH injections (days 3 and 5, respectively). Responses were subdivided into four ascending patient age groups: <35, 35-49, 50-64, and >64 years. TSH concentrations after rhTSH administration were documented according to patient age.

RESULTS

There was a significant correlation between the serum TSH concentrations at both days 3 and 5 and patient age (p < 0.0001). None of the other factors examined (gender, menopausal status, weight, body mass index, baseline TSH, serum creatinine, and estimated glomerular filtration rate) were significant in multivariate analyses. The mean TSH concentration on day 3 increased significantly when patients were divided into the aforementioned groups of ascending age (96, 107, 142, and 196 mIU/L, p < 0.0001). Day 5 concentrations increased in a similar manner.

CONCLUSIONS

Both days 3 and 5 TSH concentrations were higher in older individuals after rhTSH administration. This finding did not appear to be related to body weight, body mass index, or glomerular filtration rate in a simple manner. The TSH concentration achieved may be a result of complex interactions between distribution within fat and muscle body compartments, hepatic function, and renal function. Prospective studies could examine whether the magnitude of the TSH elevation after rhTSH administration affects diagnostic or therapeutic efficacy.

Acute exogenous TSH administration stimulates leptin secretion in vivo

TSH-receptor (TSHR) has been found in a variety of cell types, including preadipocytes and adipocytes. In vitro, TSH-mediated preadipocyte and adipocyte responses include proliferation, differentiation, survival, and lipolysis. Objective To measure the response of serum leptin to exogenous administration of recombinant human TSH (rhTSH) in vivo. Patients One hundred patients with differentiated thyroid cancer already treated by total thyroidectomy and (131)I remnant ablation were enrolled. Mean (+/-s.e.m.) body mass index (BMI) was 26.9+/-0.6 kg/m(2). Methods Patients received a standard dose of rhTSH for measurement of thyroglobulin in the follow-up of their disease. Blood samples were taken for the assay of TSH and leptin before the first administration of rhTSH (time 0), and 24 h (time 1), 48 h (time 2), 72 h (time 3), and 96 h (time 4) after the first administration of rhTSH. Results Significant mean serum leptin increments, with respect to basal value, were 16, 13, 18, and 11% at times 1, 2, 3, and 4 respectively. Significant positive correlations of leptin-area under the curve with respect to basal leptin levels (r=0.43; P<0.0001) and BMI (r=0.32; P<0.005) were observed. Conclusions Acute rhTSH administration in hypothyroid subjects under l-thyroxine therapy produces a rise in serum leptin. This increase is proportional to the adipose mass suggesting that a functioning TSHR is expressed on the surface of adipocytes. The role that TSHR activation in adipocytes might play in physiological and pathological conditions remains a matter of investigation.

Serum Basal thyroglobulin measured by a second-generation assay correlates with the recombinant human thyrotropin-stimulated thyroglobulin response in patients treated for differentiated thyroid cancer

BACKGROUND

Recombinant human thyrotropin (rhTSH) stimulation is frequently used to assess the disease status of patients treated for differentiated thyroid cancer (DTC) when basal (unstimulated) thyroglobulin (b-Tg) is below the assay sensitivity limit. The objective of this study was to determine relationships between the b-Tg and the 72-hour rhTSH-stimulated Tg (rhTSH-Tg) using a second-generation immunochemiluminometric assay with a functional sensitivity of 0.05 ng/mL (microg/L).

METHODS

Serum Tg was measured in paired b-Tg and rhTSH-Tg specimens from 1029 rhTSH tests performed on 849 TgAb-negative patients during long-term monitoring for DTC.

RESULTS

Basal Tg correlated with rhTSH-Tg across b-Tg concentrations ranging from 0.05 to 1000 ng/mL (microg/L) (r = 0.85, p < 0.0001). The b-Tg concentration was unrelated to age, sex, basal TSH, 72-hour TSH, or the Tg fold response (rhTSH-Tg/b-Tg). Further, only 2/655 (0.3%) tests with b-Tg below 0.1 ng/mL (microg/L) had rhTSH-Tg above 2.0 ng/mL (microg/L) (2.9 and 3.8 ng/mL [microg/L], respectively). Thirty-three patients with three or more rhTSH tests performed over a 2- to 5-year period displayed high indexes of individuality for both the 72-hour TSH and the Tg fold response (indexes of individuality = 0.30 and 0.38, respectively). Basal Tg measured using a first-generation assay with a functional sensitivity of 0.9 ng/mL (microg/L) failed to reliably detect an rhTSH-Tg response above 2.0 ng/mL (microg/L).

CONCLUSIONS

An rhTSH-Tg response above 2.0 ng/mL (microg/L) was highly unlikely when b-Tg was below 0.1 ng/mL (microg/L). Second-generation b-Tg measurements correlated with the degree of rhTSH-Tg stimulation and thus the likelihood of having rhTSH-Tg above the customary cut-off of 2.0 ng/mL (microg/L), whereas b-Tg measured by a first-generation assay did not. Correlations between four different assays showed that the use of a fixed Tg cut-off was influenced by assay selection. Patients receiving repetitive rhTSH tests had highly reproducible rhTSH-Tg/b-Tg fold responses, suggesting that repetitive testing is unnecessary and that second-generation measurement of b-Tg trends without rhTSH stimulation would be satisfactory for the long-term monitoring of most patients with DTC.

Age influences TSH serum levels after withdrawal of l-thyroxine or rhTSH stimulation in patients affected by differentiated thyroid cancer

Recombinant human TSH (rhTSH) has been recently suggested for radioiodine ablation in patients with differentiated thyroid cancer (DTC). To date, studies are still not available about the effectiveness of rhTSH stimulation depending on the age, since serum TSH clearance may be different in younger and in older patients. The aim of this study was to investigate the influence of age to serum TSH levels after rhTSH stimulation and thyroid hormone withdrawal (THW). We retrospectively evaluated two groups of consecutive DTC patients: group 1 (311 patients, age 49.0+/-13.6 years, ranging 15-86) underwent rhTSH stimulation 6-12 months after thyroid ablation (rhTSH-group); group 2 (84 patients, age 46.9+/-13.5 years, ranging 20-77) was followed by THW (THW-group). The influence of age, gender, body mass index and body surface area to serum TSH levels were evaluated in both groups. RhTSH-group: on day 5 (d5), TSH levels were 32.7+/-21.4 microU/ml (range 0.8-136.6). By univariate analysis, d5-TSH was positively related to age (r=0.27, p=0.0001) and no correlations were found with the other parameters. At multivariate analysis, both age and gender (female) were independently associated with d5-TSH levels. THW-group: after thyroid hormone withdrawal, TSH levels were 71.1+/-36.4 microU/ml (range 8.5-200). At univariate analysis, only age was significantly and negatively related to serum TSH levels (r=-0.31, p=0.004). Our data indicate that age and gender seem to positively influence serum TSH levels after rhTSH stimulation. An opposite effect of age on serum TSH levels has been observed after THW. Therapeutic implications ((131)I-treatment) of these findings have to be better investigated in prospective studies.

Stimulation test in the follow-up of thyroid cancer: Plasma rhTSH levels are dependent on body weight, not endogenously stimulated TSH values

BACKGROUND

Stimulation testing in the first year following thyroid ablation has important prognostic value in thyroid cancer patients. Recombinant human TSH (rhTSH) is better tolerated than thyroid hormone withdrawal but provides only transient stimulation so that the TSH threshold of 30 mIU x l(-1) which defines adequate testing during thyroid hormone withdrawal is not appropriate for rhTSH stimulation. We looked at rhTSH levels after a standard two intramuscular injections of 0.9 mg rhTSH.

METHODS

Plasma rhTSH levels were measured 24 h after the second injection in 143 consecutive patients.

RESULTS

rhTSH levels showed large inter-patient variation (range: 44-240; mean+/-SD: 131+/-48). There was a strong inverse correlation between TSH levels and body weight (P<0.001). Levels lower than 80 mIU x l(-1) (corresponding to 1 SD below average) were recorded in 24 patients (16.8%). These patients had an average body weight of 79.7 kg, as compared to 67.9 kg for those patients with TSH levels higher than 80 mIU x l(-1). A withdrawal test in the first year after thyroid ablation was available in 64 patients. Only one patient (1.6%) had inadequate endogenous TSH stimulation, and there was no dependence of endogenous plasma TSH levels upon weight.

CONCLUSION

Contrary to endogenous stimulation, TSH levels after rhTSH injection vary with body weight. The dosage of rhTSH may need to be adapted in patients with more than 80 kg body weight.