Moderate hypothyroidism in preparation for whole body 131I scintiscans and thyroglobulin testing

Is 3-4 Weeks Required for TSH to Rise Post Thyroidectomy? A prospective Study and Discussion of its Implications on Patient Care

CONTEXT

In patients with differentiated thyroid cancer (DTC), for the purpose of radioiodine (¹³¹I) whole-body scan and treatment of remnant, or residual tumor, or metastatic disease, thyroid hormone withdrawal remains the standard approach for raising thyroid-stimulating hormone (TSH) levels to ensure adequate radioiodine uptake. Thyroid hormone is withdrawn 3-4 weeks prior radioiodine therapy (RAIT) to allow the serum-TSH concentration to rise to above 25-30 mU/L.

AIMS

We studied the time taken for TSH to rise in 40 patients after total thyroidectomy operated for DTC.

SETTINGS AND DESIGN

Prospective observational study.

METHODS AND MATERIALS

40 patients with proven differentiated thyroid cancer attending a tertiary care center were studied.

STATISTICAL ANALYSIS USED

Data was analyzed by using SPPSS software for windows (version 15, SPSS Inc., Chicago, USA).

RESULTS

After performing preoperative TSH in all patients excluding preoperative TSH elevation, it was planned to collect weekly postoperative samples till TSH ≥30. The mean (standard deviation, SD) age of the cohort was 40 (13) years with 35 females (88%) and their mean (SD) preoperative TSH was 3.6 (1.35) mIU/L. At the end of the first week postoperatively, the mean TSH of the cohort was 24.25 (6) with 8 patients (20%) achieving the cut-off of TSH ≥30 mIU/L and 30 patients (75%) achieving TSH level ≥20 mIU/L. At the end of the second week, the mean TSH was 53 (17) with all patients (100%) achieving a TSH level >30 mIU/ml.

CONCLUSIONS

An iodine whole-body scan can be performed in 10-14 days after total thyroidectomy instead of the usual wait time of 4 weeks. This could improve patient QOL and avoid complications related to prolonged hypothyroidism.

A new appraisal of iodine refractory thyroid cancer

Thyroid cancer incidence is increasing all over the world - mostly due to an increase in the detection of small tumors that were previously undetected. A small percentage of these tumors lose the ability to uptake and/or to respond to radioiodine (RAI) therapy, especially in metastatic patients. There are several new therapeutic options that have emerged in the last 5 years to treat RAI refractory thyroid cancer patients, however, it is very important to properly identify RAI refractory patients and to clarify those appropriate for these treatments. In this review, we discuss the RAI refractory definitions and the criteria that have been suggested based on RAI uptake in the post therapy scan, as well as the response after RAI therapy and the possible molecular mechanisms involved in this process. We offer a review of the therapeutic options available at the moment and the therapeutic considerations based on a patient's individualized personal characteristics, primary tumor histology, tumor burden and location and velocity of lesion growth.

Postoperative stimulated thyroglobulin level and recurrence risk stratification in differentiated thyroid cancer

BACKGROUND

Postoperative preablative stimulated thyroglobulin (ps-Tg) has been evaluated in predicting prognosis and success of ablation regarding differentiated thyroid cancer (DTC); however, its relationship with recurrence risk and radioiodine decision-making remains uncertain, especially in Chinese DTC patients. We aimed to evaluate the association between ps-Tg and recurrence risk stratification in DTC, to provide incremental values for ps-Tg in postoperative assessment and radioiodine management.

METHODS

Seven hundred and seven patients with DTC were included; low-risk (L; n = 90), intermediate-risk (I; n = 283), and high-risk (H; n = 334, 117 with distant metastasis [M1]) patients were divided according to recurrence risk stratification. The M1 group was further analyzed regarding evidence of metastasis. Cut-off values of ps-Tg were obtained using receiver operating characteristic analysis.

RESULTS

Patients with more advanced disease at initial risk stratification were more likely to have higher ps-Tg levels (I vs. L: P < 0.05; H vs. I: P < 0.001; H vs. L: P < 0.001). The corresponding cut-off value of ps-Tg for distinguishing sensitivity and specificity in each of the two groups was 2.95 ng/ml (I vs. L: 61.5%, 63.3%), 29.5 ng/ml (H vs. I: 41.9%, 92.6%), 47.1 ng/ml (M1 vs. M0 in the H group: 79.5%, 88.9%) and 47.1 ng/ml (M1 vs. M0 in all patients: 79.5%, 93.7%). With the cut-off value at 47.1 ng/ml, ps-Tg was the only factor that could be used to identify distant metastases, and consequently if measured before radioiodine therapy would prevent 10.26% of patients with M1 from undertreatment.

CONCLUSIONS

Ps-Tg, as an ongoing reassessment marker, favors differential recurrence risk grading and provides incremental values for radioiodine treatment decision-making.

Comparison of conventional L-thyroxine withdrawal and moderate hypothyroidism in preparation for whole-body 131-I scan and thyroglobulin testing

PURPOSE

After thyroidectomy for thyroid cancer, patients often withdraw L-T4 for diagnostic or therapeutic purposes, showing signs and symptoms of hypothyroidism. A slighter hypothyroidism (reducing L-T4 to one-half) has been proposed to limit these inconveniences. We evaluated half-dose L-T4 protocol, in comparison to conventional L-T4 withdrawal, in terms of effectiveness and improvement of clinical and biochemical disorders.

METHODS

We randomized 55 thyroid cancer patients into two groups: 29 patients underwent 5 weeks of half-dose of previous L-T4 treatment (HD group); 26 patients replaced L-T4 with L-T3 for 3 weeks followed by 2 weeks of withdrawal (TW group). Clinical features (Zulewsky clinical score) and biochemical parameters (lipids, liver, and muscle enzymes) were evaluated in all patients at baseline and after 5 weeks.

RESULTS

Total cholesterol, creatine kinase, lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase increased at 5 weeks in both groups, but significantly more in TW, but no difference was found by clinical score. Patients who achieved the thyroid-stimulating hormone (TSH) target value (25 µU/ml) were 92.3% in TW group and 48.3% in HD group (p < 0.001). In the HD group, only basal TSH statistically correlated with the achievement of the TSH target. Receiver operating characteristic curves indicated that a basal TSH ≥0.52 μU/ml is required to reach an adequate TSH level.

CONCLUSIONS

Half-dose L-T4 protocol, compared to conventional L-T4 withdrawal, is associated with less biochemical disorders but no significant clinical advantage. Therefore, the half-dose protocol reaches an adequate TSH target in 48.3% of patients and is not effective unless basal serum TSH is ≥0.52 μU/ml.

Revised American Thyroid Association management guidelines for patients with thyroid nodules and differentiated thyroid cancer

BACKGROUND

Thyroid nodules are a common clinical problem, and differentiated thyroid cancer is becoming increasingly prevalent. Since the publication of the American Thyroid Association's guidelines for the management of these disorders was published in 2006, a large amount of new information has become available, prompting a revision of the guidelines.

METHODS

Relevant articles through December 2008 were reviewed by the task force and categorized by topic and level of evidence according to a modified schema used by the United States Preventative Services Task Force.

RESULTS

The revised guidelines for the management of thyroid nodules include recommendations regarding initial evaluation, clinical and ultrasound criteria for fine-needle aspiration biopsy, interpretation of fine-needle aspiration biopsy results, and management of benign thyroid nodules. Recommendations regarding the initial management of thyroid cancer include those relating to optimal surgical management, radioiodine remnant ablation, and suppression therapy using levothyroxine. Recommendations related to long-term management of differentiated thyroid cancer include those related to surveillance for recurrent disease using ultrasound and serum thyroglobulin as well as those related to management of recurrent and metastatic disease.

CONCLUSIONS

We created evidence-based recommendations in response to our appointment as an independent task force by the American Thyroid Association to assist in the clinical management of patients with thyroid nodules and differentiated thyroid cancer. They represent, in our opinion, contemporary optimal care for patients with these disorders.

Diagnostic and therapeutic use of recombinant human TSH (rhTSH) in differentiated thyroid cancer

Traditionally, withdrawal of thyroid hormone to increase serum levels of thyroid-stimulating hormone (TSH) has been used in patients with differentiated thyroid carcinoma (DTC) to optimize radio-iodine uptake and serum thyroglobulin (Tg) stimulation during follow-up and in preparation for radio-iodine therapy. However, this procedure is associated with signs and symptoms of hypothyroidism which negatively affect the patient's quality of life. Recombinant human thyrotropin (rhTSH) has provided an effective alternative to thyroid hormone withdrawal. After favourable experimental trials in humans, rhTSH obtained regulatory approval in North America and in Europe as a diagnostic tool, and more recently as a preparation for radio-iodine thyroid remnant ablation. Since then, rhTSH has radically changed the diagnostic and therapeutic management of DTC patients. This review will focus on the clinical application of rhTSH in the management of DTC, highlighting current indications and future perspectives.

Health status, mood, and cognition in experimentally induced subclinical hypothyroidism

OBJECTIVE

The objective of the study was to determine whether subclinical hypothyroidism causes decrements in health status, mood, and/or cognitive function.

DESIGN

This was a double-blinded, randomized, crossover study of usual dose l-thyroxine (L-T4) (euthyroid arm) vs. lower dose L-T4 (subclinical hypothyroid arm) in hypothyroid subjects.

PATIENTS

Nineteen subjects on L-T4 therapy for primary hypothyroidism participated in the study.

MEASUREMENTS

Subjects underwent measurements of health status, mood, and cognition using validated instruments: Short Form 36, Profile of Mood States, and tests of declarative memory (paragraph recall, complex figure), working memory (N-back, subject ordered pointing, digit span backward), and motor learning (pursuit rotor). The same measures were repeated after 12 wk on each of the study arms.

RESULTS

Mean TSH levels increased to 17 mU/liter on the subclinical hypothyroid arm (P < 0.0001). Mean free T4 and free T3 levels remained within the normal range. The Profile of Mood States fatigue subscale and Short Form 36 general health subscale were slightly worse during the subclinical hypothyroid arm. Measures of working memory (N-back, subject ordered pointing) were worse during the subclinical hypothyroid arm. These differences did not depend on mood or health status but were related to changes in free T4 or free T3 levels. There were no decrements in declarative memory or motor learning.

CONCLUSIONS

We found mild decrements in health status and mood in L-T4-treated hypothyroid subjects when subclinical hypothyroidism was induced in a blinded, randomized fashion. More importantly, there were independent decrements in working memory, which suggests that subclinical hypothyroidism specifically impacts brain areas responsible for working memory.

Managing thyroid cancer without thyroxine withdrawal

Thyroxine (T4) withdrawal or recombinant TSH is used for the stimulation of thyroglobulin (Tg), whole-body scanning (WBS) and iodine-131 treatment in patients with thyroid carcinoma. This study evaluated the T4 dose reduction protocol as an alternative for patients' preparation. Fifty-one patients were submitted to total T4 withdrawal for WBS and Tg measurement. T4 treatment was then resumed and maintained until TSH reached levels < 0.3 mIU/l. The T4 dose was then decreased to 0.8 µg/kg/day and TSH was measured weekly. Tg was assayed when TSH was > 30 mIU/l. Patients diagnosed with the disease upon initial evaluation were treated. We also evaluated the clinical and laboratory changes observed for both preparations. Using the reduced dose protocol, TSH levels > 30 mIU/l were reached within 6 and 8 weeks in 84.6 and 100% of the patients, respectively. T4 withdrawal was associated with more common symptoms of hypothyroidism and elevation of creatine kinase (CK) and LDL cholesterol. The T4 dose reduction protocol proved to be useful for Tg stimulation and ablative therapy, without the complication of severe hypothyroidism or the cost of recombinant TSH.

Acute changes in clinical parameters and thyroid function peripheral markers following L-T4 withdrawal in patients totally thyroidectomized for thyroid cancer

After total thyroidectomy, differentiated thyroid cancer (DTC) patients have to undergo L-T4 withdrawal for measuring serum thyroglobulin and 131I whole-body scan (131I WBS) to evaluate residual/recurrent malignant disease. The aim of the present work was to study in these patients the effects of acute thyroid hormone deficiency on various target organs and tissues. Clinical parameters and thyroid function peripheral markers were evaluated in 20 DTC patients, both before and after L-T4 withdrawal. A 24-h urine collection, a fasting blood sample for laboratory examinations, a clinical score for hypothyroidism and cardiovascular, neurological and neuropsychological evaluations were carried out. After L-T4 withdrawal, the clinical score significantly increased, as well as total cholesterol, triglycerides, creatine kinase, lactate dehydrogenase, aspartate aminotransferase and alanine aminotransferase, whereas SHBG, osteocalcin and urine hydroxyproline levels significantly decreased. The acute thyroid hormone deficiency caused a systolic dysfunction of the left ventricle associated with an increase in systemic vascular resistance without cardiac contractility alterations. A significant increase in the left ventricular mass and thickness was also observed. Carpal tunnel syndrome appeared in 30% of patients and a significant reduction in the immediate auditive memorization and in attentive performance was also detected. These observations indicate that acute hypothyroidism causes significant clinical alterations of peripheral tissue function. In the follow-up of DTC patients, therefore, L-T4 withdrawal procedure should be restricted to cases where the cost/benefit ratio is favorable. Alternative procedures, such as the use of recombinant human TSH, should be used whenever possible.

Thyroid hormone withdrawal in patients with differentiated thyroid carcinoma: a one hundred thirty-patient pilot survey on consequences of hypothyroidism and a pharmacoeconomic comparison to recombinant thyrotropin administration

The study objective was to elucidate clinical, quality-of-life, and pharmacoeconomic effects of hypothyroidism secondary to thyroid hormone withdrawal (withdrawal) in athyroid patients with differentiated thyroid cancer (DTC). We also intended to compare societal costs of withdrawal and recombinant human thyroid-stimulating hormone administration (rhTSH) in this population. We mailed a 13-item pilot survey to patients with DTC who had undergone withdrawal before diagnostic whole-body scan (dxWBS). Using survey results and actual and estimated cost data, we retrospectively constructed a societal cost model comparing withdrawal versus rhTSH and performed a sensitivity analysis by increasing the conservatism of 8 assumptions about withdrawal costs. One hundred thirty (55%) of 236 patients answered the questionnaire. Among respondents, 92% had symptomatic and 85% multisymptomatic hypothyroidism. Almost half sought medical attention for hypothyroid complaints. Approximately one third drove motor vehicles while hypothyroid. Median absence from salaried work was 11 days per withdrawal. In the pharmacoeconomic model, societal costs per dxWBS were approximately 326 euro (25%) greater for withdrawal than for rhTSH. In the sensitivity analysis, societal costs of rhTSH exceeded those of withdrawal by approximately 307 euro (30%). In conclusion, hypothyroidism secondary to withdrawal causes important morbidity, safety risks, and productivity impairment. rhTSH avoids these drawbacks at roughly equivalent societal cost to that of withdrawal.

Clinical value of different responses of serum thyroglobulin to recombinant human thyrotropin in the follow-up of patients with differentiated thyroid carcinoma

In the present study we examined the clinical value of a differential response of thyroglobulin (Tg) concentration after recombinant human thyrotropin (rhTSH) stimulation (rhTSH Tg testing) and its correlation with (131)I uptake and whole-body scanning (rhTSH-WBS) in 104 patients who had previously undergone near-total thyroidectomy and (131)I ablation for differentiated thyroid carcinoma (DTC). rhTSH Tg testing was considered negative for rhTSH-Tg less than 0.9 ng/mL, low positive for rhTSH-Tg of 1-5 ng/mL and high positive for rhTSHTg greater than 5 ng/mL. rhTSH Tg testing was negative in 70 patients, 1 of whom had a lymph-node metastasis, but no (131)I uptake. Seven patients had low positive rhTSH Tg testing and no (131)I uptake, but 2 of these patients had cervical lymph node metastases. Twenty-seven patients had high positive rhTSH Tg testing and (131)I uptake was detected in lung, bone, or mediastinum in 11. Imaging techniques (computed tomography [CT], magnetic resonance imaging [MRI], fluorine-18 2-fluoro-2-deoxy-D-glucose-positron emission tomography [FDGPET]) documented metastatic disease in 22. In conclusion, our results suggest that any rise in rhTSH-Tg, even at low level, should raise the suspicion of persistent or recurrent DTC. Patients with rhTSH-Tg at high level should be carefully evaluated, because DTC persistence is highly probable. TSH-WBS provides little adjunctive information.

Clinical value of different responses of serum thyroglobulin to recombinant human thyrotropin in the follow-up of patients with differentiated thyroid carcinoma

In the present study, we examined the clinical value of a differential response of thyroglobulin (Tg) concentration after recombinant human thyrotropin (rhTSH) stimulation (rhTSH Tg testing) and its correlation with (131)I uptake and whole body scanning (rhTSH-WBS) in 104 patients who had previously undergone near total thyroidectomy and (131)I ablation for differentiated thyroid carcinoma (DTC). RhTSH Tg testing was considered negative for rhTSH-Tg < 0.9 ng/mL, low positive for rhTSH-Tg of 1-5 ng/mL and high positive for rhTSHTg > 5 ng/mL. RhTSH Tg testing was negative in 70 patients, one of whom had a lymph-node metastasis, but no (131)I uptake. Seven patients had low positive rhTSH Tg testing and no (131)I uptake, but two of these patients had cervical lymph-node metastases. Twenty-seven patients had high positive rhTSH Tg testing and (131)I uptake was detected in lung, bone, or mediastinum in 11. Imaging techniques (CT, MRI, FDG-PET) documented metastatic disease in 22. In conclusion, our results suggest that any rise in rhTSH-Tg, even at low level, should raise the suspicion of persistent or recurrent DTC. Patients with rhTSH-Tg at high level should be carefully evaluated, since DTC persistence is highly probable. TSH-WBS provides little adjunctive information.

Manifestações clínicas e diagnóstico de metástases distantes de carcinoma diferenciado de tireóide após a terapia inicial

Avaliamos 58 pacientes com metástases distantes de carcinoma de tireóide diagnosticadas após a terapia inicial. Metástases linfonodais na apresentação inicial foram verificadas em 65%. Todas as metástases linfonodais, 90% das pulmonares e apenas 25% das metástases ósseas eram assintomáticas. Radiografia revelou metástases líticas em todos os casos com acometimento ósseo; foi normal em 39,6%, mostrou micrometástases em 34,5% e macrometástases em 25,8% nos pacientes com doença pulmonar. A tireoglobulina (Tg) em uso de tiroxina foi detectável (> 1ng/ml) em todos sem anticorpos anti-tireoglobulina (TgAb), > 5ng/ml em 90% e > 10ng/ml em 80% e, após a suspensão da terapia, > 5ng/ml em 100% e > 10ng/ml em 94%. Nos pacientes com TgAb (13,8%), Tg foi indetectável em metade. Varredura diagnóstica com 5mCi de iodo 131 foi positiva em 83% e 77,6% dos pacientes com metástases ósseas e pulmonares, respectivamente e após dose ablativa, a sensibilidade foi de 100 e 93%. Dos pacientes com varredura diagnóstica negativa, 85% tinham metástases pulmonares visíveis na radiografia. Concluímos que a Tg é o método mais sensível, seguro e de menor custo no seguimento de câncer diferenciado de tireóide, e reforçamos a administração direta de uma dose ablativa de radioiodo com realização de varredura pós-dose quando a Tg estiver elevada.

Cognitive changes in short-term hypothyroidism assessed with event-related brain potentials

Hypothyroidism is a common clinical problem during (131)Iodine-therapy of thyroid cancer. In the present investigation, possible cognitive dysfunction during hypothyroid state was assessed by means of neuropsychological tests and the recording of event-related brain potentials (ERPs). Fifteen patients undergoing therapy for thyroid cancer were examined twice: (1) substituted with thyroid hormones, (2) during hypothyroid state immediately prior to treatment. Standard neuropsychological tests were applied during both sessions and subjects showed a mild-to-moderate impairment in their hypothyroid state. In addition, ERPs were recorded from 19 scalp sites while subjects performed two visual search tasks. The serial task required the effortful one-by-one scanning of several items within a visual array, while the parallel task allowed processing of all stimulus items in parallel and automatically. ERPs showed a marked amplitude decrement and delay of the P3 component known to index the speed of stimulus evaluation and the amount of available processing resources. This effect was present only for the serial search task, while no changes were seen in the parallel search task. These data show that hypothyroidism during (131)Iodine-therapy is associated with clinically relevant cognitive dysfunctions, especially with effortful attention demanding tasks.

Quality of life with well-differentiated thyroid cancer: treatment toxicities and their reduction

INTRODUCTION

Patients with well-differentiated thyroid cancer have a good prognosis but a significant chance for local recurrence. In the past, limited surgery with postoperative 131I only for extremely high-risk cases or recurrence was not uncommon. As more aggressive surgical and postoperative treatments appear to gain wider acceptance, toxicity and long-term morbidity become more important issues. Our goal is to present the experience of a single institution with emphasis on oral side effects related to 131I as well as acute and chronic symptoms related to this diagnosis and their impact on quality of life.

METHODS

Fifty-seven patients were followed for a median time of 19.3 months. All patients received therapeutic 131I (mean dose, 154.7 mCi) between January 1, 1996 and August 30, 2002.

RESULTS

Fifty-four patients (94.7%) were alive at the time of analysis. Sixteen (28.1%) required a second treatment: any sign of persistence resulted in retreatment. Complaints with 131I treatment included altered taste, 26.3%; acute xerostomia, 21.1%; and acute sialoadenitis, 15.8%. Chronic xerostomia occurred in 6 (35.3%) of all patients who received multiple treatments. The incidence of chronic xerostomia was reduced to 1 of 11 (9.1%) with amifostine pretreatment. Other chronic side effects associated with this disease included fatigue 54.4%, weight gain of more than 6 months duration 24.6%, with 12 (27.9%) of those under 60 experiencing an average gain of 2.3 kg from initial diagnosis.

CONCLUSION

Review of treatment-related symptoms prompted policies to reduce toxicity including amifostine pretreatment for 131I therapy and thyrotropin (synthetic TSH) use in place of iatrogenic hypothyroidism for thyroglobulin testing and scanning.

Preparation for radioactive iodine administration in differentiated thyroid cancer patients

OBJECTIVE

Because in recent years the practice of TSH suppression has changed, and thyroxine doses have been reduced significantly in the treatment of patients with low-risk differentiated thyroid cancer, the goal of this study was to determine the time needed to attain a target TSH level (of 30 mIU/l) following levothyroxine withdrawal in patients treated with thyroxine according to current guidelines, in anticipation of radioactive iodine (RAI) administration.

DESIGN

Observational study.

PATIENTS

Thirteen consecutive patients with differentiated thyroid cancer on suppressive doses of levothyroxine planned for RAI administration. Five of the patients received cholestyramine in an attempt to facilitate TSH recovery.

MEASUREMENTS

Serum TSH, free-T3 and free-T4, at 3-4-day intervals.

RESULTS

In 13 patients on suppressive doses of thyroxine, on 15 separate occasions, baseline TSH levels were between 0.01 and 0.4 mIU/l. The mean interval required to reach the target TSH concentration of at least 30 mIU/l was 17 days (95% CI 15-19; range 11-28 days). Cholestyramine had no effect on the rate of TSH recovery. Once TSH concentration became detectable, it increased exponentially; and once it reached the upper limit of normal, it rarely took more than 10 days to attain target level.

CONCLUSIONS

Attaining target TSH level before radioactive iodine administration requires a considerably shorter time than is currently recommended. Reducing preparation time might improve patients' acceptance of the procedure.

Adequate thyroid-stimulating hormone levels after levothyroxine discontinuation in the follow-up of patients with well-differentiated thyroid carcinoma

BACKGROUND

In the follow-up of patients with well-differentiated thyroid carcinomas (WTC), a thyroid-stimulating hormone (TSH) >or=30 micro U/mL is generally accepted as adequate to perform whole body scans (WBS), determine thyroglobulin (Tg), and administer radioiodine therapeutically. These patients, inevitably rendered hypothyroid, are traditionally switched to T3 for 3-4 weeks prior to withdrawing all thyroid hormones for an additional 2-3 weeks. Neither TSH and Tg elevation dynamics nor WBS characteristics after simply interrupting L-T4 treatment without T3 administration have been evaluated.

METHODS

TSH, total T4 and T3, as well as FT4 were measured weekly after discontinuing L-T4 in 21 subjects (group I) and after thyroidectomy in 10 subjects (group II). WBS and Tg determination was performed upon achievement of TSH >or=30 micro U/mL.

RESULTS

By the second week, 42% of group I patients and 70% of group II patients had TSH >or=30 micro U/mL. By the third week, 90% in group I and 100% in group II had achieved this target. Group I patients who needed 4 weeks to increase TSH received a greater cumulative radioiodine dose and had higher Tg levels. Positive WBS were found in eight cases and the incidence of a negative WBS with elevated Tg was significantly higher when evaluation occurred at the second week of L-T4 withdrawal compared to the fourth week.

CONCLUSIONS

L-T4 interruption is a reasonable alternative to temporary T3 in preparation for radioiodine scanning and treatment.

Isotope imaging for metastatic thyroid cancer

Many isotopes are available for imaging patients with suspected thyroid cancer recurrence and metastases. TSH-stimulated low-dose 131I whole-body scanning with serum thyroglobulin either by standard LT4 withdrawal or rhTSH stimulation is the preferred test for monitoring patients without palpable disease or elevated serum thyroglobulin on LT4 therapy (Fig. 5). This approach has the advantage of finding disease that may be amenable to 131I therapy, although low-dose 131I scans are less sensitive than are scans with other imaging agents. 123I has better imaging characteristics than 131I and has been shown to be equivalent or superior to low-dose 131I in recent studies. As the availability of 123I increases and the cost decreases, this agent may replace 131I in imaging for recurrent or metastatic thyroid cancer. Patients who have an elevated serum thyroglobulin on LT4 therapy or after TSH stimulation but have a negative low-dose 131I scan require other imaging procedures to find the suspected disease. The authors currently perform a sensitive neck ultrasound to look for surgically remediable disease and consider a noncontrast CT scan of the chest to look for small pulmonary metastases that poorly concentrate low doses of 131I (Fig. 5). Fluoro-18-deoxyglucose PET, 99mTc MIBI, 201Tl, and 99mTc tetrofosmin are primarily useful in the setting of a negative whole-body 131I scan and elevated serum thyroglobulin. 18FDG-PET seems to have the highest sensitivity in this setting and would be the preferred imaging agent, but availability and cost are major issues (Fig. 5). Although some researchers have advocated these radiopharmaceuticals as first-line agents replacing 131I, there is little support for this position. This approach to imaging is not cost-effective because positive scans in these patients would most likely require 131I scintigraphy to determine whether the lesions are amenable to radioiodine therapy. 99mTc pertechnetate, 99mTc furifosmin, and somatostatin receptor scintigraphy have a limited role in imaging for recurrent or metastatic differentiated thyroid carcinoma. In choosing among 99mTc MIBI, 201Tl, and 99mTc tetrofosmin, the technetium label of sestamibi and tetrofosmin results in better image quality and faster imaging than 201Tl. Although 99mTc sestamibi and 99mTc tetrofosmin have not been compared in a large series, the higher tumor-to-background ratio and consistently high sensitivities of 99mTc tetrofosmin suggest that it could potentially have additional value over 99mTc sestamibi, but there is still limited experience with 99mTc tetrofosmin.

Detection of residual and recurrent thyroid cancer by radionuclide imaging

Radioiodine-131 imaging is the traditional method of detecting residual or recurrent differentiated thyroid cancer. The stimulation of such tissues to take up radioiodine may be achieved either by complete cessation of thyroid hormone, by partial thyroid hormone withdrawal, or by the administration of recombinant human thyrotropin (TSH). Complete or partial thyroid hormone withdrawal may result in serum TSH concentrations adequate for radioiodine imaging in up to 90% of patients. When known or suspected recurrent or metastatic disease is not evident on radioiodine imaging, single photon emission tomographic imaging with either thallium-201 chloride or technetium-99m-MIBI compounds may detect up to 80%-90% of cancers at least 1 to 1.5 cm in size, although specificity is less than with 131I. Fluorine-18-FDG positron emission tomography is a somewhat less available but acceptable substitute for thallium-201 or 99mTc-MIBI imaging. Tumor foci that concentrate either TI-201 or 18FDG intensely with little or no 131I uptake appear to behave more aggressively than those concentrating 131I avidly.

Comparison of administration of recombinant human thyrotropin with withdrawal of thyroid hormone for radioactive iodine scanning in patients with thyroid carcinoma

BACKGROUND

To detect recurrent disease in patients who have had differentiated thyroid cancer, periodic withdrawal of thyroid hormone therapy may be required to raise serum thyrotropin concentrations to stimulate thyroid tissue so that radioiodine (iodine-131) scanning can be performed. However, withdrawal of thyroid hormone therapy causes hypothyroidism. Administration of recombinant human thyrotropin stimulates thyroid tissue without requiring the discontinuation of thyroid hormone therapy.

METHODS

One hundred twenty-seven patients with thyroid cancer underwent whole-body radioiodine scanning by two techniques: first after receiving two doses of thyrotropin while thyroid hormone therapy was continued, and second after the withdrawal of thyroid hormone therapy. The scans were evaluated by reviewers unaware of the conditions of scanning. The serum thyroglobulin concentrations and the prevalence of symptoms of hypothyroidism and mood disorders were also determined.

RESULTS

Sixty-two of the 127 patients had positive whole-body radioiodine scans by one or both techniques. The scans obtained after stimulation with thyrotropin were equivalent to the scans obtained after withdrawal of thyroid hormone in 41 of these patients (66 percent), superior in 3 (5 percent), and inferior in 18 (29 percent). When the 65 patients with concordant negative scans were included, the two scans were equivalent in 106 patients (83 percent). Eight patients (13 percent of those with at least one positive scan) were treated with radioiodine on the basis of superior scans done after withdrawal of thyroid hormone. Serum thyroglobulin concentrations increased in 15 of 35 tested patients: 14 after withdrawal of thyroid hormone and 13 after administration of thyrotropin. Patients had more symptoms of hypothyroidism (P<0.001) and dysphoric mood states (P<0.001) after withdrawal of thyroid hormone than after administration of thyrotropin.

CONCLUSIONS

Thyrotropin stimulates radioiodine uptake for scanning in patients with thyroid cancer, but the sensitivity of scanning after the administration of thyrotropin is less than that after the withdrawal of thyroid hormone. Thyrotropin scanning is associated with fewer symptoms and dysphoric mood states.

Dosimetric considerations in the radioiodine treatment of macrometastases and micrometastases from differentiated thyroid cancer

When macrometastases are delineated clearly using current radiographic techniques and/or physical examination and can be shown to concentrate 131I, the therapeutic activity to be administered may be determined quantitatively. Administrations of 131I that will deliver 30,000 rad to residual thyroid tissue or 10,000 +/- 2,000 rad to lymph node metastases will ablate them successfully 80% of the time, and bone marrow depression that is severe enough to require specialized treatment will be avoided if the whole blood dose from a single administration does not exceed 200 rad. When micrometastases are detected only by diagnostic radioiodine imaging and/or elevations of serum thyroglobulin levels, and when a clinical decision is made to treat them with radioiodine, then 131I may not be the isotope choice. With small lesions < 0.05 mm in diameter, the lower energy emissions of 125I therapy may be more suitable. With the advent of alternative methods of patient preparation for radioiodine therapy, empiric approaches that were derived from experience with endogenously hypothyroid patients will require full re-evaluation. Approaches based on quantitative radiodosimetric calculations will continue to be valid because they already consider individual differences in radioiodine kinetics.