ORIGINAL
ARTICLE
Thiamazole Pretreatment Lowers the 131I Activity
Needed to Cure Hyperthyroidism in Patients With
Nodular Goiter
Aglaia Kyrilli, Bich-Ngoc-Thanh Tang, Valérie Huyge, Didier Blocklet,
Serge Goldman, Bernard Corvilain, and Rodrigo Moreno-Reyes
Division of Endocrinology (A.K., B.C.), Department of Nuclear Medicine (D.B., S.G., R.M.-R.), Erasme
Hospital, Université Libre de Bruxelles, 1070 Brussels, Belgium; Department of Nuclear Medicine (B.-N.T.T.), Clinique St Joseph, 6700 Arlon, Belgium; and Department of Nuclear Medicine (V.H.), Clinique
Sainte Anne St Rémi, 1070 Brussels, Belgium
Context: Relatively low radioiodine uptake (RAIU) represents a common obstacle for radioiodine
(131I) therapy in patients with multinodular goiter complicated by hyperthyroidism.
Objective: To evaluate whether thiamazole (MTZ) pretreatment can increase
efficacy.
131
I therapeutic
Design and Setting: Twenty-two patients with multinodular goiter, subclinical hyperthyroidism,
and RAIU ⬍ 50% were randomized to receive either a low-iodine diet (LID; n ⫽ 10) or MTZ 30 mg/d
(n ⫽ 12) for 42 days. Thyroid function and 24-hour RAIU were measured before and after treatment.
Thyroid volume was evaluated by either magnetic resonance imaging or single photon emission
computed tomography.
Results: Mean 24-hour RAIU increased significantly from 32 ⫾ 10% to 63 ⫾ 18% in the MTZ group
(P ⬍ .001). Consequently, there was a 31% decrease in the calculated median therapeutic 131I
activity after MTZ (P ⬍ .05). No significant changes in 24-hour RAIU were observed after diet. In the
MTZ group, median serum TSH levels increased significantly by 9% and mean serum free T4 and free
T3 concentrations decreased by 22% and 15%, respectively, whereas no changes in thyroid function
were observed in the LID group. Thyroid volume did not significantly change in either of the two
groups. At 12 months after radioiodine treatment, median serum TSH was within the normal range
in both groups.
Conclusions: MTZ treatment before 131I therapy resulted in an average 2-fold increase in thyroid
RAIU and enhanced the efficiency of radioiodine therapy assessed at 12 months. MTZ pretreatment
is therefore a safe, easily accessible alternative to recombinant human TSH stimulation and a more
effective option than LID. (J Clin Endocrinol Metab 100: 2261–2267, 2015)
M
ultinodular goiter (MNG) is an important public
health problem, and its prevalence depends mainly
on the population’s iodine status ranging from 1% in the
iodine-sufficient population of the Framingham study to
15% in Danish populations with mild iodine deficiency
similar to Belgium (1–3). The development of variable de-
grees of thyroid autonomy is a frequent complication of
MNG. It is estimated that approximately 22% of patients
with long-standing MNG will develop subclinical or overt
hyperthyroidism (2, 4). Because international guidelines
do not recommend one particular therapeutic option for
autonomous MNG, the treatment choice is guided by the
ISSN Print 0021-972X ISSN Online 1945-7197
Printed in USA
Copyright © 2015 by the Endocrine Society
Received January 6, 2015. Accepted April 6, 2015.
First Published Online April 13, 2015
Abbreviations: CT, computed tomography; CV, coefficient of variation; FT3, free T3; FT4,
free T4; LID, low-iodine diet; MNG, multinodular goiter; MRI, magnetic resonance imaging;
MTZ, thiamazole; RAIU, radioiodine uptake; rhTSH, recombinant human TSH; ROI, region
of interest; SPECT, single-photon emission CT; Tg-Ab, antithyroglobulin antibodies; TPOAb, thyroid antiperoxidase antibodies; UIC, urinary iodine concentration; WBC, white
blood cell.
doi: 10.1210/jc.2015-1026
J Clin Endocrinol Metab, June 2015, 100(6):2261–2267
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Thiamazole and Radioiodine Therapy Efficacy
clinical presentation, patients’ preferences, and local medical practices (5, 6). Surgery is certainly the treatment of
choice for patients with MNG carrying a risk of malignancy and for those with compressive symptoms (6). Radioiodine therapy (131I) has been increasingly used to treat
autonomous MNG in view of its safety, low cost, and the
possibility of administration on an outpatient basis. An
average reduction in goiter volume of 40% has been reported 1 year after treatment, and this reduction may
reach 50 – 60% after 3–5 years with considerable individual variations (4). Radioiodine therapy increases the risk
of hypothyroidism that occurs in 22–58% of cases 5– 8
years after therapy (4). The frequent finding of relatively
low radioiodine uptake (RAIU) in MNG can compromise
the efficacy of 131I therapy, and very high activities of 131I
may be required in these circumstances. To address this
problem, recombinant human TSH (rhTSH) has been used
successfully to increase RAIU in MNG (7–12). However,
the use of rhTSH in this indication is not formally recommended (5). In addition, its high cost constitutes a major
limitation for its use in many countries.
The aim of this study was to determine whether pretreatment with thiamazole (MTZ) could increase the effects of 131I by enhancing 24-hour RAIU and thereby decreasing the 131I activity needed to treat patients with
subclinical hyperthyroidism and MNG.
Subjects and Methods
Study population and design
This is a single-center, prospective, randomized case-control
trial involving a total of 22 patients referred for 131I therapy for
autonomous MNG at the Nuclear Medicine Department of Université Libre de Bruxelles (ULB) Erasme Hospital in Brussels,
Belgium. Inclusion criteria were the presence of subclinical hyperthyroidism (serum TSH ⬍ 0.4 mU/L, and normal level of
thyroid hormones) and RAIU at 24 hours ⬍ 50%. Graves’s disease was ruled out on the basis of clinical presentation and thyroid scintigraphy. Thyroid stimulating Ig and TSH-binding inhibitor Ig were not measured. Malignancy was ruled out by fineneedle aspiration biopsy in suspected nodules. Exclusion criteria
included prior thyroid surgery, use of thiamazole (synonym of
methimazole) within the 6 months preceding their enrollment,
and prior radioiodine treatment. Patients with solitary autonomous nodules were also excluded. Autonomous nodules were
scintigraphically defined by the presence of an area of increased
radionuclide intake in comparison with remaining extranodular
parenchyma as previously described (7)
Baseline serum TSH, free T4 (FT4), free T3 (FT3), thyroid
antibodies, and a urinary iodine concentration in spot samples
were determined. Initial evaluation also included a thyroid scintigraphy, estimation of thyroid volume, and RAIU measurement
at 24 hours. Patients were randomized into two groups to receive
either MTZ 30 mg/d or a low-iodine diet (LID) for 42 days.
Randomization was done according to a computer-generated
J Clin Endocrinol Metab, June 2015, 100(6):2261–2267
model with a block size of two. In one patient recruited in the
MTZ group, MTZ was discontinued because he developed urticaria and raised liver transaminases. This patient was not included in the study and did not participate at any evaluation.
Food sources rich in iodine in Belgium are few. Patients received
written instructions to avoid iodized salt, any iodine-containing
vitamins or medication, fish, shellfish, and other seafood, and
dairy products. During the second visit, 42 days after baseline, a
re-evaluation of thyroid function tests, scintigraphy, thyroid volume, thyroid RAIU, and urinary iodine determination was performed to exclude subsequent iodine contamination. MTZ was
stopped 3 days before the second RAIU measurement. Radioiodine therapeutic activity was calculated based on the second
RAIU, and 131I was administered within 2 days on an outpatient
basis in accordance with the Belgian radioprotection rules. Serum TSH and FT4 were measured 12 months after treatment to
evaluate 131I efficacy in all 10 patients in the LID group and in
10 of 12 patients in the MTZ group. In the MTZ group, one
patient was lost during follow-up, and the other patient received
levothyroxine 2 months after administration of 131I. The ethics
committee of ULB Erasme Hospital approved the study protocol,
and all patients provided informed consent.
Thyroid function
Serum TSH was measured by immunochemiluminometric assay (Roche). The assay coefficient of variation (CV) of TSH was
2.4% at a mean of 0.09 mU/L. Serum FT4, FT3, thyroid antiperoxidase antibodies (TPO-Ab), and antithyroglobulin antibodies (Tg-Ab) were measured by electrochemiluminescence
competition assay (Module E; Roche). The CV of FT4 was 3.6%
at a mean of 1 ng/dL, and the CV of FT3 was 3.5% at a mean of
3 pg/mL.
The CV of TPO-Ab was 4.3% at a mean of 100 U/mL, and the
CV of Tg-Ab was 6.3% at a mean of 50 U/mL. Urinary iodine
concentrations (UICs) were measured by spectrophotometric detection based on the Sandell-Kolthoff reaction. The CV of UIC
was 4.9% at a mean of 53 ␮g/L.
Scintigraphy
Scintigraphy was performed 20 minutes after iv injection of
222 MBq of 99mTc- pertechnetate using a ␥-camera Sopha Medical DSX (SMV International) equipped with a pinhole collimator with 205-mm height, 295-mm diameter, and a 5-mm
aperture.
Estimation of thyroid volume
Thyroid volume was evaluated with either magnetic resonance imaging (MRI) or single-photon emission computed tomography (SPECT)-computed tomography (CT) to adapt administered 131I activities to thyroid size. All patients had thyroid
volume measured with the same method at the two study points.
The first 11 patients had an MRI, using a 1.5-T whole body
magnetic resonance imager (Gyroscan ACS-Power Trak 6000;
Philips), with a maximum gradient strength of ⫾20 mT/m. In the
subsequent 11 patients, thyroid volume was estimated by
SPECT-CT on a Phillips Brightview camera equipped with a
low-energy parallel-hole high resolution collimator. A low-dose
flat panel CT acquisition (120 kV, 30 mA, 30 cm FOV) was first
obtained, followed by a SPECT of 64 steps in a 256 ⫻ 256 matrix
(energy window, 140 keV ⫾ 20%). CT data were reconstructed
using the filtered back projection method. SPECT acquisition
doi: 10.1210/jc.2015-1026
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was reconstructed iteratively using the Astonish method
(Philips), with three iterations and eight subsets. Fused CT and
SPECT reconstructed data were displayed with the Fusion
Viewer software (Phillips), and three-dimensional regions of interest (ROIs) were placed on the SPECT volume to delineate the
functional volume of the gland. Because SPECT and CT are
coregistered, the three-dimensional ROIs were automatically
displayed on the CT, allowing measurement of ROI volume in
milliliters.
RAIU and calculated
131
I activity
The thyroid RAIU was determined at 24 hours after the oral
administration of 10 ␮Ci (0.37 MBq) of sodium 131I. The 131I
activity needed for the treatment was calculated according to the
following formula:
␮Ci activity ⫽
R activity ␮Ci ⫻ thyroid size (gr)
24 h uptake (%)
R activity (required activity) varied between 90 and 200 ␮Ci/g
according to thyroid size to compensate for the relatively high
radio resistance of large glands (8).
Statistical analysis
Statistical analysis was performed with the help of GraphPad
Prism, version 5.04 (GraphPad Software Inc). Normally distributed data were expressed as the mean ⫾ SD; non-normally distributed data (TSH, thyroid volume, and calculated 131I activity)
were expressed as the median (Interquartile range: 25–75 percentile). Depending on the normality of the variable studied,
parametric or nonparametric tests were used. The t test and
Mann-Whitney test were used to evaluate the differences at baseline between the two groups. Paired t test and the Wilcoxon
matched-pairs signed rank test were used to evaluate withingroup changes before and after treatment. The level of statistical
significance was chosen as P ⬍ .05.
Results
All patients were treated with radioiodine at the end of the
42-day protocol. The 12-month follow-up was completed
by all patients in the LID group and by 10 of 12 patients
in the MTZ group. Mean age was 70.7 ⫾ 7 years in the LID
Table 1.
2263
group and 66.5 ⫾ 14 years in the MTZ group (non significant). Similarly, the female:male ratio did not vary significantly between the two groups: 8:2 in the LID group
and 10:2 in the MTZ group, respectively. All patients were
TPO-Ab and Tg-Ab negative. Baseline thyroid function
and volume and their evolution after 42 days of LID or
MTZ treatment are shown in Table 1. Only three patients
had a thyroid volume above 100 mL: 120, 134, and 206
mL, respectively. None of the patients spontaneously complained of local compressive symptoms before treatment
or during the follow-up.
As expected, serum TSH increased significantly (P ⬍
.001), although within the normal range in the MTZ
group. Serum FT4 levels decreased by 22% (P ⬍ .05) and
serum FT3 by 15% (P ⬍ .05) in the MTZ group. In three
of 12 patients in the MTZ group, FT4 fell below normal
levels without any symptom of hypothyroidism. No modifications of thyroid function were found in the LID group.
Thyroid volume did not vary after 42 days of LID or MTZ
treatment. Median UIC was low and was similar in both
groups at baseline and 42 days after LID or MTZ treatment. In the LID group, but not in the MTZ group, median
UIC was significantly lower at 42 days compared to baseline median.
In the MTZ group, the increase in RAIU was associated
with a more homogenous distribution of 99mTc-pertechnetate after treatment, as illustrated in Figure 1.
A 2-fold increase in mean 24-hour RAIU from 32 ⫾
10% at baseline to 63 ⫾ 18% was observed after 42 days
of MTZ treatment (Figure 2) (P ⬍ .001). No increase in
24-hour RAIU was observed in the LID group: mean RAIU
of 37 ⫾ 7% at baseline and 39 ⫾ 10% after 42 weeks of
LID.
The MTZ-enhanced RAIU led to a 31% decrease in the
required median 131I activity needed to treat the patients,
from 16.0 mCi (Interquartile range: 12.3–34.5) at baseline
to 11.0 mCi (Interquartile range: 8.3–14.0) after treatment (P ⬍ .001) (Figure 2). The maximal activity autho-
Thyroid Function and Thyroid Volume Before and After 42 Days of LID and MTZ Treatment
Baseline
TSH, mU/L
FT4, ng/dL
FT3, pg/mL
Volume, mL
MRI
SPECT-CT
UIC, ␮g/L
After Treatment
LID
MTZ
LID
MTZ
0.09 (0.04 – 0.17) [10]
1.27 ⫾ 0.20 [10]
3.60 ⫾ 0.5 [10]
0.13 (0.04 – 0.30) [12]
1.25 ⫾ 0.20 [12]
3.30 ⫾ 0 .6 [12]
0.09 (0.04 – 0.20) [10]
1.25 ⫾ 0.16 [10]
3.40 ⫾ 0.7 [10]
1.55 (0.78 –1.85) [12]a,b
0.98 ⫾ 0.33 [12]a,b
2.80 ⫾ 0.4 [12]a,b
87 (45.7–184.5) [4]
39 (31–56) [6]
110 (70 –116) [9]
55 (29 – 63) [7]
44 (31.5– 61) [5]
64 (47–129) [12]
74 (46 –180) [4]
42 (35.5– 61.3) [6]
68 (34 –147) [10]a
58 (30 – 63) [7]
50 (42.5– 60.0) [5]
40 (20 –56) [11]
Data are expressed as median (25th-75th percentiles) [number of cases] or median ⫾ SEM [number of cases].
a
Different from baseline, P ⬍ .05,
b
Different from LID group after treatment, P ⬍ .05.
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Thiamazole and Radioiodine Therapy Efficacy
J Clin Endocrinol Metab, June 2015, 100(6):2261–2267
ALARA (as low as reasonably
achievable) principle, aiming to reduce the unnecessary exposure of patients, health personnel, and the general public to ionizing radiation.
Concerning the patients, it is noteworthy that this reduction lowers the
extra thyroidal tissue radiation
burden.
Whether it is beneficial to treat
subclinical hyperthyroidism has
long been a controversial issue. EviFigure 1. Typical aspect of 99mTc-pertechnetate thyroid scintigraphy before (left) and after
dence for increased risk of atrial fi(right) 42 days of MTZ treatment.
brillation, increased cardiovascular
and overall mortality, fracture risk,
rized by Belgian law for an outpatient administration is 15 and diminished quality of life associated with subclinical
mCi. After MTZ-induced RAIU enhancement, a greater hyperthyroidism in a variety of studies has prompted conproportion of patients who initially exceeded the legal sensus groups to consider treatment as a reasonable option
threshold could receive the outpatient calculated 131I ac- for patients over 60 years old and/or with evidence of heart
tivity in the MTZ group as compared to the LID group: disease and/or bone loss (9, 10). Treatment options inseven of 12 (58.3%) in the MTZ group vs two of 10 clude thionamides and radioiodine—the latter being pre(20.0%) in the LID group (P ⬍ .05). The patients whose ferred especially in the presence of toxic or autonomous
calculated activity exceeded the legal threshold at the end MGN or solitary nodules. Surgery is a valid option in
of the study received the maximal authorized activity of 15 young patients or in cases of suspicious nodules (9).
mCi: one of 12 (8.3%) in the MTZ group (instead of a
Two previous nonrandomized studies evaluated MTZ
calculated 131I activity of 32 mCi) vs six of 10 (60.0%) in as an adjuvant treatment for 131I therapy of MNG (11,
the LID group (instead of calculated 131I activities of 18, 12). In the first study, the authors treated nine patients
18, 106, 45, 16, and 35 mCi).
with different doses of MTZ to obtain a serum TSH ⬎ 6
The evolution of serum TSH 12 months after 131I admU/L and then administered a fixed activity of 1110 MBq
ministration in the two groups is shown in Figure 3. Ra(30 mCi) (11). The duration of therapy was considerably
dioiodine treatment cured hyperthyroidism in all patients
longer (2.8 mo), and RAIU significantly increased from
in both groups despite the fact that patients in the MTZ
21.3 ⫾ 8.1% to 78.3 ⫾ 15.3%. Hypothyroidism ensued
group received a lower 131I activity. Moreover, in the
after radioiodine therapy in five of nine patients. In the secMTZ group, three of 10 patients (30%) developed hypoond study, 10 –15 mg/d of MTZ were administered to inthyroidism after 131I therapy, but none in the LID group.
crease RAIU above 50%, and a fixed 1110 MBq 131I activity
Median TSH at 12 months after 131I was significantly
was administered. The average duration was 3 months, and
higher in the MTZ group compared to the LID group, 2.55
all five patients developed hypothyroidism (12).
mU/L (1.65–5.38) vs 1.21 mU/L (1.0 –1.78), respectively
Our results confirm that MTZ induces a significant
(P ⬍ .05).
RAIU enhancement within a considerably shorter period
of time (42 d vs 3 mo). The strength of our study lies in its
randomized design. Furthermore, by using a calculated
Discussion
instead of a fixed therapeutic 131I activity, the extra thyTo our knowledge, this is the first randomized clinical trial roidal tissue radiation was probably lowered without
131
designed to evaluate the effect of MTZ pretreatment on compromising the therapeutic efficacy of I. Because the
131
I calculated activity was not given to 60% of patients in
radioiodine therapy in patients with subclinical hyperthyroidism and MNG. Our results clearly demonstrate that the LID group, the interpretation of differences of thyroid
the use of MTZ before 131I therapy induced an average function at 12 months between MTZ and LID groups is
2-fold increase in 24-hour RAIU and a significant reduc- difficult. The design of the study does not permit compartion of the 131I activity needed to cure subclinical hyper- ison of the efficacy of both treatments. However, the sigthyroidism in patients with MNG, without compromising nificantly higher TSH at 12 months in the MTZ group
therapeutic efficacy as shown by 12-month TSH values. suggests that lowering 131I activities in patients treated
This reduction in administered 131I activity follows the with MTZ did not affect the efficacy of radioiodine ther-
doi: 10.1210/jc.2015-1026
Figure 2. A, Change in mean RAIU after 42 days of LID or MTZ.
**, P ⬍ .001. Error bars represent SEM. B, Calculated median 131I
activity after 42 days of LID or MTZ. *, P ⬍ .05; **, P ⬍ .001. Error
bars represent interquartile range of median.
apy. In addition, our results indicated that prior MTZ
washout of 3 days did not interfere with radioiodine outcome. The increase in RAIU can be explained by two different mechanisms. First, by inhibiting thyroid peroxidase, MTZ blocks iodine organification and depletes the
intrathyroid iodine pool. Second, the inhibition of thyroid
hormone synthesis by MTZ induces a slight increase in
Figure 3. TSH serum levels (mU/L) before and after 12 months of 131I
treatment in the LID and MTZ groups. Data are available for all patients
in the LID group and for 10 of 12 patients in the MTZ group. *, P ⬍
.05.
press.endocrine.org/journal/jcem
2265
serum TSH, which is known to stimulate the expression of
the Na/I symporter, responsible for the uptake of iodine.
It is well known that minor side effects of MTZ include
rash, urticaria, pruritus, and gastrointestinal intolerance
(13). One of our patients could not be included in the study
because he developed urticaria and pruritus with increased serum liver transaminase levels. Withdrawal of
MTZ rapidly restored hepatic function tests to normal
levels. Major side effects comprise rare cases of agranulocytosis (0.2– 0.5%) and hepatotoxicity, for which incidence is not clearly known (0.1– 0.2%) (13, 14). We
checked baseline white blood cell (WBC) count and liver
function tests for all our patients, but we did not routinely
monitor their hepatic function tests or WBC count during
the 6 weeks of therapy. Risk of MTZ-induced agranulocytosis is known to be dose dependent (8.6-fold increase
with doses ⬎ 40 mg/d) and age related (6-fold increase in
patients ⬎ 40 y old), and WBC count fails to predict its
onset (14). Although others have reported that WBC
count may help predict granulocytopenia (15), routine
blood counts are not recommended by current guidelines
including those of the American Thyroid Association (5).
rhTSH has recently been used in clinical trials to optimize
radioiodine treatment of MNG. Thyroid stimulation by
rhTSH can result in an approximately 2- to 4-fold increase
in RAIU and in a 35–56% gain in goiter volume reduction
(16 –30). Mean RAIU obtained after rhTSH stimulation
displays interindividual variations. It is dose dependent
and inversely correlated with baseline RAIU (22, 23, 25–
28). The dose of rhTSH used varied from 0.01 to 0.9 mg
given at different time intervals from 24 to 72 hours before
radioiodine therapy, although 24 hours was found to be
the optimal time point for the greatest increase of RAIU.
In most studies, rhTSH-stimulated RAIU reaches an absolute value of 60 – 65%, which is similar to our findings.
In contrast with the supranormal acute TSH peaks induced by rhTSH, MTZ-induced stimulation of thyroid
uptake is a slow process that leads to a progressive normalization of TSH levels.
Nieuwlaat et al (31) have shown that rhTSH induces
significant changes in the regional distribution of radioiodine in nodular goiters. Recombinant TSH stimulates
radioiodine uptake in relatively “cold” areas more than in
relatively “hot” areas, as depicted on scintigraphy, resulting in a more homogenous radioiodine distribution. In our
study, we observed the same effect with MTZ, although
TSH was only moderately enhanced after treatment. After
MTZ treatment, previously “resting” tissues surrounding
hyperfunctioning areas were reactivated. The consequence of the homogenization of radioiodine uptake is
that besides hyperfunctioning nodules, perinodular thyroid tissue is also irradiated, explaining the greater fre-
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Kyrilli et al
Thiamazole and Radioiodine Therapy Efficacy
quency of hypothyroidism and goiter volume reduction
compare to the administration of 131I alone. A significant
increase in permanent hypothyroidism after rhTSH-stimulated 131I treatment (52% 5 y after rhTSH compared to
16% after 131I alone) has been reported (21, 28). We similarly found a greater proportion (30%) of patients developing hypothyroidism 12 months after MTZ-enhanced
131
I therapy, suggesting that there may be a possibility for
further lowering of the administered 131I therapeutic activity for those patients without indication for thyroid volume reduction.
Another relevant issue is that rhTSH can induce a transient thyroid swelling and cervical pain within the first
week of treatment. This effect seems to be dose dependent
and is mostly reported in trials using 0.3– 0.9 mg of rhTSH
(23, 24). On the contrary, in our patients MTZ treatment
did not affect thyroid volume, and this is obviously a potential advantage for patients with large goiter volumes.
rhTSH stimulation can also lead to a pronounced increase in serum levels of FT4 and FT3 and transient hyperthyroidism, mainly when doses ⱖ 0.3 mg are used.
Patients with mild or overt toxic MNG are most at risk of
developing a significant rise in thyroid hormone levels,
even with 0.1 mg of rhTSH (21–23). In contrast, in our
study, MTZ administered for a short period of time before
131
I therapy restored a normal thyroid function in most
patients.
Our study has several limitations. We were not able to
measure 131I kinetics with dosimetry because that would
require frequent hospital visits and would compromise
patients’ adherence to the protocol because most of our
patients were older than 70 years. Although one could
raise concerns about our simplified algorithm of calculation of 131I activity and potential MTZ interference in
iodine kinetics and therapeutic efficacy, results of thyroid
function tests 12 months after therapy showed that our
strategy was also efficient in the MTZ group, despite the
lower 131I activities administered. Another important limitation is that we do not have at our disposal data of the
thyroid volume at 12 months for all patients. However, the
main objective of radioiodine administration in our study
was not volume reduction, but rather normalization of
thyroid function. Finally, we did not perform a cost-benefit analysis to compare overall costs of MTZ vs rhTSHstimulated 131I therapy in patients with subclinical
hyperthyroidism.
In conclusion, MTZ treatment before 131I therapy resulted in an average 2-fold increase in thyroid RAIU, with
a subsequent significant reduction in the 131I activity required to treat subclinical hyperthyroidism in patients
with MNG, without compromising efficacy. Therefore, in
cases of relatively low RAIU, MTZ pretreatment is a safe,
J Clin Endocrinol Metab, June 2015, 100(6):2261–2267
easily accessible alternative to rhTSH stimulation and a
more effective option than a LID.
Acknowledgments
We thank all caring physicians that have addressed their patients
for our study protocol, as well as the secretary, nurses, and staff
of the Endocrinology and Nuclear Medicine Department for
their precious collaboration throughout our study. We thank
Global Science Editing, UK, for English language revisions.
Address all correspondence and requests for reprints to:
Rodrigo Moreno-Reyes, MD, PhD, Department of Nuclear Medicine, Erasme Hospital, Université Libre de Bruxelles, Route de Lennik 808, 1070 Brussels, Belgium. E-mail: [email protected].
Disclosure Summary: The authors have nothing to disclose.
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