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World J. Surg. 24, 1295–1302, 2000
DOI: 10.1007/s002680010215
WORLD
Journal of
SURGERY
© 2000 by the Société
Internationale de Chirurgie
Total Thyroidectomy or Thyroid Lobectomy in Patients with Low-risk
Differentiated Thyroid Cancer: Surgical Decision Analysis of a
Controversy Using a Mathematical Model
Electron Kebebew, M.D.,1 Quan-Yang Duh, M.D.,2 Orlo H. Clark, M.D.1
1
Department of Surgery, University of California, San Francisco, School of Medicine, UCSF/Mount Zion Medical Center, 1600 Divisadero
Street, San Francisco, California 94120, USA
2
Surgical Services, Veteran Affairs Medical Center, 4200 Clement Street, San Francisco, California 94121, USA
Abstract. There is a general consensus that total or near-total thyroidectomy is the optimal treatment for patients with high risk differentiated
thyroid cancer (DTC), but the optimal extent of thyroidectomy in patients
with low risk DTC continues to be controversial. To determine the optimal
extent of thyroidectomy in patients with low risk DTC, we used decision
analysis to compare the trade-offs of total thyroidectomy (TT) to thyroid
lobectomy (TL). The decision analysis model included the probabilities of
thyroidectomy complications, risk of DTC recurrence, and death from
DTC. This information was obtained from the literature and from outcome data for patients with low risk DTC from our institution. In addition, the concept of utilities was used in the analysis. To determine the
utility of each health outcome state (thyroidectomy complication, DTC
recurrence, and DTC mortality for low risk patients) a survey was conducted. Overall, prospective patients viewed DTC recurrence as less
desirable than thyroidectomy complication. The utilities assigned by the
survey participants varied over a wide range, with 61.5% of the individuals
viewing the occurrence of a thyroidectomy complication as better than
DTC recurrence. At baseline utilities and probabilities, TT had a higher
expected utility than TL. One-way sensitivity analysis varying the rates of
(1) thyroidectomy complication, (2) DTC recurrence, and (3) DTC mortality over the possible range showed that complication from initial
thyroidectomy was the most important factor that determined the preferred extent of thyroidectomy. TL was the preferred surgical approach
only if a complication rate of > 33:1, TT/TL complication rate ratio, was
assumed. When no differences in DTC recurrence between the two approaches was assumed in the model, TL had a higher expected utility
using the baseline utilities of thyroidectomy complication and DTC mortality. The analysis indicates that TT in patients with low risk DTC is
preferable to TL. However, TL is preferred if (1) no difference in the DTC
recurrence rate between the two approaches is assumed, (2) a higher
complication rate for TT is used (> 33 times higher), or (3) the utility
ratio of thyroidectomy complication to DTC recurrence is < 0.8 TL. We
believe this decision analysis model provides an objective approach that
others can use to select the optimal extent of thyroidectomy based on
patient preference of health outcome states, institution-specific outcome
data for DTC recurrence or mortality, and the surgeon-specific complication rate.
This International Association of Endocrine Surgeons (IAES) article
was presented at the 38th World Congress of Surgery International Surgical Week (ISW99), Vienna, Austria, August 15–20, 1999.
Correspondence to: E. Kebebew, M.D., Department of Surgery, University of California, San Francisco, 513 Parnassus Avenue, S-343, San Francisco, CA 94143-0470, USA
There have been significant advances in the risk stratification of
patients with differentiated thyroid cancer (papillary and follicular
thyroid cancer) over the past four decades [1]. Based on clinical
and pathologic data, numerous investigators have established
helpful risk assessment models in patients with differentiated
thyroid cancer (DTC) [2– 6]. For example, the AMES (age, distant
metastasis, extrathyroid invasion, and primary tumor size) and the
AGES (age, histologic grade of tumor, extrathyroid invasion and
distant metastasis, and tumor size) prognostic scoring systems
separate patients with DTC into high and low risk groups [3, 4].
Shaha and associates at the Memorial Sloan Kettering Cancer
Center have also suggested that some patients with DTC have an
intermediate risk [6]. In general, patients with large tumors, extrathyroidal tumor invasion, distant metastasis, and gross bilateral
lobe tumors are considered to have high risk tumors. Although
there is a general consensus that patients who have high risk DTC
warrant total or near-total thyroidectomy, controversy continues
as to the most optimal extent of initial thyroidectomy for most
patients (about 80%) who present with low risk DTC (small,
unilateral tumor) [7].
The debate has largely centered around the extent of disease,
the risks associated with each surgical approach, and patient
outcome (differences in DTC recurrence and mortality from
DTC) (Fig. 1). A wide range of surgical approaches has been
advocated for patients with DTC including thyroid lobectomy
(TL), subtotal thyroidectomy, near-total thyroidectomy, and total
thyroidectomy (TT) [7]. In general, proponents of TL suggest that
a higher risk of recurrent laryngeal nerve injury and hypoparathyroidism are associated with the contralateral neck dissection for
TT. Advocates of TT or near-TT frequently report that a lower
recurrence rate and a small benefit in survival can be achieved in
patients with DTC. The controversy persists largely because no
prospective randomized trial evaluating the various surgical approaches for DTC has been completed. Because of the relatively
low incidence of DTC and its good prognosis, such a trial would
require a large, multicenter study with a long follow-up. There
are, however, numerous large, long-term retrospective studies in
patients with DTC that evaluated the influence of extent of initial
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Fig. 1. The main clinical factors considered when selecting the appropriate extent of thyroidectomy in patients with differentiated thyroid cancer
have been the extent of disease and patient outcome (Cancer). Additional
factors that could affect selection of the optimal surgical approach are the
surgeon-specific complication rate (Surgeon) and patient preference (Patient) with respect to the health status that follows each surgical procedure.
thyroidectomy on patient outcome [7]. Most studies have reported
that a reduced recurrence rate and lower mortality are associated
with more extensive thyroidectomy procedures [7]. Nevertheless,
divergent recommendations exist for the optimal surgical resection in patients with low risk DTC even among treatment guidelines and consensus statements [8 –12].
The patient’s viewpoint and differing surgeon complication
rates have not been systematically addressed in this controversy
(Fig. 1). Patients express varying beliefs as to whether they would
prefer to have a “higher risk” procedure if it offered a long-term
lower risk of recurrence or mortality. Such factors could be important in situations where the clinical benefits of various treatment options are uncertain or debated such as exists for DTC.
Decision analysis is increasingly utilized for developing patient
care policies [13]. This approach is especially useful in a clinical
setting where decision-making is based on uncertain or conflicting
data or viewpoints [13–16]. In addition to the advantage of being
able to compare clinical management approaches, decision analysis also allows incorporation of patient perspectives on health
outcomes when arriving at his or her optimal treatment strategy
[13, 17]. In this study, we performed a quantitative, structured
risk– benefit analysis for selecting the optimal extent of thyroidectomy that incorporates patient preference and surgeon-specific
complication rates. The study model considered three outcome
states relative to the extent of initial thyroidectomy in patients
with low risk DTC: (1) complications of thyroidectomy; (2) risk of
DTC recurrence; and (3) the risk of DTC mortality (Fig. 2).
Methodology
Decision Model
In a clinical decision analysis, a structured framework (decision
tree) is used to represent the management options for identifying:
(1) the treatment options; (2) consequences of the treatment
options (the likely events that follow those options); and (3) the
World J. Surg. Vol. 24, No. 11, November 2000
Fig. 2. Decision tree for the extent of thyroidectomy (Thx) in patients
with low risk differentiated thyroid cancer. The tree includes the immediate event that follows thyroidectomy (complication) and the long-term
events that occur (tumor recurrence and death from thyroid cancer). Each
event is associated with a probability of a complication (Pc), recurrence
(Pr), and death (Pd) and a utility (Uc, Ur).
time sequence in which they occur [15, 17]. The most credible
probability estimates of each of those events in the decision tree
were gathered from the literature and from our experience at the
UCSF/Mount Zion Medical Center over a 10-year period. The
decision model used in our study is illustrated in Figure 2. It is a
simple model in which two surgical approaches were compared at
the time of diagnosis: thyroid lobectomy (TL) and near-total or
total thyroidectomy (TT). The model includes three major, easily
measured objective variables: (1) thyroidectomy complication
(i.e., risk of permanent recurrent laryngeal nerve injury and permanent hypoparathyroidism); (2) DTC recurrence; and (3) death
from DTC. The probability of each event from the decision node
to the terminal branch is the product of the probability. Furthermore, the impact of a possible outcome on the preference of an
option was weighted with the respective utility of that event
occurring from the time of initial thyroidectomy. Therefore the
total utility function for each surgical approach in Figure 2 is
Total utility function ⫽ 共1 ⫺ Pd兲 兵共1 ⫺ Pr兲共1 ⫺ Pc兲
⫹ UrPr共1 ⫺ Pc兲 ⫹ UcPc共1 ⫺ Pr兲 ⫾ UrPrUcPc}
where P ⫽ probability of the event occurring; U ⫽ utility of health
state; c ⫽ thyroidectomy complication; r ⫽ DTC recurrence; and
d ⫽ death from DTC. This is the expected total utility, which is a
quantitative measure of the most preferred option. The preferred
extent of thyroidectomy is the approach with the highest total
utility from the patient’s perspective.
Outcome Variable Probabilities
The analysis required establishing sound probability estimates of
the thyroidectomy complication rates, the risk of DTC recurrence
in low risk patients, and mortality from DTC in low risk patients.
These values were determined by focused review of the available
literature (in English) from long-term follow-up studies and from
10-year outcome data collected at our institution (1986 –1996).
Listed in Table 1 are probability estimates for each health outcome state [18 – 47]. The baseline probability estimates were
weighted averages from the listed studies based on sample size
and follow-up time in patients with low risk DTC.
Kebebew et al.: Thyroidectomy for Differentiated Thyroid Cancer
Table 1. Probabilities for each health outcome state in the decision
model culled from review of the English literature and UCSF/Mount
Zion clinical outcome data in 156 patients with low risk DTC.
Variable
Thyroidectomy complications
RLNI
Hypoparathyroidism
TT vs. TL
UCSF TT vs. TL
Baseline TT vs. TL
DTC recurrence
Overall
TT vs. TL*
UCSF TT vs. TL
Baselinea
DTC mortality
Overall
TT versus TL
UCSF TT versus TL**
Baseline
Rate of
events (%)
Reported
range (%)
Refs.
0.077
0.05
0.39 vs.
0.075
0 vs. 0
1 vs. 2
0 –14
0 –30
[18 –38]
15.5
11.5 vs.
23.0
6.7 vs.
30.9
15.2 vs.
34.7
8.3– 40
[39 – 46]
0.1–9.0
[39 – 46]
3.2
3.2 vs. 4.6
0 vs. 5.2
3.8 vs. 6.4
RLNI: recurrent laryngeal nerve injury; DTC: differentiated thyroid
cancer; TT: total thyroidectomy; TL: thyroid lobectomy; UCSF: University
of California, San Francisco.
a
DTC recurrence at 10 to 15 years median or mean follow-up time.
*Significant difference in DTC recurrence by ␹2 test (p ⫽ 0.0001).
**Not significant (p ⫽ 0.10) by Kaplan-Meier product limit method.
Utilities
To determine the value individuals place on the various health
outcome states, we used the concept of utilities as a quantitative
measure of a decision-maker’s relative preference for an outcome
state [13, 14]. This approach is based on how an individual views
certain outcome states based on uncertain data balancing the
risk– benefit ratio relative to the individual’s perspective. Because
we did not want to use arbitrary utility estimates, we conducted a
survey to obtain baseline utility estimates for each of the health
outcome states. Survey participants were asked to assign a numerical value for each of the health outcome states based on anchor
states of 100% (utility of 1) for a perfect state of health and 0%
(utility of 0) for being dead. The survey included the following
questions: (1) unilateral recurrent laryngeal nerve injury— having
a hoarse voice, a weakening voice, and unable to sing high notes
now and possibly for the rest of your life; (2) bilateral recurrent
laryngeal nerve injury—not being able to speak and potentially
requiring a tracheostomy to breath; (3) hypoparathyroidism—
having to take vitamin D, calcium or both orally every day for the
rest of life to avoid having muscle cramping, tingling sensation,
tetany, or seizures; and (4) recurrent thyroid cancer within 10
years, which could be treated with reoperation, radioactive iodine
treatment, or both. A time point for DTC recurrence of 10 years
was used in the questionnaire because this length of time was most
commonly reported as the mean follow-up time from which the
probability estimates of recurrence and mortality were derived
[39 – 46]. Furthermore, the survey questionnaire for determining
the utility of recurrence and mortality from DTC accounts for the
later time frame in which these events occur from initial thyroidectomy.
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The following assumptions were made when establishing the
utility of thyroidectomy complications rates for the two surgical
approaches: (1) the major difference in complication rate between
the two approaches (TT versus TL) are the risk of recurrent
laryngeal nerve injury and hypoparathyroidism; (2) the chance of
hypoparathyroidism or bilateral laryngeal nerve injury in patients
undergoing initial TL is zero because the contralateral recurrent
laryngeal nerve or parathyroid gland(s) is not manipulated and
thus not at risk; (3) the chance of injury to the recurrent laryngeal
nerve injury is equal on both sides and independent—therefore
patients who undergo TT have twice the risk of unilateral recurrent laryngeal nerve injury than patients who have TL; and (4) the
total complication risk for the two approaches is the sum of the
risk of hypoparathyroidism and recurrent laryngeal nerve injury
(unilateral and bilateral) for each procedure. Patients with low
risk DTC were defined as having TNM stage I or II DTC [47].
TT refers to the total extracapsular removal of the thyroid gland,
and TL was defined as unilateral total lobectomy with isthmusectomy [7].
Decision Model Analysis
The decision Markov model was constructed in a Microsoft Excel
6.0 spreadsheet. The baseline analysis was performed using the
baseline probability and utility values for each health outcome
state. The total expected utility was determined based on
weighted products of the chance of each outcome in the decision
model. The total utility function for the extent of thyroidectomy
was determined such that the surgical approach yielding a higher
total utility was the more desirable procedure. Sensitivity analyses
were conducted by varying the utility and probabilities over the
possible ranges. The threshold point was when both surgical
approaches yielded an equal total expected utility (i.e., no difference existed).
Results
A wide range of thyroidectomy complication rates has been reported in the literature (⬍ 1% to 30%) (Table 1). In 156 patients
with low risk DTC who underwent initial thyroidectomy at our
institution from 1986 to 1996 (30.8% TL and 69.2% near-TT or
TT), no permanent recurrent laryngeal nerve injuries or hypoparathyroidism occurred. The overall average weighted probability of
thyroidectomy complication was 1% for TL and 2% for TT. In low
risk patients, DTC recurrence and death from DTC have been
reported to occur in 8.3% to 40.0% and 0.1% to 9.0%, respectively (Table 1). A few investigators, specifically in patients with
low risk DTC, have reported DTC recurrence and mortality rates
relative to the extent of thyroidectomy (Table 1) [41, 49]. At our
institution, the recurrence and mortality rates from DTC in low
risk patients were 6.7% and 0%, respectively, for patients who had
initial TT, and 30.9% and 5.2% in patients who had initial TL,
respectively (Table 1). In patients with low risk DTC, the overall
average weighted probabilities of DTC recurrence were 15.2% for
TT and 34.7% for TL. The lower mortality rate in low risk DTC
patients who underwent TT compared to those with TL was not
statistically significant in our cohort, consistent with other studies
[41, 49].
The results of the questionaire indicated that, on average,
individuals viewed the recurrence of DTC as less desirable than
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World J. Surg. Vol. 24, No. 11, November 2000
Table 2. Utilities of each health outcome state (event) in the decision
treea obtained from questionnaire (n ⫽ 42).
Health state
Thyroidectomy complications
Unilateral RLNI
Bilateral RLNI
Hypoparathyroidism
DTC recurrence
DTC mortality
Dead
Alive
Baseline utility
Range of utilities
0.627
0.205
0.778
0.54
0.10 – 0.95
0.02– 0.60
0.20 – 0.98
0.03– 0.60
0
1
—
—
a
See Figure 2.
Table 3. Rank order of possible health outcome states after initial TT
and TL based on overall baseline utilities.
Outcome from decision mode
Compounded
utilities for TT
Compounded
utilities for TL
No complication, no recurrence, alive
Complication, no recurrence, alive
No complication, recurrence, alive
Complication, recurrence, alive
No complication, no recurrence, dead
Complication, no recurrence, dead
No complication, recurrence, dead
Complication, recurrence, dead
1.00
0.54
0.41
0.22
0
0
0
0
1.00
0.86
0.41
0.35
0
0
0
0
having a complication from thyroidectomy (DTC recurrence/thyroidectomy complication ratio utility was 1:1.32 for TT and 1:1.53
for TL) (Table 2). The utility survey participants assigned to each
outcome state, however, varied over a wide range, with 38.5% of
the survey participants viewing thyroidectomy complications as
less desirable than DTC recurrence. The utilities participants
assigned from the questionnaire were highly reproducible (r ⫽
0.96 by Pearson product-moment correlation cofficient), when
repeated by the same individuals (n ⫽ 12). Participants assigned
lower utility for TT than TL for a health outcome state of being
alive with a thyroidectomy complication and a recurrence of DTC
or having only a thyroidectomy complication (Table 3).
At baseline probabilities, initial TT in patients with low risk
DTC had a higher total expected utility (0.867) than initial TL
(0.741). Based on clinical outcome data from our institution,
initial TT had an even higher expected utility than TL (23.9%
higher). If no difference in the probability of death from DTC was
assumed between TT and TL, TT still had a higher total expected
utility than initial TL. Only when a thyroidectomy complication
rate of 30% for TT and 0.9% for TL was used did the total
expected utility for TL become higher than that for TT. Furthermore, if no differences were assumed in the rates of DTC recurrence and DTC mortality for the two approaches, TL had a higher
total expected utility at baseline probability of thyroidectomy
complication.
Differences in the rates of (1) thyroidectomy complication, (2)
DTC recurrence, and (3) DTC mortality relative to the extent of
thyroidectomy remain controversial and have inconsistently been
reported as significantly different [6, 18 – 46]. Table 4 shows the
various clinical outcome scenarios possible in which differences
(or no differences) in the three variables can be assumed to
determine the optimal extent of thyroidectomy for each scenario
(i.e., TL versus near-TT or TT). Varying the probabilities of
Table 4. Preferred extent of thyroidectomy in patients with low risk
DTC: varying outcome variables of observed differences or no
difference relative to the extent of thyroidectomy (TT vs. TL).
Thyroidectomy
complication
rates
DTC
recurrence
DTC
mortality
Preferred extent
of thyroidectomy
⫹
⫹
⫹
⫹
⫺
⫺
⫺
⫺
⫹
⫹
⫺
⫺
⫹
⫺
⫹
⫺
⫹
⫺
⫹
⫺
⫹
⫹
⫺
⫺
TT
TT
TL
TL
TT
TL
TT
TT
⫹: a difference between TL and TT was used (in Pc, Pr, and Pd); ⫺:
no difference between TL and TT was assumed (in Pc, Pr, and Pd).
Fig. 3. Two-way sensitivity analysis of Uc versus Ur at baseline probabilities.
thyroidectomy complication, DTC recurrence, or DTC mortality
over the range of possible values indicated that the difference in
thyroidectomy complication is the most important variable affecting the optimal extent of thyroidectomy at baseline utilities (Uc
and Ur). In fact, TL becomes the preferred approach for patients
with low risk DTC only when TT is expected to have more than 33
times the complication rate of TL at baseline probabilities for
DTC recurrence and mortality.
The finding that initial TT is preferred in patients with low risk
DTC depends not only on the rates of thyroidectomy complications, DTC recurrence, and DTC mortality but also on the utilities
of thyroidectomy complication (Uc) and DTC recurrence (Ur)
used in the analysis. Figure 3 shows the threshold of a two-way
sensitivity analysis for Uc and Ur. For example, a patient who
assigns a utility of 0.5 for DTC recurrence would have to view the
utility of thyroidectomy complication as ⬍ 0.4 for TL to become
the preferred extent of thyroidectomy at baseline probabilities.
An individual would have to view the Uc/Ur ratio as ⬍ 0.80 for TL
to be the preferred extent of thyroidectomy.
Discussion
Surgeons who advocate TL for patients with low risk DTC cite the
following reasons: (1) About half of all local DTC recurrences can
Kebebew et al.: Thyroidectomy for Differentiated Thyroid Cancer
be treated by reoperation, and fewer than 5% of DTC recurrences
are found in the thyroid bed; (2) total thyroidectomy may be
associated with a higher complication rate than lesser procedures;
(3) tumor multicentricity in papillary thyroid cancer has little
clinical significance; and (4) most patients with low risk DTC
enjoy an excellent prognosis regardless of the extent of initial
thyroidectomy [49 –54]. Surgeons who perform TT suggest the
following rationale: (1) Radioiodine scanning or treatment for
detecting or ablating remnant normal thyroid tissue or for local
and distant metastases is more effective after all thyroid tissue is
removed; (2) the postoperative serum thyroglobulin level is a
more accurate marker of recurrence or persistent DTC after all
normal thyroid tissue has been removed; (3) because up to 80% of
papillary thyroid cancers are multicentric, possible sites of DTC
recurrence in the contraleral lobe are eliminated as possible sites
of recurrence; (4) although recurrent/persistent DTC may be
treated with reoperation and radioiodine ablation, about 50% of
these patients die from their recurrence, and thyroid reoperation
may be associated with a higher complication risk; (5) about 1%
of DTC progresses to anaplastic thyroid cancer, which is almost
uniformly lethal; and (6) DTC recurrence is lower in patients who
undergo TT than in patients who have lesser procedures, and
some studies even show an improved survival rate [48 –50]. It is
therefore not surprising, given these conflicting observations, that
surgeons continue to debate the optimal extent of thyroidectomy.
Moreover, the natural history and biologic behavior of DTC has
changed over the last 30 years [49]. As previously noted, numerous prognostic scoring systems have been proposed for DTC that
accurately predict patient survival and risk of DTC recurrence [1].
Unfortunately, none of these risk assessment systems relies completely on information available preoperatively. Such a system
would be invaluable for prospectively planning and directing the
extent of initial thyroidectomy necessary.
Although a number of retrospective studies have evaluated the
extent of thyroidectomy for DTC on patient outcome, as a whole
the findings have been equivocal [39 – 46]. Furthermore, most of
the retrospective studies that report more extensive thyroidectomy reduces the risk of DTC recurrence or mortality have not
exclusively examined patients with low risk DTC [43, 44, 46].
Udelsman and colleagues have shown that a prospective randomized trial evaluating the optimal extent of thyroidectomy for patients with DTC would require an enormous study population
encompassing 12,000 patients to compare thyroidectomy complication, up to 800 patients to compare DTC recurrence, and at
least 3100 patients to compare DTC mortality [53]. These figures,
however, were derived for a study that would include all patients
with DTC. A prospective trial in patients with only low risk DTC
would require an even larger study population and thus would be
prohibitive. Considering these alternatives, we believe a decision
analysis of the most relevant variables provides a rational, practical framework in which to study the optimal extent of the initial
thyroidectomy in low risk DTC.
Using the concept of utilities to measure the quality of life
preference among the survey participants not only provides an
estimate of the value individuals place on a health outcome state,
it also allows a comparison between different possible outcomes.
It is clear that patients view trade-offs between treatment differently from each other. Therefore, the baseline utilities
represent an overall expected preferential outcome with interindividual variability. It is intriguing that most survey participants
1299
viewed DTC recurrence as less desirable than an immediate
thyroidectomy complication. Given the survey result reproducibility, these preferences likely reflect a general public phobia of
“cancer” recurrence, combined with a poor understanding of
the relatively good prognosis associated with DTC. The two-way
sensitivity analysis demonstrates that patients would have to
view complications from thyroidectomy as 1.25 times less
desirable than DTC recurrence for TL to be the preferred approach.
A wide range in thyroidectomy complication rates has been
reported in the literature [18 –38]. Most experts agree that the
major complications of thyroidectomy are recurrent laryngeal
nerve injury and hypoparathyroidism. A thyroidectomy complication depends on the extent of disease, the experience of the
surgeon, the type of thyroid pathology, and the presence of any
anatomic variations [7, 18, 19]. The extent of thyroidectomy has
also been suggested by some to be associated with the risk of
complications [49, 54]. In contrast, based on our experience and
our review of studies that compared complication rates for the
types of thyroidectomy, there was no significant difference between TT and lesser procedures [20, 21]. Furthermore, our analysis demonstrated that TT would have to be associated with more
than 33 times the complication rate of TL for TL to yield a higher
total expected utility at baseline probabilities. Most studies found
that in all patients with DTC, or in patients with low risk DTC, TT
was associated with a lower DTC recurrence rate [39 – 44]. For this
reason and because of the lower overall utility of DTC recurrence
than thyroidectomy complication, it is not surprising that our
analysis suggests that among patients with low risk DTC TT had
the highest total expected utility. Because patients with occult
papillary thyroid cancer or minimally invasive follicular thyroid
cancer essentially have near-normal life expectancy, TL would
probably be sufficient in these patients [7]. Furthermore, in patients with low risk DTC who view the possibility of thyroidectomy
complication as worse than DTC recurrence TL is the preferred
extent of thyroidectomy. More extensive thyroidectomy has been
reported to be associated with a significantly improved survival in
all patients with DTC [43, 44, 46, 48]. Our experience and other
studies in patients with low risk DTC show a lower mortality rate
associated with TT, but the difference was not statistically significant [41, 49, 50]. This is consistent with our analysis indicating
that death from DTC was not the most important factor when
selecting the optimal extent of thyroidectomy.
The clinical environment in which surgeons practice is rapidly
changing. Patients, medical centers, and insurers are expected to
have more input into the clinical decision process. Increasingly,
patients also want to know about all the treatment options that are
available and how it might affect their long-term quality of life.
Decision analysis has been applied in many areas of medicine and
is helpful for making rational management decisions based on
readily available, objective clinical data [14 –17]. The quality of a
decision analysis depends on a representative model being used
and the accuracy of the data used to estimate outcome variables
[13]. In addition to an impartial selection of outcome data from
the literature, we have included our experience at UCSF/Mount
Zion Medical Center. The model used in this decision analysis
includes the important variables that affect thyroidectomy choices.
The effects of the surgical approach relative to the utility of
radioiodine scanning and serum thyroglobulin levels for follow-up
of patients with DTC, however, were not included in the model
1300
and may also be important factors [7]. Furthermore, our model is
limited in that it does not include a cost-effectiveness analysis [13,
15]. TL could be associated with a higher cost expenditure for the
treatment of DTC recurrence and possibly a higher mortality rate.
The need for lifelong thyroid hormone replacement in patients
who have undergone TT may also be an important cost factor.
Nonetheless, the decision analysis model used in this study is easy
and practical, and it includes the most important factors used to
select the extent of initial thyroidectomy for DTC. We propose
that our simplified decision analysis model can be used by others
to determine the optimal extent of thyroidectomy in patients with
low risk DTC using outcome data from individual institutions,
surgeon-specific complication rates, and patient preference.
Based on our experience and data reported in the literature, TT
is the treatment of choice for patients with low risk DTC. Alternatively, if a patient views the utility of the risk of thyroidectomy
complication as less desirable than DTC recurrence (e.g., a professional singer) with a Uc/Ur ratio ⬍ 1.25, TL would be the
preferred extent of thyroidectomy.
Résumé
Il y a un consensus général pour dire que la thyroı̈dectomie totale
ou presque totale est le traitement optimal pour les patients ayant
un risque élevé de cancer différencié de la thyroı̈de (CDT), mais
le type de thyroı̈dectomie chez les patients à bas risque de CDT
continue d’être sujet à controverse. Afin de déterminer le choix de
l’intervention chez les patients à bas risque de CDT, nous avons
comparé les résultats de risque/bénéfices (trades-off) par une
analyse de la décision entre la thyroı̈dectomie totale (TT) et la
lobectomie (L). Le modèle d’analyse de la décision a inclus les
probabilités de complications de la thyroı̈dectomie, le risque de
récidive de cancer et de décès en rapport avec le CDT. Cette
information provenait de la littérature et de l’évolution des
patients ayant un risque peu élevé de CDT suivis dans notre
institution. De plus, on a employé le concept des utilités. On a fait
une enquête pour déterminer l’«utilité» de chaque événement
possible de santé (complication de la thyroı̈dectomie, récidive de
cancer ou mortalité en rapport avec un cancer) pour le patient à
bas risque. Globalement, les patients ont estimé que la récidive de
leur cancer était «moins désirable» qu’une «complication» de la
thyroı̈dectomie. Les «utilités» assignées par les participants de
l’enquête ont varié dans une large gamme avec 61.5% des
individus qui pensaient qu’une complication de la thyroı̈dectomie
était mieux qu’une récidive d’un CDT. Avec les valeurs de base
pour les «utilités» et les probabilités, la TT avaient une «utilité»
attendue plus haute que la L. En variant toutes les valeurs: 1) des
complications, 2) de la récidive de CDT et 3) de la mortalité du
CDT, l’analyse des sensibilités a montré que les complications de
la thyroı̈dectomie initiale était le facteur le plus important dans la
détermination du type de la thyroı̈dectomie. La L était l’approche
chirurgicale préférée seulement si on supposait que le rapport de
complications TT/L était supérieur à 33. Quand on supposait qu’il
n’existait pas de différences de récidive de CDT dans le modèle, la
L avait une utilité attendue plus élevée compte tenue des
complications éventuelles de la thyroı̈dectomie, d’une part, et de
la mortalité de CDT, d’autre part. L’analyse montre que la TT est
préférée à la lobectomie chez un patient à bas risque de CDT. La
L, cependant, est préférée si 1) on ne suppose qu’il n’y aura
aucune différence dans le taux de récidive de CDT entre les deux
World J. Surg. Vol. 24, No. 11, November 2000
approches, 2) on postule que le taux de complication (avec la TT)
est supérieur (plus de 33 fois), 3) le rapport des «utilités» des
complications de la thyroı̈dectomie par rapport à la récidive de
CDT est ⬍ 1.25. Nous croyons que le modèle de l’analyse de la
décision fournit une approche objective du type de
thyroı̈dectomie, basée sur les préférences des patients, sur leur
état de santé, sur les chiffres des résultats spécifiques de
l’institution quant à la récidive ou à la mortalité et aux taux de
complications spécifiques du chirurgien.
Resumen
Por lo general, se acepta que el tratamiento más adecuado para
pacientes de alto riesgo con cáncer diferenciado de tiroides
(DTC) es la tiroidectomia total o cuasi total. Sin embargo, se
discute sı́ esta extensa intervención constituye el tratamiento de
elección para el DTC en pacientes de bajo riesgo. Para
determinar la amplitud óptima de la tiroidectomı́a en este grupo
de pacientes, se efectúa un análisis comparativo entre los
resultados de la tiroidectomı́a total (TT) vs. lobectomı́a tiroidea
(TL). El modelo analı́tico de toma de decisiones tuvo en cuenta
las posibles complicaciones inherentes a la tiroidectomı́a, el riesgo
de recidiva del DTC y la mortalidad por DTC. La información se
obtuvo de la revisión bibliográfica al respecto y de los resultados
de los pacientes con DTC de bajo riesgo, tratados en nuestro
Hospital. En nuestro análisis se introdujo además el concepto de
utilidad. Para determinar ésta se efectuó un seguimiento de cada
uno de los casos, evaluando: complicaciones de la tiroidectomia,
recidiva del DTC y mortalidad. En general, de forma prospectiva,
los pacientes consideran que la recidiva del DTC es menos
deseable que una complicación tras tiroidectomı́a. La utilidad
valorada por los pacientes en seguimiento varı́a ampliamente pero
un 61.5% asumen mejor una complicación tras tiroidectomı́a que
una recidiva del DTC. En la lı́nea basal de utilidades y
posibilidades se espera de la TT una mayor utilidad que de la TL.
Un análisis lineal de la sensibilidad demuestra: 1) las diferentes
complicaciones tras tiroidectomia, 2) recidiva del DTC, 3)
mortalidad por DTC; el factor más importante, determinante de
la amplitud de la tiroidectomı́a, fue la frecuencia de las
complicaciones. La TL se prefirió sólo cuando el cociente de
complicaciones entre la TT y TL fue ⬎ 33:1. Cuando la recidiva
del DTC se suprimió del modelo analı́tico, la TL tuvo una mayor
utilidad dada la menor tasa de complicaciones y de mortalidad
por DTC. Los análisis indican que la TT es preferible a la TL en
pacientes con DTC de bajo riesgo; sin embargo, la TL es la técnica
de elección sı́: 1) se asume que no existe deferencia entre las
dos técnicas por lo que a la recidiva se refiere, 2) cuando se
registran numerosas complicaciones con la TT (superiores 33
veces a las producidas por la TL) ó 3) cuando el cociente de
utilidad entre las complicaciones post-tiroidectomı́a y la recidiva
del DTC es ⬍ 1.25 TL. Creemos que estos modelos analı́ticos de
toma de decisiones (algoritmo) pueden constituir una
aproximación objetiva para decidir la amplitud óptima de la
tiroidectomı́a, pues se basa en las preferencias de los pacientes,
los resultados especı́ficos de cada hospital por lo que a recidivas y
mortalidad se refiere y los resultados de cada cirujano por lo que
a las complicaciones atañe.
Kebebew et al.: Thyroidectomy for Differentiated Thyroid Cancer
1301
Acknowledgments
We thank Philip H.G. Ituarte, Ph.D., M.P.H. for his helpful
suggestions and critical review of the manuscript. This work was
supported in part by Mt. Zion health systems. E.K. was supported
by a NIH T32 Surgical Oncology Training Grant.
22.
23.
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