Comment
Recent technical improvement including miniaturization, improved
deflection and enhanced optical quality have increased the use of
flexible ureterorenoscopes in renal stones. Although f-URS is not
recommended as a first line treatment modality for renal stones
<2cm at current guidelines, a recent meta-analysis resulted an
average of 91% stone-free rate with acceptable complication rates and
with an average of 1.45 procedures per patient (range 1.11-1.82)
[6,8]. As being more widely used, we need some scoring systems that
can be used to predict the success and potential complications after
f-URS for counseling of the patients preoperatively.
The variables that were used in these four studies were not standard.
Although abnormal renal anatomy is one of the parameters of RUSS,
patients with musculoskeletal and renal abnormality directly excluded in
R.I.R.S. Also, renal anomaly was not studied in modified S-ReSC. IPA was
an independent predictive factor in RUSS and R.I.R.S., however it was
not studied in modified S-ReSC and nomogram by Ito et al. So, if a
variable was not evaluated in a study we cannot know if it is an
independent predictive factor or not.
The success was defined as stone-free status in all scoring systems.
However, no standard imaging modality was used and also the timing of
imaging was different between studies. And thus, there can be a
significant bias between studies. In R.I.R.S stone-free status was
evaluated with kidney-ureter-bladder (KUB) plane graphy at 1st month and
>2mm fragments were accepted as not-stone free, computed
tomography (CT) was used whenever necessary. In the nomogram of Ito et
al. stone-free status was evaluated with non-contrast CT at 3rd month.
In RUSS, treatment success was defined as stone-free or residual
fragment ≤1mm at 1st month non-contrast CT imaging. In modified S-ReSC
stone free was defined as no evidence of residual stone at 1st month
NCCT.
The success of a procedure can be defined as to reach a targeted
end-point without any complication or with acceptable complication
rates. Thus, an ideal f-URS scoring system scoring system should foresee
complications besides stone-free. None of the scoring systems examined
the relation of complexity scores and complications. Only in R.I.R.S.
authors indicated that the score is correlated with operation time and
thus it can be used to predict to leave the operation for a second
session and complications can be avoided. All four scoring systems were
able to predict complications in the present study, but only nomogram by
Ito et al. could predict Clavien ≥2 complications.
Stone burden is one of the most important predictors of stone-free after
f-URS as we know from previous studies [8,9]. As expected, stone
burden was an independent predictor of success in all scoring systems
except modified S-ReSC. This is unsurprising for modified S-ReSC,
because the mean stone burden was significantly lower compared to other
studies. The authors indicated that patients with high stone burden were
underwent percutaneous nephrolithotomy and excluded from the study.
Although modified S-ReSC can be predicted stone free status even in our
study, it can be no doubtfully said that success of f-URS for 1cm stone
cannot be equivalent to 3 cm stone in the same location that both was
given same score in S-ReSC.
There are two studies comparing the current nomograms. Erbin et al.
compared the RUSS and modified S-ReSC and found out that RUSS,
musculoskeletal deformity and stone size were independent factors in
logistic regression analysis [10]. And the AUC values were not
satisfactory in terms of nomogram’s predictive accuracy (0.655 and 0.596
for RUSS and modified S-ReSC, respectively). In another recent study by
Richard et al. RUSS, modified S-ReSC, S.T.O.N.E and Ito’s nomogram were
compared [11]. The major limitation of that study was evaluation of
the stone-free status that they made it via visual inspection using
ureterorenoscope and fluoroscopy at the end of the procedure in the
absence of clinical complications. They concluded that all scoring
systems were predicted the stone-free status but none of them were
predictive of complications after RIRS. Different from the former study
all nomograms could predict the stone-free status and complications in
our study as being the Ito’s nomogram most sensitive.
In the present study all four nomograms were underwent external
validation in a significantly high number of patient population.
Although all nomograms were predictive of stone-free status, the AUC
values were lower than that in original study and were not satisfactory.
The AUC values in original study and in our study were 0.806 vs 0.657,
0.87 vs. 0,697 and 0.904 vs.0.690 for modified S-ReSC, Ito’s nomogram
and R.I.R.S., respectively. The AUC value was not calculated in RUSS.
Strengths of our study include high number of study group, standardized
post-operative imaging at a determined time period and various cases
including different anatomical abnormalities. Limitation of our study is
its retrospective design.
We think that none of these four scoring systems is ideal. Because the
success definition is not standard and studied variables are limited. To
constitute an ideal nomogram a multi-center study examining the all
known potential variables with a strict success definition in a defined
time period can be planned with high number of patients. The ideal
scoring system could also be used in daily clinical practice. In
clinical practice it is hard to calculate stone burden by measuring the
diameter of all calculi (especially in multiple stones) or to measure
the IPA. In our opinion a stone score should be given by radiologists in
imaging reports whenever a widely used ideal nomogram can be developed.