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Evaluation and Comparison of Urolithiasis Scoring Systems Used in Percutaneous Kidney Stone Surgery
Author's Accepted Manuscript Evaluation and Comparison of Urolithiaisis Scoring Systems in Percutaneous Kidney Stone Surgery Kevin Labadie, Zhamshid Okhunov, Arash Akhavein, Daniel Moreira, Jorge Moreno-Palacios, Michael del Junco, Zeph Okeke, Vincent Bird, Arthur D. Smith, Jaime Landman PII: DOI: Reference:
S0022-5347(14)04142-1 10.1016/j.juro.2014.07.104 JURO 11679
To appear in: The Journal of Urology Accepted Date: 22 July 2014 Please cite this article as: Labadie K, Okhunov Z, Akhavein A, Moreira D, Moreno-Palacios J, del Junco M, Okeke Z, Bird V, Smith AD, Landman J, Evaluation and Comparison of Urolithiaisis Scoring Systems in Percutaneous Kidney Stone Surgery, The Journal of Urology® (2014), doi: 10.1016/ j.juro.2014.07.104. DISCLAIMER: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our subscribers we are providing this early version of the article. The paper will be copy edited and typeset, and proof will be reviewed before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to The Journal pertain. All press releases and the articles they feature are under strict embargo until uncorrected proof of the article becomes available online. We will provide journalists and editors with full-text copies of the articles in question prior to the embargo date so that stories can be adequately researched and written. The standard embargo time is 12:01 AM ET on that date.
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EVALUATION AND COMPARISON OF UROLITHIAISIS SCORING SYSTEMS IN PERCUTANEOUS KIDNEY STONE SURGERY
Kevin Labadie1*, Zhamshid Okhunov1*, Arash Akhavein2, Daniel Moreira3, Jorge Moreno-Palacios1, Michael del Junco1, Zeph Okeke3, Vincent Bird2, Arthur D. Smith3 and Jaime Landman1
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1. Department of Urology, University of California, Irvine 2. Department of Urology, University of Florida, Gainesville 3. Smith Institute for Urology, North Shore LIJ Health System
Corresponding Author:
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*Co-first authors
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Jaime Landman, MD Professor of Urology and Radiology, Chairman, Department of Urology University of California, Irvine Email: [email protected] Tel: 714-456-3330 333 City Boulevard West, Suite 2100 Orange, CA 92868
Keywords: percutaneous nephrolithotomy, urolithiasis, scoring system, nomograms Abbreviations: percutaneous nephrolithotomy (PCNL), computerized tomography (CT), stone free status (SFS)
ACCEPTED MANUSCRIPT Abstract Introduction: Contemporary predictive tools for PCNL outcomes include Guy’s Stone Score, S.T.O.N.E. Nephrolithometry, and CROES (Clinical Research Office of the Endourological Society) nephrolithometric nomogram. We compared each scoring
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system using the same cohort to determine which was the most predictive of surgical outcomes.
Methods: We retrospectively reviewed patients who underwent PCNL between 2009 and 2012 at three academic institutions. We calculated Guy’s Stone Score, S.T.O.N.E.
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Nephrolithometry, and CROES nephrolithometric nomogram based on preoperative computerized tomography (CT) images. A single observer at each institution reviewed
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all images and assigned scores. Univariate and multivariate analysis was performed to determine the most predictive scoring system.
Results: We enrolled 246 patients. Mean Guy’s Scores for patients who were stonefree versus who had residual stones were 2.2 and 2.7 respectively (p<0.001). Mean S.T.O.N.E. scores for patients who were stone-free versus who had residual stones were 8.3 and 9.5, respectively (p<0.001). Mean CROES nomogram scores for patients
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who were stone free versus those who had residual stones were 222 and 187, respectively (p<0.001). In logistic regression analysis, Guy’s Score, S.T.O.N.E. Nephrolithometry and CROES nomogram were significantly associated with stone-free status (SFS), (p= 0.02, 0.004, <0.001 respectively). Guy’s Score and S.T.O.N.E.
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Nephrolithometry were associated with estimated blood loss (EBL) (p<0.0001, p=0.03) and length of stay (LOS) (p=0.03, p=0.009 respectively). The CROES nomogram was
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not predictive of EBL or LOS.
Conclusions: All scoring systems and stone burden were equally predictive of SFS. Guy’s Score and S.T.O.N.E. Nephrolithometry were associated with EBL and LOS. A single scoring system should be adopted to unify reporting.
ACCEPTED MANUSCRIPT INTRODUCTION There has been a marked increase in the prevalence of kidney stone disease in the United States within the last two decades approaching 7% in females and 10.3% in
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males in 20101. With this dramatic increase in incidence and prevalence of stone disease, the use of percutaneous nephrolithotomy (PCNL) for the treatment of large burden stones has continued to rise2-4. Despite continuous refinements in surgical
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techniques and technology, the overall complication rates for PCNL have increased5. An accurate estimate of treatment success is crucial for optimal decision-making and
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informed patient counseling. To characterize the complexity of kidney stones, preoperative radiologic evaluation with computerized tomography (CT) has become common practice in the United States. CT scans provide high resolution spatial imaging for accurate characterization of stone size and distribution, pelvicaliceal anatomy, anomalies and anatomical relationships which may dictate the feasibility and risks of
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different treatment modalities. With these measurable stone and patient features, the Guy’s Stone Score6, S.T.O.N.E. Nephrolithometry7, and CROES nephrolithometric been introduced for systematic and quantitative assessment of
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nomogram8 have
kidney stones. In addition to imaging characteristics, these models also take into
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account other patient features that contribute to disease outcome such as obesity, prior renal surgical history, spinal cord injury and spina bifida status, as well as surgeon experience. These different parameters are thought to provide the surgeon with an assessment of the complexity and intricacies of each individual patient. These scoring systems serve as disease stratification tools that allow the surgeon to more accurately predict outcomes of PCNL in order to improve patient counseling and surgical planning68
.
ACCEPTED MANUSCRIPT Another potential advantage of scoring systems is the uniform and standardized reporting across the different series. To date, comparative evaluation of treatment for urolithiasis has been limited by the lack of a widely accepted standardization system 9,10
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. Uniform academic and clinical reporting empowers physicians to better compare
data from different institutions, and will improve overall quality of urologic research. To date, there has been no direct comparison of existing scoring systems
6-8
.
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Comparison and analyses of these tools support refinements and improvements in these systems that may ultimately facilitate creation of a more universal and widely
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accepted scoring system. As such, we evaluated and compared these scoring systems in order to assess their relative predictive value for surgical outcomes. Additionally, we review features of each of these systems, their similarities and differences, their
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applicability in clinical practice and relevance in academic reporting
ACCEPTED MANUSCRIPT METHODS After obtaining Institutional Board Review approval, we performed a retrospective chart review on patients who underwent PCNL between 2009 and 2012 at three
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academic institutions. Selection criteria
Exclusion criteria included patients younger than 18 years old, a history of prior
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surgery on the ipsilateral kidney, nephrostomy tube or stent placement in the ipsilateral kidney prior to surgery, and patients with no available preoperative CT images. Patients
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who underwent repeat PCNL for recurrent stones on the ipsilateral kidney were included in the analysis. If a patient had bilateral procedures we selected one side at random to improve the independence of the data points.
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Measurements
We calculated the Guy’s Score, S.T.O.N.E. Nephrolithometry, and CROES nephrolithometric nomogram on all patients based on preoperative CT images as 6 7 8
. A single observer from
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described by Thomas, Okhunov and Smith respectively
each institution reviewed all images and performed scoring according to each system.
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We provided standardized instructions to all reviewers on the application of each scoring system prior to data collection. Perioperative Data
We collected patient demographic, clinical, perioperative and follow-up data in a retrospective fashion. The information collected included age, gender, body mass index (BMI), previous surgical history, medical history, presence of renal anomalies, American Society of Anesthesiologists Score (ASA), estimated blood loss (EBL), fluoroscopy time
ACCEPTED MANUSCRIPT (FT), operative time (OT), stone location and size, number of renal punctures, number and location of tracts dilated, and intraoperative and postoperative complications within 30 days and length of stay (LOS).
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Outcomes
The primary outcome of our study was to compare the ability of the Guy’s Score, S.T.O.N.E. Nephrolithometry and CROES nomogram to predict stone free rates
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following PCNL. We defined stone free rate status in our study as absence of residual stones or stone fragments <2mm at the termination of the procedure as confirmed by 11,12
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. CT scans were obtained on all patients prior to
postoperative CT imaging
discharge or within the 3 months of the surgery.
The secondary outcome was to evaluate the ability of the scoring systems to predict perioperative and postoperative complications within 30 days of the procedure.
modified Clavien system
Our
. Additionally, we evaluated perioperative variables such as
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FT, OT, EBL, and LOS.
13
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We classified all intraoperative and postoperative complications according to the
surgical
techniques
have
been
described
previously14,15.
All
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participating institutions have substantial experience with the PCNL procedure and the surgical technique is performed in a similar fashion between the three academic institutions. Statistical analysis
We divided patients in two groups based upon postoperative SFS (SFS). Comparisons of baseline characteristics between stone free and non-stone free subjects were performed using chi-square test for categorical variables and Student t
ACCEPTED MANUSCRIPT test for continuous data. Guy’s Score and CROES nomogram were divided in 4 groups and S.T.O.N.E. Nephrolithometry in 3. Descriptive statistics were used to show the stone free rate across the 4-category groups for each scoring system. Receiver
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operator characteristic (ROC) curves were generated for each scoring system and for stone burden (measured in mm2). Area under the curve and asymptotic 95% confidence intervals were calculated for each ROC curve. All statistical analyses were two-tailed
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and performed using Stata 12.0 (StataCorp, College Station, TX) and R 3.0.1 (R Foundation for Statistical Computing, Vienna, Austria). A p value of <0.05 was
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considered statistically significant.
ACCEPTED MANUSCRIPT RESULTS: We identified a total of 246 patients who underwent a PCNL between 2009 and 2012 who met the inclusion criteria. Patient demographics and stone characteristics are
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demonstrated in Table 1. Perioperative Data
The overall single procedure stone free rate in the study was 56%. The mean
respectively
(p<0.001).
Overall,
42
(17%)
patients
experienced
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1525mm2,
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stone size in stone free patients and patients with residual stones was 654mm2 and
postoperative complications including 23 Clavien grade I (fever, pain management with NSAIDS), 8 Clavien grade II (fever treated with antibiotics, AKI managed with IV fluids), 5 Clavien grade IIIA (obstruction requiring nephrostomy tube placement, double JJ stent causing infundibular rupture), 3 Clavien grade IIIB (significant bleeding requiring
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angioembolization, bleeding requiring nephrectomy, renal abscess treated with nephrectomy in the postoperative period) and 3 Clavien grade IVA (AKI hemodialysis,
Scoring Systems
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septic shock). There were no mortalities.
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The mean Guy’s Score for patients who were stone free or had residual stones was 2.2 and 2.7 respectively (p<0.001). The mean S.T.O.N.E. Nephrolithometry scores for patients who were stone free or had residual stones was 8.3 and 9.5 respectively (p<0.001). The mean CROES nomogram score for patients who were stone free or had residual stones was 222 and 187 respectively (p<0.001). The stone free percentages for each
scoring
system
are
illustrated
in
Table
2.
Guy’s
Score,
S.T.O.N.E.
ACCEPTED MANUSCRIPT Nephrolithometry and the CROES nomogram divided in groups were significantly associated with SFS (P = 0.002, 0.004 and <0.001 respectively). Table 3 and Figure 1 show the AUC and ROC curves for each of the scoring
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systems and stone burden alone. All scoring systems demonstrated similar accuracy. None of the scoring systems were more predictive of SFS than stone burden alone. The Guy’s Score and S.T.O.N.E Nephrolithometry were significantly associated with EBL
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and LOS (p <0.0001, p=0.03 and p=0.03, p=0.009 respectively), whereas CROES nomogram was not found to be significantly associated with neither complications, EBL
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or LOS.
ACCEPTED MANUSCRIPT DISCUSSION: Prediction and decision-aiding tools are different in their design and methodology. Nomograms, risk groupings, probability tables and classification and
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regression tree analyses are the few most commonly applied examples. Although the three scoring systems evaluated in this study are different in their development concept, they all are aimed at predicting stone free rates and complications while serving as disease stratification tools that provide both the surgeon and the patient with information
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on the individual procedure complexity6-8.
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Cumulatively, the Guy’s Score, S.T.O.N.E. Nephrolithometry and CROES nomogram incorporate a total of 11 variables. Of these, only four are shared: stone location, staghorn status, stone size and number. The seven other variables (tract length, renal pelvic obstruction, stone density, case volume/year, number of stones, prior treatment history, renal anatomy and presence of spina bifida or spinal injury) are
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included separately in each scoring system. Additional key differences are the method by which each accounts for anatomical features of the patient. The Guy’s Score includes
abnormal
renal
anatomy
and
calyceal
diverticulum.
S.T.O.N.E.
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Nephrolithometry and CROES nomogram do not take into account renal anomalies, but
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S.T.O.N.E. Nephrolithometry does account for other anatomical features mentioned above. However, results from large-scale studies demonstrated that abnormal renal anatomy is not associated with inferior surgical outcomes16,17. In this study, we compared the three scoring systems in a single cohort of patients that underwent PCNL. Although the heterogeneity of the scoring systems make analysis and direct comparison complex, they can be generally compared using a single
ACCEPTED MANUSCRIPT patient cohort via reliable statistical methods. To our best knowledge, our study provides the first comparison of the three scoring systems in the same patient cohort. We
demonstrated
equal
capacities
of
the
Guy’s
Score,
S.T.O.N.E.
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Nephrolithometry, and CROES nephrolithometric nomogram in predicting SFS. In the current series none of the scoring systems were more predictive of SFS than stone burden alone.
This finding is contradictory to the initial series presented for these 6,7
. This discrepancy may be a function of the fact that each
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classification systems
system was constructed based on the population of patients tested. This introduces an
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intrinsic biased favoring predictive efficacy. Consistent with all previous reports, stone size undoubtedly remains the leading predictor of perioperative outcomes. In addition to the primary outcome, the Guy’s Score and S.T.O.N.E. Nephrolithometry were significantly associated with perioperative outcomes. Overall,
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these scoring systems attempt to incorporate important variables in an efficient and simple manner to quantitate renal stone complexity. Given the similar predictive abilities of all three systems, it is up to urologists to decide which of these will be implemented
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and used in clinical practice and academic reporting.
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There have been numerous studies published that have externally validated Guy’s Score and S.T.O.N.E. Nephrolithometry. External validation of the Guy’s Score was reported in two separate studies by Mandal
18
and Ingirmasson
19
demonstrating
the scoring system effectively predicted SFS. External validation of S.T.O.N.E. Nephrolithometry was conducted in a multi-institutional study with 850 patients, showing that the model was significantly associated with SFS, overall complication rate (P=0.008), EBL (P=0.001), OT (P<0.001), and LOS (P=0.016)20. Akhavein and colleagues evaluated S.T.O.N.E. Nephrolithometry including 117 patients with strict
ACCEPTED MANUSCRIPT criteria for surgical outcomes21. In this study, the stone free rate was 75% and the S.T.O.N.E. score ranged from 6 to 12. In a logistic regression model, the scoring system was significantly associated with SFS. Both the Guy’s Score and S.T.O.N.E.
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Nephrolithometry have been demonstrated to show excellent interobserver reliability 19,22
. To date, the CROES nomogram has yet to be externally validated.
Guy’s Score and S.T.O.N.E. Nephrolithometry use risk groups to determine the
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risk of an event. Having categories of potential risk groups allows for improved differential stratification and selection of homogeneous patients that will serve as a
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benchmark to assess the quality of various interventions in efforts to achieve superior patient care and outcomes. Although grouping homogenous patients into risk groups allows discriminating of low, medium and high-risk patients, this methodology is associated with assumption that patients within a risk group are equal. Initial report of S.T.O.N.E. Nephrolithometry demonstrated that each increase in score is associated
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with 1.5 more likelihood of experiencing a complication. Indeed, patients with S.T.O.N.E. scores of 9-13, which are high-risk group patients, have different risks of
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having adverse events. This differs from the Guy’s Score in which there is significant overlap in the way patients are graded. For example, patients with partial or complete
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staghorn are classified into grades 3 and 4 respectively. Given the poor and vague definitions of partial and complete staghorn stones, significant overlap and variations may potentially under or over grade the patient thus reducing the accuracy of the scoring system. Thomas and colleagues indeed have highlighted this in their original manuscript. Their data demonstrated a poor interobserver agreement when reviewers graded patients with partial versus complete staghorn stones6. In contrast, nomograms have been shown to be of superior performance in other areas of urological research
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. However, the lack of validation data as well as the large continuous scale of
CROES nomogram makes it difficult and impractical to implement in a busy clinical routine.
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The imaging modalities in which the scoring systems were developed also demonstrate inconsistencies. Since the preoperative CT is the gold standard imaging modality, it is important that these scoring systems are attainable from a CT scan and
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have been validated based on CT images. The Guy’s Score and CROES nomogram were initially developed using abdominal x-ray, while S.T.O.N.E. Nephrolithometry was
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developed based on CT and consists of variables that are obtained specifically from CT images making it best suited for use with the contemporary imaging modalities. Stone size is an example of a variable easily and most accurately measured on CT imaging that was not taken into account by the Guy’s Score. Other important variables like tract
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length, stone density and severity of hydronephrosis are also measured exclusively on CT and are only incorporated into S.T.O.N.E. Nephrolithometry. When considering the optimal scoring system, it is essential that it must be
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reproducible, easily implementable and adequately comprehensive for thorough reporting and comparison. While considering all the limitations, we believe that the
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S.T.O.N.E. Nephrolithometry provides more accurate risk stratification data than the Guy’s Score, yet offers easier application than the CROES nomogram. After careful review of these systems we believe that the S.T.O.N.E. Nephrolithometry is the most comprehensive scoring system while remaining simple to implement in every day practice. It is easily remembered and applied with a simple acronym that has been demonstrated to be reproducible22. Furthermore, S.T.O.N.E. Nephrolithometry is the only scoring system that has been developed strictly from CT imaging, which is routinely
ACCEPTED MANUSCRIPT obtained on almost all patients with urolithiasis. Although the Guy’s Score’s also was very easy to implement, being confined to only four grades provides limited information on the extent of disease25. This hinders its ability to stratify disease complexity thus
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limiting its utility in academic reporting and patient education26. Although limitations are inherent with retrospective design of this study, we minimized these limitations with standardized data collection methods and strict
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outcomes definitions and follow up protocols11,12. Another possible limitation of this study was the exclusion criteria, which included patients with prior ipsilateral
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surgery and those with a stent or nephrostomy tube placed prior to the procedure. These patients were excluded as these cases are often more complex and do not reflect the typical PCNL experience. In addition, the data included in this study represents the experience of fellowship-trained surgeons from three academic
generalizability of the data.
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CONCLUSIONS
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centers. Although surgical techniques may slightly differ, our results support
Guy’s Score, S.T.O.N.E. Nephrolithometry, and CROES nomogram were equally
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predictive of SFS in patients undergoing PCNL. Guy’s Score and S.T.O.N.E. Nephrolithometry were associated with EBL and LOS. Further investigation is needed to determine a single scoring system to be adopted for unified academic reporting and preoperative prediction for the treatment of renal calculi with PCNL.
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ACCEPTED MANUSCRIPT Table 1. Patient demographics and clinical characteristics.
N Age (years)
Stone Free
Non-Stone Free
N (%) or Mean (SD)
N (%) or Mean (SD)
137 (56)
107 (44)
-
55.7 (14.9)
55.1 (15.0)
0.774
68 (63)
40 (37)
69 (51)
67 (49)
Gender
-
Male Female
1 2 3 4
13 (68)
Laterality
Left Right
BMI (Kg/m2) Punctures Operative time (min)
LOS (days) Stone Size (mm2)
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Calyces (n)
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EBL (mL)
Staghorn Stones (%) Essence (HU)
0.056
0.432
42 (48)
60 (59)
42 (41)
4 (80)
1 (20)
77 (58)
55 (42)
60 (54)
52 (46)
30.6 (8.6)
30.2 (7.7)
0.711
1.0 (0.1)
1.2 (0.6)
0.009
122 (53)
152 (65)
<0.001
68 (71)
101 (113)
0.005
3.1 (2.7)
3.2 (2.7)
0.608
654 (617)
1525 (1869)
<0.001
1.86 (1-4)
2.5 (1-5)
0.001
19
36
0.001
937 (305-1580)
937 (389-1849)
0.435
41 (53)
36 (47)
0.135
24 (59)
17 (41)
68 (61)
44 (39)
4 (29)
10 (71)
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-
6 (32)
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46 (52)
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ASA Score
-
p-value
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Variable
0.455
Location (%)
-
Upper pole Mid pole Lower pole Multiple Locations
ACCEPTED MANUSCRIPT Table 2: Stone free rate for all three scoring systems. Scoring systems
Stone Free Rate
Guy’s Score Grade 1
33/47 (70.2%)
-
Grade 2
53/81 (65.4%)
-
Grade 3
37/77 (48.1%)
-
Grade 4
14/39 (35.9%)
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-
S.T.O.N.E. Score categories
5-6
-
7-8
-
9-13
24/34 (70.6%)
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-
-
130-169
-
170-219
-
>=220
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80-129
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-
TE D
CROES Nomogram
53/80 (66.3%) 70/130 (46.2%)
5/22 (22.7%) 26/56 (46.4%) 25/55 (45.5%) 80/110 (72.7%)
ACCEPTED MANUSCRIPT Table 3: ROC curve values for Guy’s Score, S.T.O.N.E. Score, CROES nomogram and stone burden. Asymptotic Interval
Scoring System
ROC Curve (95% Confidence Interval) 0.634
0.566-0.702
S.T.O.N.E. Score
0.670
0.602-0.738
CROES Nomogram
0.671
0.602-0.739
Stone Burden
0.668
0.599-0.737
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Guy’s Score
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Figure 1: ROC curve for STONE score, Guy’s score, CROES nomogram and stone size.
S0022-5347(14)04142-1 10.1016/j.juro.2014.07.104 JURO 11679
To appear in: The Journal of Urology Accepted Date: 22 July 2014 Please cite this article as: Labadie K, Okhunov Z, Akhavein A, Moreira D, Moreno-Palacios J, del Junco M, Okeke Z, Bird V, Smith AD, Landman J, Evaluation and Comparison of Urolithiaisis Scoring Systems in Percutaneous Kidney Stone Surgery, The Journal of Urology® (2014), doi: 10.1016/ j.juro.2014.07.104. DISCLAIMER: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our subscribers we are providing this early version of the article. The paper will be copy edited and typeset, and proof will be reviewed before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to The Journal pertain. All press releases and the articles they feature are under strict embargo until uncorrected proof of the article becomes available online. We will provide journalists and editors with full-text copies of the articles in question prior to the embargo date so that stories can be adequately researched and written. The standard embargo time is 12:01 AM ET on that date.
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EVALUATION AND COMPARISON OF UROLITHIAISIS SCORING SYSTEMS IN PERCUTANEOUS KIDNEY STONE SURGERY
Kevin Labadie1*, Zhamshid Okhunov1*, Arash Akhavein2, Daniel Moreira3, Jorge Moreno-Palacios1, Michael del Junco1, Zeph Okeke3, Vincent Bird2, Arthur D. Smith3 and Jaime Landman1
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1. Department of Urology, University of California, Irvine 2. Department of Urology, University of Florida, Gainesville 3. Smith Institute for Urology, North Shore LIJ Health System
Corresponding Author:
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*Co-first authors
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Jaime Landman, MD Professor of Urology and Radiology, Chairman, Department of Urology University of California, Irvine Email: [email protected] Tel: 714-456-3330 333 City Boulevard West, Suite 2100 Orange, CA 92868
Keywords: percutaneous nephrolithotomy, urolithiasis, scoring system, nomograms Abbreviations: percutaneous nephrolithotomy (PCNL), computerized tomography (CT), stone free status (SFS)
ACCEPTED MANUSCRIPT Abstract Introduction: Contemporary predictive tools for PCNL outcomes include Guy’s Stone Score, S.T.O.N.E. Nephrolithometry, and CROES (Clinical Research Office of the Endourological Society) nephrolithometric nomogram. We compared each scoring
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system using the same cohort to determine which was the most predictive of surgical outcomes.
Methods: We retrospectively reviewed patients who underwent PCNL between 2009 and 2012 at three academic institutions. We calculated Guy’s Stone Score, S.T.O.N.E.
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Nephrolithometry, and CROES nephrolithometric nomogram based on preoperative computerized tomography (CT) images. A single observer at each institution reviewed
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all images and assigned scores. Univariate and multivariate analysis was performed to determine the most predictive scoring system.
Results: We enrolled 246 patients. Mean Guy’s Scores for patients who were stonefree versus who had residual stones were 2.2 and 2.7 respectively (p<0.001). Mean S.T.O.N.E. scores for patients who were stone-free versus who had residual stones were 8.3 and 9.5, respectively (p<0.001). Mean CROES nomogram scores for patients
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who were stone free versus those who had residual stones were 222 and 187, respectively (p<0.001). In logistic regression analysis, Guy’s Score, S.T.O.N.E. Nephrolithometry and CROES nomogram were significantly associated with stone-free status (SFS), (p= 0.02, 0.004, <0.001 respectively). Guy’s Score and S.T.O.N.E.
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Nephrolithometry were associated with estimated blood loss (EBL) (p<0.0001, p=0.03) and length of stay (LOS) (p=0.03, p=0.009 respectively). The CROES nomogram was
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not predictive of EBL or LOS.
Conclusions: All scoring systems and stone burden were equally predictive of SFS. Guy’s Score and S.T.O.N.E. Nephrolithometry were associated with EBL and LOS. A single scoring system should be adopted to unify reporting.
ACCEPTED MANUSCRIPT INTRODUCTION There has been a marked increase in the prevalence of kidney stone disease in the United States within the last two decades approaching 7% in females and 10.3% in
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males in 20101. With this dramatic increase in incidence and prevalence of stone disease, the use of percutaneous nephrolithotomy (PCNL) for the treatment of large burden stones has continued to rise2-4. Despite continuous refinements in surgical
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techniques and technology, the overall complication rates for PCNL have increased5. An accurate estimate of treatment success is crucial for optimal decision-making and
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informed patient counseling. To characterize the complexity of kidney stones, preoperative radiologic evaluation with computerized tomography (CT) has become common practice in the United States. CT scans provide high resolution spatial imaging for accurate characterization of stone size and distribution, pelvicaliceal anatomy, anomalies and anatomical relationships which may dictate the feasibility and risks of
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different treatment modalities. With these measurable stone and patient features, the Guy’s Stone Score6, S.T.O.N.E. Nephrolithometry7, and CROES nephrolithometric been introduced for systematic and quantitative assessment of
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nomogram8 have
kidney stones. In addition to imaging characteristics, these models also take into
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account other patient features that contribute to disease outcome such as obesity, prior renal surgical history, spinal cord injury and spina bifida status, as well as surgeon experience. These different parameters are thought to provide the surgeon with an assessment of the complexity and intricacies of each individual patient. These scoring systems serve as disease stratification tools that allow the surgeon to more accurately predict outcomes of PCNL in order to improve patient counseling and surgical planning68
.
ACCEPTED MANUSCRIPT Another potential advantage of scoring systems is the uniform and standardized reporting across the different series. To date, comparative evaluation of treatment for urolithiasis has been limited by the lack of a widely accepted standardization system 9,10
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. Uniform academic and clinical reporting empowers physicians to better compare
data from different institutions, and will improve overall quality of urologic research. To date, there has been no direct comparison of existing scoring systems
6-8
.
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Comparison and analyses of these tools support refinements and improvements in these systems that may ultimately facilitate creation of a more universal and widely
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accepted scoring system. As such, we evaluated and compared these scoring systems in order to assess their relative predictive value for surgical outcomes. Additionally, we review features of each of these systems, their similarities and differences, their
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applicability in clinical practice and relevance in academic reporting
ACCEPTED MANUSCRIPT METHODS After obtaining Institutional Board Review approval, we performed a retrospective chart review on patients who underwent PCNL between 2009 and 2012 at three
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academic institutions. Selection criteria
Exclusion criteria included patients younger than 18 years old, a history of prior
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surgery on the ipsilateral kidney, nephrostomy tube or stent placement in the ipsilateral kidney prior to surgery, and patients with no available preoperative CT images. Patients
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who underwent repeat PCNL for recurrent stones on the ipsilateral kidney were included in the analysis. If a patient had bilateral procedures we selected one side at random to improve the independence of the data points.
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Measurements
We calculated the Guy’s Score, S.T.O.N.E. Nephrolithometry, and CROES nephrolithometric nomogram on all patients based on preoperative CT images as 6 7 8
. A single observer from
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described by Thomas, Okhunov and Smith respectively
each institution reviewed all images and performed scoring according to each system.
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We provided standardized instructions to all reviewers on the application of each scoring system prior to data collection. Perioperative Data
We collected patient demographic, clinical, perioperative and follow-up data in a retrospective fashion. The information collected included age, gender, body mass index (BMI), previous surgical history, medical history, presence of renal anomalies, American Society of Anesthesiologists Score (ASA), estimated blood loss (EBL), fluoroscopy time
ACCEPTED MANUSCRIPT (FT), operative time (OT), stone location and size, number of renal punctures, number and location of tracts dilated, and intraoperative and postoperative complications within 30 days and length of stay (LOS).
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Outcomes
The primary outcome of our study was to compare the ability of the Guy’s Score, S.T.O.N.E. Nephrolithometry and CROES nomogram to predict stone free rates
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following PCNL. We defined stone free rate status in our study as absence of residual stones or stone fragments <2mm at the termination of the procedure as confirmed by 11,12
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. CT scans were obtained on all patients prior to
postoperative CT imaging
discharge or within the 3 months of the surgery.
The secondary outcome was to evaluate the ability of the scoring systems to predict perioperative and postoperative complications within 30 days of the procedure.
modified Clavien system
Our
. Additionally, we evaluated perioperative variables such as
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FT, OT, EBL, and LOS.
13
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We classified all intraoperative and postoperative complications according to the
surgical
techniques
have
been
described
previously14,15.
All
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participating institutions have substantial experience with the PCNL procedure and the surgical technique is performed in a similar fashion between the three academic institutions. Statistical analysis
We divided patients in two groups based upon postoperative SFS (SFS). Comparisons of baseline characteristics between stone free and non-stone free subjects were performed using chi-square test for categorical variables and Student t
ACCEPTED MANUSCRIPT test for continuous data. Guy’s Score and CROES nomogram were divided in 4 groups and S.T.O.N.E. Nephrolithometry in 3. Descriptive statistics were used to show the stone free rate across the 4-category groups for each scoring system. Receiver
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operator characteristic (ROC) curves were generated for each scoring system and for stone burden (measured in mm2). Area under the curve and asymptotic 95% confidence intervals were calculated for each ROC curve. All statistical analyses were two-tailed
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and performed using Stata 12.0 (StataCorp, College Station, TX) and R 3.0.1 (R Foundation for Statistical Computing, Vienna, Austria). A p value of <0.05 was
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considered statistically significant.
ACCEPTED MANUSCRIPT RESULTS: We identified a total of 246 patients who underwent a PCNL between 2009 and 2012 who met the inclusion criteria. Patient demographics and stone characteristics are
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demonstrated in Table 1. Perioperative Data
The overall single procedure stone free rate in the study was 56%. The mean
respectively
(p<0.001).
Overall,
42
(17%)
patients
experienced
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1525mm2,
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stone size in stone free patients and patients with residual stones was 654mm2 and
postoperative complications including 23 Clavien grade I (fever, pain management with NSAIDS), 8 Clavien grade II (fever treated with antibiotics, AKI managed with IV fluids), 5 Clavien grade IIIA (obstruction requiring nephrostomy tube placement, double JJ stent causing infundibular rupture), 3 Clavien grade IIIB (significant bleeding requiring
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angioembolization, bleeding requiring nephrectomy, renal abscess treated with nephrectomy in the postoperative period) and 3 Clavien grade IVA (AKI hemodialysis,
Scoring Systems
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septic shock). There were no mortalities.
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The mean Guy’s Score for patients who were stone free or had residual stones was 2.2 and 2.7 respectively (p<0.001). The mean S.T.O.N.E. Nephrolithometry scores for patients who were stone free or had residual stones was 8.3 and 9.5 respectively (p<0.001). The mean CROES nomogram score for patients who were stone free or had residual stones was 222 and 187 respectively (p<0.001). The stone free percentages for each
scoring
system
are
illustrated
in
Table
2.
Guy’s
Score,
S.T.O.N.E.
ACCEPTED MANUSCRIPT Nephrolithometry and the CROES nomogram divided in groups were significantly associated with SFS (P = 0.002, 0.004 and <0.001 respectively). Table 3 and Figure 1 show the AUC and ROC curves for each of the scoring
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systems and stone burden alone. All scoring systems demonstrated similar accuracy. None of the scoring systems were more predictive of SFS than stone burden alone. The Guy’s Score and S.T.O.N.E Nephrolithometry were significantly associated with EBL
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and LOS (p <0.0001, p=0.03 and p=0.03, p=0.009 respectively), whereas CROES nomogram was not found to be significantly associated with neither complications, EBL
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or LOS.
ACCEPTED MANUSCRIPT DISCUSSION: Prediction and decision-aiding tools are different in their design and methodology. Nomograms, risk groupings, probability tables and classification and
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regression tree analyses are the few most commonly applied examples. Although the three scoring systems evaluated in this study are different in their development concept, they all are aimed at predicting stone free rates and complications while serving as disease stratification tools that provide both the surgeon and the patient with information
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on the individual procedure complexity6-8.
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Cumulatively, the Guy’s Score, S.T.O.N.E. Nephrolithometry and CROES nomogram incorporate a total of 11 variables. Of these, only four are shared: stone location, staghorn status, stone size and number. The seven other variables (tract length, renal pelvic obstruction, stone density, case volume/year, number of stones, prior treatment history, renal anatomy and presence of spina bifida or spinal injury) are
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included separately in each scoring system. Additional key differences are the method by which each accounts for anatomical features of the patient. The Guy’s Score includes
abnormal
renal
anatomy
and
calyceal
diverticulum.
S.T.O.N.E.
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Nephrolithometry and CROES nomogram do not take into account renal anomalies, but
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S.T.O.N.E. Nephrolithometry does account for other anatomical features mentioned above. However, results from large-scale studies demonstrated that abnormal renal anatomy is not associated with inferior surgical outcomes16,17. In this study, we compared the three scoring systems in a single cohort of patients that underwent PCNL. Although the heterogeneity of the scoring systems make analysis and direct comparison complex, they can be generally compared using a single
ACCEPTED MANUSCRIPT patient cohort via reliable statistical methods. To our best knowledge, our study provides the first comparison of the three scoring systems in the same patient cohort. We
demonstrated
equal
capacities
of
the
Guy’s
Score,
S.T.O.N.E.
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Nephrolithometry, and CROES nephrolithometric nomogram in predicting SFS. In the current series none of the scoring systems were more predictive of SFS than stone burden alone.
This finding is contradictory to the initial series presented for these 6,7
. This discrepancy may be a function of the fact that each
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classification systems
system was constructed based on the population of patients tested. This introduces an
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intrinsic biased favoring predictive efficacy. Consistent with all previous reports, stone size undoubtedly remains the leading predictor of perioperative outcomes. In addition to the primary outcome, the Guy’s Score and S.T.O.N.E. Nephrolithometry were significantly associated with perioperative outcomes. Overall,
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these scoring systems attempt to incorporate important variables in an efficient and simple manner to quantitate renal stone complexity. Given the similar predictive abilities of all three systems, it is up to urologists to decide which of these will be implemented
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and used in clinical practice and academic reporting.
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There have been numerous studies published that have externally validated Guy’s Score and S.T.O.N.E. Nephrolithometry. External validation of the Guy’s Score was reported in two separate studies by Mandal
18
and Ingirmasson
19
demonstrating
the scoring system effectively predicted SFS. External validation of S.T.O.N.E. Nephrolithometry was conducted in a multi-institutional study with 850 patients, showing that the model was significantly associated with SFS, overall complication rate (P=0.008), EBL (P=0.001), OT (P<0.001), and LOS (P=0.016)20. Akhavein and colleagues evaluated S.T.O.N.E. Nephrolithometry including 117 patients with strict
ACCEPTED MANUSCRIPT criteria for surgical outcomes21. In this study, the stone free rate was 75% and the S.T.O.N.E. score ranged from 6 to 12. In a logistic regression model, the scoring system was significantly associated with SFS. Both the Guy’s Score and S.T.O.N.E.
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Nephrolithometry have been demonstrated to show excellent interobserver reliability 19,22
. To date, the CROES nomogram has yet to be externally validated.
Guy’s Score and S.T.O.N.E. Nephrolithometry use risk groups to determine the
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risk of an event. Having categories of potential risk groups allows for improved differential stratification and selection of homogeneous patients that will serve as a
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benchmark to assess the quality of various interventions in efforts to achieve superior patient care and outcomes. Although grouping homogenous patients into risk groups allows discriminating of low, medium and high-risk patients, this methodology is associated with assumption that patients within a risk group are equal. Initial report of S.T.O.N.E. Nephrolithometry demonstrated that each increase in score is associated
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with 1.5 more likelihood of experiencing a complication. Indeed, patients with S.T.O.N.E. scores of 9-13, which are high-risk group patients, have different risks of
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having adverse events. This differs from the Guy’s Score in which there is significant overlap in the way patients are graded. For example, patients with partial or complete
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staghorn are classified into grades 3 and 4 respectively. Given the poor and vague definitions of partial and complete staghorn stones, significant overlap and variations may potentially under or over grade the patient thus reducing the accuracy of the scoring system. Thomas and colleagues indeed have highlighted this in their original manuscript. Their data demonstrated a poor interobserver agreement when reviewers graded patients with partial versus complete staghorn stones6. In contrast, nomograms have been shown to be of superior performance in other areas of urological research
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. However, the lack of validation data as well as the large continuous scale of
CROES nomogram makes it difficult and impractical to implement in a busy clinical routine.
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The imaging modalities in which the scoring systems were developed also demonstrate inconsistencies. Since the preoperative CT is the gold standard imaging modality, it is important that these scoring systems are attainable from a CT scan and
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have been validated based on CT images. The Guy’s Score and CROES nomogram were initially developed using abdominal x-ray, while S.T.O.N.E. Nephrolithometry was
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developed based on CT and consists of variables that are obtained specifically from CT images making it best suited for use with the contemporary imaging modalities. Stone size is an example of a variable easily and most accurately measured on CT imaging that was not taken into account by the Guy’s Score. Other important variables like tract
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length, stone density and severity of hydronephrosis are also measured exclusively on CT and are only incorporated into S.T.O.N.E. Nephrolithometry. When considering the optimal scoring system, it is essential that it must be
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reproducible, easily implementable and adequately comprehensive for thorough reporting and comparison. While considering all the limitations, we believe that the
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S.T.O.N.E. Nephrolithometry provides more accurate risk stratification data than the Guy’s Score, yet offers easier application than the CROES nomogram. After careful review of these systems we believe that the S.T.O.N.E. Nephrolithometry is the most comprehensive scoring system while remaining simple to implement in every day practice. It is easily remembered and applied with a simple acronym that has been demonstrated to be reproducible22. Furthermore, S.T.O.N.E. Nephrolithometry is the only scoring system that has been developed strictly from CT imaging, which is routinely
ACCEPTED MANUSCRIPT obtained on almost all patients with urolithiasis. Although the Guy’s Score’s also was very easy to implement, being confined to only four grades provides limited information on the extent of disease25. This hinders its ability to stratify disease complexity thus
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limiting its utility in academic reporting and patient education26. Although limitations are inherent with retrospective design of this study, we minimized these limitations with standardized data collection methods and strict
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outcomes definitions and follow up protocols11,12. Another possible limitation of this study was the exclusion criteria, which included patients with prior ipsilateral
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surgery and those with a stent or nephrostomy tube placed prior to the procedure. These patients were excluded as these cases are often more complex and do not reflect the typical PCNL experience. In addition, the data included in this study represents the experience of fellowship-trained surgeons from three academic
generalizability of the data.
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CONCLUSIONS
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centers. Although surgical techniques may slightly differ, our results support
Guy’s Score, S.T.O.N.E. Nephrolithometry, and CROES nomogram were equally
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predictive of SFS in patients undergoing PCNL. Guy’s Score and S.T.O.N.E. Nephrolithometry were associated with EBL and LOS. Further investigation is needed to determine a single scoring system to be adopted for unified academic reporting and preoperative prediction for the treatment of renal calculi with PCNL.
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ACCEPTED MANUSCRIPT Table 1. Patient demographics and clinical characteristics.
N Age (years)
Stone Free
Non-Stone Free
N (%) or Mean (SD)
N (%) or Mean (SD)
137 (56)
107 (44)
-
55.7 (14.9)
55.1 (15.0)
0.774
68 (63)
40 (37)
69 (51)
67 (49)
Gender
-
Male Female
1 2 3 4
13 (68)
Laterality
Left Right
BMI (Kg/m2) Punctures Operative time (min)
LOS (days) Stone Size (mm2)
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Calyces (n)
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EBL (mL)
Staghorn Stones (%) Essence (HU)
0.056
0.432
42 (48)
60 (59)
42 (41)
4 (80)
1 (20)
77 (58)
55 (42)
60 (54)
52 (46)
30.6 (8.6)
30.2 (7.7)
0.711
1.0 (0.1)
1.2 (0.6)
0.009
122 (53)
152 (65)
<0.001
68 (71)
101 (113)
0.005
3.1 (2.7)
3.2 (2.7)
0.608
654 (617)
1525 (1869)
<0.001
1.86 (1-4)
2.5 (1-5)
0.001
19
36
0.001
937 (305-1580)
937 (389-1849)
0.435
41 (53)
36 (47)
0.135
24 (59)
17 (41)
68 (61)
44 (39)
4 (29)
10 (71)
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-
6 (32)
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46 (52)
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ASA Score
-
p-value
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Variable
0.455
Location (%)
-
Upper pole Mid pole Lower pole Multiple Locations
ACCEPTED MANUSCRIPT Table 2: Stone free rate for all three scoring systems. Scoring systems
Stone Free Rate
Guy’s Score Grade 1
33/47 (70.2%)
-
Grade 2
53/81 (65.4%)
-
Grade 3
37/77 (48.1%)
-
Grade 4
14/39 (35.9%)
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-
S.T.O.N.E. Score categories
5-6
-
7-8
-
9-13
24/34 (70.6%)
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-
-
130-169
-
170-219
-
>=220
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80-129
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-
TE D
CROES Nomogram
53/80 (66.3%) 70/130 (46.2%)
5/22 (22.7%) 26/56 (46.4%) 25/55 (45.5%) 80/110 (72.7%)
ACCEPTED MANUSCRIPT Table 3: ROC curve values for Guy’s Score, S.T.O.N.E. Score, CROES nomogram and stone burden. Asymptotic Interval
Scoring System
ROC Curve (95% Confidence Interval) 0.634
0.566-0.702
S.T.O.N.E. Score
0.670
0.602-0.738
CROES Nomogram
0.671
0.602-0.739
Stone Burden
0.668
0.599-0.737
AC C
EP
TE D
M AN U
SC
RI PT
Guy’s Score
ACCEPTED MANUSCRIPT
AC C
EP
TE D
M AN U
SC
RI PT
Figure 1: ROC curve for STONE score, Guy’s score, CROES nomogram and stone size.