Change of Trends in the Treatment Modality for Pediatric Nephrolithiasis: Retrospective Analysis of a US-Based Insurance Claims Database

Abstract

Purpose:

The objective of this study was to show the prevalence and investigate treatment trends of pediatric nephrolithiasis based on a large population of U.S. insurance individual's data.

Materials and Methods:

This research involved a retrospective observational cohort study. Administrative claims data were extracted from the IBM^® MarketScan^® Research Database. We included all patients newly diagnosed with nephrolithiasis, aged <18 years old at the time of diagnosis from January 1, 2007, to December 31, 2014. The patient cohort with nephrolithiasis was selected using the International Classification of Disease, 9th Revision, Clinical Modification (ICD-9-CM) code for nephrolithiasis. Each treatment method was searched by Current Procedural Terminology (CPT) code.

Results:

A total of 28,014 patients were found to have nephrolithiasis in our cohort. Of nephrolithiasis patients, 701 (2.5%) patients were treated by surgical methods. The mean age of patients at the time of treatment was 13 years old. Extracorporeal shockwave lithotripsy (SWL) was the most used treatment modality during the period. SWL was performed in 66% of patients. The number of cases of SWL did not tend to change according to year, whereas retrograde intrarenal surgery (RIRS) tended to increase from 15% to 31%. Percutaneous nephrolithotripsy (PCNL) decreased from 13% to <10 cases. The number of open surgeries was very small and did not show any tendency.

Conclusion:

During the study period, SWL is stable. RIRS has become more popular in treating renal stones, whereas PCNL has decreased. These results suggest that the RIRS has become more popular than PCNL in treating large renal stones.

Introduction

Urolithiasis, or urinary tract stones, is one of the most common urologic diseases. The prevalence of nephrolithiasis ranges from 7% to 13% in North America.¹ Recent data show an increasing incidence and number of treatment cases of nephrolithiasis in the United States.^1,2

The incidence of urinary stones varies by age, but usually peaks in the fourth to sixth decades of life. Therefore, the incidence of nephrolithiasis in children is not very high and ranges from 8 to 18 per 100,000 children.³ However, the incidence of and interventions for pediatric nephrolithiasis have been steadily increasing, with a particularly concerning increase in health care costs for treatments.^3

–6 Although the interventions data are very important for making health care policy, most data on interventions for pediatric nephrolithiasis are based only on hospitals, emergency departments, or limited county data; these data are not based on nationwide population data. Moreover, most of them were all reported nearly 10 years ago, so it is necessary to investigate the current incidence trend data based on a large population-based study.

In 2007, the joint American Urological Association and European Association of Urology Nephrolithiasis Guideline included recommendations for treating pediatric patients as well as adults and noted that ureteroscopy (URS) or extracorporeal shockwave lithotripsy (SWL) appeared to be effective in patients with urolithiasis.⁷

Recently, there have been many changes in treatment trends of treating renal stones, such as improvements in retrograde intrarenal surgery (RIRS) and percutaneous nephrolithotripsy (PCNL) instrument and technology. The number of RIRS and PCNL cases has increased in adult patients.⁸ Especially recent trend analysis reported that the ureteroscopic treatment of upper ureteral stones is on a rise in adults.⁹

However, the choice of a surgical procedure in children is not the same as in adults. The SWL procedure, which is often performed in outpatient clinics, requires general anesthesia in children patients, and small ureteral diameters can make RIRS more difficult or even impossible. Therefore, the treatment trend in pediatric nephrolithiasis would be very different from that of adults, but there have been few reports on it.

The objective of this study was to show the recent treatment trends of pediatric nephrolithiasis based on a large population of U.S. insurance individual's data.

Materials and Methods

Data source

This research involved a retrospective observational cohort study. Administrative claims data were extracted from the IBM^® MarketScan^® Research Database. These databases include retrospective claims information, such as outpatient and inpatient enrollment demographics in the United States. To comply with Health Insurance Portability and Accountability Act (HIPAA) regulations, all data were deidentified. The Institutional Review Board (IRB) determined that IRB approval was not required because this research did not involve prospective testing on human subjects. Data source is well described in another study.¹⁰

Patients and data inclusion

We included all patients newly diagnosed with nephrolithiasis, aged <18 years old at the time of diagnosis, who underwent any form of treatment, such as SWL, RIRS, PCNL, or open surgery, from January 1, 2007, to December 31, 2014. The patient cohort with nephrolithiasis was selected using the International Classification of Disease, 9th Revision, Clinical Modification (ICD-9-CM) code for nephrolithiasis. Each treatment method was searched by Current Procedural Terminology (CPT) code. Demographic factors such as age and gender were extracted from the database. Race, impatient medication information, and laboratory results were not included in the database.

We excluded patients who were found to have concurrent ureteral and nephrolithiasis by codes. Because ureteral stones might affect the choice of treatment modality for the nephrolithiasis, we only included the patients with only nephrolithiasis.

In cases of several SWL treatments, we considered up to three separate SWL treatments within 3 months as a single treatment session. If patients received two or more treatment modalities within 3 months, only the first treatment was regarded as the study treatment, whereas two or more treatments after a 3-month treatment interval were considered independently.

According to data policy, we could not describe the exact number of data points for parameters with <10 data points. We described these cases as “less than 10.”

Statistical analysis

The Cochran-Armitage Trend Test was applied so as to evaluate the treatment trend over time. The beta coefficients and 95% confidence intervals were reported. All tests were two sided with p < 0.05 considered to be significant. Statistical software SAS (SAS Institute Inc., version 9.4) was used.

Results

The prevalence of nephrolithiasis

A total of 100,968,589 subjects were enrolled between 2007 and 2014. Among this population, a total of 28,014 patients were diagnosed with nephrolithiasis. The mean annual incidence of nephrolithiasis was 2.78 per 10,000 (range 2.71–2.96) (Table 1).

Table 1.

The Mean Annual Incidence of Nephrolithiasis

Year	No. of patients found to have renal stone	Total population	Renal stone incidence per 10,000 person
2007	2779	9,391,709	2.96
2008	3651	13,122,214	2.78
2009	3783	13,919,180	2.72
2010	3677	13,766,432	2.67
2011	3983	14,243,574	2.80
2012	3831	14,127,293	2.71
2013	2995	10,952,557	2.73
2014	3315	11,445,630	2.90

The trend of nephrolithiasis treatment

Of 28,014 nephrolithiasis patients, 701 (2.5%) patients were treated by surgical methods including SWL. The mean number of patients per year was 88, and this was not changed during the study period. The mean age of patients at the time of treatment was 13 years old (range 0–17). The male:female ratio was 1:1.3. The annual demography of patients is given in Table 2.

Table 2.

Nephrolithiasis Patients Who Were Treated by Surgical Methods

Year	2007	2008	2009	2010	2011	2012	2013	2014
No. of renal stone patients	72	113	80	84	92	98	78	84
Mean age at treatment (SD)	11.7 (4.6)	13.1 (4)	13.7 (3.6)	13.5 (3.9)	12.7 (4.6)	13.3 (4.1)	13.6 (4.1)	12.3 (4.8)
Gender
No. of male patients	32 (44.44)	51 (45.13)	34 (42.5)	38 (45.24)	36 (39.13)	53 (54.08)	30 (38.46)	31 (36.9)
No. of female patients	40 (55.56)	62 (54.87)	46 (57.5)	46 (54.76)	56 (60.87)	45 (45.92)	48 (61.54)	53 (63.1)

SD = standard deviation.

The treatment trend is shown in Figure 1. SWL was the most used treatment modality during the period. SWL was performed in 66% of patients, and this did not tend to change according to year. However, there were definite changes in the trends for RIRS and PCNL (p < 0.0001). RIRS tended to increase from 28 cases (15%) to 51 cases (31%), whereas the number and percentage of PCNL decreased from 24 cases (13%) to <10 cases. The number of open surgeries was very small and did not show any tendency.

FIG. 1.

The treatment trend of pediatric nephrolithiasis. SWL = extracorporeal shockwave lithotripsy; PCNL = percutaneous nephrolithotripsy; RIRS = retrograde intrarenal surgery.

Discussions

Although urolithiasis in children is less common than in adults, several reports show that its incidence is rising and can cause many complications, leading to significant medical costs.

The mean annual incidence of nephrolithiasis was 28 per 100,000. That is lower than that reported by the Routh study and higher than that reported by South Carolina study.^5,11

Routh et al.⁵ conducted a study using the Pediatric Health Information System national database and demonstrated an increased incidence of urolithiasis in children. The incidence of urolithiasis was 18 per 100,000 patients in 1999 and increased to 57 per 100,000 patients in 2008. Routh and colleagues⁵ used ICD-9-CM diagnosis code for urolithiasis (592.0 or 592.1), so they included not only nephrolithiasis but also ureter stones. This difference made the incidence higher than our study. In several articles, nephrolithiasis often refers to renal stone, ureter stone, or combined renal and ureter stone, whereas nephrolithiasis in this study means only renal stone.

Emergency department data from South Carolina also showed a similar trend. The incidence in 1996 was ∼8 per 100,000 children and increased to ∼18 per 100,000 children in 2007.¹¹ Our study period starts from 2007 and stone incidence was on the rise, which would make some differences in incidence.

The surgical procedures for the treatment of renal stones in children are the same as in adults, which include SWL, RIRS, PCNL, and laparoscopic or open surgery. Our study showed that SWL is the most used treatment modality, as nearly 70% of renal stone patients were treated by SWL. This percentage remained constant during the study period. The percentage of SWL in the treatment is higher than adults. Recently, Heers and Turney⁹ reported stable renal stone incidence and SWL use in adult patients between 2009 and 2014. These results supported our results regarding stable renal stone incidence and SWL treatment.

EAU guideline recommended SWL for the treatment of stones with a diameter of <20 mm.¹² In addition, as pediatric renal stones are usually small and soft, and patient tissue volume is small for shockwave transmission, crushed stone fragments are easy to pass out. That is the reason why SWL as a monotherapy in pediatric patients is as effective as in adults.^13,14 SWL as a monotherapy is a relatively more effective method in pediatric patients than in adults. It is also notable that the total sum of RIRS and PCNL cases is also stable, like SWL. These results suggest that the SWL role in renal stones is sustained.

In adults, both RIRS and PCNL were increased, but our study showed only RIRS was increased.⁹ EAU guideline recommended PCNL as a choice of treatment in the treatment of nephrolithiasis >20 mm and second choice for lesser sized stone.¹² With the improvement of instruments including mini PCNL and ultramicro PCNL, the use of PCNL in adult cases has increased. However, the PCNL technique requires extensive surgeon experience, which is a hurdle for pediatric surgeons to perform PCNL in pediatric patients.

Contrary to PCNL, URS or RIRS is a relatively easier technique to perform. In addition, the mean age of our study population was 13 years old, and RIRS cases can be much more feasible at that age. Sen and colleagues reported that stone-free rates in the micro-percutaneous nephrolithotomy and RIRS groups were reported to be 84% (21/25) and 82.6% (19/23), respectively, and that there was no statistical difference between these.¹⁵ A recent comparison study showed that there was no significant difference of success between PCNL and RIRS for moderate sized renal stones in children.¹⁶ Our study showed that SWL is stable and RIRS has increased, whereas cases of PCNL have decreased according to time. It suggests that the RIRS has become more popular than PCNL in treating large renal stones in which SWL was not an option.

This study has some limitations: First, we used a large retrospective cohort-based database to obtain patient and study data. In this database, several important pieces of information were not recorded and could not be collected, including stone location, size, multiplicity, and composition of the renal calculi. Therefore, we could not tell which treatment option was used according to stone size. Especially the choice for PCNL or RIRS often depends on the stone burden. Therefore, lack of information regarding the stone burden in each child in the study would limit the utility of these results. In addition, we could not know the exact clinical situation when nephrolithiasis was diagnosed. Therefore, we do not know whether the stone is detected by chance or related to significant clinical symptoms.

Previous articles about nephrolithiasis often include proximal ureter stone as well as renal stone. We investigated only renal stone as nephrolithiasis. As renal stone is hardly painful, we assumed that most renal stones in this study were discovered by chance and that is why only 2% to 3% of the pediatric cohort received surgery.

Despite all of these limitations, this is based on the one of the largest population data, and our study shows the current trend of pediatric and treatment modality for renal stones.

Conclusions

The mean annual incidence of nephrolithiasis was 2.78 per 10,000 (range 2.71–2.96). We identified a change in the trend for the treatment of renal stones: SWL is stable, whereas RIRS increased and PCNL decreased. These results suggest that the RIRS has become more popular in treating large renal stones in child cases compared with adult cases.

Footnotes

Acknowledgment

This article was written as part of Konkuk University's research support program for its faculty on sabbatical leave in 2017.

Author Disclosure Statement

There is no known conflict of interest in this study.

Abbreviations Used

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