A new nomogram for prediction of outcome of pediatric shock-wave lithotripsy

Despite the fact that shock-wave lithotripsy (SWL) remains a very good treatment option for smaller stones, it is being challenged by endourologic treatment modalities, which offer similar or even higher success rates in a shorter time, with minimal morbidity and invasiveness. The present study aimed to bring a new and practical insight in order to predict the outcomes of pediatric SWL and to provide objective information about pediatric SWL outcomes.

To design a nomogram for predicting the outcomes of pediatric shock-wave lithotripsy.

The study was conducted with a retrospective design and included 402 renal units who underwent SWL between January 2009 and August 2013. Patients with known cystine stone disease and cystinuria, with internal or external urinary diversion, were excluded. Analysis was performed on 383 renal units. Postoperative imaging was performed by plain abdominal graphy and ultrasonography with 3-month intervals. Patients who were completely free of stones were considered to be a success and statistical analysis was done regardingly Multivariate analysis was conducted by logistic regression analysis and a nomogram was developed.

The male/female distribution was 216/167, with a mean age of 48 ± 40 months and a mean stone size of 9 ± 3.5 mm. The overall stone-free rate was 70% (270/383) and efficacy quotient was 0.57. Mean follow-up was 11 ± 11 months (3-54 months). The number of shock waves and amplitude of energy were higher in failed cases. Multivariate analysis showed that gender, stone size, number of stones, age, location of the stone, and history of previous intervention were found to be the independent prognostic factors for assessing the stone clearance rates. A nomogram was developed using these parameters. In this nomogram, the points achieved from each parameter are summed and total points correspond to the risk of failure in percent.

A previous nomogram study by Onal et al. showed that younger age (<5 years), smaller stone burden (<1 cm), absence of previous stone treatment history, single stone, pelvis or upper ureter location (in girls) were favorable prognostic factors for successful outcome. As being the first pediatric study, it had some shortcomings. The study included 381 patients within a time period of 16 years. The present study included a similar number of cases within a 4-year period, which may reflect more homogeneity of data collection. Another issue is concern about the practical use of that nomogram. It constitutes two pages, which is a limiting factor for daily use. From a statistical point of view, they performed 200 bootstrapings with the aim of internal validation, which is less than the ideal number of 1000 bootstrapings, which was performed in the present nomogram. The presented nomogram is more practical, in that the pre-operative factors can be placed on the nomogram, the points can be added up and the parents can be given the approximate percentage of predicted stone-free rate after a single session. The expected treatment modality shown to the parents and patients ought to be the least minimally invasive, have the highest success rate, the least complication rate, and show the efficacy in one procedure at a time within the shortest period. However, SWL does not completely meet these criteria. The results gained from the present critical analysis of SWL in children, which was based on a strict definition of success, showed that outcome after a single session is not that good. Therefore, defining the patients who will benefit the most became one of the main issues. A more objective and skeptical look at SWL data enabled a nomogram to be developed that brings a new and practical insight in order to predict the outcomes of pediatric SWL.

In most of the pediatric stone cases, SWL is the first-line treatment option. However, it is wise to define the patients who will benefit the most. Therefore, nomograms can be useful for this purpose. The nomogram in the present study revealed that gender, stone size, number of stones, age, location of the stone, and history of previous intervention were found to be the independent prognostic factors for assessing the stone clearance rates. This nomogram can practically be used to inform the parents, and for proper patient selection for SWL.