Nomogram and scoring system for predicting stone-free status after extracorporeal shock wave lithotripsy in children with urolithiasis

Abstract

What's known on the subject? and What does the study add? Extracorporeal shock wave lithotripsy is often considered to be the first-line treatment method for the majority of urinary tract stone disease in children. The stone clearance rate in children treated with ESWL is higher than that in adults. Recently, nomograms for several diseases, e.g. for specific cancers, have been developed and validated in large patient populations. They have become very popular predictive tools that provide the most objective, evidence-based, and individualized risk estimation. These nomograms have gained acceptance as useful guides in clinical practice for use by physicians and patients. In adults, a nomogram has been created to predict stone-free outcome after ESWL; however, to our knowledge none has been developed for children with urolithiasis. This is the first study-generated nomogram table and scoring system for predicting the stone-free rate after ESWL in children. This predictive tool could be useful for clinicians in counselling the parents of children with urolithiasis and in recommending treatment. Objective To determine the stone-free rate after extracorporeal shock wave lithotripsy (ESWL) and its associated factors to formulate a nomogram table and scoring system to predict the probability of stone-free status in children. Patients and Methods A total of 412 children (427 renal units [RUs]) with urolithiasis were treated with ESWL using a lithotriptor between 1992 and 2008. Cox proportional hazards regression was used to model the number of treatment sessions to stone-free status as a function of statistically significant demographic characteristics, stones and treatment variables. A bootstrap method was used to evaluate the model's performance. Based on the multivariate model, the probabilities of being stone-free after each treatment session (1, 2 and >3) were then determined. A scoring system was created from the final multivariate proportional hazard model to evaluate each patient and predict their stone-free probabilities. Results Complete data were available for 395 RUs in 381 patients. Of the 395 RUs, 303 (76.7%) were considered to be stone-free after ESWL. Multivariate analysis showed that previous history of ipsilateral stone treatment is related to stone-free status (hazard ratio [HR]: 1.49; P = 0.03). Stone location was a significant variable for stone-free status, but only in girls. Age (HR 1.65, P = 0.02) and stone burden (HR 4.45, P = 0.002) were significant factors in the multivariate model. Conclusion We believe that the scoring system, and nomogram table generated, will be useful for clinicians in counselling the parents of children with urolithiasis and in recommending treatment.