Multicentre external validation of the imamura nomogram for the prediction of success after semi-rigid ureterolithotripsy

INTRODUCTION AND OBJECTIVE: Recently the Japanese group of Imamura et al developed the first clinical nomogram for the preoperative prediction of the stone-free rate in patients with ureteral stones undergoing laser semi-rigid ureterolithotripsy. Aim of our study was to externally validate Imamura nomogram for the prediction of the stone-free rate in patients undergoing ureterolithotripsy (ULT) in two centers. METHODS: From January 2014 onwards, 359 patients undergoing semi-rigid Ho:YAG laser ureterolithotripsy for ureteral stones were prospectively enrolled in two centers. Patients were preoperatively evaluated with accurate clinical history, urinalysis, renal function, Body Mass Index (BMI). KUB and/or non-contrast CT were used to define number, location and length of the stones and eventually the presence of hydronephrosis. The parameters evaluated in Imamura nomogram are: pyuria, length, location and number of stones. Treatment efficacy was evaluated by a KUB and/or CT 3 months after ULT, and stone-free was defined as no fragments detected. Calibration and discrimination of the nomogram were assessed using calibration plots and ROC analysis RESULTS: Median age was 54 years (IQR:44/65), median BMI 23.4 kg/m2 (IQR:22/28), median length of the stone was 8 mm (IQR:6/11). 272/359 (71%) patients presented hydronephrosis, pyuria on urinalysis was detected in 46/360 (2.1%). 232/359 (65%) patients were stone free at 3 months. Calibration plots showed an overall overestimation of the stone free rate by the nomogram. On ROC analysis, Imamura nomogram presented an AUC of 0.71 (95% CI 0.65-0.76 p=0.000) for the prediction of the stone-free rate in patients treated with ULT CONCLUSIONS: In our experience the Imamura nomogram represents a valid tool to preoperatively discuss with the patient the outcome of laser ureterolitothripsy. Implementation of the Imamura nomogram in clinical practice will define its role in counselling patients with ureteral stones