External validation of nephrolithometric nomograms in patients treated with minimally invasive percutaneous nephrolithotomy: a multicentric prospective study

Introduction:Minimally invasive percutaneous nephrolithotomies(PNL) are associated with lower complication rates (CR), stone freerates (SFR) and operative times are still debated. In the last decade,nomograms have been introduced to estimate the SFRs and CRof PNLs.However, no data are available regarding their reliability in case ofutilization of miniaturized devices. Herein we present a prospectivemulticentric study to evaluate reliabilityof Guy’s Stone Score (GSS), S.T.O.N.E. nephrolithometry Score and CROES Score in patients treatedwith minimally invasive PNLs.Materials and methods:We included 222 patients, the AUC of GSS, S.T.O.N.E. and CROES were 0.69 (95% CI 0.61–0.78), 0.64 (0.56–0.73) and0.62 (0.52–0.71) respectively. At multivariate binomial logisticregression, only the GSS had significance with an OR 0.54 (95% CI0.31–0.93, p = 0.03). We didn’t find significant correlation withcomplications, with only a trend for GSS (OR 1.44, 95% CI 0.95–2.18,p = 0.08).Results:This is the first study evaluating nomograms in miniaturizedPNLs. They still shows good reliability, however, our data show lowerperformances compared to standard PNLs. We emphasize the need offurther studies to confirm this trend. A dedicated nomogram forminimally invasive PNLs may be necessary.Conclusions:Although patients≥80 years old were significantly morecomorbid than younger ones, RIRS was a safe procedure with similaroutcomes and complication rates at an expense of higher operativetime and hospital stay. Younger patients visited more the emergencydepartment due to double J stent morbidity.