Novel Prediction Scoring System for Simple Assessment of Stone-free Status After Flexible Ureteroscopy Lithotripsy: T.O.HO. Score

Objectives: To develop a novel simple quantitative scoring model for predicting stone-free status after a flexible ureteroscopy lithotripsy procedure by standardizing the complexity of ureteral stone characteristics.

Methods: We retrospectively reviewed 586 patients with renal or ureteral stones who underwent flexible ureteroscopy lithotripsy at Abiko Toho Hospital, Chiba, Japan, from 2015 to 2018. Multivariate regression was applied to examine the relationship between preoperative descriptors and stone-free status, and a nomogram was developed using significant predictors. Next, the individual components of the nomogram were assigned points to form a simple scoring system. The predictive performance of this new scoring system was compared with the STONE score at optimal cut-off values using receiver operating characteristic curve and area under the curve analyses.

Results: Multivariate logistic regression findings showed that factors associated with stone-free status were length, Hounsfield unit and stone location. A nomogram prediction model was developed with an area under the curve value of 0.845, then consequently used to develop a new simple score system termed the T.O.HO. score consisting of three stone characteristics: (T)allness (1-5 points), (O)ccupied lesion (1-3 points) and (HO)unsfield units evaluation (1-3 points). The T.O.HO. score was significantly higher in stone remaining (7.66) than stone-free (5.27; P < 0.001) cases. The area under the curve for the T.O.HO. score was 0.833 at an optimal cut-off value of 7, whereas that for the STONE score was 0.683 at an optimal cut-off value of 9, showing the superiority of this new scoring system.

Conclusion: The T.O.HO. score is a useful tool for predicting stone-free status in patients who have undergone a flexible ureteroscopy lithotripsy procedure.