Robot-assisted laparoscopic radical prostatectomy (RARP) is becoming a standard treatment for localized prostate cancer, and it is being performed worldwide. Stress urinary incontinence (SUI), one of the most important complications after prostatectomy, has been reported to affect the quality of life (QOL) negatively. De novo SUI after RARP improved within a year after surgery in majority of the patients; however, some patients continued to suffer from SUI for over a year after RARP. A decrease in urethral functions after RARP, such as maximum urethral closing pressure (MUCP) and functional profile length (FPL), has been reportedly associated with the occurrence of SUI. In patients with a greater decrease in urethral function, the postoperative urinary incontinence (UI) tends to be prolonged. Hence, the evaluation of urethral function is useful in predicting the UI recovery period; however, this evaluation is invasive because catheterization is required to measure the urethral pressure. Therefore, there is a need for easily obtainable parameters to evaluate the long-term UI after RARP, in order to provide an appropriate course of treatment for patients undergoing RARP in a timely fashion. Recently, some studies have reported that the amount of urine loss on day 1 after catheter withdrawal was the most important predictor of urinary continence recovery after prostatectomy. Thus, the present study aimed to investigate easily obtainable parameters in clinical practice, including the amount of urine loss on day 1 after catheter withdrawal, to predict the long-term SUI after RARP.

We prospectively examined 350 patients who underwent RARP for localized prostate cancer. We divided the patients into two groups (continence group and incontinence group) 12 months after surgery, according to the presence or absence of SUI evaluated using a 24-hour pad test. The following parameters were compared between the groups to identify clinical signs associated with long-term SUI: pre-operative parameters including age, body mass index (BMI), initial serum prostate-specific antigen (PSA) level, total-international prostate symptom score (IPSS), IPSS-voiding sub-score, IPSS-storage sub-score, total overactive bladder symptom score (OABSS), MUCP, and FPL; operative parameters including blood loss, resected prostate volume, nerve-sparing, and amount of UI using the 24-hour pad test after catheter removal (on postoperative day 6 [6POD]); and postoperative parameters including MUCP and FPL (3 months postoperatively). In the present study, UI was defined as less than 2 g of UI using the 24-hour pad test.

A total of 315 patients with a mean age of 66.7 years were included in this analysis. At 12 month after RARP, Urinary continence was obtained in 250 patients (79.4%), and 65 patients (20.6%) had SUI. The comparison between the continence and incontinence groups for pre-operative parameters showed that age (66.2 years vs. 68.7 p = 0.004), total-IPSS (9.7 vs. 11.7, p = 0.004), and IPSS-storage score (4.3 vs. 5.3, p = 0.006) were significantly lower in the continence group. For the operative parameters, the nerve-sparing rate was significantly higher in the continence group (58% vs. 25%, p < 0.001). Furthermore, the 24-hour amount of UI at the time of catheter removal (6POD) was significantly lower in the continence group (166 g vs. 706 g, p< 0.001). As for the postoperative parameters, the MUCP (60.1 cmH2O vs. 40.9 cmH2O, p < 0.001) and FPL (25.2 mm vs. 21.3 mm, p < 0.001) at postoperative 3 months were significantly higher in the continence group. A multivariate logistic regression analysis using the parameters that showed significant differences in the univariate analysis revealed that the 24-hour UI immediately after catheter removal and postoperative MUCP were significant predictors of long-term SUI after RARP. Receiver operating characteristic (ROC) curve analysis identified 325 g/day and 50 cmH2O as the optimal cut-off values for 24-hour amount of UI at 6POD and postoperative MUCP, respectively, as the predictors of long-term UI. The values of 24-hour UI at 6POD and postoperative MUCP yielded sensitivities of 91% and 78%, respectively, and specificities of 84% and 80%, respectively (Figure). The area under the curve value in the ROC curve analysis of the 24-hour amount of UI at 6POD and postoperative MUCP were 0.928 and 0.840, respectively. Additionally, 24-hour UI at 6POD showed a positive correlation with the urinary continence recovery period (r = 0.74, p < 0.001).

The detailed mechanism explaining how the 24-hour UI at 6POD efficiently predicts the long-term UI after RARP remains unclear, but we can offer a plausible hypothesis. The 24-hour UI after catheter removal negatively correlated with postoperative MUCP (r = –0.55, p < 0.001) and postoperative FPL (r = –0.34, p < 0.001). Thus, the 24-hour UI after catheter removal probably reflected the postoperative urethral functions.

The 24-hour amount of UI at the time of catheter removal after RARP can be an efficient predictor of the recovery time of urinary continence following RARP.