Study design, materials and methods
This was prospective, observational study conducted on male patients subjected to laparoscopic radical prostatectomy (LPR). Urodynamic studies were performed at the day before surgery (visit 1), 3 to 6 months postoperatively (visit 2) and more than 12 months after surgery (visit 3). Incidence of DU that occurred after LPR (de novo DU) and incidence of persisting de novo DU after 12 months were assessed. Diagnosis of DU was based on assessment of isovolumetric detrusor pressure (Piso) (cut‐off value of 50 cmH2O) with mechanical stop test during voiding phase. Moreover, clinical relevance of DU after LPR and predictive factors of de novo DU were appraised.
The flow of patients between the first and second visit in terms of DU incidence was appraised using McNemar test for the assessment of de novo DU. U Mann‐Whitney test for continuous independent variables and the chi‐square test or Fisher's exact test for independent categorical variables were utilized to access clinical relevance of DU. Univariate and multivariate logistic were used for identification of predictive factors of de novo DU. The level of significance was set to p = 0.05 for all calculations.
Results
Urodynamic findings and PROMS at each visit are presented in Table 1. Ninety nine of 100 patients underwent preoperative UDS (visit 1) and those were included in further analysis. Eighty four and 76 patients were available for follow-up at second and third visit respectively. De novo DU occurred after LPR in 25 (29.7%) patients at visit 2 (p<0.001). Sixteen from 24 patients (66,7%) who developed de novo DU after RP (visit 2) continued to have DU one year after surgery (visit 3) (p=0.04). On the multivariate analysis, urinary incontinence requiring more than 1 pad per day (OR 5.11; CI 1.69-17.19; p=0.005) and preoperative IPSS storage sub-score (OR 1.25; CI 1.03-1.63; p=0.030) were significantly associated with de novo detrusor underactivity. Post-prostatectomy patients with DU had significantly lower Urinary Assessment Urinary Assessment of the Expanded Prostate Cancer Index Composite (EPIC) total score (819 vs 911, p=0.02), EPIC Function domain score (300 vs 357, p=0.002) and EPIC Urinary incontinence domain (137 vs 224, p=0.002) when compared to their counterparts without DU (Table 2)
Interpretation of results
Our study revealed higher than expected incidence and persistence of de novo detrusor underactivity after LRP. DU after RP may be attributed to detrusor denervation related to autonomic nerve damage during surgical dissection. This applies specifically to the dissection in the proximity of the bladder neck and the removal of the seminal vesicles. There are several hypotheses proposed to explain relatively high incidence of DU in men after RP. First of all, the rate of DU appears to be strictly dependable on formula used for assessment of bladder contractility during UDS. The authors believe that optimal method to evaluate bladder contractility in men after RP is the assessment of Piso with mechanical stop test during voiding phase which was utilised in this study. In the majority of previously reported studies, however, Schafer nomogram, bladder contractility index (BCI) and other formulas based on Qmax and PdetQmax were utilized.
Co-incidence of de novo DU and postoperative SUI requiring more than 1 pad per day may be explained by both autonomic and somatic denervation during bladder neck and prostate dissection.
Moreover, significant correlation between preoperative IPSS scores and incidence of de novo DU was found. This may be explained by hypothesis that patients who have a lower reserve capacity for preoperative voiding function are more likely to develop postoperative DU after RP.