Hypothesis / aims of study
The main cause of postprostatectomy urinary incontinence (PPI) is the injury to the sphincter mechanism leadings to stress urinary incontinence (SUI). The treatment of this type of urinary incontinence requires the repair of the sphincter injury by implantation of an artificial urinary sphincter or a male sling such as the ATOMS system.
However, sometimes another type of urinary incontinence such as incontinence associated to detrusor overactivity (DO) which leading to urge incontinence, also occurs in these patients. Either coexisting with SUI (mixed urinary incontinence) or after anti-incontinence surgery (de novo detrusor overactivity). In addition, DO is associated with other lower urinary tract symptoms (LUTS) such as urgency, frequency, or the so-called overactive bladder syndrome (OAB). DO can affect quality of life of these patients because of the persistence of urinary incontinence or the presence of lower urinary tract symptoms (LUTS) associated with DO. Proper evaluation of factors that favour DO in patients after PPI treatment is crucial to predict postoperative outcomes However, we cannot infer that the presence of these LUTS is due to DO because other lower urinary tract dysfunctions can give rise to these symptoms such as the persistence of SUI . Invasive urodynamics (UDS) is the only test to diagnose DO and other lower urinary tract dysfunctions
Our hypothesis is that the presence of postoperative DO is related to the presence of other lower urinary disfunctions, both preoperative and postoperative. Consequently, the objective of this study is to assess which factors favour postoperative DO by evaluating preoperative and postoperative UDS data.
Study design, materials and methods
A prospective longitudinal study was carried out between October 2020 and March 2021 in a cohort of patients with primary ATOMS implantation for persistent SUI after prostate surgery refractory to conservative options. Inclusion criteria were baseline urodynamic study before ATOMS implant, minimum 1‐year follow‐up after ATOMS surgery and signed informed consent. The exclusion criteria the need to modify ATOMS system filling for urinary tract surgery after ATOMS adjustment and impossibility to perform urodynamic study for technical reasons.).
The urodynamic study included free uroflowmetry, filling cystometry and pressure flow study. The polygraph used was a Uro 2000 (MMS, Enschede, The Netherlands). The study was made according to the specifications of the International Continence Society (ICS) and the protocols of Good Urodynamic Practices (GUP) The diagnostic of BOO was made when the URA value was equal to or greater than 29 cm H2O.
The sample size was calculated according to Toia et al [1]. To find a preoperative DO percentage in continent patients of 27% and 55 % in incontinent patients after sling implantation to treat PPUI, an alpha error of 5% and a statistical power of 80%. This gave a minimum sample size of 54 patients.
A total of 84 cases were screened. Three patients died of another disease during follow‐up, 19 patients did not give consent to undergo postoperative urodynamic study, 3 had urinary tract surgery performed after ATOMS implant (transurethral resection of bladder tumour in 2 patients and ureteroscopy in another), 2 patients had irregular urethra in which no urodynamic catheter could be inserted, and one was not able to urinate because of perineal contraction. Consequently, the final sample size was made up of 56 patients with a mean age of 70± 6,01 years
Results
The relationship between preoperative clinical and urodynamic variables and postoperative detrusor overactivity is shown in table 1. A significant direct relationship was observed between postoperative DO and detrusor pressure at maximum flow rate (PQmax), URA and Bladder contractility index (BCI) and a significative inverse relationship between postoperative DO and age.
The relationship between postoperative clinical and urodynamic variables and postoperative detrusor overactivity are shown in table 2. A significant direct relationship was observed between postoperative DO and number of ATOMS adjustment, Pmax, PQmax, BOOI and URA and a significative inverse relationship between cystometric capacity, bladder compliance and frequency of acontractile detrusor (absence in postoperative DO). The regression model showed that he only independent variables were age and postoperative URA. The ROC graph showed that the best cut-off points for the URA value to discriminate between presence and absence of postoperative DO was a value of 10.9 H2O.
Interpretation of results
Age was the only preoperative clinical factor which influenced the presence of postoperative DO Among the preoperative urodynamic factors, the preoperative presence of DO did not influence its postoperative presence. The only significative preoperative urodynamic factors related to postoperative DO were the urethral resistance parameters BOOI and URA, and the contractility parameter BCI. Postoperatively URA remains as a factor related with the presence of DO. Other significant postoperative parameters found in our study such as Pmax and PQmax, are related to the URA parameter, or are a consequence of DO like the lower cytometric capacity, detrusor compliance or acontractile detrusor which avoids the presence of DO because of the absence of detrusor contractions
The only clinically significant postoperative factor was the number of ATOMS adjustment, which was higher in patients with DO. This fact can be due to the higher level of incontinence caused by DO, as it has been proved in other studies [1]. This confirms the utility of urodynamic studies to determine which LUTD is the cause of LUTS.
In multivariate analyse the only significative factors associated with postoperative DO were the URA urethral resistance parameter an age. The relationship between higher URA value and DO can be explained by a reaction of the detrusor muscle to an increase of work due to the increase in bladder outlet resistance that translates into an hyperreactivity of said muscle as it can be seem in benign prostatic hypertrophy [2], Although the difference with that phenomenon is that the URA values which trigger DO are below the values considered obstructive. Indeed, the cut-off point of the ROC curve (10, 5 cm H2O) is much lower than the obstruction value (set at 29 cm H2O.
The second independent variable which influenced the presence of postoperative DO was the clinical variable age. However, like the urethral resistance factor URA, its action on detrusor overactivity was not the usually known. Contrarily to the described relationship between age and DO or age and BOA, in this case the relationship was inverse, not direct. That is patients with preoperative DO are younger that patients without DO. This can be explained if we consider the relationship between age and detrusor contractility that is also inverse. Namely detrusor contractility decreases with age. Therefore, younger patients have higher detrusor contractility that reacts more frequently to increased urethral resistance with overactivity than older patients with lower contractility. This hypothesis can also explain the direct relationship between preoperative BCI and the presence of DO in the postoperative period. Yanagicuchi et al [3 ], have also observed in patients undergoing robot-assisted radical prostatectomy that patients who develop DO have a statistically higher detrusor power measured in Watt Factor than those who do not.