Patients with MUI (mixed urinary incontinence) tend to have more profound symptoms compared to stress urinary incontinence (SUI) or urge urinary incontinence (UUI), with multiple treatment options often required. The paucity of research especially in the surgical management of MUI limits optimal management. Our primary objective is to compare the objective and subjective outcomes of SUI in patients undergoing mid-urethral slings (MUS) with a pre-operative diagnosis of MUI – urodynamic stress incontinence (USI) with subjective urgency versus urodynamic-proven mixed urinary incontinence (MUI-UD) – USI with detrusor overactivity (DO).

A retrospective review of 157 patients with USI with subjective urgency and MUI-UD who underwent MUS surgeries from January 2004 to April 2017 was performed. All 3 generations of MUS (single incision slings, trans-obturator and retropubic tapes) were utilized. Patients with urgency symptoms, UUI and SUI as well as urodynamic (UD) mixed findings of urodynamic stress incontinence (USI) and DO were included. Patients with neurogenic bladder, active vaginal lesions or infection, pregnancy, urinary tract infections or history of pelvic malignancy or irradiation were excluded. All patients underwent a detailed medical history, pelvic examination, urinalysis, cough stress test, 1-hour pad test, multi-channel urodynamic studies (UDS) and Urodynamic Distress Inventory (UDI-6) questionnaire (pre-operatively and 6-12 months post-operatively). Subjective cure of urgency and SUI was defined by a negative response to UDI-6 question 2 and 3 respectively. Objective cure of SUI was defined as the absence of involuntary urinary leakage of urine during filling cystometry associated with increased abdominal pressure in the absence of detrusor contraction, and a negative cough stress test (CST) with a bladder capacity of 200ml. Objective cure of DO/detrusor overactivity incontinence (DOI) was defined as the absence of spontaneous or provoked involuntary detrusor contraction during filling cystometry.

In the study period, there were 157 among 858 women with MUS who fulfilled the study inclusion criteria. MUI was detected in 19.3% (166 out of 858) of the patient population who underwent MUS surgery. Overall post-operative objective cure with normal urodynamics results was 70.7%(111 out of 157), 80.9% with no USI (127 out of 157) and 82.4% (131 out of 157) with no DO/DOI. Subjectively, 68.8% (108 out of 157) were cured, 80.3% (126 out of 157) had no SUI, and 79.6% (125 out of 157) had no urgency. Demographic factors identified to have a significant negative effect on cure rates were postmenopausal status (p = 0.005), prior hysterectomy (p = 0.028), pre-operative smaller bladder capacity (p = 0.001), a larger volume of pre-operative pad test (p = 0.028), and the presence of DO/DOI pre-operatively (p < 0.001). Analysis of 90 women in the MUI (USI + urgency) group attained an objective cure of 82% (Table 2) whereas the remaining 67 women in the UI-UD (USI and DO/DOI) group had an objective cure of 55% (Table 3). Subjective cure was 81% and 54% respectively. The type of incontinence surgery did not affect postoperative outcomes in either of the groups. Taking into consideration UI as a whole to include the MUI (USI + urgency) group and MUI-UD (USI and DO/DOI), objective cure was achieved in 71% (111 out of 157) of the patients and subjective cure at 69% (108 out of 157). Concurrently, 81% (127 out of 157) had no USI, and 82%
(131 out of 157) had no DO/DOI (Table 1). A larger volume in the pre-operative pad test significantly led to failure of surgery in both groups: the MUI-UD group with a volume of 50.3 ± 44.3 g (95%CI, 33.7–66.8; p = 0.034; Table 3) and the MUI group with a volume of 35.9 ± 34.6 g (95% CI, 17.5–54.4; p = 0.001; Table 2). In addition, patients with lower mid-urethral closure pressure (MUCP; 68.8 ± 36.2 cmH2O vs 51.9 ± 24.7 cmH2O; p = 0.033) significantly affected the success rate in the UI-UD group. lthough the decrease was also noted in the MUI group, the calculated difference was not statistically significant. As with the overall group outcome, a smaller cystometric capacity (p = 0.002), especially <150 ml (p = 0.034), was associated with significant failure of MUS surgery.

Th presence of DO on urodynamic study is likely to influence treatment and resulted in poorer objective and subjective outcome despite an overall objective success of 70% with mid-urethral sling surgery. Preoperative DO also predicts a poorer long-term outcome as appeared 55.2% (MUI-UD) and 85.2% MUI.  A decline in maximum urethral closure pressure was also found to be a risk factor for treatment failure in our study. A smaller cystometric capacity (<150mls) in urodynamically proven MUI (MUI-UD) has a higher chance of failure. The low success rate of mid-urethral sling surgery with urodynamically proven MUI, surgery should be only be considered after optimal conservative measures. However, where there is USI and urgency, surgery can be a first line treatment option with reported objective and subjective success of more than 80%.

MUS surgeries for patients having USI with subjective urgency attained higher objective and subjective cure rates compared to those with MUI-UD, showing that DO negatively influenced surgical outcomes. Performing UDS prior to surgical management of MUI with MUS may hence facilitate better patient selection. Knowledge on adverse risk factors such as postmenopausal, prior hysterectomy, pre-operative small bladder capacity, larger volume of pre-operative pad test and low MUCP will also allow for individualized pre-operative counseling in this complex subset of patients.