Female stress urinary incontinence (SUI) is a disease that negatively affects personal life style and health-related quality of life. It has been reported to have a prevalence of 21.0%-22.9% in Korean middle-aged women [1,2]. Mixed urinary incontinence (MUI) is a disease accompanying urgency urinary incontinence (UUI) and SUI, and accounts for 36.4%-63% of total patients with urinary incontinence [2,3]. MUI has been known to more negatively affect the quality of life compared to pure SUI [3]. Since the introduction of Tension-free vaginal tape (TVT) surgery, midurethral sling surgery (MUS) has been mainly used for the treatment of SUI patients due to its advantages such as relatively simple and less invasive technique, less complications, and better efficacy [4]. Although the success rate of MUI is lower than that of SUI, Rezapour and Ulmsten [5] reported that MUS as a primary treatment method was effective in the treatment of MUI.

The mechanism of MUS is to prevent urinary leakage by providing the urethra with dynamic kinking when abdominal pressure increases [6]. Theoretically, MUS does not cause voiding dysfunctions such as weak stream, hesitancy, urgency, and straining. However, many studies reported that voiding dysfunctions such as decreased postoperative Qmax and increased postvoid residual (PVR) volume were observed [7] In addition, it was reported that persistent symptoms or the occurrence of new symptoms were shown in 11%-45% of urinary incontinence patients who had undergone MUS [8,9]. There was a chance for overactive bladder symptom to be developed after MUS surgery on pure SUI patients in the clinical field. On the other hand, there was also feasibility for SUI patients with overactive bladder symptom to improve the conditions of symptom. MUI is generally defined as a case of having both UUI and SUI. However, cases of having both urgency and SUI seem to be more frequently seen in clinical practices. Accordingly, the authors divided the subjects into the SUI group and the OAB+SUI group, and compared changes in voiding pattern after MUS between the SUI group and the OAB+SUI group.

This study was conducted on 225 female patients who had been diagnosed with SUI and undergone MUS, and who were followed-up for 3 months or longer of those who visited the Department of Urology of The Catholic University of Korea, Yeouido St. Mary's Hospital from January 2008 to February 2011.

The study was retrospectively conducted via the analysis of patient's medical records, medical interview on the current heath status of the patients, and survey, after approval from the Institutional Review Board (SC12RISI0020). The subjects were divided into the SUI group and the OAB+SUI group. Patients with complaint of involuntary loss of urine on effort or physical exertion (e.g., sporting activities), or on sneezing or coughing were assigned to the SUI group, whereas patients with SUI accompanied with overactive bladder symptom which defined as urinary urgency, usually accompanied by frequency and nocturia, with or without UUI, in the absence of urinary tract infection or other obvious pathology, were assigned to the OAB+SUI group [10]. Patients who had anticholinergic medication before the surgery or who received previous conservative treatments excluded from the subjects. Changes in the overactive bladder symptom score (OABSS) and American Urological Association-Symptom Index (AUA-SI) before and after the surgery were compared between the SUI group and the OAB+SUI group. In addition, AUA-SI was analyzed by categorizing questionnaires related to voiding symptoms (questions No. 1, 3, 5, and 6) and storage symptoms (questions No. 2, 4, and 7).

The mean age of the subjects was 54.68 years (range, 31-80 years). All patients underwent preoperative examinations including disease history taking, physical examination, urinalysis, urine culture, 1-hour pad test, Q-tip test, daily voiding check, uroflowmetry, and the measurement of the residual urine amount, and OABSS. In addition, the AUA-SI was assessed to examine the storage symptom and voiding pattern of the bladder before and after the surgery. Most patients underwent general anesthesia or spinal anesthesia before the surgery, whereas some patients underwent monitored anesthetic care (MAC) as a preoperative treatment, followed by local anesthesia of the surgery area. The surgery using outside-in transobturator tape (TOT) procedure via transobturator route was conducted.

The OABSS and AUA-SI were measured before the surgery and 3 months after the surgery in each group, and the changes in voiding pattern before and after treatment was observed by comparing the preoperative and postoperative scores in each group.

A statistical analysis was conducted using PASW Statistics 18.0 (SPSS Inc., Chicago, IL, USA). An independent t-test, and paired t-test were conducted for back-testing. If p<0.05, it was considered statistically significant.

Of the 225 patients, 165 patients (73.3%) were classified as SUI group, and 60 patients (26.7%) were classified as OAB+SUI group. The mean age of the subjects was 54.7 years (range, 31-80 years), and the mean age of patients was 53.9 years (range, 34-80 years), and 56.8 years (range, 31-78 years) in the SUI group and OAB+SUI group (p<0.05). In addition, there was no significant difference between these two groups in terms of symptom period, mean body index, mean 1-hour pad test, and mean Q-tip test (Table 1). The mean preoperative and postoperative AUA-SI were shown to be 0.96 points (range, 0-3 points) and 2.89 points (range, 0-6 points), respectively, in the SUI group. When the voiding symptom (questions No. 1, 3, 5 and 6) among the AUA-SI were compared, the mean preoperative and postoperative scores were shown to be 0.71 points (range, 0-2 points) and 2.23 points (range, 0-4 points), respectively, which showed a significant increase (p<0.05). In addition, when the storage symptom (questions No. 2, 4, and 7) among the AUA-SI was compared, the mean preoperative and postoperative scores were shown to be 0.25 points (range, 0-1 points) and 0.65 points (range, 0-3 points), respectively, which showed a significant increase (p<0.05) (Fig. 1). The mean preoperative and postoperative OABSS were shown to be 0.80 points (range, 0-3 points) and 0.90 points (range, 0-4 points), respectively, which showed a slight increase, but was statistically insignificant (p=0.847) (Fig. 2).

Meanwhile, the mean preoperative and postoperative AUA-SI were shown to be 8.55 points (range, 4-12 points) and 11.15 points (range, 2-16 points), respectively, in the OAB+SUI group. When the voiding symptom (questions No. 1, 3, 5, and 6) among the AUA-SI was compared, the mean preoperative and postoperative scores were shown to be 1.90 points (range, 0-8 points), and 3.85 points (range, 0-11 points), respectively, which showed a significant increase (p<0.05). In addition, when the storage symptom (questions No. 2, 4, and 7) among the AUA-SI was compared, the mean preoperative and postoperative scores were shown to be 6.65 points (range, 3-9 points), and 7.3 points (range, 4-10 points), respectively, which showed an insignificant increase (Fig. 3). The mean preoperative and postoperative OABSS were shown to be 6.45 points (range, 4-11 points) and 6.60 points (range, 2-9 points), respectively, which showed a significant increase (p<0.05) (Fig. 4). When the postoperative overactive bladder symptom was compared, OAB symptom newly occurred in 30 patients (18%) of the SUI group. Meanwhile, in the OAB+SUI, there were 27 patients (45%) that complained aggravated conditions of OAB symptoms after surgery. Among them, 12 patients (20%) had reported that they newly developed UUI. In addition, 15 patients (25%) improved the conditions of OAB symptoms after the surgery. As for the remaining patients, there was no difference before and after conducting the surgery.

After the surgery, there were 6 patients (3.6%) and 2 patients (3.3%) with vaginal wall injury in SUI group and OAB-SUI group, respectively. In addition, there were no bladder perforation, urethral injury, and massive bleeding in need of transfusion. There were 2 patients (1.2%) from SUI group and 1 patient (1.7%) from OAB+SUI group that had vaginal erosion after the surgery. Furthermore, all of them were solved by conservative treatment such as antibiotics therapy. Other than them, there was no complication after surgery including acute urinary retention, mesh exposure, urinary tract infection, and would infection.

MUS is most commonly used for the treatment of SUI due to its advantages such as relatively simple technique, good outcome, and less complications. Its surgical mechanism bring no change to the urethra in the case of normal abdominal pressure, and prevent SUI by providing the urethra's dynamic kinking in the case of increased abdominal pressure. Although it does not theoretically induce voiding dysfunction such as weak stream, hesitancy, urgency, and straining [6], many studies reported that voiding dysfunction was observed in patients with SUI who underwent MUS.

Jang et al. [6] reported that when MUS was conducted on 156 patients with SUI, three patients (1.9%), 2 patients (1.3%), and 7 patients (4.5%) complained of weak stream, residual urinary sensation, and frequency, respectively, and that voiding dysfunction occurred in the total 12 patients (7.7%), Salin et al. [7] reported that when MUS was conducted on 100 patients with SUI, five patients (5%) complained of urinary retention and 6 patients (6%) complained of hesitancy, slow stream, and feeling of incomplete emptying, and that voiding dysfunction occurred in the total 11 patients (11%). Kim et al. [11] have reported that voiding dysfunction was occurred after TOT surgery due to postoperative edema of bladder neck or urethra. Most of them were temporary and actually started to improve as time passed by. In this study, when the voiding symptom among the AUA-SI was compared, the mean score was shown to be 0.71 point before the surgery and 2.23 points after the surgery, which showed a significant increase. 82% of the pure SUI patients in this study complained aggravated conditions of voiding symptom after surgery, and 49% had reported aggravated conditions of storage symptoms. In addition, 35% of patients had one point more on the OABSS. Compared to previous studies, the result of this study showed a higher rate of voiding dysfunction. In the previous studies, voiding dysfunction was assessed according to objective criteria such as maximal flow rate, PVR, postoperative urodynamic study finding. Meanwhile, in this study, voiding dysfunction was assessed according to the patient's subjective symptoms. In addition, the previous studies were conducted 6-12 months after the surgery, whereas this study was conducted three month after the surgery, which showed a difference in study conduct time. Thus, the aforementioned two factors are likely to have contributed to the difference in the results between the previous studies and this study.

Medication such as antimuscarinic agent, dopamine, or serotonin, conservative treatments including behavioral therapy and pelvic muscle exercise, electric stimulation, and surgical treatment have been used for the treatment of MUI. However, since Rezapour and Ulmsten [5] recently reported that surgical treatment was effective in the treatment of not only SUI but also urgency or UUI in patients with MUI, many studies have reported that MUS was effective in the treatment of MUI [12,13]. There are various theoretical backgrounds that support the application of MUS to patients with MUI. Because urine leakage which occurred at increased abdominal pressure stimulated the proximal urethra to cause urgency, detrusor overactivity, Koonings et al. [14] reported that urgency and UUI were improved when urinary leakage caused by increased abdominal pressure was prevented. Rezapour and Ulmsten [5] reported that in the case of UUI, which is caused by detrusor instability urethral relaxation and uninhibited premature micturition, TVT improved it by supporting the pubic urethral ligament and by inducing dynamic kinking when abdominal pressure increased. At the present, however, compared to SUI, surgery success rate and patient's satisfaction are lower in MUS due to persistent urgency symptom and UUI after the surgery. Jeffry et al. [15] reported that when TVT procedure was conducted on 112 patients with MUI, 66% of the patients showed an objective success. Sinha et al. [16] reported that a success rate of 75% was shown in patients with MUI after TVT procedure, and that the success rate of MUI was lower in the TVT procedure compared to that of SUI. Kim et al. [17] reported that a SUI success rate of 96.4% was shown in patients with MUI when MUS was conducted on them, and that the resolution and improvement of urgency symptom were observed in 84.6% of the patients. In this study, when the AUA-SI was compared, 85% of the OAB+SUI patients complained aggravated conditions of voiding symptoms, and 50% had reported aggravated conditions of storage symptoms. One the other hand, when the mean OABSS was compared, 45% of patients showed a score increase of 1 point or more after the surgery. The patient's a degree of symptom improvement was shown to be lower in this study than in other studies. This is likely to be attributable to the facts that the criteria of comparing the patient's a degree of symptom improvement mainly depended on the survey in this study unlike other studies, and that the period of comparing the postoperative patient's satisfaction was shorter in this study than in other studies.

This is a retrospective study and has limitations in that the improvement of SUI and MUI were assessed only via disease history taking and questionnaire. For the accurate assessment of postoperative voiding dysfunction, a prospective study is further required via the analysis of objective tests such as urodynamic study in addition to the conduct of the survey. As no mechanism of MUS in the treatment of voiding dysfunction and MUI that occur after urinary incontinence surgery has been established yet, further follow-up and studies are additionally required.

When implementing MUS on patients with SUI, 18% of the patients newly developed OAB symptoms 3 months after the surgery as well as voiding dysfunction that aggravated voiding symptom or storage symptom. In addition 45% of the SUI patients with OAB complained aggravated condition of OAB symptoms 3 months after surgery. Therefore, it seems to be required to provide additional medicine treatment as well as special concern on sensitive bladder after the surgery especially for patients with urinary incontinence.