There are very limited data on the impact of detrusor underactivity (DUA) on stress urinary incontinence (SUI) surgery outcomes. Indeed, no definitive standardized urodynamics (UDS) criteria of DUA have been defined in women. Aim of this study was to assess the influence of DUA, according to the main UDS parameters, on the outcomes of women underwent middle urethral sling (MUS).

Women with SUI, naïve for SUI surgery, and treated with MUS were enrolled in this prospective study from January 2014 to January 2019. Informed consent was obtained. Exclusion criteria were: previous SUI surgery, associated pelvic organ prolapse, previous pelvic surgery and/or radiotherapy, neurologic diseases. All patients underwent pre-operative UDS. Patients were stratified according to the 4 main available UDS criteria of DUA: i) Pdet@Qmax ≤10 cm H2O and Qmax ≤12 mL/s (Jeong et al.); ii) Pdet@Qmax<30 cm H2O and Qmax<10 mL/s (Abarbanel and Marcus); iii) Pdet@Qmax<20 cm H2O and Qmax<15 mL/s and  BE<90% (BVE criteria); iiii) Pdet@Qmax<20 cm H2O + Qmax (PIP1 Griffiths). The control group (CG) was represented by women with no-DUA. Preoperative evaluation included also free uroflowmetry (UF), post void residual urine (PVR), PVR-ratio (PVR-R) defined as the ratio between bladder volume and PVR, and the International Continence Index Questionnaire Urinary Female LUTS (ICIQ-FLUTS). The occurrence of postoperative urinary retention (POUR), defined as the presence of PVR ≥200 ml in > 2 evaluations, was assessed. In case of POUR, a transient drainage of the bladder by clear intermittent catheterization (CIC) or indwelling catheter (IC) was share decided with the women, and counselling on the POUR management was done. The follow-up, scheduled at 1, 6 moths and then each year, included: physical examination and vaginal inspection, UF, PVR and PVR-R, ICIQ-FLUTS. Statistical tests were: T student, Mann Whitney, Q-square, ANOVA.

The 102 patients who fulfilled the 2-years follow-up were considered for the analysis. DUA rate ranged from 16.7% (BVE) to 53.9% (PIP1-Griffith). Table 1 resumes mean age of the patients, prevalence of DUA according to the UDS criteria, and the main voiding complications. POUR rate varied from 20% (PIP1-Griffith) to 35.3% (BVE) and was higher than in CG (10%). The lowest duration of postoperative catheterisation before the resolution of POUR was found in PIP1-Griffith group. An early surgical treatment for POUR (7-30 days – tape incision) was performed in 2 women with DUA and in 2 women without DUA, and the rate was higher in the BVE group (11.8%), while no patients had to be treated surgically in the Arbanel group. At 2-yrs follow-up, no patient was in CIC or in IC. Functional outcomes are reported in Table 2. No significant differences were found between preoperative and at follow-up Qmax, VV, PVR, while PVR-R decreased significantly only in BVE group. Preoperative mean PVR was low in all DUA groups, and in the BVE group was the highest (55mL). ICIQ-FLUTS scores decreased in all DUA groups, but remained still higher than in CG. Mean Valsalva Leak Point Pressure (VLPP) was similar in all groups (55-59 cmH20). Only patients of Jeong group had a SUI recurrence rate lower than CG (3.3% vs 4.5%), while in the other DUA groups was very higher (21-23.6%). Women of Jeong group had OAB de novo rate similar to CG group (13.3% vs 11.3%), while the other DUA groups patients had very higher rates (21%-29.4%). At the multivariate analysis, without control group, we found that preoperatively there were significant differences in PVR, and at follow-up in ICIQ-FLUTS scores. At the multivariate analysis with also control group, the items without significant difference were preoperative VV and ICIQ-FLUTS, and at follow-up PVR and PVR-R (Table 2).

According to DUA definitions, POUR had a twice or three times higher prevalence than the control group, and the surgery treatment rate for POUR had a high variability (3.6% to 11.8%). This finding may have a very relevant impact on the counselling and on the post-operative management. DUA did not negatively impact on voiding outcomes at 2-years follow-up, regardless the type of DUA diagnosed. However, according to the DUA type, we found very different OAB de novo and SUI rates at follow-up. Only patients of Jeong group had OAB de novo and SUI recurrence rates similar to the control group, while in the other DUA groups the prevalence of these outcomes almost doubled. The mean VLPP was similar in all groups, and so the SUI severity may not have been significant different in the patients. Thus, a possible explanation of the higher SUI recurrence could be a softer tape placement in some patients of these DUA groups to avoid POUR.

According to the UDS criteria used, DUA diagnosis had a high variability and relevantly changed. The clinical consequences have been remarkable because the women in the diverse DUA groups had also differences in terms of POUR/surgery for POUR rate, duration of postoperative catheterisation, SUI recurrence and OAB de novo rate. Thus, the choice of UDS criteria for DUA diagnosis may have a very relevant impact on the patients counselling, post-operative management, and both MUS functional and success outcomes.