There is a remarkable lack of consensus on many aspects pertaining the diagnosis of female detrusor underactivity (DU).(1) This poor agreement limited the recognition and diagnosis in clinical practice. Indeed, currently no accepted diagnostic criteria exist. Detrusor underactivity was defined by the 2010 International Continence Society (ICS) consensus report on terminology as a “detrusor contraction of reduced strength and/or duration, resulting in prolonged bladder emptying and/or failure to achieve complete bladder emptying with a normal time span”. The clinical limit of this definition was the lack of specific parameters. Detrusor underactivity incidence is reported between 2,7% and 13% with a significant correlation with elderly population. Aim of the study was to evaluate the influence of DU on outcomes of patients underwent synthetic middle urethral sling (MUS) for stress urinary incontinence (SUI).

This was a multicenter prospective study started in October 2015 and still ongoing.  Women with SUI, naïve for SUI surgery, and treated with MUS were enrolled. Informed consent was obtained. Exclusion criteria were: previous SUI surgery, associated pelvic organ prolapse, predominant urge urinary incontinence, previous pelvic surgery and/or radiotherapy, neurologic diseases. All patients underwent pre-operative UDS. As no gold standard for measuring detrusor underactivity exists, we preferred to use the most stringent urodynamics parameters described by Jeong et. al.: Pdet/Qmax </= 10 cmH2O and Qmax </= 12 ml/sec.(2) Women were divided in: (i) Group A patients with DU; (ii) Group B patients without DU as control group. Preoperative evaluation included also free uroflowmetry (UF), post void residual urine (PVR), post-void residual urine-ratio (PVR-R) defined as the ratio between bladder volume and PVR, and the International Continence Index Questionnaire Urinary Female LUTS (ICIQ-FLUTS).  
In all patients we assessed the occurrence of post-operative urinary retention (POUR), defined as the presence of PVR >/= 200 ml in >/= 2 evaluations. In case of POUR presence, 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 clinical condition was done. The follow-up was scheduled at 1 year, and included: physical examination and vaginal inspection, UF, PVR and PVR-R, ICIQ-FLUTS. Statistical analysis was performed with T student and Mann Whitney test.

Both the Groups had 34 patients, with similar demographic characteristics. Mean age was 68.4 y.o. Table 1 shows outcomes at 1-year follow-up. POUR was detected in 35.3% (12/34) of women with DU (Group A) vs 8.8% (3/34) of women without DU (Group B). POUR spontaneous resolution was achieved in 3-30 days in Group A, and in 7-20 days in Group B. In both groups, 5.9% (2/34) of patients had a tape incision within one month of the first surgery due to patients decision after counseling. At 1-year follow-up, SUI recurrence and de-novo urgency were 5.9% in Group A, and 11.8% in Group B.

Our data evidenced several important considerations on the influence of detrusor underactivity in women underwent to MUS. 
A first point was that detrusor underactivity was a risk factor for transient POUR, but not for persistent urinary retention. Although in the DU population there was a 4 times higher rate of transient POUR, in both groups there was the resolution of the POUR within one month in the patients not early surgically treated. Therefore, even in DU women with POUR it is reasonable to wait one month before to choose a surgical management. In both groups the same number of patients decided for early POUR surgical treatment after accurate counseling. 
At 1-year follow-up, results were similar in both groups showing that DU was not a negative predictive factor in terms of outcomes.
Counseling is a crucial step that should be tailored on the greater risk of transient POUR explaining that long term results are not affected by their DU condition.(3)

Detrusor underactivity did not affect cure rate in women treated with MUS for SUI. However, women with DU had four times higher early transient POUR than normal detrusor contraction patients, with the same rate of resolution of the no-DU group. DU did not affect the re-operation rate for POUR. Urodynamic investigations are useful to detect these patients allowing a tailored proper counseling.

Cohn JA, Brown ET, Kaufman MR, Dmochowski RR, Reynolds WS. Underactive bladder in women: is there any evidence? Curr Opin Urol 2016 Jul;26(4):309-14
Jeong SJ, Kim KJ, Lee YJ, et al. Prevalence and clinical features of detrusor underactivity among elderly with lower urinary tract symptoms: a comparison between men and women. Korean J Urol 2012;53:342-348
Balzarro M, Rubilotta E, Goss C, Costantini E, Artibani W, Sand P. Counseling in urogynecology: A difficult task, or simply good surgeon-patient communication? Int Urogynecol J. 2018 Jul;29(7):943-948.