Sacral neuromodulation (SNM) has become an established treatment for refractory overactive bladder (OAB) syndrome and non-obstructive urinary retention. All patients are subjected to a test phase that determines if the patient is likely to benefit from a permanent SNM implant. Currently, there are no known predictors for success for this therapy. The aim of this study was to determine if a high maximum urethral closure pressure (MUCP) correlates with sacral neuromodulation success in female patients with voiding dysfunction (VD).

This is a retrospective observational study of prospectively collected data from 65 patients who underwent static urethral pressure profilometry (UPP) as part of urodynamic investigations before sacral neuromodulation  placement in a tertiary referral center from 2012-2017. Baseline characteristics, urodynamic diagnosis and MUCP were recorded for every patient. Urodynamic diagnosis was stated as detrusor overacitvity (DO), voiding dysfunction or other. We selected female patients with VD and high postvoid residual urine (PVR), defined as more than 100mL, who where candidates for SNM. Sacral neuromodulation test phase success was defined by 50% improvement in symptoms at the outpatient clinic. We used an MUCP cut-off of 90 cmH2O, based on clinical judgment. Logistic regression analysis was performed to identify perioperative factors associated with sacral neuromodulation success.

13 women were identified with voiding dysfunction and high PVR, who would benefit from sacral neuromodulation permanent placement. From the 13 patients, 2 did not experience benefit from the test phase of SNM, and therefore  did not proceed to a permanent implant phase; but 11 patients had a successful permanent lead and battery placement, after showing improvement in their symptoms with the test phase. 
The mean age was 27.3 ± 10.5 years. The urodynamic diagnosis of the 13 females was distributed as follows: VD (8), VD+OAB (4), VD+other (1). The two unsuccessful sacral neuromodulation placements were for VD and VD+OAB, with maximum urethral closure pressure of 63cmH2O and 83cmH2O. 
A maximum urethral closure pressure value of 101 was calculated with ROC curve with the best AUC of 0.86. SNM success was recorded in 61.5% vs. 38.5%  of patients with MUCP ≥ 90 cmH2O and MUCP <90 cmH2O, respectively. On univariate analysis, MUCP ≥90 cmH2O was associated with SNM success, with an OR of 5.5 (p= 0.027).

Of the 13 women included in this study, 11 had a favourable clinical outcome after the initial test phase with sacral neuromodulation, and therefore proceeded to the permanent phase. The 2 patients with no benefit from SNM had MUCP values below our cut-off point of 90 cmH2O. From the 11 patients that succeeded, 8 had a maximum urethral closure pressure of 90 cmH2O or above, and 3 had less that 90 cmH2O. Patients with no response to SNM, had a low MUCP. Nevertheless, 27.7% of the women with a positive outcome with the first phase of SNM, had an MUCP below the cut-off value.   
After further statistical analysis, we found that a high maximum urethral closure pressure of  90 cmH2O or above, confers 5.5 more chance of having a successful clinical response with sacral neuromodulation therapy in women with voiding dysfunction and high postvoid residual urine. 
Although neuromodulation should still be offered to patients despite low MUCP, with these results, better counseling of patients can be achieved in terms of the likelihood of success with SNM therapy.

Maximum urethral closure pressure measurement appears to be a useful tool for predicting success of sacral neuromodulation therapy in  women with voiding dysfunction. Those with a maximum urethral closure pressure of 90 cmH2O or above were more likely to benefit from neuromodulation than patients with lower MUCP values. 
Further studies with larger populations are warranted to confirm this observation.