Hypothesis / aims of study
Sacral neuromodulation (SNM) is an accepted treatment modality for patients with voiding dysfunction. In many centers clinicians use urethral pressure profilometry (UPP) and a raised maximum urethral closure pressure (MUCP) as part of a patient selection criteria for an SNM trial. Whilst an MUCP ≥ 100 has been demonstrated in patients with voiding dysfunction (1), there is little evidence on whether high MUCP correlates with success rate of SNM or can predict trial outcome. The aim of this study is to assess whether high MUCP is associated with SNM success in female patients with voiding dysfunction.
Study design, materials and methods
This is a retrospective observational study of prospectively collected data, for all female patients with voiding dysfunction who underwent urethral pressure profile (UPP) as part of their urodynamic investigations prior to consideration of SNM. It included patients who underwent UPP in our tertiary referral centre from January 2012 – February 2023. Inclusion criteria incorporated those with a urodynamic diagnosis of voiding dysfunction who were suitable candidates for SNM, regardless of any other urodynamic diagnosis.
UPP was performed using water filled lines in accordance with the Brown and Wickham technique (2). MUCP was based on an average of two measurements. We used 100 cmH20 as a cut off for high MUCP based on previous work (3) and expert opinion, and defined a successful SNM test phase as ≥50% improvement in symptoms, reported through standardised patient outcome measures.
Paired t-test was performed to assess the relationship between MUCP, age and successful SNM. Logistic regression analysis was performed to look at the predictive value of MUCP for a successful outcome from SNM.
Results
A total of 114 patients with voiding dysfunction underwent a test phase of SNM, with mean age 34.5 (±14.5). The urodynamic diagnosis recorded were voiding dysfunction (n=85), voiding dysfunction and detrusor overactivity ± incontinence (n=21) and voiding dysfunction and bladder pain syndrome (n=8). Of the 114 patients, 54 had an acontractile detrusor during the voiding phase of urodynamics.
SNM was successful in 80 patients, of these 64% had an MUCP ≥ 100 (Graph 1). Patients with a MUCP ≥100 cmH 2 O had a 76.1% success rate compared to 61.7% in the group with MUCP < 100cmH 2 0. There was a statistically significant difference in the mean MUCP in the successful group 105.8 (±27.3) vs unsuccessful 89.6 (±35.9) cmH2O (p=0.010), as well as mean age (p=0.002) 31.8 vs 40.9 years respectively.
Patients diagnosed as acontractile had a success rate of 61% vs 78% success rate for those with some detrusor pressure on voiding. The average MUCP was 109 cmH20 in the acontractile group and 103 cmH20 in those with some detrusor pressure.
The odds ratio of 2.4 (95% CI 1.04 – 5.33), indicates a greater chance of success in patients with MUCP ≥ 100cmH 2 0.
Interpretation of results
SNM is successful in most (70.2%) women with voiding dysfunction irrespective of MUCP – 34% with a positive outcome had MUCP < 100cmH2O. Although MUCP ≥100 is associated with a 2.4 greater chance of success, this is a lower success rate than reported in previous studies with a smaller sample group (3). Additionally, ROC analysis has shown that MUCP is not a predictor of success for SNM with an AUC = 0.64.
Comparing success vs failure over MUCP range suggests those with very high or low MUCP are less likely to have a successful outcome. This may be related to the higher MUCP’s being indicative of a more severe pathology and the lower MUCPs being related to a primary detrusor underactivity - both potentiating a less successful outcome. MUCP within 90 - 140 cmH2O may be optimum in patients undergoing SNM (Graph 2).