Non-obstructive urinary retention (NOUR) is a voiding disorder that affects millions of people worldwide. Patients may present with slow urinary stream, hesitancy, and straining to void with the feeling of incomplete bladder emptying, acute urinary retention, or recurrent urinary tract infections. Urodynamic studies may reveal a decreased contractility of the detrusor muscle. However, NOUR is especially clinically relevant in case of significant post-void residual, which necessitates regular drainage of the bladder. Most patients with NOUR use clean intermittent catheterization (CIC), or indwelling catheters to ensure timely drainage of the bladder and prevent complications. Sacral neuromodulation (SNM) can be offered to restore voiding (thereby decreasing or abolishing the necessity for catheterization), reduce catheter associated complications, and improve quality of life. A test phase with an external stimulator precedes the implantation of a neuromodulator to assess whether the patient’s symptoms improve sufficiently with SNM. In patients with NOUR physicians usually propose a tined lead test phase (1). A tined lead test phase (first stage SNM) consists of placement of the definite tined lead, which is connected to an external neuromodulator for a duration of two to four weeks.  
Since the test phase is an invasive procedure, it would be beneficial to predict which patients with NOUR would have the highest chance on a positive test result. Therefore, the aims of this study were to 1) determine the success rate of the tined lead test phase in patients with NOUR, 2) to determine predictive factors of a successful test phase in patients with NOUR, and 3) to determine long term efficacy and patient satisfaction of SNM in patients with NOUR.

This is a multi-center retrospective study performed at two centers in the Netherlands. Patients with NOUR received a four-week tined lead test phase between January 2009 and December 2020. Success was defined as ≥50% reduction of CIC frequency or post-void residual. Patients with a successful first stage subsequently received a subcutaneous neuromodulator. Between October 2020 and March 2021 all included patients received a questionnaire to assess efficacy and treatment satisfaction. In patients with a failed test phase we determined catheterization frequency, possible other treatments received, and their perceived health. In patients with a successful test phase we determined long term success (measured as catheterization frequency), satisfaction with the SNM therapy and in the case of a rechargeable neuromodulator the patient was asked about their experience regarding recharging.  
To determine predictive factors of success, logistic regression was performed to assess the effects of age, an acontractile detrusor muscle or no detrusor activity observed (during conventional urodynamic study), a history of psychiatric illness, and a history of orthopedic surgery on the likelihood of having a successful first stage SNM. In women, a history of pelvic surgery and in men a history of prostatic resection were also measured as predictive factors.
The characteristics of the cohort as well as the outcome variables of the questionnaire are presented as descriptive statistics. For both men and women, a prediction model was made using binomial multivariable logistic regression. The factors incorporated in the two prediction models are presented as odds ratios, with their corresponding 95% confidence intervals and p-values. The predictors were identified in the literature. Only the most important possible predictors were incorporated in the prediction models.

This study consecutively included 215 patients (82 men and 133 women) who received a tined lead test phase for the treatment of NOUR at two centers (Table 1). Within this cohort, 47% of patients (n=101) had a successful first stage. The success rate in women was 62% (n=83) and in men 22% (n=18). During the first stage SNM, eleven patients had a wound infection, which was effectively treated with antibiotics in all cases. One patient had an infected lead, which was removed before the end of the first stage.  
In women, lower age and a history of psychiatric illness significantly predicted first stage SNM success (Table 2a). In men,  lower age and prior resection of the prostate were significant predictors of first stage SNM success (Table 2b). 
The questionnaire was filled out by 60% (n=68) of patients with a failed first phase, on average 3.5 years after the patients’ tined lead test phase. Of these patients 72% (n=49) reported no change in their health on the PGI (Patient Global Impression) scale, most patients (88% , n=60) still applied CIC once or more times per day and 79% (n=54) did not receive another treatment for NOUR after their first stage. Two patients received a urinary stoma. 
The response rate of patients with a successful first stage was 74% (n=75) at an average of 3.5 years after the tined lead test phase. 87% (n=65) of patients continued to use their SNM system, and 92% (n=69) were satisfied with their SNM system. 84% (n=63) reported to have an “improvement of health” since receiving the SNM system. 60% (n=45) of patients applied no CIC. Of all patients with a successful first stage, 36% (n=27) received a rechargeable SNM system. 85% (n=23) of those patients found the recharging procedure easy or achievable and 93% (n=25) of patients found the recharging frequency and duration acceptable.

Lower age and a history of psychiatric illness, were predictive of tined lead test phase success in women with NOUR. A 10 year increase in age decreased the likelihood of success 0.73 times and a history of psychiatric illness increased the likelihood of a successful test phase 3.5 times. In men, lower age and previous resection of the prostate were predictive of first stage SNM success. A 10 year increase in age decreased the likelihood of success by 0.42 and a previous prostate resection increased the likelihood of success 7.6 times. Therefore, initially resecting the prostate in men with detrusor underactivity might be favorable, after which SNM can be proposed to men with persistent significant post-void residual after de-obstruction (2). Our results imply that an acontractile detrusor or no objectivation of detrusor activity during conventional urodynamic study does not decrease the likelihood of a successful first stage SNM. This is not in line with a previous report that suggested a relationship between bladder contractility and tined lead outcome, implicating a higher success rate when contractility is preserved (3). However, we presented a multivariable analysis whereas the previous study performed a univariable analysis.

This study identified lower age and psychiatric illness in women, and lower age and resection of the prostate in men to be predictors of first stage SNM success. Psychiatric illness in women increased the likelihood of success 3.5 times and a resection of the prostate in men increased their likelihood of success 7.6 times. An older age decreased the likelihood of success in both sexes. However, this is difficult to translate into a recommendation for clinicians since a cut-off age (above which the likelihood of success is very low) was not determined. Altogether, the identified predictors can be used by clinicians when counseling their patients to undergo a tined lead test phase in an attempt to treat NOUR. Also, this study showed that those patients who receive an implant are generally satisfied with their therapy and those who receive a rechargeable system are content with the frequency and duration of recharging their device.

Marcelissen T, Leong R, Serroyen J, van Kerrebroeck P, De Wachter S. Is the screening method of sacral neuromodulation a prognostic factor for long-term success? The Journal of urology. 2011;185(2):583-587.
Dobberfuhl AD, Chen A, Alkaram AF, De EJB. Spontaneous voiding is surprisingly recoverable via outlet procedure in men with underactive bladder and documented detrusor underactivity on urodynamics. Neurourol Urodyn. 2019 Nov;38(8):2224-2232.
Drossaerts J, Rademakers K, van Koeveringe G, Van Kerrebroeck P. The value of urodynamic tools to guide patient selection in sacral neuromodulation. World J Urol. 2015 Nov;33(11):1889-95.