Detrusor underactivity (DU) is a common condition that is under-recognized, poorly understood, and challenging to treat. Traditionally, management consisted of catheterization, or transurethral prostatectomy (in men) with mixed results1.  Sacral neuromodulation (SNM) has been shown to improve outcomes in patients with DU, but there is a lack of information on predictors of success 2.3. This original research will investigate and hopefully identify predictors to allow patient selection and counselling of outcomes prior to SNM.

This was a prospective clinical study of consecutive patients who had SNM during 2013-2018 from a single surgeon. We enrolled all patients undergoing evaluation for SNM with DU, defined as Bladder Contractility Index (BCI) <100.  Patients were evaluated pre-operatively with history, examination, video urodynamic studies (VUDS), questionnaires and voiding diary. Inclusion criteria was onset of symptoms of at least 6 months, and minimum 18 years of age. VUDS was performed according to the International Continence Society (ICS) standards. Exclusion criteria were patients without urodynamic studies, BCI>100, bladder outlet obstruction, prolapse, stress urinary incontinence, or contraindication to neuromodulation.  All patients underwent staged trials for SNM; stage 1 was test implant, which would proceed to stage 2 final implant if there was 50% improvement in symptoms, catheterization usage or improved post-void residual (PVR) urine. Follow-up included clinic visit with diary, uroflowmetry, and PVR for at least 6 months.

In total, 68 patients found on VUDS with BCI < 100 were followed. There were 49 female, and 19 male patients. The mean age of patients was 64 (39-83), mean BCI was 39 (0-90) and mean PVR was 240ml (0-800). In total, 35 patients (51%) had satisfactory response with stage 1 trial with >50% improved symptoms and voiding and proceeded to SNM implant. There were 2 patients with partial response after trial that declined stage 2 implant. At follow up of at least 6 months, 3 were removed for poor efficacy and 32 were still using the SNM with good responses. 

Subgroup analysis showed 30 patients with Detrusor Overactivity with Detrusor Underactivity (DO-DU) of which 21 were female, and 9 male. There were 18 patients with detrusor acontractility (DAC), 5 males, and 13 females. 

We also looked at the response to SNM in subset of groups of DU with detrusor acontractility (DAC) and those with some preserved bladder contractility, BCI > 0.  In those with DAC, 6 had response to the initial stage 1 trial (33%), compared with those with BCI > 0, in which 26 patients responded (55%). This was statistically significant, p-value (0. 03309). When comparing pre-op voiders vs non-voiders, there was no difference in predicting response (p=value 0.094097). Additionally there was also no difference in predicting response to stage 1 trial when comparing those with neurogenic vs non-neurogenic etiology (p-value 0.1407).

Our study showed that DU patients with preserved bladder contractility are more likely to respond to SNM compared with those that have DAC. Pre-operative characteristics such as ability to void, or neurogenic etiology were unable to predict successful trial of SNM. Some voiders may be valsalva voiders with DAC. Urodynamics (UDS) is the only method to accurately identify DAC patients. Our study thus confirms the usefulness of UDS in identifying those with preserved contractility as a predictor for response to SNM.   This information will help in patient selection and pre-op counseling for SNM We acknowledge some limitations in the use of BCI for women for this study.

SNM can improve outcomes in patients with DU and quality of life. The presence of preserved bladder contractility as shown on pre-op urodynamics can predict better response rate to a staged trial of SNM. Future studies should focus on determining other predictive factors to guide patient selection.

De Ridder D, Ost D, Bruyninckx F. The Presence of Fowler’s Syndrome Predicts Successful Long-Term Outcome of Sacral Nerve Stimulation in Women with Urinary Retention. Eur Urol. 2007;51(1):229-234. doi:10.1016/j.eururo.2006.06.031
Mehmood S, Altaweel WM. Long-term outcome of sacral neuromodulation in patients with idiopathic nonobstructive urinary retention: Single-center experience. Urol Ann. 2017;9(3):244-248. doi:10.4103/UA.UA_165_16
Datta SN, Chaliha C, Singh A, et al. Sacral neurostimulation for urinary retention: 10-year experience from one UK centre. BJU Int. 2007;0(0):071027214644004-??? doi:10.1111/j.1464-410X.2007.07282.x