Efficacy of bilateral sacral neuromodulation in treating neurogenic bladder and bowel dysfunction

Abstract

Background

Neurogenic bladder-bowel dysfunction remains refractory to conventional therapies in many patients. While unilateral sacral neuromodulation (SNM) is established, comparative evidence for bilateral stimulation in combined dysfunction is lacking. This study evaluated whether bilateral SNM outperforms unilateral stimulation in this population.

Methods

In this two-center retrospective study, 20 patients with neurogenic bladder and bowel dysfunction underwent a self-paired sequential testing protocol comparing pre-operative baseline, unilateral stimulation, and bilateral stimulation stages. Outcomes included voiding diary parameters, uroflowmetry, Neurogenic Bowel Dysfunction (NBD) score, and Wexner scores. Long-term follow-up was conducted at 1 and 2 years for patients receiving permanent bilateral implantation (n=12).

Results

Bilateral stimulation significantly outperformed unilateral stimulation in 6 of 8 parameters (all P<0.05). Voided volume increased from 109.0±38.6 to 165.5±39.3 mL, while post-void residual decreased from 254.5±113.9 to 177.5±79.3 mL. Maximum flow rate improved from 7.5±2.0 to 12.0±2.4 mL/s. Bowel function also improved significantly: NBD score decreased by 33.3%, Wexner constipation score by 21.4%, and Wexner incontinence score by 40.0%. However, no significant additional benefit was observed for 24-hour voiding frequency or urgency/UUI episodes when comparing bilateral to unilateral stimulation. Among 12 patients with permanent implants, therapeutic improvements were sustained at 2-year follow-up, with further significant gains in voided volume, post-void residual, and bowel function compared to Year 1.

Conclusions

Bilateral SNM provides superior and sustained improvements in both voiding and defecatory functions compared with unilateral stimulation, offering an effective treatment for refractory neurogenic bladder-bowel dysfunction.

Highlight box.

Key findings

• In patients with combined neurogenic bladder-bowel dysfunction, bilateral sacral neuromodulation (BSNM) demonstrated significant incremental improvements over unilateral stimulation across the majority of urinary and bowel parameters, with sustained therapeutic gains observed at 2-year follow-up in those receiving permanent implantation.

What is known, and what is new?

• Unilateral sacral neuromodulation (SNM) is established for neurogenic lower urinary tract dysfunction, yet systematic evaluation of combined bladder-bowel dysfunction is lacking, and evidence for bilateral stimulation in this dual-organ population remains particularly scarce.

• This study employs a self-paired sequential design to directly compare unilateral and bilateral stimulation, demonstrating that bilateral SNM more comprehensively activates the pelviovesical-rectal reflex circuit and yields superior, sustained improvements across both urinary and bowel domains.

What is the implication, and what should change now?

• Bilateral SNM should be considered as an effective therapeutic option for refractory neurogenic bladder-bowel dysfunction, though future prospective multicenter randomized controlled trials are warranted to validate its long-term efficacy and definitive therapeutic positioning.

Introduction

Spinal cord injury (SCI), multiple sclerosis (MS), and other neurological disorders are frequently accompanied by severe lower urinary tract and bowel dysfunction (1). Although epidemiological surveys demonstrate that both conditions are highly prevalent and occur at comparable rates in affected populations, clinical attention and research investment have long been disproportionately directed toward bladder management, while investigations into the mechanisms of bowel neuromodulation and its pathophysiological characteristics remain relatively scarce (2). These two types of dysfunction typically arise as secondary complications of various neurological disorders, including SCI, MS, spina bifida, and transverse myelitis, among other central or peripheral neuropathies (3-5), and may also occur in degenerative diseases such as diabetic autonomic neuropathy and Parkinson’s disease (6,7). Regarding neurogenic bowel dysfunction (NBD), the prevalence of such gastrointestinal abnormalities is remarkably high among patients with SCI, affecting approximately 80% of this population. In terms of clinical manifestations, more than half of patients experience refractory constipation, while 60% to 75% have encountered varying degrees of fecal incontinence, with nearly half reporting monthly incontinence episodes (8). Neurogenic bladder and bowel dysfunction significantly impair patients’ quality of life, with their high hospitalization rates, recurrent healthcare utilization, and potential upper urinary tract damage imposing substantial psychological burden and social functional limitations (9).

The therapeutic modalities for neurogenic bladder encompass intermittent catheterization, antimuscarinic agents (e.g., oxybutynin, tolterodine), β3-adrenergic agonists (mirabegron), onabotulinumtoxinA injection, and augmentation cystoplasty; however, each is associated with substantial limitations, including adverse drug effects (dry mouth, constipation, cognitive impairment), transient efficacy (onabotulinumtoxinA lasting merely 6–9 months), and the irreversible risks inherent to surgical intervention (10,11). The management of NBD follows a stepwise, individualized approach, progressing from conservative measures such as dietary modification and oral laxatives, to transanal irrigation (TAI), and ultimately to surgical interventions including antegrade continence enema or colostomy; however, approximately half of patients demonstrate inadequate response to standard therapies, necessitating further regimen adjustments based on the characteristics of upper or lower motor neuron-type bowel dysfunction (12). Sacral neuromodulation (SNM), as an emerging therapeutic modality, may serve as a subsequent treatment option for these patients when conservative management proves ineffective.

Existing SNM studies have predominantly focused on patients with neurogenic bladder, lacking systematic evaluation of combined bladder-bowel dysfunction (with most investigations addressing voiding function exclusively while neglecting bowel symptoms); furthermore, the current literature has largely employed unilateral stimulation protocols, rendering research on bilateral stimulation for dual-organ dysfunction particularly scarce (13). In the present study, we retrospectively evaluated 20 patients with neurogenic voiding and defecatory dysfunction who underwent bilateral sacral neuromodulation (BSNM) therapy, employing a self-paired design to compare therapeutic outcomes between bilateral and unilateral stimulation, with the aim of providing clinical evidence for the application of BSNM in this patient population. We present this article in accordance with the STROBE reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0329/rc).

Methods

Data source

This study was a retrospective medical record analysis conducted at General Hospital of Southern Theater Command and Qilu Hospital. Patients who underwent SNM therapy between December 2015 and December 2024 were enrolled. Following systematic medical record screening, 20 patients ultimately met the criteria and were included in the analysis. All patients received standardized urodynamic examinations and clinical scoring assessments. The inclusion criteria were as follows: (I) age 18–70 years; (II) confirmed diagnosis of neurogenic bladder, with etiologies including SCI, MS, spina bifida, pelvic surgery-associated nerve injury, diabetic autonomic neuropathy, and other definitive neurological disorders. Including symptoms such as overactive bladder syndrome, urinary incontinence and dysuria; (III) concomitant NBD (constipation or incontinence); (IV) completion of the full SNM treatment protocol, including the unilateral testing phase and bilateral permanent electrode implantation; (V) complete clinical documentation, with available preoperative baseline, unilateral testing phase, and 1-month postoperative follow-up data; and (VI) follow-up duration ≥24 months after bilateral implantation (Figure 1). The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional ethics committee of General Hospital of Southern Theater Command (No. 2023-101-02), and Qilu Hospital was informed of and agreed to the study. Informed consent was waived due to the retrospective nature of this study.

Figure 1.

Research flowchart. NBD, neurogenic bowel dysfunction; PVR, post-void residual; Qmax, maximum urinary flow rate; SNM, sacral neuromodulation; UUI, urgency/urge urinary incontinence.

Intervention protocol

This study employed a sequential testing protocol, with all patients undergoing standardized SNM testing performed by experienced urologists.

Phase I: sequential unilateral testing

Patients were positioned prone, and bilateral quadripolar tined leads were percutaneously implanted via the bilateral S3/S4 posterior foramina under local anesthesia. Intraoperative fluoroscopic guidance was utilized to confirm bilateral electrode placement, with bilateral S3/S4 nerve root localization verified by evoking pelvic floor muscle contraction and/or great toe plantar flexion (Figure 2). The leads were connected to an external test stimulator, and unilateral stimulation was initiated for a 1-week testing period. Stimulation parameters were individually tailored: frequency 9–35 Hz, pulse width 150–330 μs, and amplitude 0.3–7.0 V, adjusted to the sensory threshold. If symptom improvement on the tested side was <50%, that stimulator was deactivated and the contralateral stimulator was immediately activated for an additional 1-week testing period; if improvement on either side was ≥50%, it was recorded as unilaterally effective. Patients receiving preoperative oral medications (e.g., antimuscarinic or β3-adrenergic agonists) continued their original regimens, with adjustments made as clinically indicated based on symptomatic changes.

Figure 2.

BSNM device placement. (A) Schematic illustration of bilateral quadripolar tined leads positioned via the S3 posterior foramina during the external testing phase. Adapted with permission from Wöllner et al. (14). (B) Postoperative anteroposterior X-ray of the pelvis confirming the bilateral electrode placement and IPG positioning. BSNM, bilateral sacral neuromodulation; IPG, implantable pulse generator.

Washout period

Following completion of the sequential unilateral testing, a 1-week washout period was observed, during which the test leads remained in situ but all electrical stimulation was suspended to allow symptoms to return to baseline levels, thereby excluding carryover effects from prior stimulation.

Phase II: bilateral combined testing

Upon completion of the washout period, bilateral stimulators were simultaneously activated for a 1-week combined testing period. Following testing, comprehensive comparison of therapeutic efficacy between unilateral (either side) and bilateral stimulation was performed to inform the decision regarding permanent bilateral implantation. For patients who underwent permanent bilateral implantation received an implantable pulse generator (InterStim II 3058, Medtronic, Minneapolis, MN, USA), long-term follow-up was conducted at 1 and 2 years post-operatively to assess sustained therapeutic efficacy.

Outcome measures

Therapeutic efficacy was comprehensively evaluated through 8 standardized outcome measures across two dimensions: lower urinary tract function and bowel function. Lower urinary tract assessment included voiding diary parameters [24-hour voiding frequency, voided volume per micturition, urgency/urge urinary incontinence (UUI) episodes, and post-void residual volume] and uroflowmetry (maximum urinary flow rate, Qmax). Bowel function assessment encompassed the NBD score (15) (NBD Score, comprising 10 items covering constipation severity, incontinence frequency, and bowel management time), as well as Wexner constipation score (16) (0–30 scale) and Wexner incontinence score (17) (0–20 scale) to evaluate constipation severity and fecal continence control, respectively. All parameters were obtained through standardized questionnaires, voiding/defecation diaries, and uroflowmetry at baseline (pre-operative), following unilateral stimulation, bilateral stimulation, and during long-term follow-up at 1 and 2 years post-implantation.

Statistical analysis

Data analysis was performed using R software (version 4.0) and SPSS 26.0 (IBM Corp., Armonk, NY, USA). Normality of continuous variables was assessed using the Shapiro-Wilk test. Normally distributed data are presented as mean ± standard deviation (mean ± SD), while non-normally distributed data are expressed as median (interquartile range) [median (IQR)]. Given the self-paired design of this study comparing three related time points (baseline, unilateral stimulation, and bilateral stimulation), the Friedman test was employed for overall comparisons among the three stages. When the Friedman test indicated statistical significance, pairwise comparisons (baseline vs. unilateral, baseline vs. bilateral, and unilateral vs. bilateral) were conducted using the Wilcoxon signed-rank test. A two-tailed P value <0.05 was considered statistically significant.

Results

Participant characteristics

A total of 20 patients (19 males and 1 female) with a mean age of 50.7±19.6 years were enrolled between December 2015 and December 2024. The mean disease duration was 49.2±71.7 months. Baseline characteristics revealed mixed types of lower urinary tract dysfunction (storage dysfunction: n=5, voiding dysfunction: n=10, mixed: n=5) and bowel symptoms (constipation: n=12, fecal incontinence: n=3, mixed: n=5). Mean body mass index (BMI) was 22.7±3.6 kg/m² (Table 1). Among them, 12 patients (60%) underwent stage II permanent bilateral implantation, while 8 patients (40%) did not proceed to permanent implantation. All patients completed the study protocol without loss to follow-up.

Table 1. Baseline characteristics of the study participants (n=20).

Characteristics	Values
Age (years)	50.7±19.6
Height (cm)	167.8±6.9
Weight (kg)	64.1±12.4
BMI (kg/m2)	22.7±3.6
Disease duration (months)	49.2±71.7
Gender
Male	19 [95]
Female	1 [5]
Neurological etiology
Spinal cord injury—complete	1 [5]
Spinal cord injury—incomplete	15 [75]
Tethered cord syndrome	2 [10]
Other neurological disorders	2 [10]
Hypertension
No	17 [85]
Yes	3 [15]
Diabetes
No	18 [90]
Yes	2 [10]
Alcohol
No	16 [80]
Yes	4 [20]
Smoking
No	15 [75]
Yes	5 [25]
LUT dysfunction type
Storage	5 [25]
Voiding	10 [50]
Mixed	5 [25]
Bowel symptom type
Constipation	12 [60]
Incontinence	3 [15]
Mixed	5 [25]
Stage II implantation
No	8 [40]
Yes	12 [60]

Data are presented as mean ± standard deviation or n [%]. BMI, body mass index; LUT, lower urinary tract.

Efficacy of unilateral vs. bilateral stimulation

Lower urinary tract function

Voiding volume significantly increased from 109.0±38.6 mL (pre-operative) to 132.5±44.4 mL (unilateral, P<0.001) and further to 165.5±39.3 mL (bilateral, P<0.001), representing a 51.8% improvement from baseline. Twenty-four-hour voiding frequency decreased from 15.8±2.8 (pre-op) to 14.1±3.5 (unilateral, P=0.002) and stabilized at 14.2±2.5 (bilateral, P=0.006). Urgency/UUI episodes reduced from 4.7±3.9 to 4.0±3.3 (unilateral, P=0.048) and 3.3±2.3 (bilateral, P=0.01), with a 29.8% overall reduction. Post-void residual volume decreased from 254.5±113.9 to 209.2±107.4 mL (unilateral) and 177.5±79.3 mL (bilateral), representing a 30.3% reduction from baseline (P<0.001). Maximum flow rate improved from 7.5±2.0 to 9.8±2.7 mL/s (unilateral) and 12.0±2.4 mL/s (bilateral), with a 60% increase from baseline to bilateral stimulation (P<0.001).

Bowel function

NBD score showed significant improvement: 17.7±3.5 (pre-op) → 13.3±2.7 (unilateral) → 11.8±2.6 (bilateral), with 33.3% overall improvement. Wexner constipation score decreased from 15.4±2.5 to 12.9±3.4 (unilateral) and 12.1±3.9 (bilateral), representing 21.4% improvement. Wexner incontinence score improved from 12.0±2.8 to 10.0±2.9 (unilateral) and 7.2±2.3 (bilateral), with a 40% reduction from baseline.

Pairwise comparisons revealed that bilateral stimulation was superior to unilateral stimulation in 6 out of 8 indicators (all P<0.05), specifically for voiding volume, post-void residual, maximum flow rate, NBD score, Wexner constipation score, and Wexner incontinence score. However, no significant additional benefit was observed for 24-hour voiding frequency (P=0.86) or urgency/UUI episodes (P=0.08) when comparing bilateral to unilateral stimulation (Table 2 and Figure 3).

Table 2. Comparison of outcome measures between pre-operative, unilateral and bilateral stimulation.

Outcome measure	Pre-operative	Unilateral	Bilateral	P value
				Pre-operative vs. unilateral	Pre-operative vs. bilateral	Unilateral vs. bilateral
Voiding volume (mL)	109.0±38.6	132.5±44.4	165.5±39.3	<0.001	<0.001	0.003
24-h voiding frequency	15.8±2.8	14.1±3.5	14.2±2.5	0.002	0.006	0.86
Urgency/UUI episodes	4.7±3.9	4.0±3.3	3.3±2.3	0.048	0.01	0.08
Post-void residual (mL)	254.5±113.9	209.2±107.4	177.5±79.3	0.01	<0.001	0.01
Maximum flow rate (mL/s)	7.5±2.0	9.8±2.7	12.0±2.4	<0.001	<0.001	0.008
NBD score	17.7±3.5	13.3±2.7	11.8±2.6	<0.001	<0.001	0.005
Wexner constipation score	15.4±2.5	12.9±3.4	12.1±3.9	<0.001	<0.001	0.04
Wexner incontinence score	12.0±2.8	10.0±2.9	7.2±2.3	0.02	0.007	0.007

Data are presented as mean ± standard deviation. NBD, neurogenic bowel dysfunction; UUI, urge urinary incontinence.

Figure 3.

Paired violin plots comparing pre-operative, unilateral stimulation, and bilateral stimulation stages across 8 outcome parameters (n=20). ns, not significant (P≥0.05); *, P<0.05; **, P<0.01; ***, P<0.001. NBD, neurogenic bowel dysfunction; Pre-op, pre-operative; UUI, urgency/urge urinary incontinence.

Individual response patterns

Pre-operative to unilateral improvement (Figure 4)

Figure 4.

Heatmap illustrating percentage improvement from pre-operative baseline to unilateral stimulation for each of the 20 patients (P1–P20) across 8 outcome parameters. Red gradients indicate degree of improvement, while green gradients indicate deterioration. N/A, not available; NBD, neurogenic bowel dysfunction; UUI, urgency/urge urinary incontinence.

The heatmap revealed substantial inter-individual variability in treatment response across the 8 outcome measures. Voiding volume demonstrated clinically meaningful improvement in 85% of patients (17/20). Maximum flow rate exhibited particularly pronounced improvement. Post-void residual volume decreased by a median of 18.5%, while NBD score showed a median reduction of 23.4%. However, individual response patterns varied considerably: Patients 2 and 8 showed suboptimal responses in voiding volume (deterioration), whereas Patients 4, 8, 9, and 18 demonstrated deterioration in urgency/UUI episodes, suggesting potential non-responders or temporary symptom fluctuation during the unilateral testing phase. Wexner constipation and incontinence scores improved in 88% and 87.5% of patients, respectively.

Unilateral to bilateral additional improvement (Figure 5)

Figure 5.

Heatmap depicting additional percentage improvement from unilateral to bilateral stimulation for each patient (P1–P20) across 8 outcome parameters. Red gradients indicate incremental benefit with bilateral stimulation, while green indicates deterioration or lack of additional improvement. N/A, not available; NBD, neurogenic bowel dysfunction; UUI, urgency/urge urinary incontinence.

Further enhancement was observed with bilateral stimulation, though the magnitude varied by parameter. Notably, Patients 17 through 19 demonstrated exceptional responses in voiding volume. Maximum flow rate showed additional median improvement of 32.5%. Post-void residual volume continued to improve. However, 24-hour voiding frequency and urgency/UUI episodes showed mixed responses during the bilateral phase, with some patients experiencing temporary symptom exacerbation (green cells in Figure 5), likely attributable to parameter adjustment periods or individual adaptation variability. Approximately 75% of data points indicated superior outcomes with bilateral compared to unilateral stimulation, with the remaining 25% showing comparable or transiently reduced efficacy. Wexner incontinence score demonstrated the most consistent additional benefit, with all evaluable patients (8/8) showing further improvement.

Long-term durability

In patients with permanent bilateral implantation (n=12), long-term follow-up at 2 years demonstrated significant sustained improvements compared to 1-year post-operative assessments. Voiding volume increased further (194.2±38.5 to 230.8±40.3 mL, P=0.01), while post-void residual volume decreased significantly (129.6±55.0 to 90.4±55.8 mL, P=0.004). Urgency/UUI episodes showed continued improvement (3.8±2.0 to 2.7±2.0, P=0.004), as did maximum flow rate and NBD score (both P<0.05). Wexner constipation score also improved significantly (P=0.04). However, 24-hour voiding frequency and Wexner incontinence score remained stable between Year 1 and Year 2 (both P>0.05), indicating maintained efficacy without further significant change in these parameters (Figure 6).

Figure 6.

Paired violin plots comparing Year 1 (post-operative) and Year 2 (follow-up) stages across 8 urologic and bowel outcome parameters (n=12 for most parameters, n=9 for constipation, and n=8 for incontinence). ns, not significant (P≥0.05); *, P<0.05; **, P<0.01. NBD, neurogenic bowel dysfunction; UUI, urgency/urge urinary incontinence.

Discussion

Neurogenic lower urinary tract dysfunction (NLUTD) arises secondary to a variety of neurological diseases. The existing mainstay therapeutic options—such as clean intermittent catheterization (CIC), oral medications, long-term indwelling urethral catheterization, and onabotulinumtoxinA (Botox) injections—although spanning the spectrum from conservative to invasive interventions, are all associated with significant clinical limitations. These include implementation barriers, limited levels of evidence, high risks of complications, or transient efficacy, among others (18). NBD, as a highly prevalent and substantially quality-of-life-impairing complication among patients with SCI and MS, is managed according to a stepwise treatment algorithm progressing from foundational standard therapies (dietary modifications, pharmacological agents, and rectal interventions) to TAI. Although this algorithm emphasizes individualized selection, each therapeutic tier harbors inherent limitations, including restricted efficacy, dependence on patient capability, or surgery-associated risks (19). SNM is a therapeutic modality that modulates the function of sacral spinal cord (S2–S4) neural centers through electrical stimulation. It is primarily indicated for the management of refractory neurogenic bladder dysfunction—encompassing urinary incontinence and urinary retention—and NBD, including constipation and fecal incontinence, secondary to neurological injuries such as SCI. Its underlying mechanism involves the neuromodulation of disordered storage and evacuation reflexes, thereby restoring the coordination of pelvic organ function. For patients who remain refractory to pharmacological and behavioral interventions, SNM offers a significant and reversible neuromodulatory therapeutic option (20). Moreover, unilateral SNM has been demonstrated to significantly reduce NBD scores in patients with neurogenic bladder, further substantiating its therapeutic efficacy in ameliorating concomitant bowel symptoms (21). For patients with neurogenic lower urinary tract and bowel dysfunction secondary to advanced multiple system atrophy (MSA), SNM can provide temporary symptomatic relief; notably, its therapeutic efficacy for voiding symptoms tends to diminish with disease progression, whereas the benefits for bowel symptoms may persist for a longer duration (13). Similarly, Kobberø et al. (22) recently reported the first feasibility study of a double-blind randomized controlled trial (RCT) of SNM in patients with MS and NLUTD, demonstrating not only the safety and feasibility of SNM in this specific neurogenic population but also concurrent improvements in bowel function as measured by the ICIQ-Bowel score. These findings further support the multi-organ therapeutic potential of SNM in neurogenic pelvic floor dysfunction, consistent with the bladder-bowel synergistic benefits observed in the present study. Regarding the therapeutic efficacy of BSNM, current evidence remains somewhat heterogeneous. Short-term investigations indicate that bilateral stimulation did not demonstrate superiority over standard unilateral protocols in reducing incontinence episodes or improving symptom scores, with comparable outcomes observed between the two approaches (23). However, a long-term follow-up case report on idiopathic non-obstructive urinary retention indicated that BSNM yields significant and durable improvements in quality of life for patients with this refractory condition, accompanied by reductions in post-void residual volume and decreased infection frequency (24). These findings suggest that the therapeutic value of bilateral stimulation may need to be evaluated according to specific types of lower urinary tract or bowel dysfunction. Notably, a recent systematic review and meta-analysis by Ferreira et al. (25) reported that only 13 of 143 patients with MS (9.9%) who received permanent SNM implants underwent bilateral lead placement, suggesting that the prevailing underutilization of bilateral SNM largely reflects practice patterns for isolated lower urinary tract dysfunction. By contrast, the present study demonstrates that in patients with combined neurogenic bladder-bowel dysfunction, bilateral stimulation yields significantly superior outcomes over unilateral stimulation across the majority of evaluated urinary and bowel parameters, underscoring the necessity of investigating bilateral SNM specifically in this dual-organ population.

Unilateral SNM demonstrates inconsistent therapeutic effects on urinary and bowel symptoms, presenting challenges in simultaneously resolving all issues optimally. Data from the testing phase indicate that the highest improvement rates are observed for constipation, whereas the amelioration of voiding dysfunction is significantly less pronounced, necessitating that some patients continue to rely on intermittent catheterization for bladder management (5,26). Consequently, while SNM demonstrates efficacy in ameliorating multiple symptoms, it does not invariably accomplish the synchronous and complete resolution of both urinary and bowel dysfunction, necessitating that some patients require continued adjuvant therapeutic modalities. Chen et al. (27) observed similar findings in patients with spina bifida, wherein four cases demonstrated significant improvement in bowel function exclusively without concomitant amelioration of lower urinary tract function. Furthermore, more than half of those undergoing permanent implantation continued to require concomitant intermittent catheterization for bladder emptying. These observations further corroborate the inherent limitations of unilateral stimulation in simultaneously addressing combined neurogenic bladder-bowel dysfunction, suggesting that bilateral stimulation may provide more comprehensive therapeutic outcomes. It should be noted that spina bifida is a relatively rare condition globally, and the associated spinal dysraphism often introduces considerable anatomical complexity—such as sacral bony defects and aberrant nerve root anatomy—that can substantially complicate percutaneous lead placement and intraoperative electrophysiological verification, thereby limiting the generalizability of SNM findings to this specific population. Conventional unilateral SNM demonstrates efficacy rates of approximately 50–70% for neurogenic bladder; however, improvements in urinary and bowel symptoms are frequently discordant. In contrast, the present study employed a self-paired design to directly compare stimulation paradigms, demonstrating that bilateral stimulation was significantly superior to unilateral stimulation across the vast majority of evaluated parameters. Not only did bilateral stimulation exhibit marked incremental effects on voiding functional parameters, including maximum urinary flow rate and post-void residual volume, but it also conferred additional benefits in bowel functional assessments, including NBD score (total 33.3% improvement) and Wexner constipation/incontinence scores (total 21.4% and 40.0% improvement, respectively), demonstrating comprehensive efficacy across both urinary and bowel domains. These findings suggest that bilateral SNM achieves more comprehensive activation of the pelviovesical-rectal reflex circuit and exerts synergistic amelioration of bladder and bowel function through synchronous modulation of sacral parasympathetic (S2–S4) efferent pathways. By overcoming the limitations of unilateral stimulation in simultaneously addressing dual-organ dysfunction, bilateral SNM offers a more efficacious neuromodulatory strategy for patients with combined neurogenic bladder-bowel dysfunction. Liechti et al. (28) have recently reported a randomized, sham-controlled, double-blind multicenter trial of bilateral SNM in NLUTD, representing an important controlled evaluation of this stimulation paradigm in a neurologic population.

We acknowledge that the non-randomized sequential design, together with a relatively short 1-week washout period, may not fully eliminate potential carryover effects, time-related variability, or placebo responses; accordingly, the observed incremental benefits of bilateral stimulation should be interpreted cautiously. Beyond statistical significance, the observed improvements appear clinically meaningful: the 51.8% increase in voided volume and 30.3% reduction in post-void residual may decrease the frequency of intermittent catheterization and improve patient autonomy, while the 40% improvement in Wexner incontinence score suggests reduced fecal incontinence episodes and bowel management burden. It should be noted that all enrolled patients had refractory symptoms despite conservative and pharmacological management, representing a highly selected population for whom SNM was indicated as a subsequent therapeutic option. We also acknowledge that the underlying neurological etiologies and baseline LUTD subtypes (storage, voiding, mixed) were heterogeneous, which likely contributed to the inter-individual response variability; however, the small sample size precluded meaningful subgroup stratification. The synergistic improvements in voiding and defecatory functions observed with bilateral SNM in the present study may be elucidated from the perspectives of sacral neuroanatomy and neurophysiology. Specifically, the S2–S4 sacral nerves (particularly S3) innervate the urinary bladder, pelvic floor musculature, and sphincteric complexes via somatic afferent fibers (29,30). Compared with conventional unilateral stimulation, bilateral SNM may achieve more comprehensive activation of bilateral afferent pathways and simultaneously recruit the neural fibers required for pelvic floor muscle contraction, thereby more effectively coordinating the bladder-sphincter reflex. In neurogenic patients, central sensitization and reorganization of spinal reflex pathways result in abnormal reflex hyperactivity, necessitating stronger peripheral input for inhibition. The significant superiority of bilateral over unilateral stimulation observed in the present study may be attributed to more extensive neural recruitment and reflex arc activation. Furthermore, sacral parasympathetic (S2–S4) efferent fibers simultaneously modulate bladder and bowel functions, which accounts for the synchronous improvements in NBD scores and urinary parameters with BSNM. It is noteworthy that early neuromodulatory intervention may prevent irreversible alterations in bladder dysfunction through neuroplasticity mechanisms, whereas sustained bilateral stimulation may provide more stable peripheral input to maintain spinal pathway remodeling. Future investigations incorporating urodynamic and neuroelectrophysiological monitoring are warranted to further elucidate the specific neuromodulatory mechanisms of bilateral stimulation on the pelviovesical-bowel reflex circuit.

In clinical practice, SNM has emerged as a significant second-line therapeutic option for patients refractory to conservative management, encompassing behavioral and pharmacological interventions (31). Studies have demonstrated that SNM exhibits significantly superior efficacy for storage symptoms (urgency-frequency, urinary incontinence) compared with voiding dysfunction, suggesting that patients with incomplete SCI who present with storage-predominant symptoms and retain partial neurological function are more suitable candidates for SNM treatment (32). However, the therapeutic efficacy in patients with complete SCI remains to be further validated; therefore, appropriate patient selection is crucial for SNM in neurogenic bladder (33). The cost-effectiveness of SNM exhibits a pronounced time-dependent characteristic: within the short term (<5 years), the substantial costs associated with device acquisition and surgical implantation frequently render the intervention cost-inefficient; however, as follow-up duration extends, the long-term advantages of SNM become progressively evident—modeling studies have demonstrated its cost-effectiveness or even economically dominant position within the 5- to 10-year time horizon for overactive bladder, while long-term follow-up in patients with severe fecal incontinence has further substantiated these benefits. These advantages are attributable primarily to sustained improvements in quality of life, reductions in pharmaceutical and nursing care expenditures, and the avoidance of subsequent high-cost treatments for upper urinary tract complications (34-36). Therefore, the economic value of SNM is critically dependent on appropriate patient selection and adoption of a long-term follow-up perspective; clinical decision-making necessitates balancing upfront investment against lifelong patient benefits.

There are several limitations in this study. First, as a two-center retrospective analysis with a small sample size (n=20), it lacked RCT design and sham stimulation controls, making it difficult to completely exclude selection bias and placebo effects; although the self-paired design controlled for inter-individual variation, it could not eliminate the potential influence of time effects. Second, although long-term follow-up data at 1 and 2 years were collected for patients who underwent permanent bilateral implantation, the sample size for long-term follow-up was limited (n=12), and longer-term data beyond 2 years are still needed to further assess treatment durability and device longevity. Additionally, restricting long-term follow-up to the 12 implanted patients introduces potential selection bias, as the 2-year durability may not be generalizable to non-responders. Third, the etiologies encompassed various neurological disorders; this considerable heterogeneity may have masked differential treatment responses among subgroups, yet insufficient subgroup analysis was performed. Fourth, the study population exhibited a marked gender imbalance, which may limit the generalizability of our findings to female patients and precludes meaningful sex-specific subgroup analysis. Fifth, the findings of this study are derived from patients with neurogenic bladder-bowel dysfunction; accordingly, caution should be exercised when considering their applicability to individuals with idiopathic lower urinary tract or bowel dysfunction, in whom the underlying pathophysiology and neuromodulatory mechanisms may differ. Sixth, given the exploratory nature of this study, no formal correction for multiple comparisons was performed across the eight outcome measures; the reported P-values should therefore be interpreted with caution. Finally, the selective patient population from two specialized centers limits the external validity of these findings. These factors collectively affect the generalizability of the conclusions. Future prospective, multicenter, large-scale RCTs incorporating urodynamic monitoring and extended follow-up are warranted to further validate the precise therapeutic positioning of BSNM in the management of neurogenic pelvic floor dysfunction.

Conclusions

This study demonstrates that BSNM significantly improves both voiding and defecatory functions in patients with neurogenic lower urinary tract and bowel dysfunction, exhibiting superiority over unilateral stimulation across the majority of evaluated parameters alongside a favorable safety profile. These findings suggest that BSNM represents an effective therapeutic option for patients refractory to conservative management, with bilateral stimulation potentially exerting synergistic effects through more comprehensive modulation of the pelvic floor–bladder–bowel reflex circuit. Future large-scale RCTs are warranted to further validate its long-term efficacy and establish its definitive position within the therapeutic algorithm for neurogenic pelvic floor dysfunction.

Supplementary

The article’s supplementary files as

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the institutional ethics committee of General Hospital of Southern Theater Command (No. 2023-101-02), and Qilu Hospital was informed of and agreed to the study. Informed consent was waived due to the retrospective nature of this study.

Data Sharing Statement

Available at https://tau.amegroups.com/article/view/10.21037/tau-2026-0329/dss

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DOI: 10.21037/tau-2026-0329