Introduction

Lower urinary tract dysfunction (LUTD) is a syndrome characterized by lower urinary tract symptoms (LUTS) resulting from the inability to relax the pelvic floor. This condition manifests across a broad clinical spectrum and is not linked to anatomical anomalies or neurological diseases. LUTD is frequently encountered in children, and it imposes significant economic and psychological burdens on patients and their families.

Various electrical nerve stimulation methods have been employed over the years to address lower urinary tract dysfunction in cases where intensive medical and behavioral therapies have fallen short. Sacral nerve neuromodulation (SNM) with an implantable pulse generator and tined lead electrode is approved for use in adults, but data on its effectiveness in children are limited.

Methods

We conducted a review centered on the utilization of sacral neuromodulation (SNM) as a treatment for pediatric voiding dysfunction. The inclusion criteria included English-language articles that encompassed human subjects under 18 years of age with non-neurogenic voiding dysfunction. Non-neurogenic voiding dysfunction included symptoms of urgency, frequency, urge incontinence, and non-neurogenic retention. These subjects also underwent implantable SNM. We excluded non-human studies, subjects older than 18 years whose results could not be separated from the pediatric results, those with neurogenic bladder dysfunction or diseases consistent with neurogenic bladder dysfunction such as myelomeningocele and spinal cord injury, and cases solely focused on nocturnal polyuria. Additionally, we excluded case reports with fewer than 5 subjects. Our review included studies published between 2008 and 2021.

Our search yielded a total of 676 records sourced from various outlets, including PubMed, Google Scholar, and Medbase using the search terms: sacral neuromodulation pediatric voiding dysfunction, sacral neuromodulation children, interstim pediatric, sacral neuromodulation pediatrics, voiding dysfunction in children, pediatric urological interventions. To refine our data, we applied a series of screening and filtering steps outlined in the PRISMA table. From the initial 27 records passing the abstract review, we retrieved and thoroughly analyzed the full manuscripts. Subsequently, 16 records were excluded for not meeting our inclusion criteria, as detailed in the PRISMA table. The eligibility assessment identified 11 reports relevant to our research objectives. Among these, three reports were excluded for specific reasons outlined in the PRISMA table. Ultimately, our review encompasses 8 studies that successfully passed the rigorous screening and eligibility process, aligning with our research objectives and criteria.

Outcome/Results

Among the 8 studies included in the review, a total of 427 children participated, comprising 104 boys, 316 girls, and 7 participants whose gender remained unspecified. The average age of these children was 10.7 years, with an age range spanning from 5.5 to 17.4 years. Out of the 427 patients diagnosed with non-neurogenic voiding dysfunction, 410 underwent SNM implantation. Three hundred and sixty-five patients underwent a two-stage implantation, with 348 children ultimately receiving SNM treatment with an implantable pulse generator and the remaining 17 having their stage 1 lead removed, reflecting a success rate of 96%. A total of 62 patients underwent simultaneous lead and implantable pulse generator (IPG) implantation if good responses were seen intraoperatively.

The response to SNM treatment showed variability across the studies (Tables 1 and 2). Those who reported subjective improvements predominantly experienced positive changes in urinary symptoms, including urinary incontinence, frequency, urgency, nocturnal enuresis, and urinary retention, with respective improvement rates of 78%, 62%, 61%, and 100%. It is worth noting that complete resolution of these symptoms was particularly evident, with rates of 46%, 40%, 30%, and 25%, respectively. Some studies also highlighted a subjective reduction in the recurrence of urinary tract infections (UTIs), with a subset of cases experiencing no recurrence.

Table 1 Summary of sacral neuromodulation (SNM) treatment outcomes in pediatric patients with voiding dysfunction
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Table 2 Summary of studies on sacral neuromodulation (SNM) in pediatric patients with voiding dysfunction
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In three studies involving 70 children, the Vancouver Nonneurogenic Lower Urinary Tract Dysfunction/Dysfunctional Elimination Syndrome (NLUTD/DES) questionnaire was employed [1,2,3]. Following SNM implantation, post-treatment scores exhibited significant improvements, decreasing from 74 to 42 (p = 0.002).

Additionally, two studies involving 44 children utilized the Pediatric Quality of Life Inventory (PedsQL) questionnaire [1, 2]. Post-implantation scores showed improvements in psychosocial quality of life (QOL) scores, increasing from 138 to 162 (p = 0.021), as well as total QOL scores, rising from 153 to 165 (p = 0.016). However, SNM did not significantly impact physical quality of life, as indicated by post-implant scores of 170 to 167 (p = 1.38).

In a study involving 26 children, significant urodynamic enhancements were evident those experiencing refractory urinary urgency, frequency, and/or urinary incontinence, as well as those dealing with urinary retention/incomplete bladder emptying. Marked reductions were observed in uninhibited detrusor contraction pressure during the filling phase (from 6.7 cmH2O to 4.2 cmH2O, p = 0.016) and maximum detrusor pressure during the filling phase (from 62 to 45 cmH2O, p = 0.024). Postoperatively, cystometric bladder capacity increased in most cases, although the difference was not statistically significant (194.8 ml preoperatively and 221.9 ml postoperatively, p = 0.44). Similarly, the alteration in maximum flow rate (Qmax) did not reach statistical significance (16.47 preoperatively and 20.14 postoperatively, p = 0.11). In the urinary retention/incomplete bladder emptying group, a substantial postoperative decrease in post-void residual volume (PVR) was observed, drop** from a mean of 765.25 ml to 235.5 ml (p = 0.04). Although improvements in Qmax were seen in 3 out of 4 patients (75%), with values increasing from 9.25 to 18 ml, they were not statistically significant.

Another study involving two patient groups found that those with uninhibited detrusor contractions (n = 24) had a significant improvement in NLUTD/DES scores, with 11 patients experiencing improvement. In contrast, the group without uninhibited detrusor contractions (n = 5) showed Bowel and Bladder Dysfunction symptom score improvement in only 1 patient [1]. The difference was statistically significant (p < 0.01), indicating that the presence of uninhibited detrusor contractions was associated with greater BBD symptom improvement.

Among the eight children who required Clean Intermittent Catheterization (CIC) for urinary retention, 25% were able to cease catheterization, while 38% decreased the frequency of CIC due to improved spontaneous voiding efficiency. The remainder did not experience changes in their CIC status but had the device implanted for improvements in their other urinary symptoms.

After SNM treatment, a noteworthy portion of patients managed to reduce or discontinue the use of bladder-related medications, with an estimated 51% (27 out of 53) successfully discontinuing these medications altogether.

Complications associated with SNM treatment were observed in some studies, resulting in reoperations for revisions and device explantation. These complications encompassed lead fracture or dislodgement (30%), device migration or erosion (6%), pain (7%), and IPG replacement due to battery depletion (5%). Notably, 25% of the devices were permanently explanted due to inefficacy, and 4% were removed due to infections. Three studies reported complete symptom resolution over time, with 35% (82 out of 232) of children experiencing this when their devices were temporarily turned off for 6–20 months [4, 5]. This event was not classified as a complication. It is worth noting that in one study, this approach was attempted in three additional patients, who showed a significant and prolonged response after SNM. However, upon device deactivation, these three patients experienced a rapid recurrence of symptoms, necessitating device reactivation. All three patients continue to experience positive outcomes with the reactivated device.

Discussion

Sacral Neuromodulation (SNM), FDA-approved in 1997 for adults with urge incontinence and later for overactive bladder (OAB) and nonobstructive urinary retention, has seen an increase in off-label use in children despite lacking FDA approval for those under 16, owing to positive outcomes.

While SNM has shown success rates of approximately 70–80% in randomized studies involving adults, there are unique considerations in pediatric populations that warrant further exploration, including long-term outcomes and potential mechanisms of action.

The mechanism, believed to stabilize neurological voiding mechanisms by stimulating afferent somatic sacral nerves, remains not fully understood.

Based on the review conducted, pediatric patients undergoing implantable sacral neuromodulation therapy for voiding dysfunction experienced a high rate of symptom improvement, with an overall improvement rate of 68%, and complete resolution of symptoms observed in 39% of cases. These improvements encompassed various urinary symptoms, including urinary incontinence, frequency, urgency, and nocturnal enuresis. Additionally, psychosocial and total quality of life scores improved significantly post-treatment, although physical quality of life scores did not show significant improvement.

Urodynamic improvements were also noted, with reductions in detrusor pressure, uninhibited detrusor contractions, and postvoid residual volume observed in several studies. SNM treatment also led to a decrease in the recurrence of urinary tract infections (UTIs) in some cases, and a significant proportion of patients managed to reduce or discontinue the use of bladder-related medications post-treatment.

However, it is crucial to acknowledge the complications associated with SNM therapy, such as lead issues, device migration or erosion, pain, and device removal due to inefficacy or infections. Notably, 25% of devices were permanently explanted due to inefficacy, and 4% were removed due to infections. This underscores the importance of careful patient selection and counseling regarding the potential risks and benefits of SNM therapy.

Furthermore, there is a paucity of studies addressing symptom resolution to facilitate device removal in BBD patients treated with SNM. Recently, Rensing et al. investigated SNM device survival in 67 pediatric patients over a median 2.2-year follow-up period, identifying a growing likelihood of explantation for symptom resolution, reaching up to 32% by the fourth year [1]. Patients explanted for symptom resolution showed improved symptoms and quality of life compared to those explanted due to complications, providing valuable insights into SNM outcomes in this demographic.

The higher rate of explantation for symptom resolution observed in pediatric patients compared to adults suggests a potentially greater responsiveness to SNM therapy in younger populations, possibly due to increased neuroplasticity of central and peripheral nervous systems. This leads to speculation on whether sustained effects observed from childhood interventions could modify or eliminate future adult LUTS if treatment begins during childhood.

Challenges with device placement in smaller-sized pediatric patients include technical difficulties in positioning the lead for effective stimulation, with lead breakage frequently reported in reviewed studies. Pellegrino et al. reported a reoperation rate approaching 100% in pediatric patients undergoing SNM, attributing it to factors such as battery replacement, implant migration during growth, and device removal [2]. Clark’s et al. small study found device malfunction in three pediatric patients associated with a mean somatic growth of 8.1 cm, leading to surgical revision and restored efficacy after revision [3].

Stephany et al. observed a higher rate of lead complications in patients with a lower body mass index (BMI), suggesting that the lack of adipose tissue protecting the lead could increase the risk of lead breakage [4]. Pain over the generator site was frequently reported as a cause of generator revision in reviewed studies, possibly due to insufficient adipose tissue cushioning.

Mason et al. proposed a low BMI as a predisposing factor for reoperation, citing the vulnerability of a thin layer of subcutaneous fat in protecting the neurostimulator and electrodes from damage during physical activity and frequent falls in young children compared with adolescents [5].

However, Fuchs et al. did not find a significant association between BMI and re-operative complications, necessitating further study [6].

Groen et al. reported a high reoperation rate, primarily due to lead dislocation and infection, with efforts recommended to enhance the tined lead for use in children. The infection rate was 13%, possibly related to an extended test period and a two-stage procedure [7]. Efforts should be made to minimize the interval to prevent infection.

A final concern regarding SNM use in children is the permanent placement of a device in patients who may outgrow their symptoms. Roth et al. offered patients with at least 12 months of symptom relief a trial of device deactivation; 10% did not experience a return of symptoms and subsequently had their devices explanted [8]. It remains unclear if this finding is related to the child outgrowing their symptoms or to imperfect patient selection.

Due to these challenges and concerns, patient selection in the pediatric population is crucial. A comprehensive medical history, physical examination, and relevant testing should be conducted to rule out correctable etiologies for the child’s symptoms. Extensive counseling for the child and family regarding the risks and benefits of the SNM procedure, particularly the potential need for reoperation as the risk increases with time, is imperative. This underscores the need for shared decision-making processes and informed consent, ensuring that families are well-aware of the potential benefits and risks associated with SNM therapy.

Limitations to this review include the challenge of population heterogeneity in these studies complicating direct comparisons. Variability in age, comorbidities, and the nature of voiding dysfunction adds complexity to the interpretation of results.

Additionally, the absence of standardized terminology, especially predating the International Children’s Continence Society (ICCS) standardization endorsing “bowel and bladder dysfunction” (BBD), hinders diagnosis consistency. This complexity introduces challenges in interpreting and generalizing results, especially for conditions like Overactive Bladder (OAB) and dysfunctional voiding.

Moreover, the use of diverse evaluation methods further complicates result interpretation. Some studies rely on subjective parameters like the Vancouver Non-neurogenic Lower Urinary Tract Dysfunction/Desire to Void questionnaire and the Pediatric Quality of Life Inventory (PedsQL) questionnaire, potentially introducing placebo effect bias. Others use more objective measures such as voiding diaries, ultrasound, uroflowmetry, or urodynamic studies.

Conclusions

Studies suggest that implantable sacral neuromodulation is an effective and valuable treatment option for pediatric voiding dysfunction. It leads to substantial improvements in urinary symptoms, quality of life, and medication use. Additionally, a notable proportion of patients experience complete symptom resolution, allowing for device removal. However, it is crucial to acknowledge the existence of complications associated with SNM, including infections and device-related issues. These complications should be carefully considered when determining the risk-benefit profile for individual patients. In summary, while the evidence supports the efficacy of implantable sacral neuromodulation for pediatric voiding dysfunction, further research is needed to address the varying success rates and the incidence of complications. The quality of trials should be improved to provide more robust evidence in this field.

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PRISMA chart

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