Sacral nerve stimulation for fecal incontinence

Clinical Management of Low Anterior Resection Syndrome: Review of the Current Diagnosis and Treatment

BACKGROUND

Low anterior resection syndrome (LARS) is a series of bowel dysfunction symptoms, including altered bowel frequency, irregular bowel rhythms, fecal incontinence, and constipation. LARS occurs in 80% of patients undergoing sphincter-preserving surgery, affecting patients' quality of life along with social avoidance. Different measurements and treatments have been raised to deal with LARS, but no systematic standard has been developed.

OBJECTIVE AND METHODS

To promote the standardization of clinical trials and clinical management of LARS, this review summarizes the latest findings up until 2023 regarding the diagnostic criteria, assessment protocols, and treatment modalities for postoperative LARS in rectal cancer.

RESULTS

The diagnostic criteria for LARS need to be updated to the definition proposed by the LARS International Collaborative Group, replacing the current application of the LARS score. In both clinical trials and clinical treatment, the severity of LARS should be assessed using at least one symptom assessment questionnaire, the LARS score or MSKCC BFI, and at least one scale related to quality of life. Anorectal manometry, fecoflowmetry, endoscopic ultrasonography, and pelvic floor muscle strength testing are recommended to be adopted only in clinical trials. After analysis of the latest literature on LARS treatment, a stepwise classification model is established for the standardized clinical management of LARS. Patients with minor LARS can start with first-line treatment, including management of self-behavior with an emphasis on diet modification and medication. Lamosetron, colesevelam hydrochloride, and loperamide are common antidiarrheal agents. Second-line management indicates multi-mode pelvic floor rehabilitation and transanal irrigation. Patients with major LARS should select single or several treatments in second-line management. Refractory LARS can choose antegrade enema, neuromodulation, or colostomy.

CONCLUSIONS

In clinical trials of LARS treatment between 2020 and 2022, the eligibility criteria and evaluation system have been variable. Therefore, it is urgent to create a standard for the diagnosis, assessment, and treatment of LARS. Failure to set placebos and differentiate subgroups are limitations of many current LARS studies. Randomized controlled trials comparing diverse therapies and long-term outcomes are absent, as well. Moreover, a new scale needs to be developed to incorporate the patient's perspective and facilitate outpatient follow-up. Though the establishment of a stepwise classification model for LARS treatment here is indispensable, the refinement of the guidelines may be improved by more standardized studies.

Fibers in smaller fascicles have lower activation thresholds with cuff electrodes due to thinner perineurium and smaller cross-sectional area

Objective. In nerve stimulation therapies, fibers in larger fascicles generally have higher activation thresholds, but the mechanisms are not well understood. We implemented and analyzed computational models to uncover the effects of morphological parameters on activation thresholds.Approach. We implemented finite element models of human vagus nerve stimulation to quantify the effects of morphological parameters on thresholds in realistic nerves. We also implemented simplified models to isolate effects of perineurium thickness, endoneurium diameter, fiber diameter, and fascicle location on current density, potential distributions (Ve), and activation thresholds across cuff geometries and stimulation waveforms. UsingVefrom each finite element model, we simulated activation thresholds in biophysical cable models of mammalian axons.Main results. Perineurium thickness increases with fascicle diameter, and both thicker perineurium and larger endoneurial diameter contributed to higher activation thresholds via lower peak and broader longitudinal potentials. Thicker perineurium caused less current to enter the fascicle transversely, decreasing peakVe. Thicker perineurium also inhibited current from leaving the fascicle, causing more constant longitudinal current density, broadeningVe. With increasing endoneurial diameter, intrafascicular volume increased faster than surface area, thereby decreasing intrafascicular current density and peakVe. Additionally, larger fascicles have greater cross-sectional area, thereby facilitating longitudinal intrafascicular current flow and broadeningVe. A large neighboring fascicle could increase activation thresholds, and for a given fascicle, fiber diameter had the greatest effect on thresholds, followed by fascicle diameter, and lastly, fascicle location within the epineurium. The circumneural cuff elicited robust activation across the nerve, whereas a bipolar transverse cuff with small contacts delivering a pseudo-monophasic waveform enabled more selective activation across fiber diameters and locations.Significance. Our computational studies provide mechanistic understanding of neural responses across relevant morphological parameters of peripheral nerves, thereby informing rational design of effective therapies.

Progress in research of sacral nerve stimulation

Sacral nerve stimulation (SNS) is well-known as a minimally invasive treatment. Originally, it was mainly used to treat urinary system diseases such as urge urinary incontinence. Gradually, it is used to treat digestive system diseases such as fecal incontinence and chronic constipation. SNS is a method in which electrical pulse signals are sent out through pulse generators to stimulate the sacral nerve directly or indirectly, thus modulating the nerve reflex of the bladder, urethra, anus, colon, and rectum and improving abnormal nerve regulation to achieve the therapeutic effect. The regulation of the sacral nerve is often carried out by inserting electrodes into the sacral spinal canal S_2-4 (mostly S₃), and the symptoms are improved by complex regulation of spinal reflex and supraspinal reflex. However, the exact mechanism is still unclear. Many studies have shown that SNS plays a key role in the treatment of many diseases of the urinary system and digestive system. This paper reviews the progress in the research of SNS.

Five-year single center experience of sacral neuromodulation for isolated fecal incontinence or fecal incontinence combined with low anterior resection syndrome

PURPOSE

Sacral neuromodulation (SNM) has proven to be a safe and effective treatment for fecal incontinence (FI). For low anterior resection syndrome (LARS), however, SNM efficacy is still poorly documented. The primary aim of this study was to report on efficacy of SNM therapy for patients with isolated FI or LARS. Furthermore, we evaluated the safety of the procedure and the relevance of adequate follow-up.

METHODS

A retrospective analysis was performed upon a prospectively maintained database of all patients who underwent SNM therapy for isolated FI or LARS between January 2014 and January 2019. The Wexner and LARS scores were evaluated at baseline, during test phase, after definitive implantation and annually during follow-up. Treatment success was defined as at least 50% improvement of the Wexner score or a reduction to minor or no LARS.

RESULTS

Out of 89 patients with isolated FI or LARS who had a SNM test phase, 62 patients were eligible for implantation of the permanent SNM device. At baseline, 3 weeks, and 1, 2, 3, 4 and 5 years after definitive implantation the median Wexner score of all patients was 18, 2, 4.5, 5, 5, 4 and 4.5, respectively, and 18, 4, 5.5, 5, 4, 3 and 4, respectively, for patients with FI and LARS. Patients with LARS more frequently required changes in program settings.

CONCLUSIONS

SNM therapy is a safe and effective treatment for patients with isolated FI and patients with FI and LARS. Adequate follow-up is essential to ensure long-term effectivity, especially for LARS patients.

Sacral neuromodulation for neurogenic bladder and bowel dysfunction with multiple symptoms secondary to spinal cord disease

STUDY DESIGN

Retrospective case series.

OBJECTIVES

The primary aim was to assess the clinical effects of sacral neuromodulation (SNM) for neurogenic bladder and/or bowel dysfunction with multiple symptoms secondary to spinal cord disease or injury.

SETTING

Beijing, China.

METHODS

Between 2011 and 2013, 23 patients with multiple bladder and/or bowel problems secondary to spinal cord disease or injury were treated with a preliminary test SNM. If at least 50% clinical improvement occurred, then the patient underwent a permanent SNM procedure. We evaluated the patients using a bladder diary, post-void residual volume measurement and the Wexner questionnaire score for constipation before the test phase, during the test phase and after the permanent SNM.

RESULTS

In the test phase, the rate of improvement in dysuria (29.4%) was significantly lower than urgency frequency (64.7%), urinary incontinence (69.2%) and constipation (75.0%). An implant was performed in 13 (56.5%) patients, including 4 patients who still used intermittent catheterization to exclude urine after permanent SNM because the symptom of dysuria could not be improved significantly and 1 patient who achieved ⩾50% improvement in lower urinary tract dysfunction but not in constipation. During follow-up (17.5±2.0 months), 1 patient (7.7%) failed and 1 patient had bilateral vesicoureteral reflux.

CONCLUSION

Chronic SNM cannot always resolve all the bladder and bowel symptoms secondary to spinal cord disease or injury, but combined with other treatments may help improve multiple symptoms.

Assessment and in vitro experiment of artificial anal sphincter system based on rebuilding the rectal sensation function

In this paper, a novel artificial anal sphincter (AAS) system based on rebuilding the rectal sensation function is proposed to treat human fecal incontinence. The executive mechanism of the traditional AAS system was redesigned and integrated for a simpler structure and better durability. The novel executive mechanism uses a sandwich structure to simulate the basic function of the natural human anal sphincter. To rebuild the lost rectal sensation function caused by fecal incontinence, we propose a novel method for rebuilding the rectal sensation function based on an Optimal Wavelet Packet Basis (OWPB) using the Davies-Bouldin (DB) index and a support vector machine (SVM). OWPB using a DB index is used for feature vector extraction, while a SVM is adopted for pattern recognition.Furthermore, an in vitro experiment with the AAS system based on rectal sensation function rebuilding was carried out. Experimental results indicate that the novel executive mechanism can simulate the basic function of the natural human anal sphincter, and the proposed method is quite effective for rebuilding rectal sensation in patients.

Electrical stimulation therapy for neurogenic bowel dysfunction after spinal injury

AIM: To assess the efficacy of electrical stimulation therapy in the treatment of neurogenic bowel dysfunction after spinal injury.

METHODS: PubMed, MEDLINE, EMbase, Cochrane Central Register of Controlled Trials (CENTRAL), ISI Web of Knowledge, OVID, CNKI, VIP, and Wanfang Data were searched for clinical studies that evaluated electrical stimulation therapy for neurogenic bowel dysfunction after spinal injury from the date of creation of databases to October 2012. The bibliographies of the retrieved studies were also searched. Researchers read included studies carefully and extracted data strictly.

RESULTS: A total of 11 studies were included. Electrical stimulation therapies mainly included transcutaneous electrical stimulation, transrectal electrostimulation, intravesical electrical stimulation, and sacral nerve modulation. Electrical stimulation could adjust gut innervation, increase the local blood flow of the gastrointestinal tract, promote protein synthesis, and improve bowel control of bowel and symptoms of fecal incontinence or constipation in patients with spinal injury.

CONCLUSION: The current evidence shows that to some extent, electrical stimulation therapy could improve neurogenic bowel dysfunction after spinal injury. However, the number of clinical studies that have been reported on this direction was small, especially the number of randomized controlled trials. In addition, the number of subjects included in the retrieved studies was small, and the intensity, outcomes and follow-up cycles were inconsistent. More large-sample and high-quality clinical studies need to be done to evaluate the efficacy of electrical stimulation therapy in the management of bowel function in patients with spinal injury.