Sacral Nerve Stimulation as a treatment for fecal incontinence due to LARS syndrome

Fecal incontinence is defined as the lack of control of defecation. It is a multifactor condition, involving such factors as mechanical disruption as well as neuromuscular or idiopathic dysfunction. Most of the time it is caused by a loss of anatomic continuity, for example after childbirth, surgery, or other traumatic injury. It frequently requires surgical intervention in an attempt to successfully restore normal physical structure.

The causes are multiple, although its prevalence increases with age. After 50, prevalence rises to 11 % in men and 26% in women.

The standard management for symptomatic fecal incontinence includes nonoperative management:

- Pelvic floor exercises

- Dietary changes

- Surgery for repair sphincter defect

We also know that 30% of fecal incontinence is linked to urinary incontinence. Sacral nerve stimulation has been approved for use in treating urinary incontinence in Europe since 1994, so it could also be a good option for these patients.

Different studies have had good results showing that sacral nerve stimulation is a good option in patients with fecal incontinence, and is more effective than medical treatment alone.

For all these reasons, the use of this therapy was proposed in patients who underwent rectal surgery and presented with Low Anterior Resection Syndrome (LARS). LARS is the major problem for rectal cancer patients after a low anterior resection. They have daily episodes of incontinence, obstructed defecation and constipation, causing a huge impact on the patients’ quality of life. 25% and 80 % of LARS patients develop symptoms following a sphincter-sparing rectal surgery. Mobilization of the rectum within the pelvis can lead to intramural nerve plexus injury, with long lasting sacral nerve terminal motor impairment.

For individual patients, symptoms vary in type, severity, and duration. The risk factors for developing LARS are several, in particular: neoadjuvant radiotherapy, low anastomosis and anastomotic complications.

There is evidence that denervation of the remnant sigmoid colon or left colon by means of operative maneuvers (e.g. ligation of a vascular pedicle) can result in a significant increase in motility. As a result, patients with LARS have a shorter colonic transit time and a greater increase in neorectal pressure after a meal compared to patients who do not have LARS.

Removal of the rectum and in particular of the rectosigmoid junction eliminates the physiological distal control center for the regulation of bowel transit, leaving the bowel activities with no "brakes." This lack of distal negative feedback signals to oppose increased proximal colonic motility further exacerbates LARS symptoms.

The sum of all these factors predisposes patients to develop LARS, which has a significant impact on their quality of life. The most frequently reported symptoms are: fecal incontinence, stool frequency, flatus incontinence, urgency, pad wearing, lifestyle modification, clustering and nocturnal incontinence.

By means of the Wexner Score and the LARS Score we can classify this syndrome into minor and major according to the test score. Treatment in minor LARS ranges from dietary advice to loperamide, bulking agents and amitriptyline. In the case of major LARS the different options are stool training and advanced education, counselling, biofeedback, rectal irrigation and as a new option: Sacral nerve stimulation as a treatment for fecal incontinence due to LARS syndrome.

Sacral nerve stimulation is a minimally invasive therapy. Different studies have shown its effectiveness in the treatment of pelvic floor dysfunctions, improving the severity of symptoms, restoring continence in patients and improving quality of life.

The working mechanism is based on an effect on the autonomic nervous system, modulation of anorectal reflexes, modulation of the corticospinal pathway and changes in rectal sensitivity. It improves fecal continence by improving resting and squeeze pressures of the anal sphincter, as well as rectal sensation, together with stimulation on the external anal sphincter.

Different studies show good results with this new technique in this type of patients, with improvement of symptoms in a high percentage of patients which also persists over time. We also see that quality of life improves, achieving a very significant decrease in the Wexner Score in different studies.

The device system is an implantable programmable neuromodulation system that delivers electrical stimulation to the sacral nerve. It is designed to deliver therapeutic nerve stimulation through the following system components: a neurostimulator, a lead with programmable electrodes, and a lead extension. The system works by sending electrical pulses, which are produced by the neurostimulator, through the lead system.

The implant goes through two phases. A first phase in which the device battery is external, checking if results are satisfactory. If they are, the final implantation is carried out in a second phase in which the battery is surgically implanted.

For its placement it is necessary to select a location that meets the following conditions:

- It is a minimum of 20 cm away from any other neurostimulator to minimize telemetry interference and possible inappropriate therapy.

- It is on the opposite side of the body from another active implanted device (eg, pacemaker, defibrillator) to minimize possible interaction between the devices.

- It is away from bony structures (e.g. 3 - 4 cm away) to minimize discomfort at the neurostimulator site.

- It is away from areas of restriction or pressure to minimize the potential for skin erosion, patient discomfort, or damage to components.

- It is in an area accessible to the patient for proper operation of a patient control device.

- It is necessary to locate S3 for the needle implant. For this you have to identify middle line, identify sciatic notches, join the recesses and you will locate S3 is 2 cm from the midline. The needle should enter parallel to the midline and at the medial border of the foramen. If it is not placed in the correct position, electrode migration can occur causing the device to malfunction.

Finally, we can say that with a good selection of patients, correct placement of the device and a good management program, sacral nerve stimulation can be successful in the treatment of these patients.

In summary we know that,

- LARS is related to a decreased rectal reservoir and denervation of the left colon during mobilization, which can lead to hypermotility of the neorectum and which may be a causal factor in the manifestation of multiple evacuations or urgency.

- Authors have concluded that SNS is effective for all LARS symptoms.

- Results of SNS implantation for fecal incontinence in LARS, showed significant decreases in fecal incontinent episodes, improvement in quality of life.

- However, well-designed randomized controlled trials are needed to improve patient selection criteria for this procedure.