Sacral Nerve Stimulation

Sacral nerve stimulation is the most widely published "new" technique for the restoration of fecal incontinence (Figure 6-10.9). Once again, the technology has been adapted from urology techniques where SNS is widely accepted in the current treatment of urinary incontinence (see Chapter 7-2). Patients with bladder dysfunction and concomitant fecal incontinence were noted to have improvement in both symptoms with external stimulation to the pelvic neuroplexus. It was first reported for treatment of fecal incontinence in 1995 by Matzel et al.13 Since then, it has been performed in several hundred patients in Europe. In the United States, it is currently under investigation including at our institution.

To be a candidate, a patient must have an intact sphincter without substantial defects or loss of muscle, reduced or absent sphincter function (by anal manometry), and intact residual reflex function (confirmed by pudendal stimulation) demonstrating an intact nerve-muscle connection. Performance of this technique consists of two stages: peripheral nerve evaluation (PNE) (the diagnostic stage) and the permanent implant (the therapeutic stage). Peripheral nerve evaluation of the sacral roots (S2, S3, S4) is divided into two phases: an acute phase to test the functional integrity of each spinal nerve to striated anal sphincter function and a chronic phase to assess the therapeutic potential of sacral spinal nerve stimulation in individual patients. For PNE, the patient is placed in the prone position using either local or general anesthesia and the sacral

foramina are located using bony landmarks. The acute phase test is performed under local anesthesia using a 20-gauge spinal insulated needle (Medtronic Inc., Minneapolis, MN) attached to an external neurostimulator (Medtronic Inc.). The needle is placed in the sacral foramina, and an electrical current is gradually applied to the needle until a visual muscle response is obtained. Muscle responses include movement of the external sphincter and lateral rotation of the leg (S2), contraction of pelvic floor and plantar flexion of the big toe (S3), or contraction of the anus (S4). The chronic phase of PNE involves placement of a temporary stimulator lead into the same position as the testing needle. This lead is left in place for a trial period of 1 to 2 weeks to allow evaluation of functional response. The decision to proceed from temporary to permanent stimulation is made on the basis of 50% functional improvement in either the number of episodes or incontinence-free days. For placement of the permanent stimulator, the patient is placed in the prone position. The previous scar in the upper buttocks area is opened and the temporary stimulator removed. A permanent stimulator is placed in a subcutaneous pocket and the wound is reclosed. Perioperative antibiotics are continued for 24 hours for each of the procedures.

In the patients that have undergone this procedure since 1995, all but one have had functional benefit and these results have remained consistent over a course of follow-up of up to 8 years.14-19 In addition, SNS clearly improved quality of life. The complication rate was between 0% to 33% and consisted of pain at the site of the pulse generator, electrode migration, and infection.

Patients with fecal incontinence from a wide variety of causes have been treated successfully including: deficits resulting from anal or rectal procedures, those with obstetric or neurologic trauma, scleroderma, systemic sclerosis, primary internal anal sphincter degeneration, and even sphincter disruption. The exact mechanism of action is unknown; however, the sacral nerve roots are the most

Figure 6-10.9. Sacral nerve stimulation.

proximal point of the combined dual nerve supply, somatic and autonomic, to the pelvic floor and anal sphincter mechanism. Stimulation of these sacral nerves augments the neural input to a native mechanical apparatus consisting of the muscular architecture, its associated system of neural connections involved in function of striated muscle, sacral reflexes, and the intrinsic nervous system. The effect seems to be the result of direct efferent stimulation and contraction of the muscles of the pelvic floor and sphincter and from its modulation of the afferent neural pathways is involved in the activation of the internal anal sphincter, rectal relaxation, and sacral reflexes that regulate sensitivity, motility, and the coordination of defecation.

Sacral nerve stimulation has many potential advantages over sphincter repairs, reconstruction, and replacement. The main advantage is that it is minimally invasive because it involves placement of electrodes at a proximal source of the nerve supply with no manipulation of the rectum, anus, or pelvic floor. Consequently,it has a very low complication rate, and the need for discontinuation of treatment is rare. Revisions, repeat surgeries, and removal of the apparatus do not necessarily obligate the patient to a stoma because the stimulation device can be reimplanted again if temporary removal is necessary. Other advantages include the ability to perform the temporary stimulation phase as a screening method for appropriate patients before permanent electrode placement, the absence of required bowel preparation, the performance of procedures in an outpatient setting, lack of decline in efficacy over an 8-year period, and use in a variety of causes of fecal incontinence. Despite the fact that the exact mechanism of action remains to be elucidated, satisfying clinical results have been achieved with this technique. It is an exciting treatment option in a population in whom conservative measures have failed and traditional surgical approaches are conceptually questionable,have limited success, or are considered too high risk.

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