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6 Chronic Sacral Spinal Nerve Stimulation for Fecal Incontinence: Long-Term Results with Foramen and Cuff Electrodes [2001년 1월 DCR] 2011-11-12 3049
 
Klaus E. Matzel, M.D., Ph.D.,* Uwe Stadelmaier, M.D.,*
Markus Hohenfellner, M.D., Ph.D.,t Werner Hohenberger, M.D., Prof.*
From the *Department of Surgery, University of Erlangen-Nf2rnberg, Erlangen, and tDepartment of Urology, University of Mainz, Mainz, German
 
PURPOSE: Sacral spinal nerve stimulation is a new therapeutic approach for patients with severe fecal incontinence owing to functional deficits of the external anal sphincter. It aims to use the morphologically intact anatomy to recruit residual fi.mction. This study evaluates the long-term results of the first patients treated with this novel approach applying two techniques of sacral spinal nerve stimulator implantation.
METHODS: Six patients underwent either of two techniques for electrode placement: one closed" (dectrodes placed through the sacral foramen) and one "open"(cuff electrodes placed after sacral laminectomy). Follow-up evaluation of their continence status ranged from 5 to 66 months.
 
RESULTS: incontinence improved in all patients. The percentage of incontinent bowel movements decreased during chronic stimulation from a mean of 40.2 percent to 2.8 percent, and the Wexner score decreased from a mean of 17 to 2. The function of the striated anal sphincter improved during chronic stimulation: maximum squeeze pressure increased from a mean of 48.5 mmHg to 92.7 mmHg, and
median squeeze pressure increased from a mean of 37.3 mmHg to 72.5 mmHg. No complications were encountered perioperatively or postoperatively. Two devices had to be removed because of intractable pain, in one patient at the site of the electrode after live months and in the other at the site of the impulse generator after 45 months.
CONCLUSION: Long-term sacral spinal nerve stimulation persistently improves continence and increases striated anal sphincter function in patients with fecal incontinence owing to ftmctional
deficits, but in whom the striated anal sphincter is morphologically intact. Two different operative approaches can be applied effectively.
 
DISCUSSION
Permanent stimulation of the sacral spinal nerves with an implantable neurostimulator was revealed to
be feasible and therapeutic in our patients with fecal incontinence, in whom deficient striated anal sphincteric function with no gross morphologic defect resuited in an absence of voluntary or reflexive behavior. The clinical and manometric results of short-term stimulation with foramen electrodes 14 were confirmed for a longer period of follow-up. Our findings, that the results of temporary stimulation am reproduced by chronic stimulation, revealed the appropriateness of the subchronic percutaneous nerve evaluation to justify, permanent implants.
Despite the positive therapeutic effect in two patients with foramen electrodes, pain required the removal of part of the stimulation device. Successful treatment of incontinence must not be jeopardized permanently after removal of the stimulation device because the implantation of a stimulation device is repeatable.
In the original operative procedure, a four-contact electrode, the so-called Quad lead, is slipped blindly
into the sacral canal via a sacral foramen for permanent stimulation. Its position is confirmed solely by
functional stimulation responses, depending on clinical observation of pelvic floor muscle contraction,
anorectal manometric monitoring, and the patient's perception of stimulation.
Encountering difficulties during placement of temporary testing wire electrodes through the sacral foramen in one patient (Patient 4), we modified the operative approach and the position and design of
the electrode. The spinal nerves were exposed within the sacral canal via a small sacral laminectomy, which permitted the electrodes to be attached directly to the target nerve under visual control. To maximize the effect of stimulation, electrodes were positioned bilaterally. The same technique was applied to ensure ideal placement in another patient (Patient 5) with lumbar spine trauma and equina cauda syndrome who had only residual reflexive external anal sphincteric activity and no voluntary function, perception of sphincteric muscle contraction, or sensation in the anoperineal area.
To minimize current spread to the neighboring spinal nerves, the electrodes are designed in a so-called
"guarded bipolar" configuration, offering three contacts. In this setup, current flow from the central
cathode to two embracing anodes is restricted. The direct placement increases the stimulation efficiency by rendering the electrode-nerve interaction more precise and confining the current to the target spinal nerve, thus reducing stimulation thresholds and prolonging both stimulator output and life. No complications were encountered with the cuff electrodes in our two patients; nor were any reported in a arger series of urologic patients. A potential disadvantage of this modification is that the surgical procedure is more sophisticated.
It must be borne in mind that permanent sacral spinal nerve stimulation has been applied only in
patients in whom conservative treatment has failed. Consequently, the only therapeutic alternatives for
them would have been stoma creation, dynamic graciloplasty, or artificial bowel sphincter augmentation-all invasive procedures associated with more trauma and perioperative and postoperative morbidity. This was avoided.
Since the first report of permanent sacral spinal nerve stimulation for fecal incontinence, only a few
very limited reports have been published confirming its therapeutic beneft in patients with incontinence of
widely varying etiology. The underlying physiologic effect of stimulation remains unclear; it seems
not to be attributable to a placebo effect 29 and is likely to be complex and multifactorial. The striated sphincter contractions in patients with no voluntary control--clearly visible, but to a lesser extent measurable by anorectal manometry--and the facilitation of voluntary contraction--manometrically expressed as squeeze pressure and also described in short-term stimulation 3° may result from alpha-motor fiber stimulation. It is hoped that current work focusing on measurements of latencies and nerve conduction velocity will elucidate the mechanism of sacral spinal nerve stimulation further.
One other potential effect of low-frequency sacral spinal nerve stimulation on voluntary contraction
pressure may result from a transformation of the muscle fibers to a more fatigue-resistant phenotype, as has been shown in experimental work. Low-frequency electrical stimulation transforms fast-twitch, fatigable muscle fibers (Type II) to slow-twitch, fatigue-resistant muscle fibers (Type I). Even though the percentage of Type II muscle fibers is low in healthy individuals, this percentage depends on demand and is not constant. Intermittent low-frequency stimulation was sufficient to achieve continence in our patients. One might assume, however, that continuous stimulation, as applied in dynamic graciloplasty, would have an increased therapeutic benefit in patients with insufficient anal canal closure pressure.
A study of seven patients who underwent successful short-term sacral spinal nerve stimulation suggests that incontinence is alleviated not only by a quantitative and qualitative increase in sphincteric function, but also by improved neural control of the proximal bowel and its interaction with the sphincter. Based on observed, qualitative changes in rectal and anal motility, it is hypothesized that a modulation of sacral reflex arcs, similar to the concept accepted in urology, accounts for clinical improvement.
Based on patients' reports of improved perception of defecation and the pelvic floor during the course of
chronic stimulation, an effect at the central nervous system level may also be hypothesized. Even though the physiologic effect on anorectal function remains somewhat hypothetical, permanent low-frequency electrostimulation of the sacral spinal nerves represents a new therapeutic approach for the specific group of patients with no gross morphologic defect and severe fecal incontinence owing to insufficient striated anal sphincteric muscle function.
A permanent neuroprosthetic implant may dramatically improve continence by using anatomic structures
and recruiting physiologic function. The potential therapeutic spectrum of this concept needs to be clarified by future studies. The exposition of the anatomy inside the sacral canal offers the possibility to detect and address anomalies of neural topography, which might enable a fulzher extension of the indications for this technique (e.g., to sacral malformations), bearing in mind that all patients thus far diagnosed and treated have been unresponsive to conservative treatment and not amenable to traditional operative therapy.
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