Current Position of Sacral Neuromodulation in Treatment of Fecal Incontinence

Abstract

Fecal incontinence (FI) is defined as uncontrolled passage of feces or gas for at least 1-month duration in an individual who previously had control. FI is a common and debilitating condition affecting many individuals. Continence depends on complex relationships between anal sphincters, rectal curvatures, rectoanal sensation, rectal compliance, stool consistency, and neurologic function. Factors, such as pregnancy, chronic diarrhea, diabetes mellitus, previous anorectal surgery, urinary incontinence, smoking, obesity, limited physical activity, white race, and neurologic disease, are known to be the risk factors for FI. Conservative/medical management including biofeedback are recognized as the first-line treatment of the FI. Those who are suitable for surgical intervention and who have failed conservative management, sacral nerve stimulation (SNS) has emerged as the treatment of choice in many patients. The surgical technique involves placement of a tined lead with four electrodes through the S3 sacral foramen. The lead is attached to a battery, which acts as a pulse generator, and is placed under the patient's skin in the lower lumbar region. The use of SNS in the treatment of FI has increased over the years and the beneficial effects of this treatment have been substantiated by multiple studies. This review describes SNS as a modality of treatment for FI and its position in the current medical diaspora in patients with FI.

Fecal incontinence (FI) is defined as uncontrolled passage of feces or gas for at least 1-month duration in an individual who previously had control. ¹ The overall prevalence is estimated to be 1.6 to 15% depending on age and medical comorbidities. ² A recent U.S.-based study showed prevalence of 8.3% of the noninstitutionalized population with the disease, ³ while the incidence rises to almost 50% in institutionalized populations. ⁴ This condition can be a cause for extreme physical and emotional stress, and the psychosocial stigma associated to the condition might be the reason why many patients don't seek medical care. The condition is usually managed conservatively with modifying dietary habits and surgical treatment is introduced when conservative measures fail. The surgical treatments might include repair of the sphincters, injection of bulk agents into the anorectal lumen, neosphincter placement, neural modulation, or ultimately colostomy. Sacral nerve stimulation (SNS) has emerged as a promising treatment for this condition.

Materials and Methods

A literature search was performed using PubMed, MEDLINE, and Cochrane databases for all relevant articles. The following keywords were used in various combinations to conduct the search: “sacral nerve stimulation,” “SNS,” “sacral neuromodulation,” and “fecal incontinence.” All studies which were identified in this search were analyzed for relevance and content.

Results

A total of 529 articles were found describing SNS ranging from reviews, clinical trials and meta-analyses. All the articles were analyzed for relevance and content. Of note, 12 studies from various groups were identified which studied long-term durability of SNS in patients with FI. This review article summarizes the available evidence on sacral neuromodulation for the treatment of FI.

Etiology and Evaluation

Fecal continence depends on complex relationships between anal sphincters, rectal curvatures, rectoanal sensation, rectal compliance, stool consistency, and neurologic function which includes the somatic and autonomic nervous system function. Imbalance or deficit in one or more mechanisms such that the remaining ones are unable to compensate results in FI.

Conditions that damage or impair the function of the spinal cord, central nervous system, autonomic nervous system, pelvic floor muscles, rectum, or anal sphincters can predispose to FI ( Table 1 ).

Table 1. Etiologies of fecal incontinence (reprinted by permission from Bharucha ²⁶ ) .

Anal sphincter weakness
Traumatic: obstetric trauma, injury related to surgical procedures (hemorrhoidectomy and internal sphincterotomy)
Nontraumatic: scleroderma, internal sphincter thinning of unknown etiology
Neuropathy: stretch injury, obstetric trauma, and diabetes
Anatomic disturbances of the pelvic floor: fistula, rectal prolapse, and descending perineum syndrome
Inflammatory conditions: Crohn's disease, ulcerative colitis, and radiation proctitis
Central nervous system disease: dementia, stroke, brain tumors, spinal cord lesions, multiple system atrophy (Shy–Drager syndrome), and multiple sclerosis
Diarrhea: irritable bowel syndrome and postcholecystectomy diarrhea

A detailed history is imperative which can provide an indication of the severity, etiology, and pathophysiology and guide diagnostic testing and treatment. It is important that a validated measurement of the severity of incontinence is used in the assessment. ^{5 6} One such scoring system is the St. Mark's scoring system ( Table 2 ). ⁷ This method of evaluation allows us to compare between patient populations and outcomes of medical and surgical treatments.

Table 2. St. Mark (Vaizey's score) for fecal incontinence (reprinted with permission from Vaizey et al ⁷ ) .

Type of incontinence	Frequency
	Never	Rarely	Sometimes	Usually	Always
Solid	0	1	2	3	4
Liquid	0	1	2	3	4
Gas	0	1	2	3	4
Lifestyle alteration	0	1	2	3	4
				No	Yes
Need to wear a pad or plug				0	2
Taking constipating medicines				0	2
Lack of ability to defer defecation for 15 minutes				0	4

Abbreviations: Always, 1 or more episodes a day; Never, no episodes in the past four weeks; Rarely, 1 episode in the past 4 weeks; Sometimes, >1 episode in the past 4 weeks but <1 a week; Usually, 1 or more episodes a week but <1 a day.

Note: add one score from each row. Minimum score is 0 = perfect continence; maximum score is 24 = totally incontinent.

Anorectal manometry with or without balloon expulsion test is considered the starting point in the diagnostic testing in the evaluation of FI. ^{8 9}

Endoanal ultrasound is currently the gold standard for evaluation of sphincters in patients with FI. ¹⁰

Defecography should be considered in patients with FI when contemplating definitive neuromodulation treatment to rule out rectal intussusception as SNS as a modality of treatment have shown to be ineffective in patients with rectal intussusception or internal rectal prolapse. ¹¹

Management

Conservative management is the initial treatment utilized in patients with FI. Avoiding certain foods like prunes, figs, rhubarb, and artificial sweeteners, like sorbitol, can help with the symptoms in some patients. Introduction of bulking agents, like psyllium, helps to control the symptoms in some patients. ¹² This strategy, including modifications in dietary habits, fluid management, bowel routines, and changes to medications, helps to control the symptoms of FI in about half of the patients. ¹²

Medications like loperamide can be used to control diarrheal symptoms which is usually the first-line treatment to control diarrhea and improve the symptoms of FI. ^{12 13} Cholestyramine can be used in patient with likelihood of bile salt induced diarrhea. Patients with rectal emptying problem and overflow incontinence can benefit from biofeedback and rectal emptying procedures including regular irrigation. ¹⁴

Surgical treatment is recommended if the above conservative treatments do not improve symptoms and the patient wants to move forward with a more invasive treatment. Historically, sphincteroplasty is the operation commonly performed in patients suffering from moderate-to-severe FI who do not respond to conservative treatment. In patients with anal sphincter injury, specifically those of early onset after obstetric injury (within 1 year of delivery), performing sphincteroplasty is a reasonable option. But in patients with later onset of incontinence, including those with prior obstetric injuries, there may be no benefit of sphincteroplasty as multiple mechanisms can contribute to FI. Recent studies indicate that although sphincteroplasty improves incontinence symptoms in short term (80% at 1 year), the response faded over long term (48% at 5 years). ^{15 16 17} In 2011, SNS was approved in the United States as a treatment modality for FI and it provided a treatment option for patients with or without sphincter injury and partial spinal cord injury. It has now conveniently become the primary surgical treatment for FI.

Sacral Nerve Stimulation

SNS is a novel treatment modality for FI. It was initially devised as a treatment for urinary incontinence, specifically urge incontinence, in 1981 by Tanagho and Schimdt. ¹⁸ SNS for treatment of FI was first introduced by Matzel and group with their initial results published in 1995. ¹⁹ The mechanism of action of SNS remains unknown. Studies have suggested a variety of different factors, including improved sensory function, improved anal sphincter function, improved rectal motility, and/or central nervous system effects. ²⁰ The benefits and sustained effect shown by this procedure has considerably substantiated it as a primary surgical modality in most patients. The modality can be utilized in patients who suffer from FI not improved with conservative management, with or without anal sphincter injury. Its use has also expanded to patients with partial spinal cord injuries. ¹⁸ In two comparative studies, it has shown to have better outcomes than sphincteroplasty in terms of improvement in continence scores and quality of life. ^{21 22}

Even with improved and extended uses of SNS for treatment of FI, it has been found to lack efficacy in certain scenarios. Lindsey et al has shown that SNS is ineffective in patients with rectal intussusception. ¹¹ Defecography is the imaging test of choice to identify patients with deep rectal intussusception. Evaluating SNS candidates with defecography prior to lead placement will help to identify patients who will fail to show optimal benefit from the therapy.

The initial SNS procedure described by Matzel and group was done in three stages. ¹⁹ Stage 1 was a percutaneous nerve evaluation (PNE). Following this, stage 2 included placement of temporary leads for a test phase stimulation, and the stage 3 included placement of the permanent lead along with the implantable pulse generator.

These stages have changed over time and most surgeons perform a two-stage procedure with the first stage being a test stage (either PNE or implantation of permanent lead) and the second stage being full implantation of the pulse generator device.

Percutaneous Nerve Evaluation

One benefit of SNS as treatment for FI is that the therapy is “tested” on the patient by placing a temporary device for approximately 1 week and asking the patient to keep a diary of their FI frequency. The test stage can either be done by PNE or a stage-1 procedure where a permanent tined lead is placed. The PNE option can be performed in the office under local anesthesia. The patient is placed in a prone position, and anatomic landmarks are used to help localize the S3 sacral nerve foramen. A needle is passed through the S3 sacral foramen and confirmed to be in the appropriate position if sensory responses are elicited by stimulating the needle. Under local anesthesia, a tingling or tapping sensation should be felt preferably within the perineal region. Eliciting the motor response may cause discomfort since the patient is fully awake. Usually the PNE test is performed with the temporary device pulse width set at 210μs and frequency of 14 Hz. The temporary leads are left in place for 7 to 10 days and then easily removed.

Stage 1 (Tined Lead Testing Phase)

A stage-1 procedure involves placement of a permanent tined lead (with four electrodes) which is temporarily hooked up to an external power supply. This procedure is performed in the operating room under sterile conditions since the tined lead is the permanent lead that will remain in place if this test stage is successful. This procedure can be performed under intravenous sedation or general anesthesia. This test stage offers a longer trial period of 2 weeks as opposed to 1 week with a PNE.

The patient is placed in the prone position, prepped and draped in sterile fashion, and anesthesia is administered. Anatomic landmarks and fluoroscopy are used to localize the S3 sacral foramen and a needle is placed through this foramen. Motor responses and fluoroscopic images are relied upon to verify appropriate needle placement. Flexion of big toe and bellowing of the anal opening is seen with stimulation of the S3 nerves. Flexion of entire foot/internal rotation is seen with S2 nerve stimulation, and exaggerated anal bellows without toe flexion is seen with S4 nerve stimulation. Ideally, the S3 motor response is elicited at very low voltage thresholds, which indicates optimal positioning for lead placement. Once the S3 nerve root is identified and the appropriate motor response elicited, then the permanent tined lead is placed. The permanent lead is placed under radiologic guidance. The permanent lead had four electrodes and the lead is placed such that it elicits motor response on stimulation of all four electrodes. The common configuration for placement is with the most proximal electrode (electrode 3) lying within the sacral foramen, electrode 2 being level with the anterior sacral cortex, and the remaining two distal electrodes (electrodes 1 and 0) being anterior to the sacrum ( Fig. 1 ). The permanent tined lead is attached to a temporary wire that plugs into a temporary external pulse generator. The patient undergoes a usual 2-week long testing phase.

Fig. 1.

Placements of electrodes. Reprinted with permission from Matzel et al. ³⁸

During the PNE test or stage-1 test, the patient is asked to maintain a bowel habits diary and continence scores are used to assess the benefit at follow-up. The test stage is considered to be successful if there is >50% increase in number of incontinent-free days, >50% improvement in continence score, or at least 50% reduction in number of FI episodes. A successful test stage allows the patient to proceed to permanent device implantation. If the test stage is unsuccessful, then the device is completely removed, and the patient and surgeon will need to explore alternates in evaluating or treating the patient's FI.

Stage 2 (Permanent Implantation of Sacral Nerve Stimulation Device)

After a successful test stage (PNE or stage 1), the next step is to place the permanent device. This stage is performed in the operating room under intravenous sedation or general anesthesia. If the patient underwent a PNE test, then their stage-2 procedure will involve placement of the permanent tined lead (stage 1) and implantation of the pulse generator. If the patient underwent a stage-1 test, then their stage-2 procedure will involve removal of the temporary pulse generator connection and implantation of the permanent pulse generator.

The permanent tined lead is tunneled to a subcutaneous pocket that is created in the ipsilateral upper buttock avoiding the iliac crest and lateral border or sacrum where the pulse generator implant is placed ( Fig. 2 ).

Fig. 2.

Location of permanent nerve stimulator. Reprinted with permission of Medtronic, Inc., © 2004.

Discussion

SNS has shown promising results in treatment of FI. Long-term outcomes have shown sustained benefit in the patients. ^{23 24} Most of the studies confirm that the efficacy of the treatment goes far beyond the initial phase and is sustained well beyond 5 years in majority of the patients ( Table 3 ). This treatment option has multiple benefits. The therapy is set up in multiple stages, which allows the patient to “test” the therapy prior to committing to permanent implantation. The procedures are all minimally invasive and performed in the office or in an outpatient setting, so the patient has minimal disruption to their usual activities. There is very minimal recovery time needed after permanent implantation. In comparison to sphincteroplasty, SNS is far less invasive and shows sustained long-term continence improvement.

Table 3. Published long-term outcomes of sacral nerve stimulation for fecal incontinence.

Studies	Total follow-up (mo)	Number of patients	Number of patients followed-up over the intended period	>50% improvement
Maeda et al 27	60	141	101	55.6
George et al 28	114	23	19	52 a
Moya et al 29	56	52	50	96
Matzel et al 30	118	12	9	78
Lim et al 31	51	53	41	NA
Hollingshead et al 32	60	86	18	21
Vallet et al 33	44	32	23	72
Duelund-Jakobsen et al 34	46	158	91	75
Altomare et al 35	74	60	52	74
Hull et al 23	48	120	77	87
Uludağ et al 36	84	50	36	84
Altomare et al 37	84	407	228	71

Abbreviation: NA, not available.

^aOnly full continence at the time of the follow-up was reported.

The SNS procedure can have minor complications. The most common complications associated with the procedure include pain, infection (with some requiring device removal), device dislodgement, or lead fractures. The SNS device that is currently available in the United States is manufactured by Medtronic and the tined lead is not compatible with magnetic resonance imaging (MRI). Thus, SNS with the Medtronic Interstim II system is contraindicated in patients who require MRI below the head.

Axonic Systems have come up with their own SNS devices (Model 1101) and recently got Food and Drug Administration (FDA) approval for use in FI. ²⁵ They claim to have a 15-year functional life and the ability of patients to undergo conditional full-body MRI scans without the necessity of having the device explanted. Medtronic and other device manufacturers are also developing SNS products that offer MRI compatibility. Additional areas of technologic advancement include devices with a longer battery lifespan and rechargeable batteries.

Conclusion

In patients with FI, conservative/medical management along with biofeedback is the first line treatment, which can improve symptoms in about half of the patients. In most patients who fail conservative management, SNS can safely be considered for surgical treatment of FI. More invasive surgical modalities should be reserved for failed SNS treatment. SNS has shown to be effective in controlling incontinence symptoms over a sustained period and is increasingly being used in the treatment of FI as the surgical treatment of choice. Further technologic advances in this field will allow SNS to be a treatment option for even more patients plagued by FI.

Erratum: An erratum has been published for this article (DOI: 10.1055/s-0044-1788698).