Posterior tibial nerve stimulation in the treatment of fecal incontinence: a systematic review

Arroyo-Fernández, Rubén; Avendaño-Coy, Juan; Ando-Lafuente, Sara; Martín-Correa, M.ª-Teresa; Ferri-Morales, Asunción; Arroyo-Fernández, Rubén; Avendaño-Coy, Juan; Ando-Lafuente, Sara; Martín-Correa, M.ª-Teresa; Ferri-Morales, Asunción

doi:10.17235/reed.2018.5007/2017

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Revista Española de Enfermedades Digestivas

Print version ISSN 1130-0108

Rev. esp. enferm. dig. vol.110 n.9 Madrid Sep. 2018

https://dx.doi.org/10.17235/reed.2018.5007/2017

REVIEW

Posterior tibial nerve stimulation in the treatment of fecal incontinence: a systematic review

Rubén Arroyo-Fernández¹², Juan Avendaño-Coy¹, Sara Ando-Lafuente¹, M.ª-Teresa Martín-Correa¹³, Asunción Ferri-Morales¹

^¹E.U.E. y Fisioterapia. Universidad de Castilla-La Mancha. Toledo, Spain

^²Hospital Nuestra Señora del Prado. Talavera de la Reina, Toledo, Spain

^³Hospital Virgen de la Misericordia. Toledo, Spain

INTRODUCTION

Anal incontinence is defined by the International Continence Society as "any involuntary loss of fecal material and/or gas" and can be classified as fecal incontinence (FI) or gas incontinence ¹. The prevalence is 10-15% in the general population ²^,³^,⁴, causing a significant impact on quality of life, and leads to stigmatization and social exclusion on occasions ⁵. The etiology of FI is usually multifactorial. Physiopathologic mechanisms can be classified into four categories ⁶: structural abnormalities (muscular, neurological and/or visceral); physiologic abnormalities (changes in anus-rectum sensitivity, fecal impaction); characteristics of feces (changes in their consistency, volume or frequency; presence or absence of irritants) and other mechanisms.

A wide array of techniques are available for the treatment of FI ¹. Following the failure of standard measures (diet changes, rehabilitation of pelvic floor, biofeedback, pharmacological treatment), the next line of treatment includes neuromodulation ¹. This technique uses low-frequency electric currents for the direct or indirect stimulation of the spinal nerves ⁷. This includes neuromodulation of the sacral nerve ⁸ and posterior tibial nerve stimulation (PTNS) ⁸^,⁹. PTNS is more economical ¹⁰ and does not require the surgical implantation of permanent devices. There are two modalities for PTNS application: a percutaneous route using a needle electrode and a transcutaneous route via a surface electrode ⁹.

Previous reviews ⁵^,¹¹^,¹² have concluded that PTNS is an effective technique for the treatment of FI. However, none have specified the optimal parameters for the application of the current, such as scheduling and the frequency of sessions. Furthermore, there is a lack of published randomized clinical trials (RCTs). Thus, meta-analysis to compare different controlled PTNS interventions in order to produce a quantitative synthesis cannot be performed.

The aim of this systematic review was to assess the usefulness of PTNS for the treatment of FI in terms of effectiveness, severity of incontinence and quality of life, as well as to identify any differences in protocols and/or outcomes that result from the type of electrostimulation used.

MATERIALS AND METHODS

This review was conducted in accordance with the PRISMA declaration ¹³. A literature search of Pubmed (Medline), Scopus, Web of Knowledge and PEDro databases was performed in order to identify scientific articles published up to March 2017 in Spanish, English, French, Italian or Portuguese. Bibliographic references from relevant articles were examined to identify articles that had not been identified in the primary search but met the inclusion criteria. The key words used for the search included: "fecal incontinence" OR "faecal incontinence" OR "anal incontinence"; AND "electrical stimulation" OR "tibial nerve stimulation" OR "Stoller stimulation" OR "PTNS".

The criteria for inclusion included: a) subjects: patients diagnosed with FI; b) study type: randomized controlled trials (RCTs) or prospective observational studies (also referred to as cases series); c) intervention type: PTNS programs (transcutaneous and percutaneous); and d) outcome variables: treatment effectiveness, severity of incontinence and quality of life. The criteria for exclusion included: a) studies with sample sizes of < 10 subjects; b) studies including subjects of < 18 years of age; c) intracavitary stimulation studies; d) surgical procedures for treating FI; and e) articles that did not provide specific data on any of the outcome measures previously mentioned.

Two reviewers (RAF and AFM) carried out the search, selection and evaluation of the methodological quality of the articles independently, as well as the data extraction. Possible discrepancies were resolved by a consensus. For each of the selected articles, the two reviewers independently extracted the following data: a) characteristics of subjects (sample size and age); b) treatment's characteristics (type and parameters); c) treatment planning (duration and frequency); and d) outcome variables (type of test, time points of evaluation and outcome measurements).

The Physiotherapy Evidence Database (PEDro) scale was used in order to evaluate the methodological quality of articles. This is based on the Delphi list and its reliability to assess the quality of RCTs has been validated ¹⁴. On the other hand, the methodological quality of observational studies was rated via the Quality Assessment for Cases Series scale, by the National Institute for Health and Care Excellence (NICE) ¹⁵.

RESULTS

The initial keywords search identified a total of 287 studies. After excluding duplicates and articles that did not meet the inclusion criteria, a total of 23 articles were selected for the review, five from the manual search (Fig. 1).

Fig. 1

Characteristics of studies

The characteristics of the 23 studies included are described in tables 1 and 2. Table 1 shows the RCTs ⁸^,⁹^,¹⁶^,¹⁷^,¹⁸^,¹⁹ and Table 2, the descriptive longitudinal prospective studies ²⁰^,²¹^,²²^,²³^,²⁴^,²⁵^,²⁶^,²⁷^,²⁸^,²⁹^,³⁰^,³¹^,³²^,³³^,³⁴^,³⁵.Of the six RCTs, only three included a sham stimulation ⁸^,⁹^,¹⁶. Transcutaneous PTNS was performed in four of the studies ⁹^,¹⁶^,¹⁷^,¹⁸ and percutaneous PTNS, in three ⁸^,⁹^,¹⁹. One study ⁹ included three arms in order to compare percutaneous and transcutaneous stimulation with a placebo group. Therefore, this article was selected for both stimulation modalities. The length of treatment varied between 1.5 and 6 months, with a wide variability in the frequency of sessions that ranged from two daily sessions at the beginning of treatment to one weekly session. There was also a wide variability in the current frequency, which was either 10 or 20 Hz (Table 1).

Table 1 Characteristics of randomized clinical trials

TPTNS: transcutaneous posterior tibial nerve stimulation; µs: microseconds; Hz: hertz; min: minutes; PPTNS: percutaneous posterior tibial nerve stimulation; SNS: sacral nerve stimulation. *Physiotherapy Evidence Database (PEDro) scale.

With regard to prospective studies, stimulation was performed transcutaneously in six interventions ²⁰^,²²^,²⁴^,²⁷^,³⁰^,³⁴ and percutaneously in eleven ¹⁰^,²¹^,²³^,²⁵^,²⁶^,²⁸^,²⁹^,³¹^,³²^,³³^,³⁵. The duration of the intervention treatment was 1.5 to 26 months. The variability found in the frequency of the current application and current parameters was similar to that of RCT (Table 2).

Table 2 Characteristics of case series

TPTNS: transcutaneous posterior tibial nerve stimulation; µs: microseconds; Hz: hertz; min: minutes; PPTNS: percutaneous posterior tibial nerve stimulation. *Quality Assessment of Cases Series in accordance with the National Institute for Health and Care Excellence (NICE).

The RCTs that were included in this review obtained a mean score on the PEDro scale of 6.83 (SD = 1.17, maximum = 11), whereas the 17 prospective studies obtained an average of 4.29 (SD = 0.92, maximum = 8) points on the Quality Assessment for Cases Series scale. Contrary to transcutaneous treatments, the methodological quality of trials was a decisive factor for the effectiveness of percutaneous interventions. The RCT that obtained the lowest quality score also obtained the highest therapeutic effectiveness ¹⁹ (main bias in masking of subjects and therapists). In agreement with this, the case series with the lowest quality ²⁵^,²⁶ obtained a greater reduction in incontinence episodes compared to the best quality series.

A total of 1,262 subjects diagnosed with FI participated in the studies (131 males and 1,131 females), with an average age of 58.48 (SD = 3.32) years. The average sample size of the groups was 50.52 (SD = 55.05) (Table 1 and Table 2).

Measurement tools

The studies mainly assessed treatment effectiveness via a one-week diary for a self-reported stool data ⁸^,⁹^,¹⁰^,¹⁶^,¹⁷^,¹⁸^,¹⁹^,²¹^,²³^,²⁵^,²⁶^,²⁸^,²⁹^,³⁰^,,31,32,35), which international associations recommend for the evaluation of bowel habits ³⁶. This allows data of the total number of depositions, number of incontinence episodes (solid, liquid or gas), number of urge episodes or deferral time for deposition to be obtained.

The severity of FI focuses on two aspects: loss of fecal material and the mechanisms used for coping with it ³⁷. The Wexner Scale ²⁰^,²¹^,²²^,²⁷^,³¹^,³³^,³⁴^,³⁵, Cleveland Clinic Incontinence Scale (CCIS) ¹⁰^,¹⁶^,¹⁸^,¹⁹^,²³^,²⁴^,²⁶^,²⁸^,²⁹^,³² and St. Mark's continence Score ⁸^,⁹^,¹⁷^,³⁰ were used for the evaluation, all of which are validated ³⁸^,³⁹^,⁴⁰.

Quality of life was measured using three types of validated scales ⁴¹^,⁴²^,⁴³^,⁴⁴^,⁴⁵^,⁴⁷:

Generic: Short Form 36 Health Survey (SF-36) ⁸^,⁹^,¹⁷^,¹⁸^,¹⁹^,²⁶^,³⁰^,³⁴ and European Quality of Life-5 Dimensions Questionnaire (EQ-5D) ⁸^,¹⁸^,¹⁹.

Specialized: KESS Score ²⁴, Anxiety Depression Score ²⁴ and Hospital Anxiety and Depression Scale (HADS) (25).

Specific: Fecal Incontinence Quality of Life Scale (FIQOL) ⁸^,⁹^,¹⁶^,¹⁷^,¹⁹^,²¹^,²⁴^,²⁵^,²⁶^,²⁹^,³⁰^,³²^,³³^,³⁴^,³⁵, Gastrointestinal Quality of Life Index (GIQLI) ⁸ and International Consultation on Incontinence Questionnaire-Bowel Symptoms (ICIQ-BS) ⁸^,¹⁸^,²⁵.

Outcome evaluations were conducted in the short-term (< 3 months) ⁸^,¹⁰^,¹⁶^,¹⁷^,¹⁸^,²²^,²⁸^,²⁹^,³⁰, mid-term (3-6 months) ¹⁹^,²⁰^,²³^-²⁵^,³¹^,³³ and long-term (> 6 months) ²¹^,²⁶^,²⁷^,³²^,³⁴^,³⁵. The average follow-up time was 26.43 (SD = 23.95) weeks.

A qualitative review was performed, as the lack of homogeneity in therapeutic interventions and outcome measures among the different authors did not allow a quantitative review (meta-analysis) to be performed.

Treatment effectiveness

Incontinence episodes

Only two clinical trials ⁸^,⁹ performed interventions that obtained significant improvements in the short-term. Transcutaneous PTNS obtained a greater reduction in the number of weekly FI episodes (6.4) compared to percutaneous PTNS (2.3) or sham stimulation (1.8) (p = 0.044) ⁹, whereas percutaneous PTNS obtained a greater reduction compared to sham stimulation (2.5 vs 2.1, p = 0.021) ⁸ (Table 3). Three prospective studies ²⁹^,³⁰^,³² achieved significant results at 1.5 and 3 months post-intervention; one reported a total absence of urge FI episodes ²⁹ (Table 4). Only two prospective series observed significant results in the mid-term ²³^,²⁵; both achieved a complete lack of stool escape (Table 4).

Table 3 Treatment effectiveness. severity of incontinence and quality of life in randomized clinical trials

Values in italics have a p < 0.05 intra-group. FI: fecal incontinence; min: minutes; LS: lifestyle; B: behavior; D: depression; E: embarrassment; Ini: initial; FU: follow-up; PPTNS: percutaneous posterior tibial nerve stimulation; TPTNS: transcutaneous posterior tibial nerve stimulation; SNS: sacral nerve stimulation. *St. Mark's scale. †Wexner scale. ‡FIQL scale. §GIQLI scale.

Table 4 Treatment effectiveness and severity of incontinence in case series

Values in italics have a p < 0.05 intra-group. FI: fecal incontinence; min: minutes; Ini: initial; FU: follow-up; *St. Mark's scale; P: passive; U: urge; M: mixed; G: gas; L: liquid; S: solid.

In the long-term, only three prospective studies ²⁶^,³²^,³⁵ reported significant improvements. However, none of the patients attained a complete FI control (Table 4).

The success rate for a treatment is defined as a reduction of ≥ 50% in FI episodes as reported in the stool diary ¹². In this sense, only one RCT obtained significant short-term outcomes via transcutaneous stimulation ⁹.

Capability to delay the deposition

In the short-term, only one RCT ⁹ achieved significant improvements in the number of minutes of stool delay; transcutaneous PTNS was 4.8, percutaneous PTNS was 1.9 and sham stimulation was 0.4, p = 0.010 (Table 3), whereas three prospective studies ²⁰^,³⁰^,³² obtained significant delays of up to five minutes following the defecating stimulus (Table 4). In the mid-term, two non-randomized trials ²³^,³¹ obtained significant improvements by delaying deposition by four and two minutes respectively, compared to baseline values (Table 4). Finally, in the long-term, three cases series ²⁶^,³²^,³⁵ obtained significant defecation delays of 9, 3, and 9 minutes, respectively (Table 4).

Severity of fi

Overall, none of the included RCT had statistically significant outcomes with regard to the severity scales of FI. In the short term, seven prospective studies ²⁰^,²¹^,²⁴^,²⁶^,²⁸^,²⁹^,³²^{) o}btained significant values on the Wexner scale and one reduced severity of FI to half of the baseline values ²⁰. Hotouras et al. ²⁹ achieved a similar improvement for urge and mixed incontinence, but not for passive incontinence (Table 4). In the mid-term, seven cohort studies ²⁰^,²¹^,²⁴^,³¹^,³²^,³³^,³⁴ managed to significantly reduce FI levels and one ⁽²⁰⁾ obtained an improvement of > 75% compared to baseline values of FI severity (Table 4). In the long-term, four cases series ²⁶^,²⁷^,³⁴^,³⁵ reported substantial improvements; this reached 50% in two cases ²⁶^,³⁵ compared to the pre-intervention scores (Table 4).

Quality of life

Overall, no RCT obtained statistically significant results with regard to the quality of life scales specific for FI. In the short-term, seven prospective studies ²¹^,²⁴^,²⁶^,²⁹^,³⁰^,³²^,³⁴ observed significant increases in quality of life. However, only four ²¹^,²⁴^,²⁹^,³² achieved this in the four dimensions assessed by the scale: lifestyle, behavior, depression and embarrassment (Table 5). On the other hand, two studies ²⁴^,²⁵ found statistically significant improvements in quality of life in the mid-term. However, only in the dimensions of behavior and embarrassment in the first case and lifestyle in the second case (Table 5). Finally, five interventions ²¹^,²⁶^,³²^,³⁴^,³⁵ concluded their follow-up with significant outcomes in the long-term. Only three ²¹^,³²^,³⁵ achieved this in all the quality of life dimensions (Table 5).

Table 5 Quality of life in case series

Values in italics have a p < 0.05 intra-group. LS: lifestyle; B: behavior; D: depression; E: embarrassment; P: passive; U: urge; M: mixed. *ICIQ-BS scale.

Adverse effects

Of the 23 studies included in this review, seven did not report about adverse effects ¹⁰^,²²^,²⁷^,²⁸^,³⁰^,³¹^,³³ and six stated that there were no reported complications ¹⁷^,²⁰^,²¹^,²³^,²⁴^,³⁴. The remaining studies reported a series of secondary effects that did not stop the treatment, with the exception of one case of thrombophlebitis and cellulitis ³⁵. Irrelevant adverse effects included: local symptoms at the needle insertion point (light bleeding ⁹^,²⁹^,³², irritation ¹⁸, itching and stinging ¹⁶, discomfort ¹⁹, or pain ⁸^,²⁵⁾⁾; local symptoms in the lower limb (paresthesia ¹⁹ or tingling ²⁶⁾⁾ and remote symptoms in the abdomen (constipation ¹⁶, cramps ⁹, or stomach pain ²⁶⁾⁾.

DISCUSSION

Even if the effectiveness of PTNS for the treatment of an overactive bladder has been demonstrated ⁴⁸, its applicability for the treatment of FI is still under question ⁵^,¹¹. Overall, the reviewed studies reported positive outcomes in terms of the reduction of the number of incontinence episodes, increasing deferral time for deposition and improvements in FI severity and quality of life scales. However, only two RCTs achieved statistically significant changes ⁸^,⁹ in terms of treatment effectiveness and none achieved this in terms of FI severity or quality of life.

Treatment effectiveness

The success rate of the treatment is an outcome measure that few studies provide. This review shows slightly discordant results. While observational studies report improvements in ~60% of subjects after six weeks ²⁶^,³⁰, which further increased in the mid ²³ and long-term ²⁶, RCT studies conclude otherwise. Among the RCTs, only the study by George et al. ⁹ obtained significant differences using transcutaneous PTNS compared to sham stimulation; 81.8% of subjects experienced improvements in ≥ 50% of their symptoms. Neither of the two RCTs ⁸^,⁹ that assessed reductions of ≥ 50% of the symptoms reported significant changes with percutaneous PTNS.

The session frequency was one or two times per week, with the exception of Thomas et al. ³⁰ and Leroi et al. ¹⁶, who used one and two daily sessions, respectively. No significant differences were found when varying the frequency of sessions for the application of the technique.

On the other hand, studies show that PTNS reduces the number of incontinence episodes recalled in the stool diary. Prospective studies show several cases series with a considerable reduction in the weekly stool frequency ¹⁰^,²³^,²⁵^,²⁹^,³⁰^,³²^,³⁴^,³⁵. Only two studies did not observe a significant improvement ¹⁰^,³⁴. Along these lines, two RCTs obtained substantial improvements using both transcutaneous ⁹ and percutaneous ⁸ PTNS compared to placebo intervention, unlike the trial by Leroi et al. ¹⁶, who used surface electrodes. Furthermore, the evidence to determine whether the use of longer electrostimulation sessions ¹⁸ or a higher frequency of application ¹⁶^,⁴⁹ were more beneficial for the subject was inconclusive. In terms of deferral time for deposition, the outcomes achieved are in agreement with the reduction of incontinence episodes. In particular, those studies with significant reductions in the number of involuntary losses also achieved longer deferral lapses ⁹^,²³^,²⁶^,²⁹^,³⁰^,³²^,³⁵.

Severity of FI

The FI level, measured on both the Wexner and St. Mark's scales, decreased in clinical trials and non-controlled interventions. However, statistically significant differences were only found in prospective studies ²⁰^,²¹^,²⁴^,²⁶^,²⁷^,²⁸^,²⁹^,³¹^,³²^,³³^,³⁵ and some intra-class comparisons in RCTs ¹⁶^,¹⁷. Thus indicating the effectiveness of PTNS for the treatment of FI but not its superiority over sham stimulation in terms of severity scales.

Quality of life

Similarly to the FI severity outcome, both RCT and prospective studies obtained improvements in the quality of life scales, but statistical significance was only reached in non-controlled studies ²¹^,²⁴^-²⁶^,²⁹^,³⁰^,³⁴^,³⁵. Under equal conditions, lifestyle, behavior and embarrassment were the most frequently experienced improvements. The worst results were seen with the level of depression.

Current parameters for electrostimulation

While there appears to be an agreement on adjusting the pulse width to 200 µs, this is not the case for the current frequency, which varies between 10 and 20 Hz. All the included studies on percutaneous PTNS employed 20 Hz with one exception (8), whereas transcutaneous PTNS uses 10 Hz currents, so that all study arms are equally treated, with the exception of two studies that used 20 Hz ⁹^,²⁰. It must also be noted that all studies on percutaneous PTNS, except for Knowles et al. ⁸, used an Urgent PC(r) current generator. This only allows for the application of frequencies of 20 Hz, while transcutaneous PTNS used electrostimulation devices that allow frequency modulation. Knowles et al. ⁸ showed that when using a 10 Hz frequency for percutaneous PTNS, this significantly reduced the number of incontinence episodes. George et al. ⁹ also observed this whilst using 20 Hz currents for transcutaneous PTNS. In view of this, we consider that conducting controlled clinical trials will be of interest to compare the effectiveness of different frequencies of electrostimulation and determine their optimal values. For the same treatment effectiveness, a 10 Hz frequency is preferable over 20 Hz. The former produces a subtetanic contraction in the muscles innervated by the posterior tibial nerve and the latter, a tetanic contraction. It is important to remember that the purpose of this technique is neuromodulation at the level of the spinal cord and not boosting the flexor and abductor digitorum muscles.

Technique safety

The absence of reports on severe adverse effects corroborates the safety of PTNS for the treatment of FI. Furthermore, in its transcutaneous modality, this technique can be self-applied by patients at home. PTNS is objectively less invasive and more economical ¹⁰ compared to other neuromodulation techniques, such as sacral nerve stimulation. Thus, many authors recommend it as the first choice for the treatment of FI ⁵⁰.

This review included a greater number of RCTs and cases series than previous reports, which implies a greater sample size. On the basis of the studies reviewed, it also specifies the ideal parameters and scheduling in order to attain the best outcome. Nevertheless, the heterogeneity found in RCTs between the intervention and control groups does not allow for a quantitative synthesis of the results. Since a meta-analysis was not possible, the statistical assessment of the publication bias via an Egger test was not viable. This is important when valuing the outcome of this review. If such a bias existed, there would be a predominance of publications with favorable outcomes at the expense of less favorable ones. This would imply the overestimation of positive PTNS results.

The limitations of the present review include the heterogeneity among different studies, which hindered the performance of a meta-analysis. On the one hand, no homogeneity was found between researchers in terms of their choices for measuring and presenting outcomes or between intervention and control groups in RCTs. Finally, PTNS should be considered as the first choice for the treatment of FI instead of being used as a specialized treatment ¹. This is due to the positive results of PTNS in patients where previous conservative treatments have failed and also to its effectiveness and lack of adverse effects. Possible future lines of research should focus on the comparison of standard techniques versus neuromodulation as the initial FI treatment.

CONCLUSIONS

PTNS is an effective technique for the treatment of FI. Clinical trials and cases series achieved a reduction in the number of incontinence episodes and an increase in the deferral time for deposition. Improvements in the FI severity and quality of life scales were also achieved. A substantial superiority of transcutaneous versus percutaneous applications has not been observed. Interventions consisting of one or two weekly sessions of a 30-60 minute duration are optimal in order to obtain these results. Long-term treatments are required to achieve prolonged treatment effects.

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Received: April 18, 2017; Accepted: March 19, 2018

Correspondence: Asunción Ferri-Morales. Nursing and Physiotherapy School. Universidad de Castilla-La Mancha. Av. Carlos III, s/n. 45071 Toledo, Spain. e-mail: Asuncion.Ferri@uclm.es

Este es un artículo publicado en acceso abierto bajo una licencia Creative Commons