Simultaneous perineal ultrasound and vaginal pressure measurement prove the action of electrical pudendal nerve stimulation in treating female stress incontinence

Authors


Siyou Wang, Shanghai Research Institute of Acupuncture and Meridian – Clinical Research, 650 South Wanping Road, Shanghai 200030, China. e-mail: wangsiyou1234@163.com

Abstract

Study Type – Diagnostic (case series)

Level of Evidence 4

What's known on the subject? and What does the study add?

Pelvic floor muscle training (PFMT) and transvaginal electrical stimulation (TES) are two commonly used forms of conservative treatment for stress urinary incontinence (SUI). PFMT may build up the structural support of the pelvis, but many SUI patients are unable to perform PFMT effectively and its primary disadvantage is lack of long-term patient compliance. TES is a passive treatment that produces PFM contraction and patient compliance with it is good; however, its effect is not as good as that of PFMT when performed correctly.

Electrical pudendal nerve stimulation (EPNS) combines the advantages of PFMT and TES and incorporates the technique of deep insertion of long needles. In this study, simultaneous perineal ultrasound and vaginal pressure measurement prove that EPNS can contract the PFM and simulate PFMT. It is shown that EPNS is an alternative therapy for female SUI patients who fail PFMT and TES and the therapy can also be used for severe SUI.

OBJECTIVES

  • • To prove that electrical pudendal nerve stimulation (EPNS) can contract the pelvic floor muscles (PFM) and simulate pelvic floor muscle training (PFMT).
  • • To show that EPNS is an alternative therapy for female stress urinary incontinence (SUI) that does not respond effectively to PFMT and transvaginal electrical stimulation (TES).

PATIENTS AND METHODS

  • • Thirty-five female patients with SUI who did not respond effectively to PFMT and TES (group I) were enrolled and 60 other female patients with SUI were allocated to group II (30 patients) and group III (30 patients).
  • • Long needles were deeply inserted into four sacral points and electrified to stimulate the pudendal nerves. Group I and group II were treated by a doctor skilled in performing EPNS and group III, by a doctor unskilled in performing EPNS.
  • • When EPNS was performed in group I, perineal ultrasonographic PFM movements, vaginal pressure (VP) and PFM electromyography were recorded simultaneously.
  • • The therapeutic effects were evaluated according to objective and subjective criteria

RESULTS

  • • When EPNS was performed correctly, the patient felt strong PFM contractions. Simultaneous recordings in group I showed: B-mode cranio-caudal PFM movements; M-mode PFM movement curves (amplitude: about 1 mm, n= 31); a sawtooth curve of VP changes (2.61 ± 1.29 cmH2O, n= 34); and PFM myoelectric waves (amplitude: 23.9 ± 25.3 µV).
  • • If during the EPNS process the electric current was stopped or its intensity was reduced to about 7–12 mA or the two lower needles were drawn back, then the above ultrasonographic PFM movements and VP changes disappeared.
  • • In group I, the incontinence severity and quality of life score was 16.5 ± 4.0 before treatment and decreased to 4.2 ± 4.0 after 27.5 ± 11.9 sessions of treatment (P < 0.01). At the end of treatment, 100% improvement occurred in 16 cases (45.7%). A 2-year follow-up showed that 100% improvement occurred in 14 of cases (40.0%).
  • • In group II, the incontinence severity and quality of life score was 17.1 ± 6.3 before treatment and decreased to 3.5 ± 3.7 after 10 sessions of treatment (P < 0.01) and 100% improvement occurred in 12 cases (40.0%). In group III, the incontinence severity and quality of life score was 17.6 ± 6.3 before treatment and decreased to 10.8 ± 8.2 after 10 sessions of treatment (P < 0.01) and 100% improvement occurred in one case (3.3%).
  • • The post-treatment score was lower and the therapeutic effect was better in group II than in group III (both P < 0.01).

CONCLUSIONS

  • • EPNS can contract the PFM and simulate PFMT.
  • • EPNS is an alternative therapy for female SUI patients who fail PFMT and TES.
Abbreviations
SUI

stress urinary incontinence

PFMT

pelvic floor muscle training

PFM

pelvic floor muscle

TES

transvaginal electrical stimulation

EPNS

electrical pudendal nerve stimulation

PFMEW

pelvic floor myoelectric waves.

INTRODUCTION

Conservative therapy could be considered the treatment of choice for stress urinary incontinence (SUI) because it seems to have no adverse effects and causes significant and long-term improvement in symptoms [1]. Pelvic floor muscle training (PFMT) and electrical stimulation are two commonly used forms of conservative treatment for SUI [2].

PFMT improves the structural support of the pelvis [3]. However, many patients – especially women – have difficulty identifying and isolating their pelvic floor muscles (PFM) and are unable to perform the exercise effectively. Furthermore, patients who can identify the PFM often find that the required daily exercise routine is burdensome. Hence, the primary disadvantage of PFMT is lack of long-term patient compliance [4].

Electrical stimulation is a non-invasive, passive treatment that produces a muscle contraction [5]. Transvaginal electrical stimulation (TES) has almost no adverse effects and patient compliance in published reports is 70–85% [6]. TES will result in PFM contraction by indirect nerve stimulation [4], mainly by polysynaptic reflex responses [7]. The indirect stimulation and reflexive contraction may be the reason why the effect of electrical stimulation is not as good as that of PFMT when performed correctly [8].

By combining the advantages of PFMT (better effect) and TES (passive PFM contraction and good compliance) and incorporating the technique of deep insertion of long needles, we developed electrical pudendal nerve stimulation (EPNS). Our previous research has shown that this treatment has good short-term and long-term effects on female SUI [9]. The purpose of the present study is to use simultaneous records of PFM contraction (movement), vaginal pressure and pelvic floor surface electromyogram to prove that EPNS can contract the PFM and simulate PFMT, and so is an alternative therapy for women with SUI who do not respond effectively to PFMT and TES.

PATIENTS AND METHODS

Thirty-five female SUI patients (group I) with a mean age of 54.9 ± 9.7 years (28–73 years) and who had not responded effectively to PFMT and TES, were enrolled from May 2006 to April 2008. Sixty female SUI patients were enrolled from December 2008 to October 2010. Of these 60 patients, 30 with a mean age of 55.0 ± 10.6 years (35–72 years) were allocated to group II and 30 with a mean age of 57.9 ± 10.6 years (34–76 years) to group III on the basis of which doctor they visited (skilled or unskilled in performing EPNS). Inclusion criteria were SUI history, positive stress test result, urodynamically confirmed SUI and post-void residual urine volume <50 mL. Exclusion criteria were urge incontinence (overactive bladder or detrusor overactivity incontinence) and neurogenic bladder. Written informed consent was obtained from all participating women. The research protocol was approved by the medical ethical committee of Shanghai Yueyang Hospital of Traditional Chinese and Western Medicine.

The EPNS was performed as follows. The patient was placed in a prone position. Four sacral points (Fig. 1) were selected for deep insertion of long acupuncture needles (Suzhou Shenlong Medical Apparatus Factory, China). The two upper points are located by the two edges of the sacrum on a level with the fourth sacral foramina. On the upper points, a needle of 0.40 × 100 mm was inserted perpendicularly to a depth of 80–90 mm to produce a sensation referred to the urethra or the anus by stimulating the root of the pudendal nerve. The locations of the two lower points are about 1 cm bilateral to the tip of the coccyx. On the lower points, a needle of 0.40 × 100 or 0.40 × 125 mm was inserted obliquely towards the ischiorectal fossa to a length of 90–110 mm to produce a sensation referred to the urethra by stimulating the perineal nerve.

Figure 1.

Four sacral points.

After the sensation referred to the above regions was produced, each of two pairs of electrodes from a G6805-2 Multi-Purpose Health Device (Shanghai Medical Instruments High-Techno, China) was connected with the two ipsilaterally inserted needles with the anode to the upper needle and the cathode to the lower needle. The device was set to produce electrical stimulation (biphasic, 2 ms pulse duration) at a frequency of 2.5 Hz and an intensity (45–55 mA) as high as the patient could tolerate without discomfort. The electrostimulation was set for 60 min each time. Strong rhythmic and cephalad PFM contraction around the urethra must be kept during the entire electrostimulation. Groups I and II were treated by a doctor skilled in performing EPNS and group III was treated by a doctor unskilled in performing EPNS. Patients in groups II and III did not know which doctor's treatment they received. The treatment was given three times a week and stopped after the symptoms disappeared or did not improve further for 2 weeks. Patients in groups II and III received at least 10 treatment sessions.

The evaluation of therapeutic effects was based on objective criteria: stress test and pad test; and subjective criteria: a questionnaire to measure the severity of symptoms and the quality of life in SUI women [10]. After treatment, cure (100% improvement) was defined as a negative stress test, negative pad test and a decrease of 100% in incontinence severity and quality of life score on the questionnaire. Marked improvement was defined as a decrease of 75 to <100% in the incontinence score and improvement was defined as a decrease of 50–75% in the incontinence score. The questionnaire was filled out by group I patients after completion of the treatment and by groups II and III patients after 10 treatments. A stress test and a pad test were then conducted.

Simultaneous measurements were made in group I. A urodynamic instrument with video suite (Medtronic Duet Encompass; Medtronic, Minneapolis, MN, USA) was used.

Contraction of the PFM was visualized by transperineal ultrasound. An ultrasound device (GE Medical Systems LOGIC 180; Milwaukee, WI, USA) with a 6.5-MHz curved-array transducer was connected to the urodynamic instrument. Transperineal imaging was performed with the ultrasound transducer placed in the mid-sagittal plane at the perineum to clearly visualize the vaginal canal and PFM movements. An M-mode line was placed at the most obvious PFM movements on the B-mode image for M-mode recording of PFM contractions.

Vaginal pressure (VP) was measured by a balloon catheter (Medtronic; balloon size 11/55 mm) connected to a pressure transducer of the instrument. The middle of the balloon was located 3.5 cm from the introitus.

Pelvic floor surface electromyography was performed with an anal sponge electrode (Medtronic) connected to the instrument (skin-surface electrodes (Medtronic) were used in patients with serious haemorrhoids and were placed beside the perineum).

To prove that correctly performed EPNS can contract the PFM well, simultaneous recordings were also obtained under three conditions in the process of EPNS: stopping electrical stimulation; reducing the intensity of electrical stimulation; and drawing back the two lower needles 1–2 cm.

Statistical analysis of the data was performed using SPSS 17.0 (SPSS Inc., Chicago, IL, USA). Student's t test was used to compare ages between groups II and III, and VP amplitudes between the patients with ≥1 mm PFM movement amplitudes and those with <1 mm. A Wilcoxon signed rank test was used to compare pre-treatment and post-treatment incontinence severity and quality of life scores in the three groups. A Mann–Whitney U test was used to compare the pre-treatment scores (baseline), the post-treatment scores and the therapeutic effects between groups II and III. All reported P values were two-sided, and confidence intervals were at the 95% level. P < 0.05 was considered statistically significant.

RESULTS

When EPNS was performed correctly, the patient felt strong rhythmic and cephalad PFM contractions around the urethra without discomfort. When this occurred, simultaneous measurements in group I showed: (i) cranio-caudal PFM movements on the B-mode image; (ii) M-mode curves indicating the PFM contractions (Fig. 2, upper image, amplitude: about 1 mm, n= 31; in the other four patients, the M-mode curves were not obvious); (iii) a sawtooth curve of VP changes (green a–b period in Fig. 2A, amplitude: 2.61 ± 1.29 cmH2O (range 0.7–5.9 cmH2O, n= 34); in the other patient, the sawtooth curve was not obvious); and (iv) pelvic floor myoelectric waves (PFMEWs) (red a–b period in Fig. 2A, amplitude: 23.9 ± 25.3 µV (range 5–96 µV), n= 34). The VP amplitude was significantly larger in 14 patients with ≥1 mm PFM movement amplitude (3.34 ± 1.44 cmH2O) than in 17 patients with <1 mm (2.11 ± 0.92 cmH2O) (P < 0.01) (Table 1).

Figure 2.

Simultaneous measurements. V = vagina, m = M-mode line, M = M-mode image, t = the time corresponding to the image (t in A to the upper image; t in B, C and D to the lower image).

Table 1. Relationship between pelvic floor muscle movement amplitude and vaginal pressure amplitude
Pelvic floor muscle movement amplitudeVaginal pressure amplitude
  • *

    P < 0.01 in comparison with <1 mm amplitude.

<1 mm (n= 17)2.11 ± 0.92
≥1 mm (n= 14)3.34 ± 1.44*

However, if the electric current was stopped in the process of EPNS, the patient did not feel PFM contraction and the simultaneous measurement showed the disappearances of B-mode PFM movements, M-mode curves (Fig. 2 lower image), sawtooth VP changes (green b–c period in Fig. 2B) and PFMEWs (red b–c period in Fig. 2B). If the current intensity was reduced to 7–12 mA in the process of EPNS, the patient only felt very weak peri-urethral PFM contractions and the simultaneous measurements showed that B-mode PFM movements, M-mode curves (Fig. 2 lower image) and sawtooth VP changes (green b–c period in Fig. 2C) disappeared and PFMEWs became very small but still existed (red b–c period in Fig. 2C). When the current intensity was not changed but the two lower needles were gradually drawn back until the tips were 1–2 cm away from the original positions, the patient felt gradual weakening to disappearance of peri-urethral PFM contractions. Instead, the patient felt gluteal contractions. In this circumstance, the simultaneous measurements showed that B-mode PFM movements, M-mode curves (Fig. 2 lower image) and the sawtooth VP curve (green b–c period in Fig. 2D) also became less obvious until they finally disappeared. However, PFMEWs did not decrease (red b–c period in Fig. 2D). If the current, its intensity or the positions of the needle tips were restored to their original settings, all simultaneous measurements returned to the originals also (green and red c–d periods in Fig. 2B–D).

In group I, the duration of incontinence was 74.1 ± 45.6 (range 12–240) months. Incontinence severity and quality of life score was 16.5 ± 4.0 (range 7–24, full score 28, ≥21 in seven women) before treatment and decreased to 4.2 ± 4.0 (range 0–20) after 27.5 ± 11.9 (range 3–60) sessions of treatment (P < 0.01). Three patients discontinued treatment early: two were treated three times (the scores decreased from 12 to 4 and from 22 to 11, respectively) and one was treated nine times (her score decreased from 16 to 7). At the end of treatment, cure occurred in 16 cases (45.7%; pre-treatment score ≥21 in three cases), marked improvement in four cases (11.4%; pre-treatment score ≥21 in two cases) and improvement in 10 cases (28.6%; pre-treatment score ≥21 in two cases); the ≥50% improvement rate was 85.7% (Table 2). A 2-year follow-up of group I showed that cure occurred in 14 cases (40.0%), marked improvement in three cases (8.6%) and improvement in five cases (14.3%); the ≥50% improvement rate was 62.9% (Table 2).

Table 2. The pre-treatment (Pre-T) score, the post-treatment (Post-T) score and effect, and the follow-up (F-up) therapeutic effect in group I (n= 35)
ScoreTherapeutic effect
100% improvementMarked improvementImprovement
Pre-TPost-TPost-T n (%)F-up n (%)Post-T n (%)F-up n (%)Post-T n (%)F-up n (%)
  • *

    P < 0.01 in comparison with the pre-treatment score.

16.5 ± 4.04.2 ± 4.0*16 (45.7)14 (40.0)4 (11.4)3 (8.6)10 (28.6)5 (14.3)

There were no significant differences in the age and pre-treatment score between group II and group III (both P > 0.05). In group II incontinence severity and quality of life score was 17.1 ± 6.3 (range 6–28, ≥21 in 12 cases) before treatment and decreased to 3.5 ± 3.7 (range 0–15) after 10 sessions of treatment (P < 0.01), and 100% improvement occurred in 12 cases (40.0%; pre-treatment score ≥21 in seven cases), marked improvement in four cases (13.3%; pre-treatment score ≥21 in one case) and improvement in 12 cases (40.0%; pre-treatment score ≥21 in four cases), with a ≥50% improvement rate of 93.3%. In group III, incontinence severity and quality of life score was 17.6 ± 6.3 (range 6–28) before treatment and decreased to 10.8 ± 8.2 (range 0–28) after 10 sessions of treatment (P < 0.01), and 100% improvement occurred in one case (3.3%), marked improvement in four cases (13.3%) and improvement in 11 cases (36.7%), with a ≥50% improvement rate of 53.3%. The post-treatment score was lower and therapeutic effect was better in group II than in group III (both P < 0.01) (Table 3; Fig. 3).

Table 3. Comparisons of the pre-treatment scores, the post-treatment scores and the therapeutic effects between groups II and III
 ScoreTherapeutic effect, n (%)
Pre-TPost-T100% improvementMarked improvementImprovement
Group II (n= 30)17.1 ± 6.33.5 ± 3.712 (40.0)4 (13.3)12 (40.0)
Group III (n= 30)17.6 ± 6.310.8 ± 8.21 (3.3)4 (13.3)11 (36.7)
P value>0.05<0.01<0.01
Figure 3.

Flow diagram of the patients through the stages of this study.

DISCUSSION

The site beside the sacral edge on a level with the fourth foramen is where the root of the pudendal nerve passes, so the body surface over it (the upper point) was selected for deep perpendicular insertion of a long needle. Because the pudendal nerve contains sensory fibres innervating the external genitalia and anus, the sensation is referred to the urethra or anus during needle insertion. In the ischiorectal fossa, the pudendal nerve branches into (i) the perineal nerve innervating the external urethral sphincter (including the sphincter urethra, compressor urethra and urethrovaginal sphincter, namely deep transverse perineal muscles), part of the levator ani muscle, the superficial perineal muscles and the skin of the labium majus and (ii) the dorsal nerve of the clitoris innervating the skin of the clitoral shaft. Therefore, the sensation is only referred to the urethra when a long needle is inserted beside the tip of the coccyx laterally towards the ischiorectal fossa to make the needle tip reach the perineal nerve, and strong rhythmic and cephalad peri-urethral PFM contractions are felt when strong electrical stimulation is provided. Sensation is subjective, however, and objective evidence is needed for validation. For this reason the simultaneous measurements were performed.

Perineal B-mode ultrasonography can visualize PFM contractions [11] and the M-mode can show the curve and amplitude of its contraction. When EPNS was provided, the ultrasonic image showed cranio-caudal PFM contractions with an amplitude of about 1 mm (>0 but <2 mm), indicating that this treatment can exactly contract the PFM. Owing to the limitation of the precision of the instrument (1 mm), we could not calculate the mean and standard deviation of the amplitudes. The PFM contraction amplitude measured using transperineal ultrasound during EPNS in our study is similar to that during PFMT in the study by Thompson et al. [11], indicating that this treatment can simulate PFMT. The vagina is surrounded by the PFM and PFM contraction will compress it [12]. Therefore, VP changed with rhythmic PFM contractions and a sawtooth curve of its changes was recorded. This also explains why VP amplitude was significantly larger in the patients with ≥1 mm PFM movement amplitude than in the patients with <1 mm.

When the current intensity was not changed but the two lower needles were gradually drawn back until the tips were 1–2 cm away from their original positions but still in the pelvic region, the patient felt gradual weakening (up to disappearance) of peri-urethral PFM contractions and instead felt gluteal contractions. The simultaneous measurements showed that B-mode PFM movements, M-mode curves and the sawtooth VP curve also became less and less obvious and finally disappeared. When the positions of the needle tips were restored, the patient's sensation and the simultaneous records returned to their original levels, indicating that the correct position of the needle tip was very important. Only if the needle tip was very close to the pudendal nerve could the PFM contract most effectively. Because the current intensity was not changed during the withdrawal of the needle tips, PFMEWs did not decrease. When the electric current was stopped or the current intensity was reduced, all B-mode PFM movements, M-mode curves and sawtooth curve of VP changes disappeared. This indicates that strong electrical stimulation is needed for effective PFM contraction.

Modern exercise science provides an excellent foundation for understanding PFMT in the context of strength training. PFM strength training (contraction) builds up long-lasting muscle volume and so provides structural support for the pelvis. This theory explains the effectiveness of PFM training for SUI. To date there are randomized controlled trials and basic anatomy studies to support this theory [3]. Therefore, it can be concluded that any therapy (including electrical stimulation) that can contract the PFM effectively can be used to treat female SUI. In this study, simultaneous measurements have shown the mode of therapeutic action of EPNS on SUI, that is, it can contract the PFM and simulate PFMT. We developed EPNS because we clinically found that many of female SUI patients, especially those who were perimenopausal or menopausal, failed to respond effectively to PFMT and TES. We describe the reasons in this paper. We enrolled women for whom PFMT and TES failed as subjects in this study because we hoped that EPNS (combining the advantages of PFMT and TES) could become an alternative therapy for them.

To exclude the placebo effect of an instrumental procedure using deeply inserted needles in EPNS, we compared the therapeutic effect of EPNS performed by a skilled doctor (group II) with that of EPNS performed by an unskilled doctor (group III) in the treatment of female SUI. The results showed that after 10 treatments, the effect was significantly better in group II (a 100% improvement rate of 40.0% and a ≥50% improvement rate of 93.3%) than in group III (a 100% improvement rate of 3.3% and a ≥50% improvement rate of 53.3%), indicating that the placebo effect of EPNS is not predominant and the therapeutic effect depends mainly on the correct performance of EPNS. The reason why the 100% improvement rate was lower in group III is that a doctor unskilled in performing EPNS is often unable to place the needle tip very close to the pudendal nerve, which will affect effective PFM contraction.

In group I, a 100% improvement rate of 45.7% and a ≥50% improvement rate of 85.7% at the end of treatment showed that EPNS has a good therapeutic effect on women with SUI who do not respond effectively to PFMT and TES and is an alternative therapy for these women. A 100% improvement rate of 40.0% and a ≥50% improvement rate of 62.9% at the 2-year follow-up show that EPNS also has a good long-term effect. Of 19 patients with pre-treatment scores ≥21 in groups I and II, cure occurred in 10 cases, marked improvement in three cases and improvement in six cases after treatment, indicating that EPNS can also be used for severe SUI. Slight discomfort during insertion of needles and no discomfort during stimulation make EPNS well tolerated by patients. This therapy deserves further clinical study.

ACKNOWLEDGEMENTS

This research was funded by the Shanghai leading academic discipline project (S30304); the Shanghai Municipal Science and Technology Commission (09dZ1974900); and the National Basic Research Program of China (9732 program: No. 2009CB522900).

CONFLICT OF INTEREST

None declared.

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