Short-term clinical and manometric outcomes of percutaneous tibial nerve stimulation for faecal incontinence: a large single-centre series.

BACKGROUND: Faecal incontinence (FI) is common, with a significant impact on quality of life. Percutaneous tibial nerve stimulation (PTNS) is a therapy for FI; however, its role has recently been questioned. Here we report the short-term clinical and manometric outcomes in a large tertiary centre. METHODS: A retrospective review of a prospective PTNS database was performed, extracting patient-reported FI outcome measures including bowel diary, the St Marks's Incontinence Score (SMIS) and Manchester Health Questionnaire (MHQ). Successful treatment was > 50% improvement in symptoms, whilst a partial response was 25-50% improvement. High-resolution anorectal manometry (HRAM) results before and after PTNS were recorded. RESULTS: Data were available from 135 patients [119 (88%) females; median age: 60 years (range: 27-82years)]. Overall, patients reported a reduction in urge FI (2.5-1) and passive FI episodes (2-1.5; p < 0.05) alongside a reduction in SMIS (16.5-14) and MHQ (517.5-460.0; p < 0.001). Some 76 (56%) patients reported success, whilst a further 20 (15%) reported a partial response. There were statistically significant reductions in rectal balloon thresholds and an increase in incremental squeeze pressure; however, these changes were independent of treatment success. CONCLUSION: Patients report PTNS improves FI symptoms in the short term. Despite this improvement, changes in HRAM parameters were independent of this success. HRAM may be unable to measure the clinical effect of PTNS, or there remains the possibility of a placebo effect. Further work is required to define the role of PTNS in the treatment of FI.

Placement of a fine-bore rectal balloon catheter in the anal canal does not affect anal sphincter pressures: improving our understanding of physiological function with anal acoustic reflectometry.

AIM: The recto-anal inhibitory reflex (RAIR) is currently measured using anorectal manometry catheters, which may distort the anal canal. Anal acoustic reflectometry (AAR) is considered a catheter-free technique for evaluating the physiological function of the anal canal; however, it has yet to be used to elicit the RAIR. For the RAIR to be measured with AAR, the effect of placing an additional rectal balloon catheter on the measured AAR parameters needs to be investigated: that is the aim of this work. METHOD: Patients aged over 18 years attending hospital for the investigation of pelvic floor disorders were included. AAR parameters were obtained before and after a rectal balloon catheter was placed alongside the AAR catheter. The following parameters were measured: opening pressure (Op, cmH2 O), opening elastance (Oe, cmH2 O/mm2 ), closing pressure (Cp, cmH2 O), closing elastance (Ce, cmH2 O/mm2 ), hysteresis (Hys, %), squeeze opening pressure (SqOp, cmH2 O) and squeeze opening elastance (SqOe, cmH2 O/mm2 ). RESULTS: Thirty-five patients were included in the analysis, of whom 28 were women. The median age was 58 years. Comparison of median AAR parameters before and after catheter placement showed no significant difference: Op (36.36 vs 33.42, P = 0.09), Oe (1.27 vs 1.39, P = 0.19), Cp (18.62 vs 19.73, P = 0.13), Ce (1.2 vs 1.28, P = 0.33), Hys (41.08 vs 40.11, P = 0.17), SqOp (81.85 vs 81.65, P = 0.93) and SqOe (1.44 vs 1.49, P = 0.55). DISCUSSION: Placement of a rectal balloon catheter alongside the AAR catheter has no significant effect on the measured AAR parameters. The results of this study add to the fundamental basic science and understanding of the physiological function of the anal canal.

A novel method for measurement of the recto-anal inhibitory reflex using anal acoustic reflectometry.

AIM: The recto-anal inhibitory reflex (RAIR) is currently measured using manometry catheters, which potentially distort the anal canal. Anal acoustic reflectometry (AAR) is considered to be a catheter-free technique and primarily measures the function of the internal anal sphincter. We sought to determine if RAIR could be measured using AAR. METHOD: Patients aged 18 and over attending the hospital for investigation of pelvic floor dysfunction were included. AAR parameters were obtained before (prerectal distension) and after (postrectal distension) inflation of a rectal balloon catheter with 100 ml of air. Minimum opening pressure (Op, cmH2 O), opening elastance (Oe, cmH2 O/mm2 ), closing pressure (Cp, cmH2 O), closing elastance (Ce, cmH2 O/mm2 ) and hysteresis (Hys, %) were recorded. The presence of RAIR was defined by a reduction of prerectal distension Op by 20% or more. RESULTS: Thirty-two patients were included, 26 of whom were women. The mean age of patients was 57.5 years (SD 11.3 years). Nine patients had faecal incontinence, six patients had obstructive defaecation and 17 patients had both. RAIR was seen in 30/32 patients. The mean reduction in Op was 58.8% (range -59.18% to 100%). Three patients had 100% reduction. Comparison of pre- and post-RAIR parameters showed a significant difference in Op (34.44 vs 15.41, P < 0.0001), Oe (1.39 vs 1.1, P = 0.004), Cp (20.06 vs 8.00, P < 0.0001) and Ce (1.31 vs 1.13, P < 0.0001) but not Hys (39.71 vs 39.90, P = 0.88). CONCLUSION: We describe a novel method for the measurement of RAIR. Rectal distension appears to alter resting pressure and the resistance of the anal canal to opening and closing, with complete inhibition of the sphincter complex in three patients.

Anal acoustic reflectometry predicts the outcome of percutaneous nerve evaluation for faecal incontinence.

BACKGROUND: Sacral nerve stimulation (SNS) is effective for some patients with faecal incontinence. Before insertion of a costly implant, percutaneous nerve evaluation (PNE) is undertaken to identify patients likely to report success from SNS. The aim of this study was to determine whether variables of anal sphincter function measured by anal acoustic reflectometry (AAR) could predict the outcome of PNE for faecal incontinence. METHODS: Women with faecal incontinence undergoing PNE were recruited. AAR, followed by anal manometry, was performed on the day of surgery, immediately before PNE. The outcome of PNE was determined by bowel diary results and incontinence severity score. Patients with a successful PNE outcome were compared with those with an unsuccessful outcome; logistic regression analysis was used to identify any independent predictors of success. RESULTS: Fifty-two patients were recruited, of whom 32 (62 per cent) had a successful PNE outcome and 20 (38 per cent) an unsuccessful outcome. The AAR variable opening pressure was significantly greater in patients who subsequently had a successful PNE result compared with the pressure in patients who did not (28 versus 17 cmH2 O; P = 0·008). No difference was seen in the manometric equivalent, maximum resting pressure. Opening pressure was an independent predictor of success with an odds ratio of 1·08 (95 per cent confidence interval 1·01 to 1·16; P = 0·018). CONCLUSION: AAR is a sensitive test of sphincter function and can identify differences between patients who respond to PNE and those who do not. Opening pressure is an independent predictor of success in PNE, and may be of value in the selection of patients for this expensive treatment option.

Compound muscle action potential of the external anal sphincter.

AIM: Pudendal nerve terminal motor latency (PNTML) assesses distal innervation of the external anal sphincter (EAS) but it is insensitive to early nerve damage. We propose to extend the assessment of PNTML to the measurement of the compound muscle action potential (CMAP) of the EAS to understand its progressive denervation. METHOD: Ninety women with faecal incontinence were prospectively examined and compared with 36 asymptomatic women who acted as controls. PNTML was performed bilaterally and the muscle response analysed for CMAP to include amplitude, area and duration. Anorectal manometry was measured by a station-pull technique using a water-filled microballoon. spss version 11.5 was used for statistical analysis. RESULTS: In asymptomatic women the CMAP on the left side was greater in nulliparous (n = 7) than parous (n = 27, P < 0.05) individuals. There was a positive correlation with maximum squeeze pressure and area on the left side (P < 0.05, r = 0.397). In women with faecal incontinence, CMAP on the left side had a negative correlation with age (n = 75, P < 0.05), there was no correlation with parity or anorectal manometry. Nulliparous asymptomatic women had a greater CMAP (P < 0.05) on the left side than asymptomatic parous women and parous women with faecal incontinence. Right-side measurements were not conclusive. CONCLUSION: Compound muscle action potential demonstrated progressive denervation with age in women with faecal incontinence but did not reliably identify early signs of denervation in asymptomatic women. The area on the left side related to muscle function in asymptomatic women but not in women with faecal incontinence. CMAP can distinguish between parous women with faecal incontinence and nulliparous asymptomatic women but is not a useful test of function of the EAS.

Comparative study of anal acoustic reflectometry and anal manometry in the assessment of faecal incontinence.

BACKGROUND: Anal acoustic reflectometry (AAR) is a reproducible technique providing a novel physiological assessment of anal sphincter function. It may have advantages over conventional anal manometry. The aims of this study were to determine the ability of AAR and anal manometry to identify changes in anal sphincter function in patients with faecal incontinence (FI) and to relate these changes to the severity of FI. METHODS: Women with FI underwent assessment with AAR and anal manometry. All patients completed the Vaizey FI questionnaire and were classified according to symptom type (urge, passive or mixed) and integrity of the anal sphincters. The ability of AAR and anal manometry to correlate with symptom severity was evaluated. AAR was compared with anal manometry in detecting differences in anal sphincter function between symptomatic subgroups, and patients with and without a sphincter defect. RESULTS: One hundred women with FI were included in the study. The AAR variables opening pressure, opening elastance, closing elastance and squeeze opening pressure correlated with symptom severity, whereas the manometric measurements maximum resting pressure and maximum squeeze pressure did not. Unlike anal manometry, AAR was able to detect differences in anal sphincter function between different symptomatic subgroups. [corrected]. An anal sphincter defect was not associated with a significant change in anal sphincter function determined by either AAR or anal manometry. CONCLUSION: In the assessment of women with FI, AAR variables correlated with symptom severity and could distinguish between different symptomatic subgroups. AAR may help to guide management in these patients.

Fatigue rate of the external anal sphincter.

AIM: Studies of skeletal muscle show that fatigue rate corresponds to the proportion of fast-twitch and slow-twitch fibres that are present in the muscle. Limited work has been done on the fatigue rate of the external anal sphincter. We have prospectively studied fatigability of the external anal sphincter in women with faecal incontinence and women with normal bowel control. METHOD: Anorectal manometry was measured by a station-pull technique using a water-filled microballoon. Fatigue rate was calculated from anal pressure measurements taken every 0.1 s over a 20-s squeeze. RESULTS: Women with faecal incontinence (n=88, median -12 cmH(2) O/min) were less susceptible to fatigue than women with normal bowel control (n=36, median -43 cmH(2) O/min) (P<0.01). The external anal sphincter was less susceptible to fatigue with increasing age (P<0.01, r=0.499). In women with normal bowel control and in women with faecal incontinence fatigue rate was negatively correlated with maximum squeeze pressure (P<0.01, r=-0.287; P<0.01, r=-0.579). CONCLUSION: The external anal sphincter was less susceptible to fatigue with increasing age. Women with faecal incontinence have a weaker but more fatigue-resistant external anal sphincter. This might correspond to a higher proportion of slow-twitch muscle fibres. Histological studies are needed to examine this hypothesis.

Insertion under local anaesthetic of temporary electrodes for sacral nerve stimulation testing is reliable and cost effective.

AIM: The aim of this study was to determine whether temporary electrode implantation under local anaesthesia (LA), with reliance on sensory response rather than motor response, gives as good a result as implantation under general anaesthesia (GA). METHOD: A retrospective review of a prospectively maintained database of patients with faecal incontinence treated with sacral nerve stimulation (SNS) was performed. RESULTS: A total of 111 consecutive patients underwent a 2-week trial of SNS. Forty-seven (42%) had the temporary electrode implanted under LA and 64 (58%) under GA. There was no significant difference between the two groups in relation to the improvement in Vaizey score (P = 0.15), incontinent episodes per day (P = 0.73) and incontinent episodes per week (P = 0.93). There was no significant difference (P = 0.14) in the percentage of successful trials between the LA group (64%) and the GA group (77%); however, only 62% of the GA group were discharged home on the same day when compared with 89% of the LA group (P < 0.0001). CONCLUSION: Similar success rates for temporary trial with SNS can be achieved with LA and GA. Insertion under LA is associated with reduced cost, shorter hospital stay and quicker recovery, and it avoids the risk of general anaesthesia.

Anal acoustic reflectometry: a new technique for assessing anal sphincter function.

OBJECTIVE: Anal acoustic reflectometry (AAR) is a new technique that offers an assessment of anal sphincter function by the measurement of additional parameters not available with conventional manometry. The aim of this study is to describe the technique, methodology and initial pilot study results. METHOD: Wideband sounds (100 Hz to 16 kHz) are transmitted into a thin polyurethane bag placed within the anal canal. Calculation of cross-sectional area from reflected sound waves, over a range of pressures (0-200 cm H(2)O) during inflation/deflation of the bag, results in five physiological parameters of anal canal function. Five patients [three continent (two female) and two incontinent (both female)] were assessed with AAR and anal manometry. RESULTS: Anal acoustic reflectometry parameters were reduced in incontinent when compared with continent patients. Resting Opening Pressures (cmH(2)O) were 27 and 16 in patients with faecal incontinence (FI) vs 44 and 72 in continent patients; Resting Opening Elastance (cmH(2)O/mm(2)) was 0.88 and 1.08 in FI patients vs 1.65 and 1.34 in continent patients. The Resting Opening Pressure of a similarly aged continent male (55 cmH(2)O) was greater than three of the females. During assessment of voluntary contraction (one FI female vs one continent female), Squeeze Opening Pressure (cmH(2)O) was 31 vs 100 and Elastance (cmH(2)O/mm(2)) 0.61 vs 2.07. CONCLUSION: Anal acoustic reflectometry appears to be promising technique. Further work is in place to clarify whether it will be useful in clinical assessment of incontinent patients.

Changes in fatigability of the striated anal canal after childbirth.

AIM: Anal manometry is an established assessment tool for patients with faecal incontinence. Fatigue rate index (FRI) has been shown to discriminate between symptomatic patients and controls. The aim of this study was to compare manometry and fatigability of the anal canal in nulliparous women before and after childbirth. METHOD: An air-filled manometry device was used to record maximum resting and squeeze pressures, fatigue rate (recorded over 20 s) and FRI. Recordings were made before and after vaginal delivery. RESULTS: Nineteen women were studied. Resting anal canal pressure was not significantly different before and after delivery (57.1 +/- 13.6 vs 51.1 +/- 11.9 cmH(2)O, P = 0.1). Squeeze pressure was significantly lower postpartum (106.5 +/- 43.6 vs 75.5 +/- 45.6 cmH(2)O, P < 0.001). Fatigue rate was significantly reduced postpartum (-129.5 +/- 74.7 vs-76.1 +/- 54.8 cmH(2)O/min, P = 0.001), but FRI was not significantly altered (1.23 +/- 1.49 vs 1.41 +/- 1.27 min, P = 0.09). CONCLUSION: Maximal squeeze pressure and fatigue rate of the anal canal are significantly reduced after childbirth. Resting anal canal pressure and FRI are not significantly different.

Programming InterStim for faecal incontinence.

OBJECTIVE: Sacral nerve stimulation (SNS) for faecal incontinence (FI) is achieved by implanting a pulse generator attached to a tined lead with individually programmable electrodes. Our aim was to establish whether the 'ideal' programme for the treatment of FI has been used most commonly. We also wished to determine whether re-programming changed the symptom severity scores. METHOD: The following data were extracted from our SNS patient database: the frequency with which each programme was used, the length of time it was effective for, the number of months from implantation that the programme was started and the symptom severity scores prior to a change or no change in programme. RESULTS: Thirty-eight patients have had implanted pulse generators inserted since 2004. One hundred and two programme changes were documented in the database. The 'ideal' programme was not most commonly programmed. The common programmes were effective for longest. The electrode furthest from the tip was used in the initial programme only once and the median duration from implantation to the start of a programme including it is 13 months. Symptom severity scores were significantly higher in patients who required re-programming than in those whose programme remained unchanged. CONCLUSIONS: In our patients the 'ideal' programme was not the programme used most frequently, nor for the longest duration. The theoretical migration of the tined lead inwards with time is upheld by our results. Patients who feel the sensation of SNS perianally have lower symptom scores than those who do not and who require re-programming.

Investigation of stimulus position in the production of the strength duration curve of the external anal sphincter muscle in women with anorectal dysfunction.

OBJECTIVE: The strength duration test (SDT) is a minimally invasive test of the innervation of a muscle and has been successfully adapted for use on the external anal sphincter (EAS). The SDT has previously been performed on the EAS placing a stimulating probe in the 3 o'clock position. The aim of this study was to determine whether there was any variation in the strength duration curves (SDC) produced at different positions around the EAS. PATIENTS AND METHODS: Thirty-one patients with anorectal dysfunction attended our Institution for Anorectal Physiology Studies and were recruited to the study. After undergoing anal manometry, pudendal nerve terminal motor latency measurement and endoanal ultrasonography, the SDT was performed in four stimulus positions (3, 6, 9 and 12 o'clock). The sequence of positions was randomly selected. RESULTS: Four SDCs were obtained successfully in 25 patients. There was no significant difference seen between the four positions at the longer current durations (1-100 ms). Significant differences occurred at the shortest current durations (0.3 and 0.1 ms) when comparing adjacent stimulus positions except between the 6 and 9 o'clock positions, which were comparable. When opposing positions were compared (3-9 and 6-12 o'clock) at these short durations no significant difference was found. CONCLUSION: There was no significant difference between the SDC produced at 3 and 9 o'clock. These positions closely correspond to where the pudendal nerves enter the EAS. It therefore appears acceptable to perform the SDT in either of these positions, though 3 o'clock remains our preferred position.

Sacral nerve stimulation reduces corticoanal excitability in patients with faecal incontinence.

BACKGROUND: Sacral nerve stimulation (SNS) can produce symptomatic relief in patients with faecal incontinence. Moreover, peripheral nerve stimulation has been shown to affect brain function. The aim of this study was to determine whether SNS might produce important changes in cortical activity linked to improved continence. METHODS: In an experimental study, ten women with intractable faecal incontinence (mean age 51.3 years) were serially mapped with transcranial magnetic stimulation before and immediately after 14 days of temporary SNS (15 Hz, pulse width 210 micros), and then 2 weeks later. Anal sphincter electromyographic responses were recorded to cortical stimulation of multiple points over a scalp grid covering the bilateral medial cortex. Continence scores, anorectal manometry and rectal sensitivity data were also collected. RESULTS: SNS improved global symptom scores in the majority of patients; mean(s.e.m.) continence scores fell from 16.9(1.6) to 10.6(1.8) (P = 0.042). Cortical mapping showed a consistent decrease in corticoanal representation and overall excitability immediately after SNS compared with baseline (mean(s.e.m.) 38,083(13,669) versus 42,507(13,297) microV s; P = 0.017), which was reversed 2 weeks after SNS wire removal. CONCLUSION: SNS produces symptom benefit in patients with faecal incontinence that is associated with a reversible reduction in corticoanal excitability. SNS therefore drives dynamic brain changes that may play a functional role in influencing anal continence.

Routine symptom screening for postnatal urinary and anal incontinence in new mothers from a district.

Parous middle-aged women present with urinary and faecal incontinence and childbirth trauma is thought to be a causal factor. Both symptoms are common after childbirth but usually go under-reported. It has been suggested that new mothers are likely to benefit from routine symptom screening because by actively identifying symptomatic women they could then be helped to access continence services. The main objective of this study was to pilot a programme of routine symptom screening for postnatal urinary and anal incontinence in new mothers from a district general hospital. Self-completion questionnaires for both urinary and anal incontinence were sent by post to 442 primiparous women who had delivered consecutively 10 months previously in a district general hospital. Two hundred and seventy-five new mothers responded to the survey. Ninety-two women had new symptoms of incontinence at 10 months, 82 had urinary incontinence and 25 had anal incontinence. However, only six new mothers had discussed the problem with a health professional. Although nine women requested a hospital appointment none of the women attended the appointment arranged for them. The domain scores on both questionnaires were significantly less for symptomatic new mothers when compared to women with established symptoms of incontinence. The programme of screening successfully identified women with symptoms of incontinence. However, all of the symptomatic women declined a follow-up appointment at hospital which questions the benefits of routine screening 10 months after childbirth.

The strength duration test: a novel tool in the identification of occult neuropathy in women with pelvic floor dysfunction.

OBJECTIVE: The Strength-duration test (SDT) is a simple minimally invasive measure of muscle innervation, recently adapted for the assessment of the external anal sphincter (EAS). This test can discriminate women with faecal incontinence from controls. The purpose of this study was to determine if the SDT could detect denervation of the EAS in women with weak but anatomically intact EAS and normal pudendal nerve terminal motor latency (PNTML). PATIENTS AND METHODS: Thirteen women with weak but intact EAS on endoanal ultrasound (EAUS) with normal maximum resting pressure and PNTML were recruited to undergo the SDT. The results from this group were compared to control data for the SDT previously collected in our unit. RESULTS: Nine of 13 women were found to have SDT above a 95% confidence interval of the mean curve for controls and six had a SDT outside a 90% confidence interval for individuals derived from control data, suggesting denervation of the EAS. The mean area under the curve was significantly higher in our study group compared to controls (91.0 microsmA vs 72.2 microsmA, P = 0.047) as was the current intensity measured at the 1 ms pulse duration (18.2 mA vs 12.94 mA, P = 0.048), typical of denervation with this test. CONCLUSION: The SDT was abnormal in nine of the 13 study patients. This may partly explain reduced maximum voluntary contraction seen in this group of patients. SDT may be a more sensitive tool in detecting neuropathy than latency measurement.

Stoma formation for functional bowel disease.

OBJECTIVE: To assess the results of stoma formation for functional bowel disease. METHODS: A retrospective study of the indications for and complications of stoma formation in this group. A quality of life questionnaire was sent to the group. RESULTS: A very small proportion of patients with functional bowel disease have a stoma formed (< 1%). Stoma formation is often associated with problems requiring further operations. Their QOL is reported as poor and is improved upon by stoma formation. Most patients with a temporary stoma elected to keep it rather than suffer their previous problems. CONCLUSION: Some patients with functional bowel disease can be successfully managed by stoma formation. Their treatment is difficult, emotionally demanding and labour-intensive.

Fatigability of the external anal sphincter in anal incontinence.

INTRODUCTION: Anal incontinence commonly results from external anal sphincter dysfunction. The muscle is routinely assessed by anorectal physiology studies. Fatigability is not routinely measured but should be an important factor in the maintenance of continence. The fatigue rate index has been developed to address this. The purpose of this study was to investigate the fatigability of the external anal sphincter in incontinent patients compared with that in controls and to determine its correlation with symptom severity and pudendal nerve terminal motor latency measurement. METHODS: Forty-two patients with anal incontinence (33 female, 9 male) and 20 control patients (17 female, 3 male) were studied. As part of anorectal physiology studies, manometry was measured by a station pull-through technique with a closed-system microballoon. After a rest period of one minute, fatigue was measured over a 20-second squeeze at 1.5 cm in the anal canal with two consecutive readings separated by a further one-minute rest period. The fatigue rate index was calculated from the maximum squeeze pressure and fatigue rate. A validated symptom severity scoring system was used to assess symptomatology in patients with anal incontinence. RESULTS: No difference was detected in demographic factors between the two groups. The fatigue rate index was significantly different between the control and incontinent groups (1.85 vs. 0.67 minutes, P = 0.001). No other factors were significantly different between the two groups (maximum squeeze pressure, 89.1 vs. 79 cm H(2)O, P = 0.42; fatigue rate, -85.8 vs. -101.2 cm H(2)O/min, P = 0.62). The fatigue rate index demonstrated a significant correlation with symptom score ( r = -0.44, P = 0.005). The fatigue rate index did not correlate with latency measurement. CONCLUSIONS: A significant difference was detected in the fatigue rate index between incontinent and control patients. The Fatigue Rate Index demonstrated a significant correlation with symptom severity score and it may be a useful discriminating measure of external anal sphincter function.

Strength-duration testing of the external anal sphincter in females with anorectal dysfunction.

PURPOSE: The strength-duration test has been suggested as a means of assessing external anal sphincter function. This study was designed to investigate this claim by comparing the strength-duration test with established measures of external anal sphincter function. METHODS: Forty-nine females undergoing diagnostic anorectal testing (manometry, rectal sensation, electromyogram, pudendal nerve terminal motor latency, and endoanal ultrasound) also had the strength-duration test performed (which was repeated for each patient after a short rest period). RESULTS: The strength-duration test was repeatable. Statistically significant correlations were found between this test at pulse durations of 3 ms, 1 ms, and 0.3 ms with electromyographic activity of the external anal sphincter and with pressure in the anal canal during voluntary contraction. Significant correlations were found for durations of 100 ms, 30 ms, 10 ms, and 3 ms with the pudendal nerve terminal motor latency on the right and for the 3 ms and 0.3 ms durations with latency on the left. There were no correlations between the strength-duration test and resting pressure in the anal canal. CONCLUSION: The strength-duration test significantly correlates with the established measures of external anal sphincter function and its innervation. Therefore, this simple test appears to provide a simple measure of external anal sphincter denervation.