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Role of urethral electromyography in predicting outcome of Burch retropubic urethropexy
Role of urethral electromyography in predicting outcome of Burch retropubic urethropexy Kimberly Kenton, MD, Mary Pat FitzGerald, MD, Susan Shott, PhD, and Linda Brubaker, MD Chicago, Ill OBJECTIVE: To establish preoperative urethral electromyographic parameters that predict which women are unlikely to be cured of genuine stress incontinence by Burch retropubic urethropexy procedures. STUDY DESIGN: Eighty-nine women who underwent preoperative urodynamic testing with urethral electromyography and retropubic urethropexy for genuine stress incontinence were prospectively studied. Raw electromyographic signals were processed by an electromyographic instrument equipped with automated motor unit analysis software programs. Quantitative electromyographic software was used to analyze the electrical activity of the urethral sphincter with use of mean rectified voltage (MRV)—mean amplitude calculated over the entire tracing after the waveform is rectified—with women at rest and during voluntary urethral squeezing, repetitive coughing, and bladder filling. Objective outcomes were determined 3 months after the operation with single-channel cystometrograms performed while subjects were standing. Nonparametric statistical analyses included the χ2 test of association for nominal data and the Mann-Whitney test for comparison of population medians. RESULTS: All women had urethral hypermobility and met our standard clinical criteria for retropubic urethropexy. Fifteen women had incomplete follow-up data and were excluded from final analysis. Fifty-nine of 74 women (80%) were objectively cured, and 15 women had persistent genuine stress incontinence. Women who were cured did not differ from those who were not cured in age, parity, menopausal status, maximum urethral closure pressure, Valsalva leak point pressure, maximum cystometric capacity, detrusor instability, or prolapse stage. Women with persistent genuine stress incontinence were more likely to have had previous pelvic operations (P = .01). There were no differences in any electromyographic parameters at rest, with urethral squeezing, or during bladder filling between the groups. Women who were objectively cured had larger MRV values with repetitive coughing (P = .05) and larger increases from resting MRV values (∆MRV) with repetitive coughing (P = .04). Twenty-seven of 30 women with MRV values ≥25 µV with repetitive coughing were cured (positive predictive value [PPV] = 90%; negative predictive value [NPV] = 32%), and 22 of 24 women with more than a 10-µV increase in resting MRV values with repetitive coughing (∆MRV > 10 µV) were cured (PPV = 92%; NPV = 29%). If women had both an MRV value ≥25 µV and a ∆MRV value >10 µV, the PPV was 100%; however, the NPV remained at 30%. CONCLUSION: Women who were cured of genuine stress incontinence with Burch retropubic urethropexy procedures had better motor unit action potential activation with repetitive coughing than women with persistent genuine stress incontinence. Urethral electromyography may be used to assess the neuromuscular integrity of the striated urethral sphincter and to help predict which women will have successful retropubic urethropexy procedures. (Am J Obstet Gynecol 2001;185:51-5.)
Key words: Electromyography, urethra, Burch urethropexy, stress incontinence
Neuromuscular injury to the striated urethral sphincter is one of several important factors in the cause of stress incontinence in women.1, 2 Electrodiagnostic testing with concentric needle electromyography provides a more direct assessment of the neuromuscular function of the striated sphincter muscle than the commonly used From the Department of Obstetrics and Gynecology, Division of Urogynecology and Reconstructive Pelvic Surgery, Rush-Presbyterian–St Luke’s Medical Center. Presented at the American Urogynecologic Society Twenty-first Annual Scientific Meeting, Hilton Head, SC, October 26-28, 2000. Reprints not available from the authors. Copyright © 2001 by Mosby, Inc. 0002-9378/2001 $35.00 + 0 6/6/116374 doi:10.1067/mob.2001.116374
urodynamic tests, Valsalva leak point pressure, and maximum urethral closure pressure. Motor unit action potential analysis with electromyography provides information about denervation, reinnervation, upper and lower motor neuron function, and the chronicity of neurologic processes that affect the sphincter muscle. This valuable information about the neuromuscular function of the urethral sphincter may help to identify patients at risk for surgical failure from traditional repositioning operations. The purpose of this study was to quantify the neuromuscular function of the striated urethral sphincter in women with genuine stress incontinence who undergo Burch retropubic urethropexy procedures. Our specific aims were to identify electrodiagnostic criteria for ure51
52 Kenton et al
thral sphincter integrity with concentric needle electromyography of the striated urethral sphincter and to establish preoperative electromyographic parameters that accurately predict which women will have unsuccessful urethropexy procedures. Material and methods Eighty-nine consecutive women who underwent preoperative multichannel urodynamic testing with urethral sphincter electromyographies and Burch retropubic urethropexy procedures at our tertiary care referral center were prospectively studied. All women completed a comprehensive urogynecologic history and had a physical examination. Multichannel urodynamic testing with urethral electromyography was performed in women with stress incontinence who desired surgical correction. Standardized urodynamic evaluation was performed with use of a Life-Tech multichannel urodynamic instrument (model 1106, Life-Tech, Inc, Houston, Texas) and included retrograde water cystometry at a fill rate of 80 mL/min, static urethral pressure profilometry, vesicle Valsalva leak point pressure determinations, and pressure-flow studies. Cystometry was performed while the subject was in a birthing chair reclined at 45 degrees. An 8F catheter with a microtip was placed in the vagina or rectum to record abdominal pressure, and an 8F dualmicrotipped catheter with infusion port (Millar Instruments, Houston, Texas) was placed with the distal transducer in the bladder and the proximal transducer in the midurethra facing the 9-o’clock position to record vesicle pressure and urethral pressure, respectively. True detrusor pressure and urethral closure pressure were electronically subtracted and recorded throughout the study. Stage II or greater prolapse was reduced during the study with the hand of the examiner. Maximum urethral closure pressure values were determined at maximum cystometric capacity with use of a profilometer set at a withdrawal rate of 1 mm per second. With the urethral transducer positioned in the midurethra, pressureflow studies were then performed. Cystometric evaluations were repeated while subjects were standing. With the bladder of the subject filled to 150 mL, vesicle Valsalva leak point pressure values were measured at the precise instant that transurethral fluid leakage was observed. Genuine stress incontinence was diagnosed if transurethral urine loss occurred with coughing in the absence of a detrusor contraction. Intrinsic sphincter deficiency was diagnosed if maximum urethral closure pressure values were ≤20 cm H2O, if Valsalva leak point pressure values were positive to less than 60 cm H2O, or both. Urodynamic and pelvic organ prolapse quantification methods, definitions, and units conformed to the standards recommended by the International Continence Society,3 including the use of the Pelvic Organ Prolapse Quantification (POP-Q) system.4
July 2001 Am J Obstet Gynecol
Urethral sphincter electromyography was performed on all subjects during the cystometry portion of the urodynamic study. A disposable 30-gauge, 1-inch concentric needle electrode (Medelec, Surrey, England) was inserted into the striated urethral sphincter at the 12-o’clock position, 5 mm from the external urethral meatus. The raw electromyographic signal was processed by a Nicolet Viking IIe electromyographic instrument (Nicolet Instrument Corporation, Madison, Wis) equipped with automated motor unit analysis software programs. Data were recorded during the filling phase after audio and oscilloscopic findings established correct needle placement. Quantitative maximum voluntary activity software was used to analyze electrical activity of the urethral sphincter. Maximum voluntary activity included peak-to-peak amplitude, mean rectified voltage (MRV), root mean square, and number of turns. Peak-to-peak amplitude measures the actual waveform amplitude in microvolts from the highest to lowest displayed point. The MRV is the mean amplitude calculated over the entire tracing after the waveform is rectified, whereas the root mean square is the calculated root mean square value of the recorded tracing. The number of turns represents the number of positive and negative extremes >100 µV per second. A comparison of motor unit action potential activation was made among women at rest and during voluntary urethral squeezing, repetitive coughing, and bladder filling with use of the automated maximum voluntary activity analysis program. The concentric needle was kept in place during the cystometric portion of the study and during the voiding study to evaluate for motor unit action potential activation silencing and coordinated voiding. All women met our standard clinical criteria for Burch retropubic urethropexy procedures, which are urethral hypermobility and urodynamically proved genuine stress incontinence. Women with intrinsic sphincter deficiency were excluded unless they had stage III or IV anterior vaginal wall prolapse, as we modify our selection criteria for surgical procedures in this select patient group. Burch retropubic urethropexy procedures were performed by fellows or residents under the supervision of 3 attending surgeons according to the modification of Tanagho5 with use of cv-2 Gore-Tex sutures (WL Gore & Associates, Flagstaff, Ariz). If subjects had concomitant pelvic organ prolapse, additional surgical procedures were performed as indicated. Three months after the operation, all subjects underwent standardized postoperative assessment, including comprehensive urogynecologic history and physical examination and cystometrogram in the standing position to determine objective cure rates. Subjects were considered to be objectively cured if no urine loss was noted during the standing cystometrograms with repetitive coughing at maximum cystometric capacity. If subjects lost even 1 drop of urine at maximum cystometric capac-
Kenton et al 53
Volume 185, Number 1 Am J Obstet Gynecol
Table I. Previous pelvic surgical procedures of the 74 women studied
Table II. Concomitant surgical procedures of the 74 women studied
Procedure
No. of women
Percent
Procedure
No. of women
Percent
Vaginal hysterectomy Abdominal hysterectomy Anterior colporrhaphy Posterior colporrhaphy Needle urethropexy Retropubic urethropexy Urethral dilation
21 16 17 8 4 4 2
28% 22% 23% 11% 5% 5% 3%
Culdeplasty Sacrocolpopexy Abdominal paravaginal repair Hysterectomy Posterior repair Sacrospinous ligament suspension
37 30 21 17 14 1
50% 41% 28% 20% 19% 1%
ity, they were not considered to be objectively cured. Nonparametric statistical analyses included the χ2 test of association for nominal data and the Mann-Whitney test for comparison of population medians. Results Fifteen women had incomplete follow-up data, mostly because of geographic constraints, and were excluded from final analysis. The 74 women studied had a median age of 57 years (range, 31 to 85), with a median vaginal parity of 3 children (range, 0 to 12). All women had urodynamically proved genuine stress incontinence, with 23 of 74 women (31%) having mixed incontinence. The median maximum urethral closure pressure was 38 cm H2O (range, 4-88 cm H2O). Sixty of the 74 women (81%) were postmenopausal, and 17 of those women (23%) were not receiving hormone replacement therapy. Thirty-six women (49%) had undergone previous pelvic or incontinence surgical procedures (Table I). Forty-six of the women (67%) were sexually active, and 17 of those women (37%) reported dyspareunia or coital urine loss. Most women (70%) had concomitant pelvic reconstructive operations in addition to Burch retropubic urethropexy procedures. Table II contains a list of these procedures. Fifty-nine of 74 women (80%) were objectively cured, whereas cystometrograms performed standing 3 months after the operation showed that 15 women (20%) had persistent genuine stress incontinence. Women who were cured did not differ from those who were not cured in age, parity, menopausal status, hormone replacement therapy, maximum urethral closure pressure, Valsalva leak point pressure, maximum cystometric capacity, preoperative detrusor instability, or prolapse stage (Table III). Women with persistent genuine stress incontinence were more likely to have had previous pelvic operations (P = .01). There were no differences in any electromyographic parameters at rest, with urethral squeezing, or during bladder filling between the cured groups. There were significant differences in electromyographic measures of urethral sphincter activation. Women who were objectively cured had larger MRV values with repetitive coughing (P = .04) and larger increases from resting MRV val-
ues (∆MRV) with repetitive coughing (P = .04; Table IV). Twenty-seven of 30 women (90%) with MRV values ≥25 µV after repetitive coughing were cured. An MRV value ≥25 µV after repetitive coughing therefore had a positive predictive value (PPV) of 90% and a negative predictive value (NPV) of 32% for objective cure of genuine stress incontinence after Burch retropubic urethropexy procedures. Twenty-two of 24 women with more than a 10-µV increase in resting MRV values with repetitive coughing (a ∆MRV > 10 µV) were cured (PPV = 92%; NPV = 29%). If women had both an MRV ≥25 µV with coughing and a ∆MRV > 10 µV, the PPV was 100% and the NPV was 30%. In other words, all women who met these 2 electromyographic parameters were cured. Table V shows the PPV and NPV of an maximum urethral closure pressure ≤20 and a Valsalva leak point pressure <60, as well as the electromyographic parameters. Comment Burch retropubic urethropexy is one of the most commonly used and studied surgical procedures for the treatment of genuine stress incontinence in women and has consistently been shown to have primary success rates of 80% to 90%.6-8 Despite our best attempts, we have not been able to preoperatively identify the 10% to 20% of women who will not be cured with this procedure. It is possible that women who have persistent stress incontinence after stabilization of the urethrovesical junction may have a previously unrecognized intrinsic sphincter weakness. These patients may have sustained a significant neural injury that is not detectable by indirect urethral pressure measurements, and electromyography may provide additional information that will aid in optimization of treatments. Other authors have clearly shown the importance of a neuromuscularly intact striated sphincter in the maintenance of urinary continence. However, most studies have relied on indirect measures of the neuromuscular integrity of the urethral sphincter, including pudendal nerve terminal motor latencies and electromyography of other pelvic floor muscles.1, 2, 9-11 It appears that urethral electromyography is a useful adjunct to conventional urodynamic testing in accurately selecting patients with genuine stress incontinence for
54 Kenton et al
July 2001 Am J Obstet Gynecol
Table III. Demographics
Age (y) Vaginal parity Prolapse stage Detrusor instability Postmenopausal MUCP (cm H2O) MCC Positive VLPP
Cured (n = 59)
Persistent GSI (n = 15)
Statistical significance
54 (31-85) 3 (0-9) 2 (0-4) 36% 76% 36 (1-88) 500 mL (33-920) 31%
60 (50-76) 3 (1-6) 3 (0-4) 87% 100% 32 (4-60) 500 mL (2-700) 36%
P = .07* P = .928* P = .243* P = .093† P = .059† P = .829* P = .239* P = .732†
GSI, Genuine stress incontinence; MUCP, maximum urethral closure pressure; MCC, maximum cystometric capacity; VLPP, Valsalva leak point pressure. Ranges are given in parentheses. *Mann-Whitney test for comparison of population medians. †χ2 test of association.
Table IV. Median (range) MRV values for cure groups Cure group
Persistent GSI
Median
Range
Median
Range
Statistical significance*
10 14 24 25 9
1-28 1-64 2-120 1-63 0-37
10 13 16 17 4
3-23 7-27 5-33 3-36 0-15
P = .680 P = .905 P = .106 P = .044 P = .040
Rest MRV (µV) Fill MRV (µV) Squeeze MRV (µV) Cough MRV (µV) ∆MRV (µV)
MRV, Mean rectified voltage. *Mann-Whitney test for comparison of population medians.
Table V. Predictive values for objective cure Test Urodynamic parameters MUCP ≤ 20 cm H2O* VLPP < 60 cm H2O† Electromyography parameters MRV ≥ 25 ∆MRV > 10 MRV ≥ 25 and ∆MRV > 10
PPV
NPV
79% 82%
10% 40%
90% 92% 100%
32% 29% 30%
*Performed while subjects were in a birthing chair reclined at 45 degrees with their bladders filled to MCC and the urethral transducer facing the 9-o’clock position. †Performed while subjects were standing and their bladders were filled to 150 mL.
Burch retropubic urethropexy. Electomyography provides a more direct assessment of the neuromuscular function of the striated urethral sphincter than maximum urethral closure pressure or Valsalva leak point pressure. The electromyographic changes observed in women with successful Burch retropubic urethropexy procedures in this study suggest better innervation of their urethral sphincters than the women with unsuccessful operations. MRV reflects the amplitude of the motor unit action potential activation values over a fixed time interval. Large amplitude potentials reflect denervation with subsequent reinnervation and result in larger MRV values. It is therefore not surprising that women in whom
retropubic urethropexy procedures failed had smaller MRV values. These women likely had more severe neural injuries to their sphincter muscles, with incomplete reinnervation, and were unable to adequately activate necessary motor unit action potential activation values to prevent urine loss. Electrodiagnostic equipment is not yet readily available at many centers, limiting the usefulness and applicability of our findings at this time. Furthermore, we used a stringent definition of objective cure, which may overestimate or underestimate the usefulness of urethral electromyography in these women. Numerous automated motor unit action potential activation analysis programs exist for measurement neuromuscular function, and those programs may be used to evaluate urethral sphincter integrity. The maximum voluntary activity program used in this study is relatively easy to learn and does not require extensive electrodiagnostic training. These data suggest that direct measures of sphincter neuromuscular function are fertile ground for investigation and may ultimately provide the missing information necessary to preoperatively identify women who will not have successful urethropexy procedures. REFERENCES
1. Snooks SJ, Swash M. Abnormalities of the innervation of the urethral striated sphincter musculature in incontinence. Br J Urol 1984;56:401-5. 2. Smith AR, Hosker GL, Warrell DW. The role of pudendal nerve
Volume 185, Number 1 Am J Obstet Gynecol
3.
4.
5. 6.
damage in the aetiology of genuine stress incontinence in women. Br J Obstet Gynaecol 1989;96:29-32. Abrams P, Blavis G, Stanton SL, Anderson GT. The standardization of terminology of lower urinary tract function as recommended by the International Continence Society. Int Urogynecol J 1990;1:45-58. Bump RC, Mattiasson A, Bo K, Brubaker LP, DeLancey JO, Klarskov P. The standardization of terminology of female pelvic organ prolapse and pelvic floor dysfunction. Am J Obstet Gynecol 1996;175:10-7. Tanagho EA. Colpocystourethropexy: the way we do it. J Urol 1976;116:751-6. Bergman A, Elia G. Three surgical procedures for genuine stress incontinence: five-year follow-up of a prospective randomized study. Am J Obstet Gynecol 1995;173:66-71.
Kenton et al 55
7. Walters MD. Genuine stress incontinence: Retropubic surgical procedures. In: Walters MD, Karram MM, editors. Clinical urogynecology. St Louis: Mosby Year Book; 1993. p. 203. 8. Feyereisl J, Dreher E, Haenggi W, Zikmund J, Schneider J. Longterm results after Burch colposuspension. Am J Obstet Gynecol 1994;171:647-52. 9. Weidner A, Barber MD, Visco AG, Bump RC, Sanders DB. Pelvic muscle electromyography of levator ani and external anal sphincter in nulliparous women with pelvic floor dysfunction. Am J Obstet Gynecol 2000;183:1390-9. 10. Allen RE, Hosker GL, Smith ARB. Pelvic floor damage and childbirth: a neurophysiological study. Br J Obstet Gynaecol 1990;97: 770-9. 11. Snooks SJ, Swash M, Henry MM. Risk factors in childbirth causing damage to pelvic floor innervation. Int J Colorectal Dis 1986;1:20-4.
Key words: Electromyography, urethra, Burch urethropexy, stress incontinence
Neuromuscular injury to the striated urethral sphincter is one of several important factors in the cause of stress incontinence in women.1, 2 Electrodiagnostic testing with concentric needle electromyography provides a more direct assessment of the neuromuscular function of the striated sphincter muscle than the commonly used From the Department of Obstetrics and Gynecology, Division of Urogynecology and Reconstructive Pelvic Surgery, Rush-Presbyterian–St Luke’s Medical Center. Presented at the American Urogynecologic Society Twenty-first Annual Scientific Meeting, Hilton Head, SC, October 26-28, 2000. Reprints not available from the authors. Copyright © 2001 by Mosby, Inc. 0002-9378/2001 $35.00 + 0 6/6/116374 doi:10.1067/mob.2001.116374
urodynamic tests, Valsalva leak point pressure, and maximum urethral closure pressure. Motor unit action potential analysis with electromyography provides information about denervation, reinnervation, upper and lower motor neuron function, and the chronicity of neurologic processes that affect the sphincter muscle. This valuable information about the neuromuscular function of the urethral sphincter may help to identify patients at risk for surgical failure from traditional repositioning operations. The purpose of this study was to quantify the neuromuscular function of the striated urethral sphincter in women with genuine stress incontinence who undergo Burch retropubic urethropexy procedures. Our specific aims were to identify electrodiagnostic criteria for ure51
52 Kenton et al
thral sphincter integrity with concentric needle electromyography of the striated urethral sphincter and to establish preoperative electromyographic parameters that accurately predict which women will have unsuccessful urethropexy procedures. Material and methods Eighty-nine consecutive women who underwent preoperative multichannel urodynamic testing with urethral sphincter electromyographies and Burch retropubic urethropexy procedures at our tertiary care referral center were prospectively studied. All women completed a comprehensive urogynecologic history and had a physical examination. Multichannel urodynamic testing with urethral electromyography was performed in women with stress incontinence who desired surgical correction. Standardized urodynamic evaluation was performed with use of a Life-Tech multichannel urodynamic instrument (model 1106, Life-Tech, Inc, Houston, Texas) and included retrograde water cystometry at a fill rate of 80 mL/min, static urethral pressure profilometry, vesicle Valsalva leak point pressure determinations, and pressure-flow studies. Cystometry was performed while the subject was in a birthing chair reclined at 45 degrees. An 8F catheter with a microtip was placed in the vagina or rectum to record abdominal pressure, and an 8F dualmicrotipped catheter with infusion port (Millar Instruments, Houston, Texas) was placed with the distal transducer in the bladder and the proximal transducer in the midurethra facing the 9-o’clock position to record vesicle pressure and urethral pressure, respectively. True detrusor pressure and urethral closure pressure were electronically subtracted and recorded throughout the study. Stage II or greater prolapse was reduced during the study with the hand of the examiner. Maximum urethral closure pressure values were determined at maximum cystometric capacity with use of a profilometer set at a withdrawal rate of 1 mm per second. With the urethral transducer positioned in the midurethra, pressureflow studies were then performed. Cystometric evaluations were repeated while subjects were standing. With the bladder of the subject filled to 150 mL, vesicle Valsalva leak point pressure values were measured at the precise instant that transurethral fluid leakage was observed. Genuine stress incontinence was diagnosed if transurethral urine loss occurred with coughing in the absence of a detrusor contraction. Intrinsic sphincter deficiency was diagnosed if maximum urethral closure pressure values were ≤20 cm H2O, if Valsalva leak point pressure values were positive to less than 60 cm H2O, or both. Urodynamic and pelvic organ prolapse quantification methods, definitions, and units conformed to the standards recommended by the International Continence Society,3 including the use of the Pelvic Organ Prolapse Quantification (POP-Q) system.4
July 2001 Am J Obstet Gynecol
Urethral sphincter electromyography was performed on all subjects during the cystometry portion of the urodynamic study. A disposable 30-gauge, 1-inch concentric needle electrode (Medelec, Surrey, England) was inserted into the striated urethral sphincter at the 12-o’clock position, 5 mm from the external urethral meatus. The raw electromyographic signal was processed by a Nicolet Viking IIe electromyographic instrument (Nicolet Instrument Corporation, Madison, Wis) equipped with automated motor unit analysis software programs. Data were recorded during the filling phase after audio and oscilloscopic findings established correct needle placement. Quantitative maximum voluntary activity software was used to analyze electrical activity of the urethral sphincter. Maximum voluntary activity included peak-to-peak amplitude, mean rectified voltage (MRV), root mean square, and number of turns. Peak-to-peak amplitude measures the actual waveform amplitude in microvolts from the highest to lowest displayed point. The MRV is the mean amplitude calculated over the entire tracing after the waveform is rectified, whereas the root mean square is the calculated root mean square value of the recorded tracing. The number of turns represents the number of positive and negative extremes >100 µV per second. A comparison of motor unit action potential activation was made among women at rest and during voluntary urethral squeezing, repetitive coughing, and bladder filling with use of the automated maximum voluntary activity analysis program. The concentric needle was kept in place during the cystometric portion of the study and during the voiding study to evaluate for motor unit action potential activation silencing and coordinated voiding. All women met our standard clinical criteria for Burch retropubic urethropexy procedures, which are urethral hypermobility and urodynamically proved genuine stress incontinence. Women with intrinsic sphincter deficiency were excluded unless they had stage III or IV anterior vaginal wall prolapse, as we modify our selection criteria for surgical procedures in this select patient group. Burch retropubic urethropexy procedures were performed by fellows or residents under the supervision of 3 attending surgeons according to the modification of Tanagho5 with use of cv-2 Gore-Tex sutures (WL Gore & Associates, Flagstaff, Ariz). If subjects had concomitant pelvic organ prolapse, additional surgical procedures were performed as indicated. Three months after the operation, all subjects underwent standardized postoperative assessment, including comprehensive urogynecologic history and physical examination and cystometrogram in the standing position to determine objective cure rates. Subjects were considered to be objectively cured if no urine loss was noted during the standing cystometrograms with repetitive coughing at maximum cystometric capacity. If subjects lost even 1 drop of urine at maximum cystometric capac-
Kenton et al 53
Volume 185, Number 1 Am J Obstet Gynecol
Table I. Previous pelvic surgical procedures of the 74 women studied
Table II. Concomitant surgical procedures of the 74 women studied
Procedure
No. of women
Percent
Procedure
No. of women
Percent
Vaginal hysterectomy Abdominal hysterectomy Anterior colporrhaphy Posterior colporrhaphy Needle urethropexy Retropubic urethropexy Urethral dilation
21 16 17 8 4 4 2
28% 22% 23% 11% 5% 5% 3%
Culdeplasty Sacrocolpopexy Abdominal paravaginal repair Hysterectomy Posterior repair Sacrospinous ligament suspension
37 30 21 17 14 1
50% 41% 28% 20% 19% 1%
ity, they were not considered to be objectively cured. Nonparametric statistical analyses included the χ2 test of association for nominal data and the Mann-Whitney test for comparison of population medians. Results Fifteen women had incomplete follow-up data, mostly because of geographic constraints, and were excluded from final analysis. The 74 women studied had a median age of 57 years (range, 31 to 85), with a median vaginal parity of 3 children (range, 0 to 12). All women had urodynamically proved genuine stress incontinence, with 23 of 74 women (31%) having mixed incontinence. The median maximum urethral closure pressure was 38 cm H2O (range, 4-88 cm H2O). Sixty of the 74 women (81%) were postmenopausal, and 17 of those women (23%) were not receiving hormone replacement therapy. Thirty-six women (49%) had undergone previous pelvic or incontinence surgical procedures (Table I). Forty-six of the women (67%) were sexually active, and 17 of those women (37%) reported dyspareunia or coital urine loss. Most women (70%) had concomitant pelvic reconstructive operations in addition to Burch retropubic urethropexy procedures. Table II contains a list of these procedures. Fifty-nine of 74 women (80%) were objectively cured, whereas cystometrograms performed standing 3 months after the operation showed that 15 women (20%) had persistent genuine stress incontinence. Women who were cured did not differ from those who were not cured in age, parity, menopausal status, hormone replacement therapy, maximum urethral closure pressure, Valsalva leak point pressure, maximum cystometric capacity, preoperative detrusor instability, or prolapse stage (Table III). Women with persistent genuine stress incontinence were more likely to have had previous pelvic operations (P = .01). There were no differences in any electromyographic parameters at rest, with urethral squeezing, or during bladder filling between the cured groups. There were significant differences in electromyographic measures of urethral sphincter activation. Women who were objectively cured had larger MRV values with repetitive coughing (P = .04) and larger increases from resting MRV val-
ues (∆MRV) with repetitive coughing (P = .04; Table IV). Twenty-seven of 30 women (90%) with MRV values ≥25 µV after repetitive coughing were cured. An MRV value ≥25 µV after repetitive coughing therefore had a positive predictive value (PPV) of 90% and a negative predictive value (NPV) of 32% for objective cure of genuine stress incontinence after Burch retropubic urethropexy procedures. Twenty-two of 24 women with more than a 10-µV increase in resting MRV values with repetitive coughing (a ∆MRV > 10 µV) were cured (PPV = 92%; NPV = 29%). If women had both an MRV ≥25 µV with coughing and a ∆MRV > 10 µV, the PPV was 100% and the NPV was 30%. In other words, all women who met these 2 electromyographic parameters were cured. Table V shows the PPV and NPV of an maximum urethral closure pressure ≤20 and a Valsalva leak point pressure <60, as well as the electromyographic parameters. Comment Burch retropubic urethropexy is one of the most commonly used and studied surgical procedures for the treatment of genuine stress incontinence in women and has consistently been shown to have primary success rates of 80% to 90%.6-8 Despite our best attempts, we have not been able to preoperatively identify the 10% to 20% of women who will not be cured with this procedure. It is possible that women who have persistent stress incontinence after stabilization of the urethrovesical junction may have a previously unrecognized intrinsic sphincter weakness. These patients may have sustained a significant neural injury that is not detectable by indirect urethral pressure measurements, and electromyography may provide additional information that will aid in optimization of treatments. Other authors have clearly shown the importance of a neuromuscularly intact striated sphincter in the maintenance of urinary continence. However, most studies have relied on indirect measures of the neuromuscular integrity of the urethral sphincter, including pudendal nerve terminal motor latencies and electromyography of other pelvic floor muscles.1, 2, 9-11 It appears that urethral electromyography is a useful adjunct to conventional urodynamic testing in accurately selecting patients with genuine stress incontinence for
54 Kenton et al
July 2001 Am J Obstet Gynecol
Table III. Demographics
Age (y) Vaginal parity Prolapse stage Detrusor instability Postmenopausal MUCP (cm H2O) MCC Positive VLPP
Cured (n = 59)
Persistent GSI (n = 15)
Statistical significance
54 (31-85) 3 (0-9) 2 (0-4) 36% 76% 36 (1-88) 500 mL (33-920) 31%
60 (50-76) 3 (1-6) 3 (0-4) 87% 100% 32 (4-60) 500 mL (2-700) 36%
P = .07* P = .928* P = .243* P = .093† P = .059† P = .829* P = .239* P = .732†
GSI, Genuine stress incontinence; MUCP, maximum urethral closure pressure; MCC, maximum cystometric capacity; VLPP, Valsalva leak point pressure. Ranges are given in parentheses. *Mann-Whitney test for comparison of population medians. †χ2 test of association.
Table IV. Median (range) MRV values for cure groups Cure group
Persistent GSI
Median
Range
Median
Range
Statistical significance*
10 14 24 25 9
1-28 1-64 2-120 1-63 0-37
10 13 16 17 4
3-23 7-27 5-33 3-36 0-15
P = .680 P = .905 P = .106 P = .044 P = .040
Rest MRV (µV) Fill MRV (µV) Squeeze MRV (µV) Cough MRV (µV) ∆MRV (µV)
MRV, Mean rectified voltage. *Mann-Whitney test for comparison of population medians.
Table V. Predictive values for objective cure Test Urodynamic parameters MUCP ≤ 20 cm H2O* VLPP < 60 cm H2O† Electromyography parameters MRV ≥ 25 ∆MRV > 10 MRV ≥ 25 and ∆MRV > 10
PPV
NPV
79% 82%
10% 40%
90% 92% 100%
32% 29% 30%
*Performed while subjects were in a birthing chair reclined at 45 degrees with their bladders filled to MCC and the urethral transducer facing the 9-o’clock position. †Performed while subjects were standing and their bladders were filled to 150 mL.
Burch retropubic urethropexy. Electomyography provides a more direct assessment of the neuromuscular function of the striated urethral sphincter than maximum urethral closure pressure or Valsalva leak point pressure. The electromyographic changes observed in women with successful Burch retropubic urethropexy procedures in this study suggest better innervation of their urethral sphincters than the women with unsuccessful operations. MRV reflects the amplitude of the motor unit action potential activation values over a fixed time interval. Large amplitude potentials reflect denervation with subsequent reinnervation and result in larger MRV values. It is therefore not surprising that women in whom
retropubic urethropexy procedures failed had smaller MRV values. These women likely had more severe neural injuries to their sphincter muscles, with incomplete reinnervation, and were unable to adequately activate necessary motor unit action potential activation values to prevent urine loss. Electrodiagnostic equipment is not yet readily available at many centers, limiting the usefulness and applicability of our findings at this time. Furthermore, we used a stringent definition of objective cure, which may overestimate or underestimate the usefulness of urethral electromyography in these women. Numerous automated motor unit action potential activation analysis programs exist for measurement neuromuscular function, and those programs may be used to evaluate urethral sphincter integrity. The maximum voluntary activity program used in this study is relatively easy to learn and does not require extensive electrodiagnostic training. These data suggest that direct measures of sphincter neuromuscular function are fertile ground for investigation and may ultimately provide the missing information necessary to preoperatively identify women who will not have successful urethropexy procedures. REFERENCES
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