PUDENDAL
NERVE LATENCY TIME IN NORMAL WOMEN VIA INTRAVAGINAL STIMULATION
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GERALDO A. CAVALCANTI,
GILBERTO M. MANZANO, LYDIA M. GIULIANO, JOAO A. NOBREGA, MIGUEL SROUGI,
HOMERO BRUSCHINI
Departments
of Urology and Neurology, Federal University of Sao Paulo, UNIFESP, Paulista
School of Medicine, Sao Paulo, SP, Brazil
ABSTRACT
Introduction
& Objectives: Studies of motor conduction for the efferent functional
assessment of the pudendal nerve in women with pelvic dysfunctions have
been conducted through researching distal motor latency times. The transrectal
approach has been the classic approach for this electrophysiological examination.
The objective of the present study is to verify the viability of the transvaginal
approach in performing the exam, to establish normal values for this method
and to analyze the influence of age, stature and parity in the latency
value of normal women.
Materials and Methods: A total of 23 volunteers
without genitourinary pathologies participated in this study. In each,
pudendal motor latency was investigated through the transvaginal approach,
which was chosen due to patient’s higher tolerance levels.
Results: The motor response represented
by registering the M-wave was obtained in all volunteers on the right
side (100%) and in 13 volunteers on the left side (56.5%). The mean motor
latency obtained in the right and left was respectively: 1.99 ±
0.41 and 1.92 ± 0.48 milliseconds (ms). There was no difference
between the sides (p = 0.66). Latency did not correlate with age, stature
or obstetric history. The results obtained in the present study were in
agreement with those found by other researchers using the transrectal
approach.
Conclusion: The vaginal approach represents
an alternative for pudendal nerve distal motor latency time, with similar
results to those achieved through the transrectal approach. Normative
values obtained herein might serve as a comparative basis for subsequent
physiopathological studies.
Key
words: electrodiagnosis; pelvic floor; urinary incontinence;
perineum; neurophysiology
Int Braz J Urol. 2006; 32: 705-12
INTRODUCTION
Somatic
innervation of the female pelvic floor is basically represented by the
pudendal nerve. The integrity of this nerve is important for the functioning
of the skeletal musculature of this region, part of the mechanism that
sustains pelvic structures and for anal and urethral sphincteric activity
(1). This nerve is characterized by presenting sensitive and motor fibers
derived from the medullar segments S2-S4. Its inferior
rectal and perineal ramifications play an important role in external anal
and urethra sphincter innervations respectively (2).
Efferent functional neurological analysis
is performed through measurement of motor conduction speed. This method
requires access to 2 separate points of the same nerve for stimulation
and registration, making its application on the pelvic floor difficult
(3). Thus, research on distal motor latency described by Kiff & Swash
(4) became an alternative in the propedeutic of abnormalities of pudendal
nerve motor function. The advantage lies in the need to stimulate only
one point of the nerve. Registration can be made in the anal sphincteric
musculature corresponding to the compound muscular potential of action
or M-wave. These researchers also developed the St. Mark’s pudendal
electrode – a name given in honor of the institution where they
worked (St. Mark’s Hospital, London, UK). This is a self-adhesive
electrode placed on the researcher’s index finger at a fixed distance
of 3 cm with bipolar electrodes for stimulation and registration places
at the tip and base of the finger respectively (Figure-1). This method
is used to investigate lesions of the pudendal nerve associated with dysfunctions
in the pelvic floor. Patients with a previous history of obstetric rupture
of the anal sphincter presented a higher risk of fecal incontinence when
pudendal motor latency was higher than 2 milliseconds (ms) (5). A study
in nulliparous patients and in the puerperium showed an extension of latency
in the latter persisting for 5 years after vaginal delivery (6). A similar
finding was found in women with stress urinary incontinence and concomitant
genital prolapse (7). All these studies were conducted through stimulation
and transrectal registration. A single previous study comparing the transrectal
and transvaginal stimulation routes in the same normal volunteers showed
the same findings (8). The present consensus suggests that the transvaginal
approach is effective and useful (9), and it has the advantage of allowing
greater tolerability by women due to their familiarization with regular
gynecological exams.
MATERIALS
AND METHODS
Following
approval by the institution’s Ethics Committee, a prospective study
was performed on 23 normal volunteers. Their characteristics are described
in Table-1. Women without significant genitourinary alterations were included,
providing no previous history of extensive pelvic and vaginal surgery
(including women who had already undergone cesareans or unilateral adnexal
surgery), diabetes mellitus, renal insufficiency, alcoholism, hyperthyroidism,
present and previous neurological alterations, interstitial cystitis,
present urinary infection, voiding dysfunctions, pregnancy or use of a
cardiac pacemaker. Four channel Nihon-Kohden electroneuromyography equipment,
model Neuropack sigma (S), was used to perform the examination.
The study was conducted with the volunteer
in the lithotomy position. The St. Mark’s pudendal electrode (Medtronic
Functional Diagnostics A/S, Skovlunde, Denmark, model 13L4401) was attached
to the researcher’s index finger (Figure-1). In the 14 initial volunteers,
the bilateral research was performed only with the right hand of a right-handed
researcher. In the last 9 patients, we used the index finger of each hand
for the corresponding sides. The identification of the stimulation position
was determined in each case, moving the electrode from the tip of the
finger until a response with maximum amplitude be reached, using the ischial
tuberosity as reference. Stimulation for a duration of 0.2 milliseconds
(ms) was performed, and the intensity was increased until reaching the
supramaximal response (above which intensity variations do not promote
amplitude alterations in the bulbocavernosus muscle). Answers were registered
using filters of between 20 Hertz (Hz) and 10 Kilohertz (KHz) for low
and high frequency, respectively. We started from an initial sensitivity
of 50 microvolts per division (µV/div) and adjusted it as necessary. We
used a base time of 50 ms (5 ms/div). The value of the latency was determined
in the moment of starting the muscular depolarization wave deflection
or wave -M began.
To compare both side latencies, the t-Student
test was used for paired samples. The correlation between the latency
value with the age and stature of the volunteers was calculated through
Pearson’s r coefficient. The same analysis was performed in relation
to obstetric history (parity and number of vaginal deliveries) by using
the Spearman’s r coefficient. For all statistical analysis, a 5%
significance level (p = 0.05) was adopted.
RESULTS
The
exam was well tolerated by the volunteers, who did not report any alterations
or discomfort that persisted after its conduction. Registrations of both
sides presented the M-wave of the same signal when obtained with the same
hand, and inverse signals when each side was approached by fingers from
opposite hands (Figure-2). In performing the exam, the M-wave was obtained
in all 14 cases on the right side and in 8 (57.1%) on the left side when
the same hands were used for both sides. In the last 9 patients, the M-wave
was obtained in all volunteers on the right side and in 5 (55.6%) on the
left side when fingers of each hand were used for the corresponding sides.
Mean latency time obtained on the right
and left sides was, respectively, 1.99 ± 0.41 (1.00 - 2.40) and
1.92 ± 0.48 (1.00 - 2.60) milliseconds (ms). There was no difference
between latency values obtained on both sides (p = 0.66). There was no
correlation of the motor latency of each side with age, stature and obstetric
history (Table-2).
The average of the latencies obtained was
compared to the values described in the literature for the transrectal
approach. The results are showed as floating bars, and the distance between
the lateral extremities represents the values of the arithmetic mean of
each study added and subtracted from 2 corresponding standard errors.
The findings of the present study are in agreement with previously published
data (Figure-3).
COMMENTS
The
present study aimed to establish the applicability of the vaginal approach
for the research of pudendal nerve distal motor latency times in normal
women. The results achieved were compared with those obtained in other
studies through the rectal approach. As well, an analysis was made of
the impact of physiological factors, such as age, stature and parity.
Despite potential advantages in some aspects utilizing needle EMG, this
comparison was not our objective. The St. Mark’s electrode was incorporated
for clinical studies due to the facility and trustworthiness of its results
and its intravaginal use aims at making it even more practical and tolerable.
The sample size of 23 patients in our study
corresponded to the values of the studies utilized for comparison of viability
found in the literature. They describe a universal difficulty in obtaining
normal volunteers for studies of this nature, which is a probable reason
for the lack of assessments in larger populations. The definition of the
sample through well defined inclusion and exclusion criteria allowed the
determination of values of this electrophysiological exam in a group consisting
of women of different ages and obstetric histories, even though presenting
no urogenital alterations.
We could not find differences regarding
age and corporeal stature in pudendal motor conduction. There is no consensus
in the literature regarding the interference of these factors. Jameson
et al. (10) have described an extension of pudendal nerve distal motor
latency that comes with aging – both in men and women without anorectal
alterations. The same behavior in men suggest that other variables such
as menopause, potentially related with age, did not interfere in the value
of latency in women (11). Similar results were also observed when groups
of men and women below 50 years of age were compared (12). However, other
researchers did not confirm the influence of age and stature in motor
latency using the transrectal approach (13, 14). The present work corroborates
the absence of such differences, demonstrating that there are no electrophysiological
alterations with aging and stature. There is no description in the literature
of transvaginal studies similar to this.
Consequences of vaginal delivery and parity
in the neurological integrity of the pelvic floor have been a reason for
interest and studies. Alterations in pudendal motor latency could already
be observed after delivery both in primiparous and multiparous women (13).
It is probable that vaginal delivery occurrences can cause transitory
neurogenic alterations in the pelvic musculature. However, since vaginal
deliveries have not occurred recently, immediate repercussions were not
found. According to Wall (15), other associated factors such as the use
of forceps, extended expulsive periods during labor, significant perineal
ruptures and fetal macrosomia seem to be necessary so that the compromise
of pudendal innervations is permanent with definitive abnormalities in
neurophysiologic tests and clinical repercussion in the inferior and genital
urinary tract.
The utilization of the St. Mark’s
pudendal electrode for stimulation and registration of pudendal nerve
distal motor latency has shown to be effective in obtaining a clean and
distinctive answer, which favors standardizing the method. Since it is
a study of conduction speed, it assesses only the faster conduction nervous
fibers, and thus it is not a good indicator for muscular denervation (16).
The amplitude of the answer theoretically reflects the number of excitable
motor units and would be a more adequate parameter than latency to identify
peripheral neurological lesions. However, its variability with technical
and biological factors makes its practical use difficult (10). We should
also bear in mind that even though there is a delay in nervous conduction,
it is improbable that a pathological effect that would affect the nerve
would be sufficient to instigate an increase in the latency value in 1
ms, and that this would be able to influence the time of the reflex answer
of motor units (3).
However, contrary to what occurs in pathologies
of members, generally when the main nerve trunk is involved neurogenic
lesions in the pelvic floor are preferably localized in the distal portion
next to the muscle (16). This aspect permits that, despite the limitations
of motor conduction conventional studies, pudendal nerve distal motor
latency time can detect abnormalities in perineal terminal innervations.
The majority of the authors have approached
the pudendal nerve transrectally. The anal sphincter represents a muscular
structure suitable as a registration site due both to its external and
distal to stimulation, as well as the sufficient quantity of muscle fibers
for obtaining an adequate response. Differently from the classic approach,
the present study used the transvaginal approach for stimulation and registration,
since this approach offers better acceptance and comfort for the woman,
who is familiar to periodic gynecological exams. Stimulation and registration
could be performed in an efficient way on the right side (using the right
hand of a right-handed researcher). However, registration on the left
side was not obtained consistently in a significant number of cases (43.5%),
as well as the need for a higher intensity of stimulation to obtain a
supramaximal registration. The obtainment of a response on the left side
was insufficient, both with the efforts on both sides with the same hand
and with corresponding hands. Difficulties in positioning the registration
electrodes in contact with the bulbocavernosus muscle during the research
conducted on the left side seems to be the most probable cause of the
differences in findings. This means that in left-handed observers the
tendency could be reversed. According to Lefaucheur et al. (12), artifacts
and signal distortions could occur with the introduction of the finger
and attempt to adequately locate the stimulation point. The research of
the pudendal motor latency time with the index fingers of both hands caused
different signal registrations due to the opposing function performed
by bipolar registration electrodes (active and reference).
The latency value did not present any difference
between both sides. This was a different result from other researchers
that have identified a tendency in obtaining more prolonged left pudendal
latency (12). The bilateral approach, even though recommended for the
identification of unilateral neuropathies with possible clinical relevance
(17), is limited in this method due to the irregularity in obtaining registration
on both sides in normal volunteers.
The findings in the present study agree
with the results reported in the literature concerning the latencies obtained
through the transrectal approach in normal women (10,13,18,19). This suggests
that, in clinical practice, the values obtained can be interpreted independently
from the approach used and represent pudendal nerve distal motor conduction
since the anal sphincter and the bulbocavernosus muscle are supplied by
fibers of similar diameter and the distance between the site of stimulation
and registration do not change – a fact that is confirmed by the
observations of Tetzschner et al. (8). For the same reason, the results
shall present variations in relation to gender.
This examination can represent a favorable
beginning of a more encompassing study to verify the neurological integrity
of the pelvic floor involving other electrophysiological methods, such
as motor conduction studies, function and sensitive conduction (research
of electric limits and evoked potentials) and research of sacral reflexes
(20), making the investigation broader and more precise.
This study allowed familiarization with
the neurophysiologic technique described, and correlates the results with
some important variables. Our findings in volunteers without urinary symptoms
add up to the few number of cases existing on normal values in asymptomatic
people, allowing future comparison with patients that present voiding
dysfunctions.
CONCLUSIONS
The
vaginal approach has proved to be an alternative to the classical transrectal
approach for the evaluation of pudendal nerve distal motor latency time,
by using the St. Mark’s electrode. Aging, stature and parity did
not interfere in the latency value. The values of normality obtained herein
for this method might serve as a comparative basis for subsequent physiopathological
studies.
ACKNOWLEDGEMENTS
Research
partially financed by FAPESP (State of São Paulo Research Foundation),
process #99/11546-5.
CONFLICT
OF INTEREST
None
declared.
REFERENCES
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adjunctive urethral closure forces in healthy females. Scand J Urol
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of sacral and pudendal nerve anatomy. J Urol. 1988; 139: 74-80.
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427-46.
- Kiff ES, Swash M: Slowed conduction in the pudendal nerves in idiopathic
(neurogenic) fecal incontinence. Br J Surg. 1984; 71: 614-6.
- Tetzschner T, Sorensen M, Lose G, Christiansen J: Anal and urinary
incontinence in women with obstetric anal sphincter rupture. Br J Obstet
Gynaecol. 1996; 103: 1034-40.
- Snooks SJ, Swash M, Mathers SE, Henry MM: Effect of vaginal delivery
on the pelvic floor: a 5-year follow-up. Br J Surg. 1990; 77: 1358-60.
- Smith AR, Hosker GL, Warrell DW: The role of pudendal nerve damage
in the aetiology of genuine stress incontinence in women. Br J Obstet
Gynaecol. 1989; 96: 29-32.
- Tetzschner T, Sorensen M, Lose G, Christiansen J: Vaginal pudendal
nerve stimulation: a new technique for assessment of pudendal nerve
terminal motor latency. Acta Obstet Gynecol Scand. 1997; 76: 294-9.
- Vodusek DB, Amarenco G, Batra A, Benson T, Bharucha AE, Podnar S,
et al.: Clinical Neurophysiology. In: Abrams P, Cardozo L, Khoury S,
Wein A (eds.), Incontinence. 3rd International Consultation on Incontinence.
2005; pp. 675-706.
- Jameson JS, Chia YW, Kamm MA, Speakman CT, Chye YH, Henry MM: Effect
of age, sex and parity on anorectal function. Br J Surg. 1994; 81: 1689-92.
- Laurberg S, Swash M: Effects of aging on the anorectal sphincters
and their innervation. Dis Colon Rectum. 1989; 32: 737-42.
- Lefaucheur J, Yiou R, Thomas C: Pudendal nerve terminal motor latency:
age effects and technical considerations. Clin Neurophysiol. 2001; 112:
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- Barrett JA, Brocklehurst JC, Kiff ES, Ferguson G, Faragher EB: Anal
function in geriatric patients with faecal incontinence. Gut. 1989;
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- Wall LL: The muscles of the pelvic floor. Clin Obstet Gynecol. 1993;
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- Fowler CJ: Pelvic floor neurophysiology. Methods in clinical neurophysiology.
Dantec, Copenhagen. 1991; p. 1-24.
- Sangwan YP, Coller JA, Barrett RC, Roberts PL, Murray JJ, Rusin L,
et al.: Unilateral pudendal neuropathy. Impact on outcome of anal sphincter
repair. Dis Colon Rectum. 1996; 39: 686-9.
- Snooks SJ, Henry MM, Swash M: Faecal incontinence due to external
anal sphincter division in childbirth is associated with damage to the
innervation of the pelvic floor musculature: a double pathology. Br
J Obstet Gynaecol. 1985; 92: 824-8.
- Benson JT: Pelvic floor neurophysiology. In: American Association
of Electrodiagnostic Medicine, Workshop. 1998.
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____________________
Accepted
after revision:
April 5, 2006
_______________________
Correspondence address:
Dr. Homero Bruschini
Rua Barata Ribeiro, 414 / 35
São Paulo, SP, 01308-000, Brazil
Fax: + 55 11 3218-8283.
E-mail: bruschini@uol.com.br
EDITORIAL COMMENT
Pudendal
nerve distal motor latency time registration appeared as a promising alternative
in the neurofunctional assessment of the pelvic floor, since the measurement
of the speed of nervous motor conduction is not applicable in this region.
The development of the St. Mark’s electrode has made the application
of this neurophysiological test easier.
In
most centers, the research of pudendal distal motor latency time is made
through the transrectal approach. In the present study, the authors prospectively
assess the use of the vaginal approach for this neurophysical registration
in normal women. It is worth mentioning the difficulty of conducting a
study in normal patients. Yet despite the justifications presented by
the researchers regarding the discomfort reported by the patients when
undergoing the transrectal approach, both approaches (vaginal and rectal)
have not been compared in the same patient, revealing a point of uncertainty
about the method and, as a result, in analysis of the results. This demonstrates
the importance of demonstrating the viability of executing pudendal nerve
distal motor latency research through the vaginal approach, as well as
its normal reference values.
There
are a considerable number of publications establishing pudendal distal
motor latency values in patients with stress urinary incontinence, pelvic
prolapse and its variations by age, biotype and previous surgeries (1,2).
However, there is still no consensus regarding the validity of this assessment
value since there is a great variation in its specificity, sensibility
and reproducibility. An example of this is the decision of the American
Gastroenterological Association recommending the use of the pudendal distal
motor latency registration in the assessment of people with fecal incontinence
(3). Its practical application in female urology and other voiding dysfunctions
lacks complementary studies.
REFERENCES
- Benson JT, McClellan E: The effect of vaginal dissection on the pudendal
nerve. Obstet Gynecol. 1993; 82: 387-9.
- Smith AR, Hosker GL, Warrell DW: The role of pudendal nerve damage
in the aetiology of genuine stress incontinence in women. Br J Obstet
Gynaecol. 1989; 96: 29-32.
- Barnett JL, Hasler WL, Camilleri M: American Gastroenterological Association
medical position statement on anorectal testing techniques. American
Gastroenterological Association. Gastroenterology. 1999; 116: 732-60.
Dr. Jose Carlos Truzzi
Urology Department
University of Santo Amaro, UNISA
São Paulo, SP, Brazil
E-mail: jctruzzi@hotmail.com
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