Chapter 2.9
Neurophysiology in Pelvic Floor Disorders
Guillermo O. Rosato and Carlos M. Lumi
Introduction
Colorectal surgeons, gastroenterologists, gynecologists, and urologists have gained a growing interest in the neuroanatomy and neurophysiology of the pelvic floor, which is driven by an increased knowledge of the pathophysi- ology of pelvic floor disorders. Pelvic disorders of defecation and micturi- tion are common, but the true prevalence of pelvic floor disorders is still not well known.
Several diagnostic procedures have been developed to assess pelvic floor function. Some still remain as experimental tools, whereas others have gained more widespread clinical application. Neurophysiology applied to pelvic floor disorders (i.e., constipation and incontinence) has been used routinely as a diagnostic and therapeutic tool (1).
Diagnostic neurophysiology of pelvic floor muscle disorders includes three main procedures: 1) Concentric needle electromyography (CNEMG), 2) single fiber electromyography (SFEMG), and 3) pudendal nerve termi- nal motor latency (PNTML).
Sacral reflex latencies and somatosensory-evoked potentials have less general clinical application. Nerve conduction and electromyography (EMG) studies measure the efferent or motor innervation, whereas affer- ent fiber injury is more difficult to characterize and quantify. Sensory thresholds studies are also available. These studies stimulate a distal site (i.e., the anal mucosa) and determine the sensory limits of perception (anal electrosensitivity) (see Chapter 2.8). The sensory threshold is carried by afferent somatic and visceral nerve fibers to the central nervous system (probably through the pudendal nerve and pelvic plexus), whereas sacral reflexes regulate rectal sensitivity and contractility (2). Sacral reflexes measure the integrity of the afferent and efferent limbs by stimulating a distal site and measuring the time it takes for the reflex contraction of the superficial perineal muscles. After synapsing in the central nervous system by a polysynaptic pathway, efferent fibers (through the pudendal nerve) carry the response to the skeletal muscle being studied. Sensory thresholds 153
usually are low, and sacral reflexes usually require stimulation using three times the sensory threshold current with latencies measuring less than 100 milliseconds. The bulbocavernosus reflex is the most explored sacral reflex.
Somatosensory-evoked potentials assess the integrity of the afferent branches of the pelvic nerves. They are measured by applying a distal stim- ulus, such as electric stimulation or balloon distension of the rectum or anal mucosa, and recording evoked potentials from the central nervous system, such as the brain or lumbar spine. The latter can be performed with tran- scutaneous stimulation at L1 and L4 using saline-soaked pad electrodes delivering 500 to 1 500 volt single impulses. Central stimulation may be per- formed with magnetic brain stimulation and has been described for use in patients with spinal or central neurological disorders affecting the pelvic floor and in patients with polyneuropathy/myopathy syndromes. The results are less than satisfactory and not readily applicable or reproducible (3,4).
Electrophysiology tests can distinguish between the integrity of the nerve, muscle, and neuromuscular junction, where they can identify the level of nerve injury, determine if it is recent or old, and whether it is acute, chronic, or ongoing.
Concepts in Electromyography and Basic Neurophysiology
The precise measure of neuromuscular integrity is achieved through EMG, which relies on the recording of electrical activity generated by muscle fibers (5,6). Anal sphincter EMG was first recorded by Beck in 1930 (7) with a concentric needle as originally described by Adrian and Bronck in 1929 (6).
A motor unit consists of a single anterior horn cell within the central nervous system, all its peripheral nerve fibers, motor end plates, and the muscle fibers it innervates. This is the basic functional element of a skele- tal muscle. One muscle fiber (MF) is innervated by one motoneuron (MN), but one MN may supply many MFs. The motor unit is important not only for the motor control of the MF, but also in maintaining a neuromuscular trophic effect. The composition of a muscle by MF types (Table 2.9-1) depends in part on the functional demands on that muscle. Striated muscles are classified into two types—Types I and II. Type I muscle units are slow tonic fibers, and Type II muscle units are fast phasic muscle fibers. The majority of the muscle fibers of the levator ani are slow twitch fibers (Type I), which maintain constant tone. Type II fibers are more densely distrib- uted on perianal and periurethral muscles. As an example, the gastrocne- mius, which has more of a role in static postural maintenance, has predominantly Type I (S-slow twitch, fatigue resistant) alpha MNs (Table 2.9-1). In contrast, the first dorsal interosseous muscle of the hand partici-
pates in more rapid, phasic movements and has more Type II-FF (fast twitch, fast to fatigue) MNs (8).
The motor unit territory (MUT) is defined as “the area in a muscle over which the muscle fibres (MFs) belonging to an individual motor unit (MU) are distributed” (9). In humans, motor unit territories (MUTs) vary in size in different muscles. In a larger proximal limb muscle such as the biceps bracchi, the MUT has an estimated diameter of five to ten millimeters (i.e., cross section) based on scanning EMG studies (10). Experimental studies in animals have suggested greater dispersion of the MUT within a muscle that might change in size along the length of the muscle (11,12).
The motoneurons exert a trophic influence on the MFs. Cross- innervation experiments have demonstrated that MFs may change their his- tochemical type. “Fast” MUs also may be changed experimentally to “slow”
MUs by constant electrical stimulation; thymectomy, castration, and aging also may produce effects on the MU. In elderly individuals, decrease in muscle bulk typically is observed, consequent upon generalized atrophy of individual MFs rather than a decrease in the total number of MFs themselves.
There is electrophysiologic evidence of MU remodeling in elderly indi- viduals. The concentric needle (CN) motor unit action potential (MUAP) Table 2.9-1. Types of alpha motoneurons and their corresponding muscle fiber type.*
Relative Alpha Motoneuron Types
Characteristics I II II
(S= slow twitch, (FR = fast (FF= fast fatigue resistant) twitch, resistant twitch, fast
to fatigue) to fatigue)
Neuronal cell Smaller — Larger
body size
Axon diameter Smaller — Larger
Axon conduction Slow Fast Faster
velocity
Firing rate Slow and regular on Intermediate Fast on stronger
minimal effort effort
Relative excitability Lower Intermediate Higher
threshold
Twitch tension Low, longer Intermediate, High, brief
long
Contraction time >99 milliseconds Intermediate <85 milliseconds
Fatigability Slow Relatively slow Fast
Force generated Low Moderately high High
* Modified from Barkhaus PE, Nandekar SD, Quan D, Talavera F, Busis NA, Benbadis SR, Lorenzo N. EMG Evaluation of the Motor Unit: The Electrophysiologic Biopsy. eMedicine J.
2002;3(1): section 2–11.
has shown an increase in duration with increased age, although not to any significant degree until the individual is older than 60 years of age. The fiber density (as measured in SFEMG) also increases after the sixth decade (13).
During voluntary contraction of individual units within a muscle, the con- tracting units summate to form a motor unit potential (MUP) (Figure 2.9.1).
The MUP has three variables: amplitude, shape, and duration. Amplitude is determined by the algebraic summation of each single fiber potential and the distance of the recording electrode to the fiber. Shape depends on the number of muscle fibers discharging simultaneously. Duration depends on the distribution and surface extent of muscle fibers that correspond to the axon of a motor unit. Duration is the time interval between the first deflec- tion from the base line to the point at which the deflection ultimately returns.
Normally, MUPs are biphasic or triphasic. A potential with more than four phases is referred to as polyphasic. Buchthal et al. (8) defined a “phase”
as the part of the MUP that lies between two crossings of the base line.
Electromyography recordings from muscle activity can be performed by the use of: (a) Surface electrodes, (b) CN electrodes, (c) single fiber elec- trodes, and (d) wire electrodes.
Current Indications for Electromyography
The indications for EMG in the assessment of anorectal disease are dimin- ishing where EMG mapping of the sphincter is unnecessarily invasive in
Figure 2.9.1. Motor unit potential.
the age of endoanal ultrasonographic imaging of sphincter integrity.
Puborectalis EMG may be more accurate than cinedefecography in the delineation of non-relaxing puborectalis syndrome. Electromyography assessment for pelvic floor and anal sphincter muscles is mainly indicated in order to determine: (a) Denervation of muscle fibers, (b) reinnervation of muscle fibers (single fiber density), (c) sphincter integrity, and (d) ade- quate contraction or relaxation during squeeze or straining (5,6). There still may be a place for serial conventional EMG in some patients with complex perineal injuries in an effort to determine when to reverse fecal diversion or in cases where total anorectal reconstruction (with coloperineal anasto- mosis) is contemplated after abdominoperineal resection. In the pediatric age group, as well, there may be a case for its use in redo surgery where patients have had a poor functional outcome after surgery for a high anorectal anomaly (14,15).
Concentric Needle EMG Technique
Concentric needle EMG evaluates spontaneous activity, recruitment pattern, and MUAP waveform. A concentric needle electrode (CNE) con- sists of a fine platinum wire mounted inside a larger diameter metal cannula (65 mm). The inner wire is insulated from the needle cannula, which ends with a 15 degree cut point, exposing the wire electrode surface. Its record- ing surface is 0.07 square millimeters.
Optimal recording requires an amplifier frequency range of 10 hertz to 10 kilohertz and a sensitivity of 100 to 500 microvolts per centimeter with a usual set of the screen visualization to 100 microvolts per duration and a sweep speed of 20 milliseconds per duration for rest, squeeze, and strain and 500 milliseconds per duration for cough. This set-up can be modified in order to have a better view or analysis of waveforms. All patients receive a full detailed explanation about the examination to be performed. They are placed in the left lateral position, with a metal ground electrode fixed to one of the legs by a Velcro device.
The perianal skin is cleansed with a cotton swab soaked with an anti- septic reducing noise. The concentric needle electrode is introduced through the skin in both the left and the right sides with no anesthetic. This is done at one to one and one half centimeters from the anal verge. The introduction of this needle electrode (NE) is followed by a reactive dis- charge of MUPs, which is more evident in anxious patients. It is necessary to distinguish this activity from that known as “insertion activity” (IA), due to the mechanical stimulation of the muscle fibers. This is a reaction of the muscle fibers, not from a MUP discharge, and disappears very rapidly as the patient relaxes.
In order to avoid conceptual confusion, we prefer to use the term “reac- tive activity” to discriminate from IA. It is very difficult to see or register this IA at the anal sphincter because of the reactive activity of the MUP.
The insertion activity in skeletal muscles is a parameter, which in clinical EMG leads one to know the state of excitability and contractile capacity of the muscle fibers.
In the external anal sphincter (EAS) and the puborectalis (PR), MUP dis- charges also provide information concerning the contractile capacity of the muscle fibers. In cases of fibrosis, there is a loss of contractile capacity of these muscle fibers, and subsequently no MUP or fibrillation is recognized. In the case of denervation, MUP activity is replaced by fibrillation of the denerva- tion potentials.The NE is then advanced four to five centimeters, where elec- trical activity is detected. The NE having arrived at the PR level, the patient is asked to squeeze, cough, and strain (simulating rectal evacuation), and each of these events is registered on a print-out EMG paper (Figure 2.9.2).
Thereafter, the NE is withdrawn, passing across a zone where no electri- cal activity is registered, until the examination reaches another area with myoelectrical potentials, assumed to be at the EAS level. Here, again, recordings are made of the “reactive activity” and the same procedure as for the PR is repeated with squeeze, cough, and strain provocation; each registered as events on a print-out EMG paper (Figure 2.9.3).
The response to these different maneuvers in healthy individuals shows an increase in activity (recruitment of MUAPs) during squeeze and cough and a significant decrease or eventual electrical silencing during strain (8,16–18).
Any change in the number of functional muscle fibers in a MU will show an abnormal waveform of MUAP. After nerve damage, the adjacent pre- served axons will attempt to reinnervate the muscle fibers that have been denervated, resulting in one ME innervating more muscle fibers as part of the healing process. Therefore, MUAPs tend to have larger amplitudes, longer durations, and more phases (polyphasic or evidence of prior dener- vation injury). This typical feature is seen in neuropathic conditions. In myopathic pathology, there is a reduction of the number of MFs per MU, resulting in low amplitude and low duration of the waveform.
Pathological patterns are seen, for example. in: (a) Paradoxical contrac- tion of the puborectalis (increased activity during strain as compared with rest or squeeze) (19,20) (Figure 2.9.4), (b) decreased or absent activity during squeeze in traumatic lesions of the sphincter muscles, and (c) spon- taneous activity during rest (fibrillation) in denervated muscle fibers, which is difficult to recognize in sphincter muscle due to their smaller fiber size.
Under these circumstances it is easier to hear the characteristic noise pro- duced by fibrillation rather than to look at the trace on the screen of the oscilloscope. (d) Localized myoclonia of the anal sphincter (21,22).
Single Fiber EMG (23,24)
This technique is complementary to CNEMG, where additional informa- tion can be acquired. In the early 1960s, Stälberg and Trontelj described a
method to record individual muscle fiber action potentials (24). Patients are examined in the same position as used in CNEMG.
A special electrode (needle electrode), smaller in diameter than the CNE, is utilized. The recording element consists of a central wire that opens laterally near the tip of the needle electrode with a surface of 25 microm- eters and that picks up the electrical signals over a recording surface of 0.0003 square millimeters. A reference electrode is placed in a zone of elec-
Rest
Squeeze
Strain
Cough Figure 2.9.2. Needle electrode recordings at the puborectalis (PR) for rest, squeeze, strain, and cough.
trical quiescence. The characteristics of single fiber potentials (SFPs) as compared with those recorded with a CN are that the SFPs have a shorter duration, higher amplitude, and a very fast rise time.
The main additional information from SFEMG is fiber density. This is the mean number resulting of the analysis of single muscle potentials in 20 dif- ferent positions of the recording electrode within the same muscle. Poten-
Rest
Squeeze
Strain
Cough Figure 2.9.3. Needle electrode recordings in the external anal sphincter (EAS) for rest, squeeze, strain, and cough.
tials accepted for analysis should be greater than 100 microvolts. The increase in fiber density reflects reinnervation due to nerve sprouting, implying that there are more muscle fibers innervated by an individual axon, and therefore that there are more fibers closer to the uptake area of the electrode (often corresponding to polyphasic action potentials in the EMG).
The fiber density values are increased before any definitive signs of abnormality are found on CNEMG recording. The normal fiber density is 1.5± 0.16, but tends to increase after the age of 60 years (13).
Pudendal Nerve Terminal Motor Latency (25,26)
Pudendal nerve stimulation technique assesses the distal motor innerva- tions of the pelvic floor muscles. Pudendal latency measures the time inter- val between the nerve stimulus and the muscle response. Latency reflects the integrity of the nerve’s insulation with myelin, but can indicate damage to the health of the largest and fastest conducting fibers within the nerve.
Terminal motor latencies are prolonged in demyelinating diseases and in conditions in which many fast-firing nerve fibers have been damaged.
To perform this test, the patient is positioned in the left lateral decubitus position, with the knees flexed and the hips close to the edge of the exam- ination table. A flat, self-adhesive, disposable electrode is used. This device was developed at the St. Mark’s London Hospital (Dantec Electronic, Tonsbakken 16-18 DK-2740, Skovlunde, Denmark), and it is attached to the volar aspect of the index finger, covered initially by a latex glove. It con- sists of a bipolar stimulating electrode, with the recording electrode placed a standardized distance on the base of the finger. The electrode is attached to the connector cable with an input for EMG recording and an output for nerve stimulation. The examining finger is lubricated with a special gel that Normal sequence Paradoxical puborectalis contraction
Figure 2.9.4. EMG activity record in paradoxical puborectalis contraction (anismus) syndrome.
improves electric transmission and is introduced into the anal canal, direct- ing it towards the ischial spine (right and left side) (27).
A square stimulus of 0.1 or 0.2 milliseconds in duration (at one-second intervals) is delivered up to the individual threshold, usually not exceeding 15 milliamperes. The response to this stimulus is a palpable EAS contrac-
Figure 2.9.5. Pudental Nerve Terminal Motor Latency.
tion and monitor detection of a motor potential on the oscilloscope screen, with the examiner looking for the maximal response and a reproducible wave form. This action potential then is registered and can be printed out, and the maneuver is similar for both right and left pudendal nerves. Mea- surement of the latency is calculated from the onset of the stimulus to the site of onset of the response.
The normal latency reference value is 2.0 ± 0.2 milliseconds on each side (Figure 2.9.5). Prolongation of PNTML is not unusual after vaginal deliv- ery, rectal prolapse, and with ageing (13,28,29). Pudendal neuropathy has been controversial as a predictor of the functional results after anal sphinc- teroplasty. The experience of the authors is summarized in Table 2.9-1, which appears to confirm that the presence of pudendal neuropathy does not correlate with incontinence severity (incontinence score), and as a result, sphincteroplasty is not denied to patients with some degree of pudendal neuropathy because many cofactors may influence suboptimal results after sphincteroplasty (e.g., incomplete internal sphincter plication, partial or complete plication disruption, etc.) (30–34).
Unit Experience
Between June 1991 and August 2004, 281 pelvic floor neurophysiologic eval- uations were performed in our unit. All patients were submitted for PNTML study, concentric EMG, and SF EMG.
One hundred and ninety seven patients had incontinence as their main complaint, 59 presented with chronic constipation (Rome II criteria), and 25 were referred because of anal or rectal pain, anal fissure, anal stenosis, or anorectal trauma. In the incontinent group, 171 were female and 26 were male, with a mean age of 58.53 years (8–86). The constipation group had 48 female patients and 11 males, with a mean age of 43.69 years (11–86). In the incontinent group of patients, statistical analysis of the means of the recorded PNTML, SF, and recruitment of motor unit potentials (MUP) during volun- tary contraction (being 5 for full recruitment of MUPs and 0 for no response) at the level of puborectalis and external sphincters was performed.
The mean incontinence score was 13/20 (0/20–20/20) (17). The findings are summarized in Table 2.9-2.
A correlation analysis was performed between the left and right puden- dal motor unit potentials recordings and the incontinence score showing no correlation, with an r value of -0.05039642 (R2= 0.0025398) for the left side (A) and an r value of -0.074529894 (R2= 0.005554705) for the right side (B). The same procedure was carried on between SF EMG and the in- continence score, and again there was no correlation: r = 0.05969207 (R2= 0.00356314) (C).
However, we did find a correlation between the incontinence score and recruitment of MUPs at the PR and the EAS muscles ( p< 0.01) with an r
value of -0.386747407 (R2= 0.149573556) for the right PR (D), an r value of -0.33056617 (R2= 0.10927399) for the left PR (E), an R value of -0.460363364 (R2= 0.211934427) for the right EAS (G), and an R value of -0.38729309 (R2= 0.14999594) for the left EAS (F).
In our series, a prolonged PNTML and an abnormal SF EMG does not necessarily correspond to a greater degree of incontinence and a decrease in MUP recruitment at the PR and/or the EAS correlates with a greater severity of incontinence (Figure 2.9.6).
This same analysis was used in symptomatically chronically constipated patients. Emphasis was applied on recruitment of MUP regarding the ability of patients to relax the sphincter mechanism while straining and was Table 2.9-2. The mean incontinence score summary of findings.
Right Left Single Right Left Right Left
pudendal pudendal fiber puborectalis puborectalis external anal external anal motor unit motor unit motor motor unit sphincter sphincter
potential potential unit potentials motor unit motor unit
potentials potentials potentials
Mean 2.32 2.36 2.04 3.46 3.49 2.71 2.75
SD 1.07 1.12 0.436 1.40 1.33 1.51 1.48
Maximum 7.8 9.2 3.5 5 5 5 5
Minimum 0 0 1.06 0 0 0 0
(A) (B)
R2= 0,0056
R2= 0,0025 1,20%
1,00%
0,80%
0,60%
0,40%
0,20%
0,00%
0,00 2,00 4,00 6,00 8,00 10,00
1,20%
1,00%
0,80%
0,60%
0,40%
0,20%
0,00%
0,00 2,00 4,00 6,00 8,00 10,00
R2 RPNTML / IS R2 LPTML / IS
Figure 2.9.6. Correlation coefficients between left and right PNTML, incontinence score, and SF EMG recordings and for MUP recruitment versus incontinence score for the left and right PR and EAS musculature. (A)Left PNTML versus inconti- nence score; (B) right PNTML versus incontinence score; (C) SF EMG recordings versus incontinence score; (D) incontinence score versus MUP recruitment poten- tials (PR—right side); (E) incontinence score versus MUP recruitment potentials (PR—left side); (F) incontinence score versus MUP recruitment potentials (EAS—
left side); (G) incontinence score versus MUP recruitment potentials (EAS—right side).
(C)
R2= 0,0036
1,20%
1,00%
0,80%
0,60%
0,40%
0,20%
0,00%
0,00 1,00 2,00 3,00 4,00
R2 FD / IS
(D) (E)
R2 RPRMUP / IS R2 LPRMUP / IS
1,20%
1,00%
0,80%
0,60%
0,40%
0,20%
0,00%
0 2 4 6
1,20%
1,00%
0,80%
0,60%
0,40%
0,20%
0,00%
0 2 4 6
R2= 0,01415
R2= 0,1098
(F) (G)
R2 RESMUP / IS
R2 LES MUP / IS
1,20%
1,00%
0,80%
0,60%
0,40%
0,20%
0,00%
0 2 4
1,20%
1,00%
0,80%
0,60%
0,40%
0,20%
0,00%
0
R2= 0,2119 R2= 0,15
1 3 5 6 1 2 3 4 5 6
Figure 2.9.6. Continued
classified as total relaxation (r), incomplete relaxation (ir), and paradoxical contraction (pc); each being compared with MUP recruitment during rest.
In this group, CNEMG diagnosed 10 patients as having PPRC (Para- doxical Puborectalis Contraction) alone, 13 as having PR and EAS para- doxical contraction, 11 patients as having paradoxical contraction of the
EAS alone, eight with incomplete relaxation of the PR and the EAS, five with sole incomplete relaxation of the EAS, and three with incomplete relaxation of the PR alone.
A summary of results is shown in Table 2.9-3.
This procedure contributed to the diagnosis of paradoxical contraction or incomplete relaxation of the sphincter mechanism in 75% of the patients consulting for defecation disorders.
Summary
In the past, EMG was one of the principal modalities in the determination of sphincter injury potentially amenable to repair. This has been superceded by high-resolution endoanal ultrasonography and magnetic resonance imaging (MRI) and reconstructed endoluminal sonography. Its use is either confined to very specialist settings (as discussed) or to research such as in the assessment of IAS EMG (35). Formal neurophysiologic assessment of the pelvic floor in constipated patients is still occasionally a useful comple- ment to other physiology testing where non-relaxing paradoxical PR con- traction is suspected, but unclear using defecography or manometry, and when transit studies are difficult to interpret. There is no clear evidence that EMG parameters predict for successful biofeedback outcomes in these complex cases. Pudendal latency must still remain an experimental tool, often included with manometric data in many reports without confident evi- dence base that abnormal prolongation of the PNTML precludes success- Table 2.9-3. Recordings for right and left pudendal motor unit potential and SF EMG (means, standard deviation, maximum, and minimum) with right and left PR and EAS motor unit potentials for constipated patients during relaxation (r) and incomplete relaxation (ir) and in patients with paradoxical puborectalis contraction (pc) syndrome.
Right pudendal motor Left pudendal motor Single fiber unit potential unit potential
Means 2.52 2.34 1.81
SD 1.50 1.31 0.48
Maximum 9 8.2 2.8
Minimum 1.3 1.31 1
Right Left Right external Left external
puborectalis puborectalis anal sphincter anal sphincter
motor unit motor unit motor unit motor unit
potentials potentials potentials potentials
r 25 25 22 22
ir 11 11 13 13
pc 23 23 24 24
ful sphincteroplasty outcomes. Its value may be of use to document in these patients who experience delayed deterioration in their functional result.
Although a normal PNTML does not indicate an absence of nerve injury (in the same way that an abnormal PNTML is not indicative of abnormal muscle function), SF EMG is an objective marker of muscle reinnervation and may be useful in patients with failed sphincteroplasties or in the context of total anorectal reconstruction.
References
1. Rosato GO, Lumi CM, and Miguel AM. Anal sphincter electromyography and pudendal nerve terminal motor latency assesment. Sem Colon Rectal Surg.
1992;3(2):68–74.
2. Malouf AJ, Vaizey CJ, Nicholls RJ, and Kamm MA. Permanent sacral nerve stimulation for fecal incontinence. Ann Surg. 2000;232:143–8.
3. Olsen AL and Rao SS. Clinical neurophysiology and electrodiagnostic testing of the pelvic floor. Gastoenterol Clin. 2001;30(1):33–54.
4. Speakman CTM, Kamm MA, and Swash M. Rectal sensory evoked poten- tials: an assessment of their clinical value. Int J Colorectal Dis. 1993;8(1):
23–8.
5. Snooks SJ and Swash M. Nerve stimulation techniques. In: Henry MM and Swash M, editors. Coloproctology and the pelvic floor: Pathophysiology and management. London, UK: Butterworths; 1985. p. 184–206.
6. Adrian ED and Bronk DW. The discharge of impulses in motor nerve fibers: II.
The frequency of discharge in reflex and voluntary contractions. J Physiol.
1929;67:119–51.
7. Beck A. Electromyographische untersuchungen am sphinkter ani. Arch Physiol.
1930;224:278–92.
8. Buchtal F. The general concept of the motor unit: Neuromuscular disorders. Res Publ Assoc Res Nerv Ment Dis. 1961;38:3–30.
9. Stälberg E and Antoni L. Electrophysiological cross section of the motor unit.
J Neurol Neurosurg Psych. 1980;43(6):469–74.
10. Nomenclature Committee. AAEE glossary of terms in clinical electromyogra- phy. Muscle Nerve. 1987;10(8 Suppl):G1–60.
11. Barkhaus PE, Nandekar SD, Quan D, Talavera F, Busis NA, Benbadis SR, and Lorenzo N. EMG evaluation of the motor unit: the electrophysiologic biopsy.
eMedicine Journal. 2002;3(1).
12. Monti RJ, Roy RR, and Edgerton VR. Role of motor unit structure in defining function. Muscle Nerve. 2001;24(7):848–66.
13. Lauberg S and Swash M. Effects of ageing on anorectal sphincters and their innervation. Dis Colon Rectum. 1989;32:737–42.
14. Iwai N, Kanida H, Taniguchi H, Tsuto T, Yanagihara J, and Takahashi T. Post- operative continence assessed by electromyography of the external sphincter in anorectal malformations. Z Kinderchir. 1985;40:87–90.
15. Kubota M and Suita S. Assessment of sphincter muscle function before and after posterior sagittal anorectoplasty using a magnetic spinal stimulation techynique.
J Pediatr Surg. 2002;37:617–22.
16. Buchthal F, Pinelli P, and Rosenfalck P. Action potentials parameters in normal human muscle and their physiological determinants. Acta Physiol Scand. 1954;
32:219–29.
17. Buchthal F, Guld C, and Rosenfalck P. Multielectrode study of the territory of a motor unit. Acta Physiol Scand. 1957;39:83–104.
18. Buchthal F. Electromyography in evaluation of muscle disease. Method Clin Neurophysiol. 1991;2:25–51.
19. Wexner SD, Cheape JD, Jorge JMN, Heymen S, and Jagelman DG. A prospec- tive assessment of biofeedback for the treatment of paradoxical puborectalis contraction. Dis Colon Rectum. 1992;35:145–50.
20. Jorge LMN and Wexner SD. Etiology and management of fecal incontinence.
Dis Colon Rectum. 1993;36:77–97.
21. Fowler CJ. Pelvic floor neurophysioloy. Method Clin Neurophysiol. 1991;2:1–
20.
22. Goodgold J and Everstein A. Electrodiagnosis of neuromuscular disease. 2nd ed. Baltimore, MD: Williams & Wilkins; 1977. p. 210
23. Swash M and Snooks SJ. Electromyography in pelvic floor disorders. In: Henry MM and Swash M, editors. Coloproctology and the pelvic floor: pathophysiol- ogy and management. London, UK: Butterworths; 1992. p. 184–196.
24. Stälberg E and Trontelj J. Single fiber electromyography. Old walking. Surrey, UK: Mirvalle; 1979.
25. Snooks SJ and Swash M. Nerve stimulation techniques. In: Henry MM and Swash M, editors. Coloproctology and the pelvic floor: pathophysiology and management. London, UK: Butterworths; 1985. p. 196–206.
26. Wexner SD, Marchetti F, Sarlanga V, Corredor C, and Jagelman DG. The neu- rophysiological assessment of the anal sphincters. Dis Colon Rectum. 1991;34:
606–12.
27. Kiff ES and Swash M. Normal proximal and delayed distal conduction in the pudendal nerves of patients with idiopathic (neurogenic) faecal incontinence.
J Neurol Neurosurg Psych. 1984;47:820–3.
28. Ryhammer AM, Laurberg S, and Hermann AP. Long-term effect of vaginal deliveries on anorectal function in normal perimenopausal women. Dis Colon Rectum. 1996;39:852–9.
29. Swash M and Snooks SJ. Electromyography in pelvic floor disorders. In: Henry MM and Swash M, editors. Coloproctology and the pelvic floor: pathophysiol- ogy and management. London, UK: Butterworths; 1992. p. 252–6.
30. Shu-Hung Chen A, Luchtefeld MA, Senagore AJ, MacKeigan JM, and Hoyt C.
Pudendal nerve latency—does it predict outcome of anal sphincter repair? Dis Colon Rectum. 1998;41:1005–9.
31. Malouf AJ, Norton CS, Engel AF, Nicholls RJ, and Kamm MA. Long term results of overlapping anterior anal sphincter repair for obstetric trauma.
Lancet. 2000;355:260–5.
32. Karoui S, Leroi AM, Koning E, Menard JF, Michot F, and Denis P. Results of sphincteroplasty in 86 patients with anal incontinence. Dis Colon Rectum.
2000;43:813–20.
33. Lauberg S, Swash M, and Henry MM. Delayed external sphincter repair for obstetric tear. Br J Surg. 1988;75:786–8.
34. Setti-Carraro P, Kamm MA, and Nicholls RJ. Long-term results of postanal repair for neurogenic faecal incontinence. Br J Surg. 1994;81:140–4.
35. Sorensen M, Nielsen MB, Pedersen JF, and Christiansen J. Electromyography of the internal anal sphincter performed under endosonographic guidance.
Description of a new method. Dis Colon Rectum. 1994;37:138–43.
Editorial Commentary
Electromyography and pudendal nerve terminal motor latency assessment are very important facets in the evaluation of pelvic floor function. Elec- tromyography is the most useful test as a complementary examination to an ultrasonography in patients with fecal incontinence. A helpful way of viewing these two tests is to consider ultrasonography as the assessment of
“gross” anatomy and electromyography as the method of analyzing “micro- scopic” anatomy. Specifically, anal ultrasonography may show what is thought to be a defect in the anterior portion of the external anal sphinc- ter, but electromyography has found scar tissue or defunctioned muscle.
Conversely, ultrasonography may find what is thought to be intact muscle, but by electromyography, a determination can be made that the muscle is injured. Therefore, these should be used together rather than individually for those patients with fecal incontinence. When both of these studies are combined with the physical examination, then the optimal determination can be made as to the method of treatment for such patients. In addition, measurement of pudendal nerve latency is quite possibly the single most important prognosticator for postoperative function following overlapping sphincter repair. Therefore, electromyography is generally performed com- bined with pudendal nerve terminal motor latency assessment. Alterna- tively, there is little reason to perform the uncomfortable needle electromyography in patients with constipation. In this group of individu- als, surface electromyography is as reliable, (if not more reliable), than defecography in the diagnosis of paradoxical puborectalis contraction.
Regardless of the method of study, electromyography with pudendal nerve terminal motor latency assessment remain important cornerstones within the anorectal physiology laboratory.
SW
