Predictive power of motor unit potential parameters in anal sphincter electromyography

The diagnostic utility of motor unit potential (MUP) parameters is usually based exclusively on their diagnostic sensitivity, disregarding specificity. In the present study, advanced statistical methods were used to determine MUP parameters with the highest predictive power for the separation of neuropathic and normal external anal sphincter (EAS) muscles. Using multi-MUP analysis, 3,720 MUPs from 138 muscles of 52 patients with cauda equina lesion and 2,526 from 112 muscles of 64 controls were obtained. Only two principal components (PCs), which put weight on the MUP area and amplitude, were needed to explain all the data variability. On logistic and probit regression analyses, MUP area, duration, and number of turns gave results identical to all MUP parameters. Our results suggest that only these three MUP parameters are needed, and that they are as effective as PCs, in MUP analysis of chronic neuropathic EAS muscles. Reduced number of MUP parameters is expected to simplify MUP analysis and increase its specificity.     

Comparison of quantitative techniques in anal sphincter electromyography.

Data comparing results and utility of different quantitative electromyographic (EMG) techniques are limited. In the present study, we analyzed the EMG signal from the external anal sphincter (EAS) muscle using three techniques of motor unit potential (MUP) analysis, and a technique of interference pattern (IP) analysis. We examined 56 patients with damage to the cauda equina or conus medullaris, and 64 control subjects. Using manual-MUP and multi-MUP analysis about 20 MUPs, using a single-MUP technique about 10 MUPs, and using turn/amplitude (T/A) analysis about 20 IP samples were obtained. The sensitivities of these techniques in distinguishing neuropathic from control muscles were calculated. The single-MUP technique detected 63%, manual-MUP 57%, and multi-MUP analysis 62% of neuropathic muscles, and MUP parameters obtained by each of these differed significantly from the other. The sensitivity of T/A analysis of IP was 29%. Our results confirm the need for separate MUP normative data for each of the MUP analysis techniques, and favor them over the IP analysis technique. The normative data presented for the EAS muscle should improve and promote quantitative EMG in patients.     

Standardization of anal sphincter electromyography: utility of motor unit potential parameters.

Advanced electromyography systems offer quantitative analysis of a number of motor unit potential (MUP) parameters. However, only limited data are available on the diagnostic usefulness of these parameters. In the present study, we compared the sensitivities of MUP parameters in revealing "neuropathic" changes in the external anal sphincter (EAS) muscles in 56 patients examined 5-240 months after damage to the cauda equina or conus medullaris. Using multi-MUP analysis, 20 MUPs were obtained from patients' EAS muscles. Their MUP parameters were compared with normative data from 64 controls. The diagnostic sensitivities of mean values/"outliers" of MUP parameters for detecting neuropathic EAS muscles were calculated (area 25%/30%; number of turns 18%/29%; size index 13%/24%; thickness 18%/18%; amplitude 17%/17%; spike duration 20%/9%; duration 15%/12%; number of phases 15%/11%; and their combination 51%/52%). Altogether, the cumulative sensitivity of multi-MUP analysis using both mean values and "outliers" was 62%. The combination of MUP parameters improves the diagnostic yield of MUP analysis, but the influence on specificity remains unknown.     

Size of motor unit potential sample

In quantitative electromyography (EMG), a sample size of 20 motor unit potentials (MUPs) is standard. The effect of increase in the number of MUPs above 20 is not known, although advanced MUP analysis techniques make such samples practical. In the present study, using multi-MUP analysis, pools of 3,720 neuropathic and 2,526 control MUPs were obtained from external anal sphincter muscles. From each pool, 10,000 random samples of 5, 10, 15, 20, 30, 40, 50, and 100 MUPs were obtained by a computer. For each sample size, 95% normative limits for mean values, SDs, and "outliers," and sensitivities were calculated for eight MUP parameters. As the magnitude of MUP samples increased, normative limits narrowed and sensitivities increased (at 5: 20-30%; at 20: 30-55%; at 100: 80-100%) for all statistics of all MUP parameters. Our results demonstrated a substantial increase in sensitivity by increasing the MUP sample to more than 20. This option deserves consideration in an attempt to improve the usefulness of quantitative EMG.     

Sphincter electromyography in diagnosis of multiple system atrophy: technical issues

Possible technical reasons for the controversy over the role of sphincter electromyography (EMG) in the diagnosis of multiple system atrophy (MSA) were analyzed. In a review of the literature, a high sensitivity (>60%) was found reported in 11 studies that included late components, and no value of the test was found in 4 studies that excluded them. This was also corroborated in a pilot study of 5 patients with probable MSA. With late components included, the mean motor unit potential (MUP) duration was prolonged in all 4 patients with an adequate single-MUP analysis sample and, with late components excluded, in 2 of 5 patients on multi-MUP analysis. At least in diagnostic EMG of MSA patients, late components should be included in the measurement of MUP duration.     

Standardization of anal sphincter electromyography: normative data.

OBJECTIVES: Electromyography (EMG) of the external anal sphincter (EAS) is important in the evaluation of conus/cauda lesions, the differential diagnosis of parkinsonism and anal incontinence. The aim of our study was to establish normative data in a sufficiently large group of healthy subjects, using a rigorously standardized examination technique. METHODS: Sixty-four subjects (aged 19-83 years) without pelvic or neurological disorders were included. Motor unit potentials (MUPs)/interference pattern (IP) samples were obtained from the EAS using multi-MUP and turn/amplitude analyses, respectively. The effect of age, gender, parity, and constipation on MUP/IP parameters was studied. For MUP parameters the lower/upper limits for mean values, and 'outlier' limits, and for IP parameters normal 'clouds' were calculated. RESULTS: From 112 muscles 15-30 MUPs were sampled. As no effect of evaluated factors on mean values could be demonstrated, common reference values were calculated. Lower/higher limits for mean values were: amplitude 148/661 microV, duration 3.2/7.8 ms, area 87/625 microVms, and number of phases 2. 3/3.7. 'Outlier' limits for individual MUPs were: amplitude 84/1315 microV, duration 1.6/13.8 ms, area 46/1222 microVms, number of phases 2/6. From 95 muscles 2706 IP samples were obtained. CONCLUSIONS: The presented normative data should allow valid quantitative EMG of the EAS muscle in patients.     

运动神经元病患者的肛门外括约肌肌电图特征

目的总结运动神经元病(motor neuron disease,MND)患者的肛门外括约肌肌电图(EAS-EMG)特点。方法分析20例不同临床亚型MND患者的EAS-EMG资料,并与无二便障碍症状和体征的阴性对照组(对照组)对比。结果与对照组〔(12.21±2.26)ms、(512.89±363.55)(ms.μV)〕比较,MND患者的肛门外括约肌(EAS)运动单位电位(motor unit potential,MUP)平均时限延长〔(14.55±2.27)ms,P=0.000〕,面积增大〔(718.47±236.57)(ms.μV),P=0.05〕,MUP波幅、多相波比例、平均相在两组间无统计学差异(P>0.05)。结论 MND患者EAS存在临床下神经源性损害,MUP时限、面积是反映MUP特征的敏感指标。     

The external anal sphincter and the role of surface electromyography

Abstract  Assessment of the neuronal control of the external anal sphincter (EAS) has long been restricted to investigating patients with defecation disorders by invasive tools such as needle electromyography (EMG), while less invasive techniques have been regarded as non-suitable for diagnostic purposes. Multichannel surface EMG by means of electrode arrays applied to anal sphincter muscle records and identifies individual motor unit action potentials, their place of origin along the circumference, their repetitive firing frequency, and their progression along the muscle fibres at different levels within the anal canal. These data shed doubts on conventional knowledge about the anatomy of the EAS muscle, and confirms new concepts of anatomical differences between gender. This may eventually be transferred to a new understanding of the role of symmetry and asymmetry of pelvic floor innervation and its role in the pathogenesis of fecal incontinence.     

The external anal sphincter operates at short sarcomere length in humans

Background The length at which a muscle/sarcomere operates in vivo (operational length) and the length at which it generates maximal stress (optimal length) can be quite different. In a previous study, we found that the rabbit external anal sphincter (EAS) operates on the ascending limb of the length–tension curve, in other words at lengths shorter than its optimal length (short sarcomere length). In this study, we tested whether the human EAS muscle also operates at a short sarcomere length. Methods The length–tension relationship of the EAS muscle was studied in vivo in 10 healthy nullipara women. EAS muscle length was altered by anal distension using custom‐designed probes of 5, 10, 15, and 20 mm diameter. Probes were equipped with a sleeve sensor to measure anal canal pressure. The EAS muscle electromyograph (EMG) was recorded using wire electrodes. Ultrasound images of anal canal were obtained to measure EAS muscle thickness and anal canal diameter. EAS muscle stress was calculated from the anal canal pressure, inner radius, and thickness of the EAS muscle. Key Results Rest and squeeze stress of the anal canal increased with the increase in probe size. Similarly, the change in anal canal stress, i.e. the difference between the rest and the squeeze, which represents the active contribution of EAS to the anal canal stress, increased with the increase in probe size. However, increase in probe size was not associated with an increase in the external anal sphincter EMG activity. Conclusions & Inferences Increase in EAS muscle stress with the increase in probe size, in the presence of constant EMG (neural input), demonstrates that the human EAS muscle operates on the ascending limb of the length–tension curve or at low sarcomere lengths. We propose that surgically adjusting EAS sarcomere length may represent a novel strategy to treat fecal incontinence in humans.     

External anal sphincter fatigue is not improved by N-acetylcysteine in an animal model

Abstract  Oxidative stress is associated with skeletal muscle fatigue. This study tests the hypotheses that N -acetylcysteine (NAC) reduces fatigue and accelerates recovery of the rat external anal sphincter (EAS). Fifteen female Wistar rats were killed humanely. The EAS was mounted as a ring preparation and electrically stimulated with 50 Hz trains of 200 ms in duration every 4 s for three and a half minutes. Three groups were analysed: a control group ( n  = 5), a group pretreated with NAC (10⁻⁴ mol L⁻¹; n  = 5) and a group pretreated with NAC (10⁻³ mol L⁻¹; n  = 5). A novel fatigue index was formulated and was compared to a conventional method of expressing fatigue. There was no significant difference at concentrations of NAC (10⁻⁴ mol L⁻¹; P  > 0.05). At high concentrations of NAC (10⁻³ mol L⁻¹) there was a significant depression in peak twitch amplitude before fatigue ( P  = 0.04). N -Acetylcysteine in both concentrations used, did not alter fatigue or recovery of the rat EAS. There was a significant positive correlation between the two methods of expressing fatigue but the conventional method produced a higher fatigue index (22.4% on average). N -Acetylcysteine does not ameliorate fatigue or accelerate recovery of the EAS and may not be a useful medical therapy for faecal incontinence.     

Pudendal afferent innervation of the guinea pig external anal sphincter

Background Sensory nerves to the external anal sphincter (EAS) contribute to mechanisms promoting continence and defecation, yet we know little about their function. We investigated the function of pudendal mechanoreceptors to the guinea pig EAS. Methods Extracellular recordings from pudendal nerve branches to 14 EAS preparations, in vitro, were used to characterize extrinsic primary afferent nerve endings activated by circumferential distension. Key Results All 42 pudendal nerve afferents were silent under non‐distended conditions. Thirty‐three of 42 afferents had slowly adapting, low‐threshold responses to circumferential stretch that correlated with stretch length (R² = 0.40, P < 0.001). Twenty of 20 slowly adapting afferents reduced firing when stretch was maintained for 60 s (P < 0.0001). They had low thresholds to von Frey hairs (0.1–0.5 mN). Firing frequency correlated with degree of compression (R² = 0.40, P < 0.0001). Nine of 42 afferents had rapidly adapting responses at the onset/offset of isometric stretch. During ramp stretch, small vibrations from the stepper motor evoked rapid bursts of firing at frequencies up to 200 Hz. Instantaneous frequency was unrelated to either the rate or degree of stretch. Rapidly adapting units had low thresholds (0.1–0.2 mN) to von Frey hairs and small punctate mechanotransduction sites. Responses to von Frey hair compression were also rapidly adapting, and instantaneous frequency was unrelated to the degree of compression. Conclusions & Inferences The EAS has two functional classes of mechanoreceptors: slowly adapting low‐threshold and rapidly adapting low‐threshold mechanoreceptors. These two classes of afferents are likely to be involved in the maintenance of continence, and the process of defecation.     

Diagnosing multiple system atrophy with greater accuracy: combined analysis of the clonidine-growth hormone test and external anal sphincter electromyography.

The clonidine-growth hormone test (CGHT) has been proposed as a means of differentiating multiple system atrophy (MSA) from idiopathic Parkinson's disease (PD). However, it is controversial whether the CGHT is valid. We sought to confirm the validity of the CGHT and to compare the diagnostic accuracy of the CGHT with that of external anal sphincter electromyelography (Sph-EMG) for MSA. We performed the CGHT and the Sph-EMG on 21 PD patients, 23 patients with probable MSA of parkinsonian type (MSA-p), and 22 patients with probable MSA of cerebellar type (MSA-c). We compared the sensitivity, specificity, and positive and negative predictive values (PPV and NPV) of CGHT, Sph-EMG, and a combination of the two tests. We also evaluated the correlations of Unified Parkinson's Disease Rating Scale (UPDRS) scores with the results of the two tests. There was no significant difference between the UPDRS scores for the PD and MSA-p groups. Serum growth hormone concentrations after clonidine significantly increased in PD (mean increase +/- SEM, 4.19 +/- 0.92 ng/ml; P < 0.0001), but remained unchanged in both MSA-p (0.83 +/- 0.61 ng/ml) and MSA-c (1.45 +/- 0.58 ng/ml). The growth hormone responses to clonidine in MSA-p were significantly different from those in PD (P < 0.05). Abnormal, denervated Sph-EMG was observed in 95.7% of MSA-p, 86.4% of MSA-c, and 33.3% of PD patients. Compared to Sph-EMG, the CGHT was less sensitive but more specific in both MSA-p and MSA-c. The result of neither test correlated with the severity of parkinsonism. Interestingly, combining the results of the CGHT and Sph-EMG markedly increased the specificity (85.7% in the CGHT and 66.7% in Sph-EMG vs. 95.2% in the combination study) and the PPV in both MSA-p (85.7% and 75.9% vs. 94.4%) and MSA-c (82.4% and 73.1% vs. 91.7%). We confirm that the CGHT can distinguish MSA-p from PD. Its sensitivity is lower and its specificity higher than Sph-EMG. Compared to either test alone, combined testing with the CGHT and Sph-EMG increased specificity and PPV, thereby enhancing accuracy in the diagnosis of MSA.     

Intrarectal ground electrode improves the reliability of motor evoked potentials recorded in the anal sphincter

Motor evoked potentials (MEPs) can be recorded in the external anal sphincter in response to magnetic stimulation of the cerebral cortex or sacral roots. However, the magnitude of the stimulus artifact may alter the reliability of anal MEP recording. An intrarectal ground electrode substantially reduces stimulus artifact and technical failure, improving MEP latency determination to sacral root stimulation in particular.     

Optimizing acquisition time in quantitative electromyography

Quantitative electromyography (QEMG) relies on a number of discharges of the same motor unit action potential (MUAP) from a train to create an averaged MUAP considered to be representative of a true potential. The train of potentials may be affected by changes in position of the electrode relative to contributing muscle fibers of the motor unit due to operator or subject movement. The effect of changes in electrode position, along with consideration for patient comfort, prompted this study to determine the shortest duration of recording time necessary for sufficient data acquisition for QEMG studies. We determined that 10 seconds of moderate muscle activity is the most reasonable acquisition duration to isolate up to 6 MUAPs at a given electrode site and minimize the effects of movement artifact in the signal. Muscle Nerve, 2009     

Electromyography of the anal sphincter: Which muscle to examine?

Electromyographic examination of the deeper external anal sphincter (EAS) muscle is far more uncomfortable than of the subcutaneous muscle, so we tested the need for its examination. We compared the findings in 85 paired examinations of ipsilateral subcutaneous and deeper EAS muscles in 67 patients with a cauda equina lesion. When the other muscle was normal, the deeper or subcutaneous muscle was pathological in 18% or 13% of pairs, respectively. In addition, the subcutaneous EAS muscle was usually more severely affected than the deeper EAS muscle. Thus, examination of the deeper EAS muscle did not increase the sensitivity of MUP analysis significantly, and did not seem clinically necessary.     

Decomposition-based quantitative electromyography: methods and initial normative data in five muscles

Quantitative electromyographic (EMG) techniques provide clinically useful information to aid in the diagnosis and follow the course or response to treatment of diseases affecting the motor system. The purpose of this study was to describe a decomposition-based quantitative electromyography method (DQEMG) designed to obtain clinically applicable information relating to motor unit potential (MUP) size and configuration, and motor unit (MU) firing characteristics. Additionally, preliminary normative data were obtained from the deltoid, biceps brachii, first dorsal interosseous, vastus medialis, and tibialis anterior muscles of 13 control subjects. DQEMG was capable of efficiently and accurately extracting MUP data from complex interference patterns during mild to moderate contractions. MUP amplitude, surface-detected MUP (S-MUP) amplitude, MUP duration, number of phases, and MU firing frequencies varied significantly across muscles. The mean parameter values for the individual muscles studied were similar to previous reports based on other quantitative methods. The main advantages of this method are the speed of data acquisition and processing, the ability to obtain MUPs from MUs with low and higher recruitment thresholds, and the ability to obtain both S-MUP or macro-MUP data as well as MU firing rate information.     

Anal sphincter electromyography: editing of sampled motor unit action potentials

During multi-motor unit action potential (MUAP) analysis of the tonically contracted external anal sphincter (EAS), a mild interference pattern often obscures the baseline, affecting the algorithm's ability to determine accurate boundaries of detected MUAPs. To assess the equivalence of methods of editing and selecting candidate MUAPs from the EAS, 17 nulliparous women underwent concentric needle electromyography (EMG) of the EAS using multi-MUAP software. The selected MUAPs either were accepted without question ("automated"), or a subset was deleted due to a noisy baseline ("manual-deletion") or manually marked ("manual-mark"). A second examiner repeated the analysis. Each examiner found that the two editing methods were equivalent and yielded results that differed from those obtained by automated analysis of unedited data. However, there was a moderate difference in MUAP amplitude when the manual-deletion method was compared between the two examiners. Editing of selected EAS MUAPs during multi-MUAP analysis is required, and development of common protocols is essential to enable meaningful comparisons between similar studies.     

Functional morphology of anal sphincter complex unveiled by high definition anal manometery and three dimensional ultrasound imaging

Background Anal sphincter complex consists of anatomically overlapping internal anal sphincter (IAS), external anal sphincter (EAS) and puborectalis muscle (PRM). We determined the functional morphology of anal sphincter muscles using high definition anal manometery (HDAM), three dimensional (3D)‐ultrasound (US) and Magnetic resonance (MR) imaging. Methods We studied 15 nulliparous women. High definition anal manometery probe equipped with 256 pressure transducers was used to measure the anal canal pressures at rest and squeeze. Lengths of IAS, PRM, and EAS were determined from the 3D‐US images and superimposed on the HDAM plots. Movements of anorectal angle with squeeze were determined from the dynamic MR images. Key Results High definition anal manometery plots reveal that anal canal pressures are highly asymmetric in the axial and circumferential direction. Anal canal length determined by the 3D‐US images is slightly smaller than that measured by HDAM. The EAS (1.9 ± 0.5 cm long) and PRM (1.7 ± 0.4 cm long) surround distal and proximal parts of the anal canal, respectively. With voluntary contraction, anal canal pressures increase in the proximal (PRM) and distal (EAS zone) parts of anal canal. Posterior peak pressure in the anal canal moves cranially in relation to the anterior peak pressure, with squeeze. Similar to the movement of peak posterior pressure, MR images show cranial movement of anorectal angle with squeeze. Conclusions & Inferences Our study proves that the PRM is responsible for the closure of the cranial part of anal canal. HDAM, in addition to measuring constrictor function can also record the elevator function of levator ani/pelvic floor muscles.     

Supraspinal control of external anal sphincter motility: effects of vesical distension in humans and cats

A pontine centre located near the micturition centre controlling external anal sphincter (EAS) motility via noradrenergic neurones has been described in cats. The aim of this study was to determine (i) whether a similar centre controls EAS motility in humans and (ii) whether this centre is involved in vesico-sphincteric reflexes in cats and humans. The effects of an alpha-1-adrenoceptor antagonist (nicergoline) and those of vesical distension on the electrical activity of the EAS were studied in paraplegic and non-paraplegic volunteers. The effects of vesical distension by injecting saline at physiological levels on the responses of the EAS to pudendal nerve stimulation were investigated in intact cats and cats with nerve sections. In non-paraplegic subjects, nicergoline and vesical distension abolished the activity of the EAS. These effects were no longer observed in paraplegic patients. In cats, vesical distension inhibited the reflex response of the EAS to pudendal nerve stimulation. This vesico-sphincteric reflex, which was no longer observed in spinal animals, persisted after nicergoline injection. These findings indicate that in humans, there exists a supra-spinal centre facilitating the tonic activity of the EAS via noradrenergic neurones not involved in the inhibitory vesico-sphincteric reflex.