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.     

Reinnervation of anal sphincter muscle by low and high-threshold motor neurones.

The external anal sphincter (EAS) has continuously active low-threshold and recruitable high-threshold motor units (MUs), the latter being 'larger'. On performing concentric needle electromyography (EMG) of the EAS, the high-threshold MUs seemed to reveal more neuropathic changes than the low-threshold MUs. To verify this hypothesis, low- and high-threshold motor unit potentials (MUPs) were compared in patients with neuropathic EAS and controls. Fifteen subjects without pelvic disorders and 29 patients with sequela after cauda equina lesions were studied. In patients, only muscles ipsilateral to severe perianal sensory loss were included. MUPs were sampled using multi-MUP analysis during relaxation ('low-threshold'), and on activation ('high-threshold' MUs). MUP parameters of low- and high-threshold MUs from controls and patients were compared, as was the sensitivity and specificity with which MUPs were classified as normal or pathological (using discriminant analysis). MUP changes due to reinnervation, and the sensitivity and specificity in classifying MUPs as normal or pathological were not significantly different between the low- and high-threshold MUPs. Stronger activation of EAS does not improve discrimination between neuropathic and normal MUPs. New EMG techniques for sampling sphincter MUPs at higher activation levels would seem not to yield additional information.     

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.     

Usefulness of an increase in size of motor unit potential sample.

OBJECTIVE: It is known that the sensitivity of quantitative electromyographic (EMG) analysis of motor unit potentials (MUPs) improves with an increase in MUP sample size to more than 20. However, no normative data and estimate of sensitivity have been published. METHODS: In the present study sample sizes of 5, 10, 15, 20, 30 and 40 MUPs were obtained from the external anal sphincter (EAS) muscles of 81 controls and 70 patients with cauda equina lesions. For each sample size normative limits and sensitivities for mean values and 'outliers' were calculated for 8 MUP parameters. RESULTS: As the size of the MUP samples increased, normative limits narrowed and sensitivities increased for both statistics of all MUP parameters (sensitivities were 26% at 10, 44% at 20, and 67% at 40 MUPs with mean values and outliers of MUP area, duration and number of turns). CONCLUSIONS: Our results confirmed a substantial increase in the sensitivity of MUP analysis by enlargement of the MUP sample size to more than 20 MUPs. The gain in sensitivity seem to be greater than the increase obtained by examination of contralateral EAS muscle. SIGNIFICANCE: Findings might be useful to clinical neurophysiologists planning strategies for electrodiagnostic evaluation of lower sacral segments.     

Criteria for neuropathic abnormality in quantitative anal sphincter electromyography

For the external anal sphincter muscle, both normative values and an optimal set of motor unit potential (MUP) parameters have been defined. However, criteria for the diagnosis of neuropathic conditions have not yet been validated. Therefore, in this study, sensitivity was examined in 86 patients with cauda equina lesions (227 muscles), and specificity in 77 controls (119 muscles), using multi-MUP analysis. Six previously defined diagnostic criteria (mean values and outliers for MUP area, duration, and number of turns) were used. An increase in the number of diagnostic criteria required for muscle abnormality (two and three instead of one), and the application of more stringent normative limits resulted in a progressive increase in specificity from 74% to 99% (controls), and a decrease in sensitivity from 70% to 21% (patients). The data suggest that no single cut-off diagnostic criterion has both satisfactory sensitivity and specificity. Introduction of the diagnostic categories of "possible," "probable," and "definite" neuropathic abnormalities into quantitative electromyographic analysis is proposed.     

The diagnostic power of motor unit potential analysis: an objective bayesian approach.

The notion of a "myopathic" or "neuropathic" electromyogram (EMG) is usually based on qualitative visual and acoustical impressions. Conventional quantification defines abnormality but not diagnosis, which requires interpretation of patterns of change. Discriminant analysis is a model for this multivariate decision. It tells how probable it is that a motor unit potential (MUP) comes from a normal, myopathic, or neuropathic muscle. Accumulation of single MUP information by a sequential Bayesian algorithm produced diagnostic probabilities above 0.95 in 91% of all muscles (223 biceps brachii muscles from 80 patients with motoneuron disorders, 56 patients with neuropathies, 71 patients with myopathies, and 34 controls). Two muscles from patients with neurogenic disorders were misclassified as "myopathic." Misclassification was more frequent only in myositis (4 of 28 muscles) and in oculopharyngeal muscular dystrophy (2 of 4 muscles). MUP discriminant classification was as sensitive as, and more specific than, conventional quantitative EMG, which discriminated between myopathic and neuropathic in only 22% of the muscles. This rate was 59% for discriminant analysis. As a knowledge-based expert system, MUP discriminant analysis successfully distinguishes between myopathic, neuropathic, and unclassifiable MUP samples. It discloses more information than conventional quantitative MUP analysis.     

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.     

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.     

Sensitivity of motor unit potential analysis in facioscapulohumeral muscular dystrophy

Template-operated motor unit potential (MUP) analysis has made quantitative electromyography (EMG) feasible, even in busy laboratories, but validation of this approach is still necessary. In the present study, the utility of multi-MUP analysis was assessed in patients with a molecular genetic diagnosis of facioscapulohumeral muscular dystrophy (FSHD). Manual assessment of muscle strength and concentric-needle EMG of the biceps brachii and vastus lateralis muscles were performed. The sensitivity for diagnosing myopathy (mean values and outliers) was tested for eight MUP parameters and four of their combinations. The group comprised 31 patients. Elbow flexion and knee extension strength was normal in 45% and 52% of patients, respectively. The most sensitive MUP parameter was thickness, followed by duration. A combination of three MUP parameters (thickness, amplitude, and duration/area) was needed for maximal sensitivity. The study demonstrated a high sensitivity of multi-MUP analysis in FSHD. Myopathic abnormalities were demonstrated in all weak biceps brachii muscles, and in 77% of biceps brachii muscles with normal strength.     

"Satellite potentials" and the duration of motor unit potentials in normal, neuropathic and myopathic muscles.

Time-locked activity in the EMG was studied in normal, neuropathic and myopathic muscles, using the averaging technique. Normal and neuropathic muscles seemed in most cases not to differ with regard to the frequency nor the quality of "satellite signals", i.e. small and short potentials joining the main component of the MUP with a constant interval, up to 26 ms in duration. In normal muscles 10% of the MUPs and in neuropathic muscles 12% had a satellite, which, when studied, showed no signs of blocking. However, in 2 patients with an apparent old spinal affection both an increased number and an increased latency of satellite signals were found. In the different myopathies studied 45% of the MUPs recorded consecutively were preceded or followed by an often increased number of tiny satellites. Sometimes the satellites joining the myopathic MUP formed a long (up to 60 ms) "tail" after the triggering component. On the basis of our results we conclude that in myopathies the total duration of MUPs is in certain cases pathologically incrased rather than decreased.     

Motor unit sound in needle electromyography: assessing normal and neuropathic units

Motor unit action potentials (MUPs) recorded by a monopolar needle electrode in normal and neuropathic muscles were computer-simulated. Five experienced electromyographers acted as examiners and assessed the firing sounds of these MUPs without seeing them on a display monitor. They judged whether the sounds were crisp or close enough to accept for the evaluation of MUP parameters and whether, when judged acceptable, they were neuropathic-polyphasic. The examiners recognized motor unit (MU) sound as crisp or polyphasic when the MUP obtained was 0.15-0.2 mm from the edge of the MU territory. When the intensity of the sound decreased, they were unable to perceive it as crisp. When the intensity exceeded the saturation level of loudspeaker output, the sound was perceived as polyphasic, but the wave form of the MUP was not. When the frequency of the neuropathic MUP was lowered, the examiners were unable to determine whether the MUP was polyphasic. MUPs recognized as acceptable for evaluation can be distinguished by listening to MU sounds. The audio amplifier gain must be appropriately adjusted for each MUP amplitude in order to assess whether an individual MU sound is crisp or polyphasic before MUP parameters are measured on a display monitor.Copyright 2000 John Wiley & Sons, Inc.     

Standardization of anal sphincter electromyography: uniformity of the muscle

The different parts of the external anal sphincter (EAS) are usually regarded as one muscle with common EMG characteristics. This assumption was addressed by comparing the number of continuously firing motor units (MUs) during relaxation, as well as the parameters of motor unit potentials (MUPs) and interference pattern (IP) in the subcutaneous and the deeper parts of EAS. MUPs and IPs were analyzed in 44 subjects (2008 MUPs and 3014 IPs) without uroneurological or proctological disorders, and the number of continuously active MUs in 34 of these subjects was recorded (221 positions). No significant difference was found in IP and most MUP parameters between the two parts of the EAS muscle, but the number of continuously firing MUs was lower in the deeper part. As far as MUP and IP characteristics are concerned, the whole EAS can be considered as one muscle, but some differences in patterns of activation of MUs may exist in different regions.     

Comparison of different outlier criteria in quantitative anal sphincter electromyography.

OBJECTIVE: Analysis based on 'outliers' has been demonstrated to be a useful adjunct to mean value analysis in quantitative needle electromyography (EMG). However, the outlier criteria applied have been arbitrarily chosen. The aim of the present study was to determine the most useful outlier criteria in motor unit potential (MUP) analysis. METHODS: The external anal sphincter (EAS) muscles were examined by multi-MUP analysis. From 115 muscles of 64 normative subjects, the 0/100, 5/95, 10/90, 15/85, 20/80, and 25/75 percentile MUP parameter values were grouped individually. From these, the 5/95, 2.5/97.5, 1/99 and 0/100% confidence limits were determined. Thus, 24 sets of outlier limits were formed. To calculate sensitivity and specificity, data from 79 patients with cauda equina lesions (189 muscles), and from 77 controls (119 muscles) were compared to normative outlier limits. RESULTS: Sensitivities were highest with outlier limits formed from the 10-90 percentile ranges, followed by the 5-95 and 15-85 percentile ranges, while specificity was highest using the 15-85, followed by the 20-80, and 25-75 percentile ranges. On direct head-to-head comparison the 10-90 percentile ranges were more sensitive and 5-95 were more specific. CONCLUSIONS: The study demonstrated considerable differences in the sensitivity and specificity of outlier limits calculated from different percentile ranges, with outlier criteria calculated from the 10-90 and from the 5-95 percentile ranges appearing to be the most useful for detection of neuropathy in the EAS muscle. SIGNIFICANCE: In future EAS muscle EMG I propose that outlier criteria calculated from the 10-90 percentile ranges be used.     

Discriminant classification of motor unit potentials (MUPs) successfully separates neurogenic and myopathic conditions. A comparion of multi- and univariate diagnostical algorithms for MUP analysis

Multivariate statistical methods may be more appropriate for the multidimensional material of quantitative motor unit potential (MUP) analysis than the multiple univariate tests of the conventional Buchthal analysis. Buchthal analysis was slightly modified before it was used as the gold standard for new multivariate diagnostical algorithms, based on principal component analysis and on MUP discriminant classification: muscle means of continuous variables were related to tolerance limits after adequate transformation. Chi-square tests were used for dichotomized variables, e.g., polyphasia. Sensitivity and specificity of the uni- and multivariate algorithms were compared for 539 muscles from patients with motor neuron diseases, neuropathies and myopathies and for 91 biceps brachii, rectus femoris and tibialis anterior control muscles. False positive results accumulated less than expected by repeat univariate tests for single MUP parameters, due to high correlation. Combination of single parameters to factor scores did not improve specificity. One advantage of factor analysis was that factor matrix and factor scores matched those of previous studies in spite of different input parameters, which may facilitate multicenter comparisons. Discriminant classification successfully separated neurogenic and myopathic conditions, even in myositic muscles and motor neuron diseases, where myopathic and neuropathic MUPs frequently intermingle. Discriminant classification may support expert decisions and add weight to EMG differential diagnosis.     

Bilateral vs. unilateral electromyographic examination of the external anal sphincter muscle.

AIM OF THE STUDY: In patients with cauda equina or conus medullaris lesions, bilateral electromyographic (EMG) examination of the subcutaneous external anal sphincter (EAS) muscles has been suggested. In spite of its circular shape, EAS should be considered as two separate semicircular muscles. The aim of the present study was to test the hypothesis that information obtained by bilateral examination of the EAS muscle outweighs inconvenience due to additional needle insertions. PATIENTS AND METHODS: A group of 67 patients with clinical and radiological data supportive of cauda equina or conus medullaris lesion was studied. From the subcutaneous EAS muscles motor unit potentials (MUPs) were sampled by the standard concentric EMG needle electrode, and an advanced EMG system with template operated multi-MUP analysis. Severity of EMG abnormalities was determined, and compared in 48 pairs of the left/right subcutaneous EAS muscles. RESULTS: In 18 patients, bilateral EMG abnormalities were found, in five of them asymmetry of involvement was demonstrated. Unilateral MUP abnormalities were found in 22 patients. The sensitivity of unilateral EMG analysis was 57% and of bilateral examination, 83%. CONCLUSION: In patients with suspected cauda equina lesions, as a rule, bilateral EMG of the subcutaneous EAS muscle is recommended.     

Standardization of anal sphincter electromyography: effect of chronic constipation

Severe chronic constipation has been implicated as a cause of damage to the pelvic floor innervation. The aim of the present study was to examine the role of mild to moderate chronic constipation, a condition more relevant for clinical electromyographers, because this complaint is common in patients sent for evaluation of possible neurogenic dysfunction of lower sacral myotomes. A group of 59 subjects without major uroneurological dysfunction, proctological disorders, or neurological abnormalities participated in the study, which involved concentric needle electromyography of the external anal sphincter (EAS). Motor unit potentials (MUPs; sampled using multi-MUP analysis) and interference pattern (IP, sampled using turn/amplitude analysis) of chronically constipated and control subjects were compared. No effect of chronic constipation on MUP/IP parameters compatible with neurogenic injury was found. Our results suggest that mild chronic constipation does not cause damage to the EAS innervation, and that no separate reference values are needed for this group of subjects.     

EMG power spectrum, turns-amplitude analysis and motor unit potential duration in neuromuscular disorders

The diagnostic value of power spectrum analysis of the needle EMG pattern at a force of 30% of maximum was compared to that of turns-amplitude analysis and to that of manual measurements of motor unit potential (MUP) duration in the brachial biceps muscle of 20 patients with myopathy and 11 patients with neurogenic disorders. In myopathy the power spectrum analysis had the same diagnostic value as the turns-amplitude analysis and MUP duration measurements and the 3 methods supplemented each other. In patients with neurogenic disorders the diagnostic value of the power spectrum analysis as well as that of the turns-amplitude analysis were lesser than that of MUP duration measurement. In diseased muscles the amount of high frequencies increased with increasing ratio of turns to mean amplitude while there was no relation between the power spectrum and the MUP changes. The results suggest that the power spectrum analysis of EMG can be used as a diagnostic tool in patients with neuromuscular disorders.     

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.     

Peripheral neuropathy in late onset spinocerebellar ataxia

We studied 10 patients with late onset spinocerebellar ataxia including electrophysiological and muscle biopsy examinations. Nerve conduction studies of eight patients revealed axonal neuropathy, and six cases also showed signs of the involvement of the lower motor neuron. In 9 patients quantitative analysis of single motor unit potentials (MUPs) of the tibialis anterior or biceps brachii muscles showed mild to severe neuropathic changes and in all 10 patients the histopathological examination of the tibialis anterior showed mild to severe neuropathic changes. Neither nerve conduction studies, quantitative MUP analysis, nor histological findings of the muscle were related to the severity of duration of the disease.