Motor Unit Potential Parameters Research Articles

Utility of the Clustering Index method for diagnosing neuromuscular disorders as compared with needle electromyography.

Concentric needle electromyography (CNEMG) is an essential examination for evaluating neuromuscular disorders, although pain is a drawback. Clustering Index (CI) method is a non-invasive quantitative analysis for surface electromyography (SEMG) that evaluates whether the signal area is clustered into the few large motor unit potentials (MUPs) or is evenly distributed. However, the diagnostic yield of the CI method in comparison with CNEMG is not known. In this study, we aimed to compare the sensitivity of the CI method with MUP parameters in CNEMG for diagnosing neurogenic or myogenic disorders. We retrospectively identified patients for whom both SEMG and CNEMG were performed on the same tibialis anterior (TA) muscle. In CNEMG, seven MUP parameters were evaluated, including size index (SI) and revised size indices for neurogenic (rSIn) and myogenic (rSIm) disorders. Identified were 21 patients with neurogenic and 21 patients with myogenic disorders. Control data were constructed from 30 control subjects. The sensitivities of the CI method for the neurogenic and myogenic groups were 76% and 62%, respectively, which were not significantly different from MUP parameters, except for being significantly higher than those of amplitude and duration for myopathy (24%). Among MUP parameters, the sensitivities of rSIn (62%) and rSIm (57%) for myopathy were significantly higher than those of amplitude and duration. The CI method significantly correlated with the strength of the TA muscle in myopathy. The CI method, having comparable diagnostic yields to MUP parameters, is promising as a non-invasive diagnostic measure.

Neurophysiological Hallmarks of Axonal Degeneration in CIDP Patients: A Pilot Analysis.

In this work, we aim to identify sensitive neurophysiological biomarkers of axonal degeneration in CIDP patients. A total of 16 CIDP patients, fulfilling the clinical and neurophysiological criteria for typical CIDP, treated with subcutaneous immunoglobulin (ScIg) (0.4 g/kg/week) were evaluated at baseline (before ScIg treatment) and after long-term treatment with ScIg (24 months) by clinical assessment scales, nerve conduction studies (NCS) and electromyography (EMG). Conventional and non-conventional neurophysiological parameters: motor unit potential (MUP) analysis, MUP thickness and size index (SI)] and interference pattern (IP) features were evaluated after long-term treatment (24 months) and compared with a population of 16 healthy controls (HC). An increase of distal motor latency (DML) and reduced compound motor action potential (CMAP) amplitude and area in CIDP patients suggest axonal damage of motor fibers, together with a significant increase of MUP amplitude, duration and area. Analysis of non-conventional MUP parameters shows no difference for MUP thickness; however, in CIDP patients, SI is increased and IP area and amplitude values are lower than HC. Despite clinical and neurophysiological improvement after ScIg treatment, neurophysiological analysis revealed axonal degeneration of motor fibers and motor unit remodeling. Correlation analysis shows that the axonal degeneration process is related to the diagnostic and therapeutic delay. MUP area and SI parameters can detect early signs of axonal degeneration, and their introduction in clinical practice may help to identify patients with the worst outcome.

The electromyographic analysis of orbicularis oculi muscle in epiphora.

Purpose:Functional epiphora is a clinical condition that presents with the complaint of watery eyes, but without anatomical stenosis in the lacrimal drainage system. Although the mechanism is not clear, there are various possibilities involving the movement of the orbicularis oculi muscle, especially its deeper segment (Horner’s muscle). We aimed to evaluate the function of the orbicularis oculi muscle in patients with patent, but dysfunctional lacrimal drainage system using a quantitative motor unit potential (MUP) analysis.Methods:Twenty-eight patients with functional epiphora (mean age = 59 years) and a control group of 28 volunteers were included in the study. Inclusion criteria were persistent and symptomatic epiphora or wiping >10 times per day and diagnosis confirmation by lacrimal irrigation test. Electromyography (EMG) was performed on the deeper segment of the orbicularis oculi muscle (medial and lateral parts). MUP parameters (duration time, amplitude, number of phases, number of turns, area, rise time, and thickness) were evaluated in both groups. Any increase in amplitude, prolongation time (>14 ms), number of turns, and satellite potential was taken as characteristic of the neurogenic type of epiphora, whereas shortened motor unit duration time, increased phase number, and low amplitude are the features of myopathic type.Results:Upon MUP analysis of the medial and lateral orbicularis oculi muscle, the increase in duration and thickness values in the medial part and the increase in duration, amplitude, area, and thickness values of the lateral part were found to be statistically significant in the patient group compared to the control group (P < 0.001). In the evaluation of the patients’ medial and lateral orbicularis oculi muscle, the increase in phase values and decrease in amplitude, area, and rise time values were found to be statistically significant (P = 0.024, P < 0.001, P < 0.001, and P = 0.010, respectively).Conclusion:These data show that functional epiphora is due to neurogenic damage of the orbicularis oculi muscle and should be investigated in more detail.

Neuromuscular recruitment strategies of the vastus lateralis according to sex.

AimDespite males typically exhibiting greater muscle strength and fatigability than females, it remains unclear if there are sex‐based differences in neuromuscular recruitment strategies e.g. recruitment and modulation of motor unit firing rate (MU FR) at normalized forces and during progressive increases in force.MethodsThe study includes 29 healthy male and 31 healthy female participants (18‐35 years). Intramuscular electromyography (iEMG) was used to record individual motor unit potentials (MUPs) and near‐fibre MUPs from the vastus lateralis (VL) during 10% and 25% maximum isometric voluntary contractions (MVC), and spike‐triggered averaging was used to obtain motor unit number estimates (MUNE) of the VL.ResultsMales exhibited greater muscle strength (P < .001) and size (P < .001) than females, with no difference in force steadiness at 10% or 25% MVC. Females had 8.4% and 6.5% higher FR at 10% and 25% MVC, respectively (both P < .03), while the MUP area was 33% smaller in females at 10% MVC (P < .02) and 26% smaller at 25% MVC (P = .062). However, both sexes showed similar increases in MU size and FR when moving from low‐ to mid‐level contractions. There were no sex differences in any near‐fibre MUP parameters or in MUNE.ConclusionIn the vastus lateralis, females produce muscle force via different neuromuscular recruitment strategies to males which is characterized by smaller MUs discharging at higher rates. However, similar strategies are employed to increase force production from low‐ to mid‐level contractions. These findings of similar proportional increases between sexes support the use of mixed sex cohorts in studies of this nature.

STUDY OF BONE MARROW ASPIRATE INJECTION EFFECT ON DENERVATED MUSCLE ACCORDING TO ELECTROMYOGRAPHY STUDIES

The aim. To study in experiment the effect of bone marrow aspirate injection on the course of denervation-reinnervation processes in skeletal muscle using neurophysiological research method. Materials and methods. Experimental study was performed on 36 mature rabbits weighing 3-4 kg. Experimental model of the peripheral nerve acute injury and neurorrhaphy is taken as a basis. Animals were divided into 4 groups of 9 animals per group (3 animals for each experimental period). At 8, 12, and 16 weeks after surgery, all rabbits underwent needle EMG of the target muscles (m. gastrocnemius, and m. tibialis anterior) to study denervation-reinnervation changes. Results. Results of target muscles electromyographic examination are shown. As norm, we took motor unit potentials parameters, which were registered during the study of contralateral (not operated) pelvic limbs. Largest number of registered MUPs at different stages of the denervation-reinnervation process was observed, and was significantly higher (α = 0.07) in the groups in which bone marrow aspirate was injected in relation to group without bone marrow aspirate injection. Changes in the parameters of the registered MUPs in all groups corresponded to the general characteristics of the denervation-reinnervation process. Conclusions. Injection of bone marrow aspirate into the target muscles during surgery and in the early stages of reinnervation (in experimental study it is 7 weeks after surgery) – reliably (α = 0.07) promotes improvement of reinnervation processes in muscles, which is manifested by registration of more motor unit potentials.

Updated size index valid for both neurogenic and myogenic changes.

Size index (SI) is a motor unit potential (MUP) parameter in concentric needle electromyography calculated from amplitude and area/amplitude, which can sensitively discriminate between control and neurogenic MUPs. In this study, we investigated the application of SI to myogenic MUPs based on expanded data. MUPs were collected from the biceps brachii (BB) and tibialis anterior (TA) muscles. Muscles showing unequivocal neurogenic or myogenic changes by visual inspection were selected for patients. In addition to the original SI, a revised SI (rSI) was defined using the logarithmic scale for area/amplitude. The coefficient for area/amplitude was varied and that achieving the best sensitivity both for BB and TA was selected. Analyzed were 1619, 340, and 498 MUPs from the BB of 26, 10, and 14 subjects (control, neurogenic, and myogenic), respectively, and 1245, 536, and 473 MUPs from the TA of 23, 18, and 13 subjects (control, neurogenic, and myogenic), respectively. For neurogenic MUPs, the original SI and the newly defined rSIn were similarly sensitive (82.1% and 81.8% sensitivity for SI and rSIn, respectively, for BB, and 68.1% and 69.6% for TA), and were more sensitive than area (72.6% for BB and 57.6% for TA), the most sensitive parameter among conventional ones. For myogenic MUPs, the sensitivity of rSIm was 9.0% for BB and 24.5% for TA, which was not significantly different from duration (7.4% for BB and 21.8% for TA), the most sensitive parameter among conventional ones. SI, rSIn, and rSIm are promising as new MUP parameters.

Motor Unit Potential Analysis of the Palatal Muscles in Obstructive Sleep Apnea Syndrome

Objectives: Among different theories about pathogenesis of obstructive sleep apnea syndrome (OSAS), dysfunction of upper airway muscles still awaits to be delineated. The aim of this study is to examine differences in motor unit potential (MUP) parameters of upper airway muscles between OSAS patients and healthy controls. Methods: Ten male patients diagnosed as OSAS by whole-night polysomnography were analyzed for MUP parameters of genioglossus (GG) muscle, palatoglossus muscle (PG), palatopharyngeus muscle, and uvular (U) muscle. Eight healthy volunteer men matched by age were enrolled as a control group. Results: In PG muscle parameters, the mean MUP area was significantly smaller (P = 0.040) in OSAS patients than those in controls. On the other hand, U muscle parameters showed a significantly larger mean MUP area (P = 0.022) in OUAS patients compared to those in the control group. In OSAS patients, the percentages of polyphasic MUPs of GG and PG muscles were significantly high (P &lt; 0.001 and P = 0.05, respectively). Body mass index was positively correlated with number of phases of GG muscle (r s = 0.63, P &lt; 0.05) and duration of U muscle (r s = 0.71, P &lt; 0.05) in OSAS patients. Other MUP parameters of palatal muscles were similar between the two groups. Conclusion: Our results showed that, although mild in severity, structural neurogenic and myogenic changes characterized as mild and nonuniform MUP changes may co-exist in OSAS patients. These changes in palatal muscles may be attributed to compensatory adaptation of muscle fibers to other precipitating factors in OSAS.

Muscle velocity recovery cycles in neurogenic muscles

ObjectiveTo examine muscle membrane properties in neurogenic muscles using Muscle Velocity Recovery Cycles (MVRCs). MethodsForty-seven patients referred to Nerve Conduction Studies (NCS) and Electromyography (EMG) for peroneal nerve entrapment neuropathy were prospectively included. The patients were categorized as peroneal nerve entrapment neuropathy across knee (n = 22), L5-radiculapathy (n = 10), normal NCS/EMG (n = 9) and other disorders (n = 6) using NCS/EMG and neuroimaging results. Strength in anterior tibial muscle was measured by Medical Council Scale (MRC) and disease duration was recorded. In addition to conventional NCS/EMG, all subjects were examined with MVRCs in anterior tibial muscle. This provided parameters of muscle relative refractory period (MRRP) and early supernormality (ESN) and late supernormality (LSN). The results were compared with 29 age-matched healthy control subjects. ResultsMRRP was prolonged and ESN and LSN were reduced in neurogenic muscles. MRRP, ESN and LSN correlated to MRC and incidence of spontaneous activity but not to motor unit potential parameters or disease duration. ConclusionsMVRC changes provide in vivo evidence of depolarization in intact human muscle fibres that could underlie reduced muscle excitability and hence weakness in neurogenic muscles. SignificanceMVRCs appear to be a useful technique for revealing disease mechanism in a broad range of neuromuscular diseases.

Motor Unit Number Index (MUNIX) as a biomarker of motor unit loss in post-polio syndrome versus needle EMG

MUNIX method (Motor Unit Number Index) had been not used to assess number of motor neurons in post-polio syndrome in contrary to needle electromyography. ObjectivesTo confirm if MUNIX reflects motor unit loss and clinical stage and to assess difference in MUNIX and EMG results between muscles in different stage. Methods132 Muscles (MUNIX) and 96 (EMG) in 12 patients were studied and divided into groups: with normal strength(N), stable weakness and atrophy(S), new weakness and atrophy(W). ResultsIn PPS group MUNIX global was 561.36 ± 282.6 (right 6 muscles) and 561.27 ± 281.1 (left) significantly lower than in control group (six muscles 1139.6 ± 164.5) (p < 0.05). MUNIX global correlated with MRC global. MUNIX was greater in muscles with normal strength (95–100% of normal values) than in those with stable weakness (48%-0% of normal values) and new weakness (65%-0% of normal values). Respectively to clinical stage of muscle MUP (motor unit potential) amplitude increased to 350% of normal value, from 250% to 110%, and from 300% to 700%. No correlation was found between MUP parameters and MRC values. ConclusionsMUNIX reflects motor dysfunction and could be a good biomarker for loss of motor neurons in PPS.

Chapter 18 - Normal and abnormal voluntary activity

An important component of needle EMG entails recording and interpreting the electrical signals generated from motor units during voluntary contraction. The recorded motor unit potentials (MUPs) reflect the number of motor units within a muscle and the distribution and density of muscle fibers within a motor unit within a portion of a muscle. Various MUP parameters are assessed to determine the integrity of the motor units, including recruitment, stability, phases and turns, duration, and amplitude. Each of these parameters is altered in a different way in various neuromuscular diseases. In neurogenic disorders, the earliest changes occur in the recruitment pattern of motor units followed by MUP morphologic changes (increased MUP phases and duration) as reinnervation occurs. MUP instability, indicating impaired neuromuscular transmission, also occurs in reinnervating neurogenic disorders as well as in neuromuscular junction disorders. In myopathies, a reduction in the size of the motor unit is manifested by MUPs of low amplitude and short duration. Interpreting the voluntary MUP changes along with spontaneous activity helps to determine the type, severity, and temporal course of neuromuscular diseases.

Neuropathic changes in the tongue protruder muscles in patients with snoring or obstructive sleep apnea

Both myopathic and neuropathic tongue protruder muscle changes have been demonstrated to occur in obstructive sleep apnea (OSA) patients using different methods. We tried to elucidate this dilemma using quantitative electromyographic (EMG) methods. In a group of consecutive patients with suspected OSA a full overnight polysomnography (PSG) and quantitative needle EMG of the tongue protruder, biceps brachii and vastus lateralis muscles were performed. EMG findings were compared to control subjects. Of 23 patients, 8 were classified as simple snorers and the remaining 15 as OSA patients by PSG. Motor unit potential (MUP) parameters obtained in tongue protruder muscles, but not biceps brachii or vastus lateralis muscles, were significantly larger in patients compared to controls. However, no correlation was found between tongue protruder muscle MUP parameters and patient characteristics. Our study confirmed previous findings of neuropathic changes in the tongue protruder muscles of OSA patients, and extended these to simple snorers. Changes were limited to the upper airway muscle, and could not been explained by the severity or duration of the sleep breathing disorder. The possible role of denervation injury caused by the upper airway vibrations should be tested in the future by appropriately designed studies.

Platform Session – Electromyography: Two novel electrophysiological methods: In the evaluation of ALS patients – MScan MUNE and MVRC

Introduction Amyotrophic Lateral Sclerosis (ALS) is characterized by progressive loss of motor units, but electromyography (EMG) with quantitative motor unit potential (MUP) analysis does not directly quantify the denervation process. A more extensive clinical use of Motor Unit Estimation Methods: (MUNE), like MScan MUNE, could hence be of potentially great value. Muscle Velocity Recovery Cycle (MVRC) recordings can provide in vivo information about changes in muscle fiber membrane properties, and may enlighten the effect of the denervation process on the muscle fibers. The aim of this study was to examine the clinical utility of MScan MUNE and MVRC in ALS patients; which also contribute to a better understanding of disease pathophysiology. Methods 27 ALS patients and 23 age and sex-matched healthy control subjects were included. All participants were evaluated electrophysiologically by a standard quantitative EMG and by the two novel methods: MScan MUNE and MVRC, all in the anterior tibial muscle (TA). MScan MUNE, MVRC and EMG parameters were compared between ALS patients and healthy controls using parametric unpaired t-tests. ROC curves were used to test how these methods distinguish patients from healthy controls. MVRC parameters were correlated to EMG results and MScan parameters using linear regression analysis. Results The MScan MUNE value for ALS patients (55 (95% CI: 42–68)) was significantly lower than for the healthy controls (108 (95% CI: 98–117)) (p 5 sites) and controls. And there was no significant correlation between MVRC and MUP parameters or incidence of spontaneous activity. Conclusion The novel MScan MUNE method is a sensitive quantitative measure of loss of motor units in ALS patients in TA. The finding of no difference in MVRC for ALS patients compared to healthy controls indicate, that the muscle fiber membranes are not prominently affected by the denervation process. This may be explained by the compensatory process of collateral reinnervation, which initially is strong and ensures that the vast majority of muscle fibers are innervated and behave normally.

The utility of motor unit number estimation methods versus quantitative motor unit potential analysis in diagnosis of ALS

ObjectiveTo compare the diagnostic utility of motor unit number estimation (MUNE) methods to motor unit potential (MUP) analysis in amyotrophic lateral sclerosis (ALS). MethodsTwenty-five patients (1 definite, 11 probable, 9 possible ALS and 4 progressive muscular atrophy) and 22 healthy controls were prospectively included. Quantitative MUP analysis and three MUNE methods; Multiple Point Stimulation MUNE (MPS), Motor Unit Number Index (MUNIX) and MScanFit MUNE (MScan) were done in abductor pollicis brevis muscle. The sensitivities were compared by McNemar chi-square test. MUNE, MUP and revised ALS Functional Rating Scale (ALSFRS-R) parameters were correlated by regression analysis. ResultsThe sensitivities of MPS (76%) and MScan (68%) were higher than MUP duration (36%) and amplitude (40%) in detecting motor unit loss (p < 0.05). MUNE methods increased the categorical probability from possible to probable ALS in 4 patients (16%). There was only significant correlation between ALSFRS-R and MScan (r = 0.443, p = 0.027) among the electrophysiological tests. MUNE methods did not correlate to MUP parameters. ConclusionsMUNE methods are more sensitive in showing abnormality than MUP analysis. SignificanceMUNE methods, in particular MScan, may have the potential to be implemented in the clinical practice for diagnosis and follow-up of neuromuscular disorders particularly ALS.

Template-operated MUP analysis is not accurate in the diagnosis of myopathic or neuropathic changes in the diaphragm

The aim of this study was to evaluate the quantitative motor unit potential (MUP) analysis in the diagnosis of myopathy and neuropathy of the diaphragm. Diaphragm template-operated quantitative EMG were performed in 30 patients with myotonic dystrophy type 1 (DM1), 17 with myotonic dystrophy type 2 (DM2) and 40 with amyotrophic lateral sclerosis (ALS). Low MUP amplitude precluded MUP analysis in 21% of DM1 patients. Only a single DM1 patient had EMG findings consistent with myopathy. In this patient, and another 4 DM1 and 3 DM2 patients, findings were consistent with neuropathy. Neuropathic MUP changes were found in 92% of ALS patients, but due to motor neuron cell loss in only 60% MUPs analyses could be done. Phrenic nerve conduction studies correlated with respiratory function tests, whereas MUP parameters did not. Quantitative MUP analysis was not able to adequately sample diaphragm MUPs in patients with chronic myopathy or motor neuronopathy.

O25 Motor unit number estimation methods compared to quantitative motor unit potential analysis in amyotrophic lateral sclerosis

Objectives To compare the sensitivity of MUNE methods to quantitative motor unit potential (MUP) analysis in amyotrophic lateral sclerosis (ALS). Methods Twenty-four patients (1 definite, 11 probable and 8 possible ALS according to awaji criteria as reference standard, and 4 progressive muscular atrophy) were included. Patients were evaluated by revised ALS functional rating scale (ALSFRS-R). In all patients, quantitative MUP analysis and three MUNE methods; MScanFit MUNA (MScan), multiple point stimulation MUNE (MPS), and Motor Unit Number Index (MUNIX) were done in abductor pollicis brevis (APB). MUNE results were compared to 20 age-matched healthy controls and EMG to laboratory controls. The sensitivity of each methods was compared using McNemar chi-square test. MUNE values and MUP parameters were correlated to ALSFRS-R by regression analysis. Results MScan (70%) and MPS (61%) more frequently showed abnormality than MUP duration (35%) whereas only MScan was more often abnormal than MUP amplitude (39%) ( p r = 0.42, p = 0.03) but not MPS ( r = 31), MUNIX ( r = 35), MUP duration ( r = 0.19) or amplitude ( r = 0.09). Discussion MUP analysis gives information about reinnervation, but not about loss of motor units. Therefore MUNE methods may be preferable in ALS electrodiagnosis. Conclusions MUNE methods, particularly MScan, had higher sensitivities than MUP analysis in detection of abnormality in APB and were correlated better to ALSFRS-R. Significance MScan is a promising novel method which should be considered in diagnosis and monitoring disease progression in ALS.

Motor unit potentials of the erector spinae muscle by concentric needle electromyography.

IntroductionThe needle electromyography (EMG) serves to supply additional information in patients with suspected neuromuscular disorders. We aimed to provide motor unit potential (MUP) data by concentric needle EMG in the erector spinae (ES) in comparison with biceps brachii (BB) and lateral vastus (LV).MethodsElectromyography MUP data (n) were obtained in ES (517), BB (539), and LV (627) in 32 healthy volunteers (16f).ResultsMotor unit potential data: amplitude (μV) 393 ± 174 (ES), 375 ± 162 (BB), and 577 ± 304 (LV); duration (ms) 10.4 ± 2.4 (ES), 10.1 ± 2.1 (BB), and 11.1 ± 2.3 (LV), area (μV × ms) 585 ± 327 (ES), 538 ± 267 (BB), and 881 ± 492 (LV); phase number 3.23 ± 0.94 (ES), 2.98 ± 0.76 (BB), and 3.19 ± 0.81 (LV); size index 0.60 ± 0.56 (ES), 0.51 ± 0.53 (BB), and 0.96 ± 0.55 (LV). LV displayed higher values (p at least <.001) for MUP amplitude, duration, area, and size index as compared to both, BB and ES.ConclusionConcentric needle EMG investigations in healthy adult human subjects revealed similar MUP parameters in the ES and BB muscles, while in the LV muscle MUP amplitude, duration, area, and size index were significantly larger. Different neuromuscular disorders display a predominant involvement of proximally located muscles such as truncal muscles. The present results given here may facilitate the diagnosis of neuromuscular disorders.

51. Reference data for quantitative motor unit potential and interference pattern analysis in the genioglossus muscle

Needle electromyography (EMG) of the genioglossus muscle is a useful tool in patients with swallowing problems, that are common in many muscle and nerve diseases. Characteristic changes in motor unit potentials (MUPs) can be distinguished with MUP and interference pattern (IP) analysis. The purpose of this study was to establish reference intervals for MUP parameters using template operated multi-MUP analysis and to evaluate the IP features in the genioglossus muscle (GM) of healthy adults. We studied 28 healthy volunteers (11 men, 17 women, mean age 39 ± 12 years) with standard disposable concentric EMG needles (recording area 0.07 mm2) and an EMG system with standard settings (filters: 5 Hz–10 kHz), using an inframandibular approach. For each MUP parameter (amplitude, duration, turns) mean values and outlier limits (5th and 95th percentile) were calculated from the first 20 sampled MUPs. Data from IP plots (turns/amplitude, activity/envelope and activity/NSS) were collected in order to build normal clouds which contain >90% of the data points. MUP parameters obtained from the GM are similar to those published in literature. IP analysis is not available for healthy GM to our knowledge and could be an objective tool to quantitate the degree of abnormality in muscle and nerve diseases.

EP 18. Normative values for motor unit potentials in the erector trunci muscle determined by concentric needle electromyography

Background Electromyography (EMG) may give important information in addition to clinical findings in various neuromuscular disorders. Beside spontaneous discharges, motor unit potential analysis is routinely used to assess the size of motor units. Normative values for motor unit potentials (MUP) have been reported for e.g. biceps brachii or vastus muscles. Hardly any information is, however, available about motor unit potential (MUP) parameters of paraspinal muscles. Such information might be of special value, since in patients with myopathies or with spinal muscular atrophy (SMA), a proximal pattern of muscular involvement is the rule. Therefore, the aim of the present investigation was to obtain normative values for MUP parameters of the erector trunci (ET) muscle. Methods Thirtytwo healthy volunteers gave informed consent (O 28.9 ± 9.9 years; 16 women) to investigate the left biceps brachii (BB), vastus lateralis (VL) and ET muscles. BB and VL were investigated for comparative purposes. All EMG investigations and MUP analyses were done by conventional technique by MEK. For the BB and VL, subjects rested in the supine position. For recording the ET, patients were positioned on the right side with their hips, trunk and head in a maximally bent position. The needle electrode was inserted between lumbar vertebrae 1 and 2, two fingers lateral to the midline at a depth of 2.5–4.5 cm. MUP were recruited by extending head and legs simultaneously. MUP data comprized: amplitude (peak-to-peak), duration, area, phase number and size-index. Statistics: Kruskall–Wallis test, Mann-Whitney-U test post hoc . Results A total of 1683 MUP from 96 muscles were available. No statistically significant differences were noted for MUP parameters were detected between females and males. Therefore, values were treated together. Statistical analyses revealed significantly higher values in the VL for amplitude (0.56 ± 0.13 mV), duration (11.9 ± 1.0 ms), area (0.86 ± 0.22 μVs) and size-index (0.94 ± 0.24) in relation to BB: amplitude 0.37 ± 0.05 mV, duration 10.2 ± 0.9 ms, area 0.54 ± 0.11 μVs, size-index 0.52 ± 0.24, and ET: amplitude 0.39 ± 0.07 mV; duration 10.6 ± 1.2 ms; area 0.59 ± 0.16 μVs; size-index 0.60 ± 0.25. For these parameters no significant differences were observed between BB and ET. However, phase numbers were significantly smaller in BB (2.96) as compared with VL (3.18) and ET (3.22). Discussion MUP values in BB and VL are well in line with previously reported values. Therefore, the MUP data given for the ET here may be regarded as valid, too. ET MUP display similar values like those of the BB. Significantly higher values have been measured in the VL, with the exception of phase numbers. Amplitude, duration, area and size-index all depend on the amount of muscle fibres of a motor unit in the close vicinity of the needle electrode. Therefore, it can be inferred that ET motor units have similar dimension like those of the BB, while VL motor units appear to be significantly larger. The smaller dimensions of BB motor units relative to those of the VL may be clear from differences in their functions. For ET, which serves simple and mainly static movements of the vertebral column, larger dimensions of the motor units might have been expected than actually found here. Our results on ET MUP parameters are important for routine clinical practice because they facilitate the diagnosis in patients with suspected neuromuscular disorders such as myopathy or SMA.

Electrophysiologic and clinico-pathologic characteristics of statin-induced muscle injury.

In this study, we aimed at evaluation of electrophysiological and histopathalogical characteristics of statin-induced muscle injury as well as clinical features of patients who develop this condition in terms of frequency and pattern of evolution. Forty patients (age 39-74 years) including 25 subjects with type 2 diabetes mellitus, 9 with cardiovascular diseases and 6 with hyperlipidemia, who were receiving atrovastatin 40 mg/day for variable period, were studied. Thirty three healthy subjects (age 31-74 years) served as control group. Creatine phosphokinease level, thyroid function, motor unit potential parameters and muscle fiber conduction velocity of biceps brachii and tibialis anterior muscles were measured. Creatine phosphokinase level was elevated in statin users, particularly in those with diabetes mellitus. Less than 50% of statin users experienced symptoms related to muscle injury. Muscle fiber conduction velocity of the biceps brachii muscle was significantly reduced. Statin users with diabetes mellitus showed significant changes in electrophysiological parameters as compared to those with cardiovascular diseases and hyperlipidemia. Muscle biopsies showed muscle fiber variation in size, fibrosis and mild inflammatory cell infiltration. Immunohistochemical evaluation of muscle biopsies showed positive expression of Bcl-2 and one patient showed positive P53 immunohistochemical expression with elevated level of creatine phosphokinase. Atorvastatin increased average creatine kinase, statins produce mild muscle injury even in asymptomatic subjects. Diabetic statin users were more prone to develop muscle injury than others. Muscle fiber conduction velocity evaluation is recommended as a simple and reliable test to diagnose statin-induced myopathy instead of invasive muscle biopsy.

Increased motor unit potential shape variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects

ObjectiveTo study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG). MethodsThe tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77±5years) and 9 young male control subjects (23±0.3years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed. ResultsNF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls (P<0.05). NF jiggle was significantly higher in the TA compared to VM (P<0.05). For TA, NF jiggle was negatively correlated with MUNE, and positively correlated with S-MUP amplitude, NF count, MUP duration, MUP peak-to-peak voltage, and MUP area (P<0.05). For VM, NF jiggle was positively correlated with NF count and MUP area (P<0.05), and no significant correlations were found between NF jiggle and S-MUP amplitude, MUP duration, or MUP peak-to-peak voltage (MUNE was not calculated for VM, so no correlation could be made). ConclusionsHealthy aging is associated with neuromuscular transmission instability (increased NF jiggle) and MU remodeling, which can be measured using DQEMG. SignificanceNF jiggle derived from DQEMG can be a useful method of identifying neuromuscular dysfunction at various stages of MU remodeling and aging.