Concentric Needle Research Articles

P49-F Single muscle fiber potential (SFP) criteria – Analysis of effectiveness and a new approach

Objectives The aim of our study was to verify the effectiveness of single fiber potential (SFP) criteria in cases when potential recorded using single fiber electrode (SFE) or concentric needle electrode (CNE) is contaminated by distant fibers. Methods Morphological counterparts of SFP were studied using computer simulations. In this study, we examined triphasic potentials using and a model of a linear source of SFP. The criteria defining SFP in the case of SFP contaminated by distant fibers were analyzed, and the effect of second fiber contamination on jitter and fiber diameter determination evaluated. Results We found that SFP criteria prevent detection of SFP from fibers smaller than about 30 μ m in diameter, but do not prevent classification of a potential as an SFP even though it is formed by two or more fibers. This suggests that the presently used criteria may lead to incorrect interpretation of SFP potentials. SFPs contaminated by fibers of diameters differing by a few percent fulfill the criteria but a negative peak may be shifted in time and therefore impact jitter and diameter measurements. This contamination generally tends to decrease both the jitter and the determined diameter. A new approach to the identification of SFP is presented, determining fiber diameter and distance from the electrode to enable maximum sensitivity to potential contamination by the effect of a second fiber. Conclusion A new parameter characterizing SFP shape changes is introduced. This parameter is used in the method by which additional fibers affecting the SFP may be detected.

O-36 Listening the sound of neuromuscular junction during voluntary contraction

Background Sound is an indispensable component of electromyography. Although neurophysiologists are familiar with the end-plate noise and spikes, it is preferred to measure the neuromuscular transmission during voluntary contraction in time domain that is expressed in microseconds (jitter). Present study is aimed to create an audible voice of jitter and enable the physician to notice the difference between a healthy and a diseased neuromuscular transmission by hearing. Material and methods During voluntary contraction of frontalis muscle, single-fiber-like action potential pairs were recorded by using smallest concentric needle with 1 kHz high-pass filtering. Traces harboring potential pairs acquired from healthy participants and myasthenia patients were transferred. Signals were de-noised, locations of the two highest peak’s amplitude and the difference between them were determined. The average of these differences was calculated (jitter). “The sound of jitter” can be composed from the difference values of the locations of two highest peak’s amplitude. These values are duplicated in same amount proportionally up to 48,000 samples for achieving a 5 s length of sound. Then, they were sampled with 8 kHz. “The sound of jitter” was heard by using a function in “Matlab”. Results Sound of a healthy junction is soft; but in patients, it’s louder and contains more high frequency components. Conclusions Increased jitter reflects high variability of neuromuscular transmission. Converting it to an audible sound serves a different perspective. By doing so, the only irregularity that is heard would be the failure in junction transmission rather than the irregular firing of motor unit.

P51-F Quantitative electromyography: Normative data in paraspinal muscles

Objectives Paraspinal muscle may be affected in neuromuscular disorders, and EMG may be crucial in the diagnosis. The aim of the study was to develop normative data at different spinal segments. Methods Sixty-five healthy subjects (49% men, 51% women) aged 21–82 years were studied. In each subject, 16–92 motor unit potentials (MUPs) were recorded bilaterally at C7, Th10 and L5 segments using concentric needle electrodes. At each segment, average MUP amplitudes, durations, incidence of polyphasic potentials, and the amplitude at maximal voluntary contraction (MVC) were measured. The incidence of spontaneous activity was examined. Results There was no relationship between the EMG parameters and age. The mean MUP duration and amplitude, and the amplitude at MVC increased caudally (ANOVA, P Conclusions In contrast to limb-muscles EMG parameters were unrelated to the age of the subject. The gradient of EMG parameters caudally from C7 suggesting larger motor units at more caudal segments. The proportion of polyphasic potentials may be due to the organization of muscle fibers. The incidence of fibrillation activity was similar to limb muscles. Significance The study describes normative data for EMG of paraspinal muscles according to the examined spinal segment. These data may be useful in quantitative EMG examination of paraspinal muscle in neuromuscular disease.

SPiQE: An automated analytical tool for detecting and characterising fasciculations in amyotrophic lateral sclerosis

ObjectivesFasciculations are a clinical hallmark of amyotrophic lateral sclerosis (ALS). Compared to concentric needle EMG, high-density surface EMG (HDSEMG) is non-invasive and records fasciculation potentials (FPs) from greater muscle volumes over longer durations. To detect and characterise FPs from vast data sets generated by serial HDSEMG, we developed an automated analytical tool. MethodsSix ALS patients and two control patients (one with benign fasciculation syndrome and one with multifocal motor neuropathy) underwent 30-minute HDSEMG from biceps and gastrocnemius monthly. In MATLAB we developed a novel, innovative method to identify FPs amidst fluctuating noise levels. One hundred repeats of 5-fold cross validation estimated the model’s predictive ability. ResultsBy applying this method, we identified 5,318 FPs from 80 minutes of recordings with a sensitivity of 83.6% (+/− 0.2 SEM), specificity of 91.6% (+/− 0.1 SEM) and classification accuracy of 87.9% (+/− 0.1 SEM). An amplitude exclusion threshold (100 μV) removed excessively noisy data without compromising sensitivity. The resulting automated FP counts were not significantly different to the manual counts (p = 0.394). ConclusionWe have devised and internally validated an automated method to accurately identify FPs from HDSEMG, a technique we have named Surface Potential Quantification Engine (SPiQE). SignificanceLongitudinal quantification of fasciculations in ALS could provide unique insight into motor neuron health.

A concentric tube-based 4-DOF puncturing needle with a novel miniaturized actuation system for vitrectomy

BackgroundVitreoretinal surgeries require precise, dexterous, and steady instruments for operation in delicate parts of the eye. Robotics has presented solutions for many vitreoretinal surgical problems, but, in a few operations, the available tools are still not dexterous enough to carry out procedures with minimum trauma to patients. Vitrectomy is one of those procedures and requires some dexterous instruments to replace straight ones for better navigation to affected sides inside the eyeball.MethodIn this paper, we propose a new vein puncturing solution with a 4-DOF motion to increase the workspace inside the eye. A two-member concentric tube-based 25G needle is proposed whose shape is optimized. To operate the concentric tube needle, a novel and miniaturized actuation system is proposed that uses hollow shaft motors for the first time. The presented prototype of actuation system has a stroke of 100 mm in a small size of 148 × 25 × 65 mm (L × W × H), suitable for approaching distant positions inside the eyeball.ResultsExperimental results validate that the targeting accuracy of the needle is less than one millimeter and the needle tip can apply a force of 23.51 mN which is enough to perform puncturing. Furthermore, the proposed needle covers maximum workspace of around 128.5° inside the eyeball. For the actuation system, experiments show that it can produce repeatable motions with accuracy in submillimeter.ConclusionThe proposed needle system can navigate to the sites which are difficult to approach by currently available straight tools requiring reinsertions. Along with the miniaturized actuation system, this work is expected to improve the outcome of vitrectomy with safe and accurate navigation.

Concentric Needle Voluntary Jitter Assessment in Patients with Mitochondrial Myopathy. (P3.7-008)

Concentric Needle Voluntary Jitter Assessment in Patients with Mitochondrial Myopathy. (P3.7-008)

Motor unit recruitment in myopathy: The myopathic EMG reconsidered

Motor unit recruitment is abnormal in myopathies. We have addressed this subject by recording motor unit potentials (MUPs) using a standard concentric needle electrode in tibialis anterior muscles of clinically normal strength in a group of patients with myopathy (15 with myositis and 4 with facioscapulohumeral muscular dystrophy Type 1). In each recording site, a minimal voluntary contraction was sought in order to activate only 2 MUPs. At least 5 pairs of MUPs were recorded in each muscle. We analysed the recruitment rate of the first activated MUP and the mean consecutive difference (MCD) of firing frequency between the individual MUPs of each recruited pair. Results were compared with 30 healthy control subjects. In myopathy the first recorded MUs fired at similar rates to controls (8.2 vs 8.0 Hz, respectively), but the MCD of the firing rate difference between the first two recruited MUPs was less than in controls (median difference 1.78 Hz vs median difference 2.47 Hz, p = 0.02). This change suggests increased lower motor neuron excitability as a functional adaptation, since muscle strength was normal in the studied muscles. These findings are consistent with spinal cord adaptation to the functional changes associated with myopathic muscle disease, although a primary muscle fibre feedback sensing mechanism could also be involved.

Electrophysiological Findings of Subclinical Lower Motor Neuron Involvement in Degenerative Upper Motor Neuron Diseases

The present study is an examination of possible subclinical involvement of lower motor neuron (LMN) in patients with primary lateral sclerosis (PLS) and hereditary spastic paraparesis (HSP) electrophysiologically. Nine PLS patients and 5 HSP patients were prospectively analyzed. Jitter measurement with concentric needle electrode (25 mm, 30 G) (CN-jitter) recorded from right extensor digitorum muscle during voluntary contraction with 1 kHz high-pass frequency filter set. European Myelopathy Score (EMS) was used to evaluate disability. The relationship between disability score and jitter values was investigated. HSP patients had suffered from the disease for longer period of time (p<0.001). Mean jitter values of patients with PLS and HSP were 26.5±12.1 µs and 30.8±34.8 µs, and the number of individual high jitters (>43 microseconds) observed in the PLS and HSP groups was 16/180 and 9/100, respectively without a significant intergroup difference. The ratio of patients with an abnormal jitter study were higher in HSP group (60%) compared to PLS (22%) (p<0.05). Potential pairs with blocking were present in HSP group (7 of 100 potential pairs) but not seen in PLS patients. EMS values were significantly lower in patients having potential pairs with high jitter and blocking compared to those without high jitter and blocking. The present study has demonstrated that early signs of LMN dysfunction can be detected electrophysiologically by CN-jitter in patients with UMN involvement. These electrophysiological findings in these patients with longer disease duration and lower clinical scores may be explained by spreading of the disease to LMNs or transsynaptic degeneration and its contribution in disease progression.

Sub-clinical neuromuscular dysfunction after envenoming by Merrem’s hump-nosed pit viper (Hypnale hypnale)

Envenoming by hump-nosed pit vipers (genus Hypnale) causes local effects, mild coagulopathy, and rarely, acute kidney injury. Neuromuscular dysfunction has not been clinically reported but, in vitro studies show a weak, reversible, neurotoxic effect on the neuromuscular junction. We investigated the neuromuscular dysfunction in H. hypnale envenoming. Eighteen patients with authenticated H. hypnale envenoming were included. All 18 had serial clinical and neurological examinations. We evaluated neuromuscular dysfunction using stimulated concentric needle single-fibre electromyography (sfEMG) of orbicularis oculi in the patients within two days of the bite and compared to 29 normal subjects. Patients with abnormal jitter were reviewed six weeks later. All 18 patients had local effects and one-third had non-specific systemic symptoms. No patient had clinical features of neuromuscular paralysis. Median jitter values of patients were statistically significantly higher than normal subjects (19.6 ± 13.0 µs compared with 15.6 ± 7.4 µs.). None of the patients or normal subjects had neuromuscular blocks. Three patients had median jitter values higher than the maximum in normal subjects, which returned to normal by six weeks. H. hypnale envenoming leads to sub-clinical neuromuscular dysfunction, despite patients not showing any clinically detectable neurotoxicity.

Concomitant myasthenia gravis, myositis, myocarditis and polyneuropathy, induced by immune-checkpoint inhibitors: A life-threatening continuum of neuromuscular and cardiac toxicity

Immune-checkpoint inhibitors (ICIs) show a unique spectrum of immune-related adverse events (irAEs), even severe (grade 3–4) [1–3]. Herein we report two cases: a 72-year-old female and a 71-year-old male with renal cancer, who had a similar clinical presentation after the first cycle of nivolumab i.e. dropped head and limb weakness, progressing to inability to walk. Also the first neurophysiological investigation revealed quite a similar pattern, i.e. sensori-motor symmetrical polyneuropathy, with axonal and demyelinating features. Furthermore, a decremental response was detected at the repetitive 3 Hz stimulation. The concentric needle electrode revealed a myopathic pattern at interference; spontaneous activity appeared two weeks later. Intravenous immunoglobulins and steroids were administered. Despite a second immunoglobulin cycle and intravenous steroid bolus, the male patient died. He had a more severe hyperCKemia earlier at laboratory tests, in line with a more severe necrotizing myopathy. The reported cases extend and confirm previous evidence of a broad clinical spectrum of autoimmune-mediated, life-threatening, neuromuscular and cardiac toxicity of ICIs. An early electromyographic investigation should be performed in case of neuromuscular symptoms in ICI-treated. Moreover, an Italian registry of neuromuscular side effects of ICI-treated patients would be welcome, in order to identify individual risk profiles.

Motor Unit Properties of the First Dorsal Interosseous in Chronic Stroke Subjects: Concentric Needle and Single Fiber EMG Analysis.

The purpose of this study was to better understand changes in motor unit electrophysiological properties in people with chronic stroke based on concentric needle electromyography (EMG) and single fiber EMG recordings. The first dorsal interosseous (FDI) muscle was studied bilaterally in eleven hemiparetic stroke subjects. A significant increase in mean fiber density (FD) was found in the paretic muscle compared with the contralateral side based on single fiber EMG (1.6 ± 0.2 vs. 1.3 ± 0.1, respectively, P = 0.003). There was no statistically significant difference between the paretic and contralateral sides in most concentric needle motor unit action potential (MUAP) parameters, such as amplitude (768.7 ± 441.7 vs. 855.0 ± 289.9 μV), duration (8.9 ± 1.8 vs. 8.68 ± 0.9 ms) and size index (1.2 ± 0.5 vs. 1.1 ± 0.3) (P > 0.18), nor was there a significant difference in single fiber EMG recorded jitter (37.0 ± 9.6 vs. 39.9 ± 10.6 μs, P = 0.45). The increase in FD suggests motor units of the paretic FDI have enlarged due to collateral reinnervation. However, sprouting might be insufficient to result in a statistically significant change in the concentric needle MUAP parameters. Single fiber EMG appears more sensitive than concentric needle EMG to reflect electrophysiological changes in motor units after stroke. Both single fiber and concentric needle EMG recordings may be necessary to better understand muscle changes after stroke, which is important for development of appropriate rehabilitation strategies. The results provide further evidence that motor units are remodeled after stroke, possibly in response to a loss of motoneurons.

Concomitant myasthenia gravis, myositis, myocarditis and polyneuropathy, induced by immune-checkpoint inhibitors: A life–threatening continuum of neuromuscular and cardiac toxicity

Immune-checkpoint inhibitors (ICIs) show a unique spectrum of immune-related adverse events (irAEs), even severe (grade 3–4) [1–3]. Herein we report two cases: a 72-year-old female and a 71-year-old male with renal cancer, who had a similar clinical presentation after the first cycle of nivolumab i.e. dropped head and limb weakness, progressing to inability to walk. Also the first neurophysiological investigation revealed quite a similar pattern, i.e. sensori-motor symmetrical polyneuropathy, with axonal and demyelinating features. Furthermore, a decremental response was detected at the repetitive 3 Hz stimulation. The concentric needle electrode revealed a myopathic pattern at interference; spontaneous activity appeared two weeks later. Intravenous immunoglobulins and steroids were administered. Despite a second immunoglobulin cycle and intravenous steroid bolus, the male patient died. He had a more severe hyperCKemia earlier at laboratory tests, in line with a more severe necrotizing myopathy. The reported cases extend and confirm previous evidence of a broad clinical spectrum of autoimmune-mediated, life-threatening, neuromuscular and cardiac toxicity of ICIs. An early electromyographic investigation should be performed in case of neuromuscular symptoms in ICI-treated. Moreover, an Italian registry of neuromuscular side effects of ICI-treated patients would be welcome, in order to identify individual risk profiles.

Identification of components from distant fibers in a recorded single muscle fiber potential (SFP) – a new approach to the SFP criteria

The aim of our study was to verify the effectiveness of single fiber potential (SFP) criteria in cases when the potential recorded using single fiber electrode (SFE) or concentric needle electrode (CNE) is contaminated by distant fibers. Morphological counterparts of SFP were studied using computer simulations. In this study, we examined triphasic potentials using a model of a linear source of SFP. The criteria defining SFP in the case of SFP contaminated by distant fibers were analyzed, and the effect of second fiber contamination on jitter and fiber diameter determination evaluated. We found that SFP criteria prevent detection of SFP from fibers smaller than about 30μm in diameter, but do not prevent classification of a potential as an SFP even though it is formed by two or more fibers. This suggests that the presently used criteria may lead to incorrect interpretation of SFP potentials. SFPs contaminated by fibers of diameters differing by a few percent fulfill the criteria but a negative peak may be shifted in time and therefore impact jitter and diameter measurements. This contamination generally tends to decrease both the jitter and the determined diameter. A new approach to the identification of SFP is presented, determining fiber diameter and distance from the electrode to enable maximum sensitivity to potential contamination by the effect of a second fiber. A new parameter characterizing SFP shape changes is introduced. This parameter is used in the method by which additional fibers affecting the SFP may be detected.

Modulation of neuroinflammation and memory dysfunction using percutaneous vagus nerve stimulation in mice

BackgroundThe vagus nerve is involved in regulating immunity and resolving inflammation. Current strategies aimed at modulating neuroinflammation and cognitive decline, in many cases, are limited and ineffective. ObjectiveWe sought to develop a minimally invasive, targeted, vagus nerve stimulation approach (pVNS), and we tested its efficacy with respect to microglial activation and amelioration of cognitive dysfunction following lipopolysaccharide (LPS) endotoxemia in mice. MethodsWe stimulated the cervical vagus nerve in mice using an ultrasound-guided needle electrode under sevoflurane anesthesia. The concentric bipolar needle electrode was percutaneously placed adjacent to the carotid sheath and stimulation was verified in real-time using bradycardia as a biomarker. Activation of vagal fibers was confirmed with immunostaining in relevant brainstem structures, including the dorsal motor nucleus and nucleus tractus solitarius. Efficacy of pVNS was evaluated following administration of LPS and analyses of changes in inflammation and behavior. ResultspVNS enabled stimulation of the vagus nerve as demonstrated by changes in bradycardia and histological evaluation of c-Fos and choline acetyltransferase expression in brainstem nuclei. Following LPS administration, pVNS significantly reduced plasma levels of tumor necrosis factor-α at 3 h post-injection. pVNS prevented LPS-induced hippocampal microglial activation as analyzed by changes in Iba-1 immunoreactivity, including cell body enlargement and shortened ramifications. Cognitive dysfunction following endotoxemia was also restored by pVNS. ConclusionTargeted cervical VNS using this novel percutaneous approach reduced LPS-induced systemic and brain inflammation and significantly improved cognitive responses. These results provide a novel therapeutic approach using bioelectronic medicine to modulate neuro-immune interactions that affect cognition.

Prediction of organophosphorus insecticide-induced intermediate syndrome with stimulated concentric needle single fibre electromyography.

BackgroundDeliberate self-poisoning (DSP) using organophosphorus (OP) insecticides are a common clinical problem in Asia. OPs inhibit acetylcholine esterase (AChE), leading to over-activity of muscarinic and nicotinic cholinergic circuits. Intermediate syndrome (IMS) is mediated via prolonged nicotinic receptor stimulation at the neuromuscular junction and its onset is between 24–96 hours post ingestion. The aims of the present study were 1) to investigate whether neuromuscular junction dysfunction within the first 24 hours following exposure, quantified by jitter in single fibre electromyography (SfEMG), can predict IMS, and 2) to compare the changes in SfEMG jitter over the course of the illness among patients who developed IMS (IMS+) and those who did not (IMS-).Methods and findingsWe conducted a prospective cohort study in a tertiary care hospital in Sri Lanka on 120 patients admitted between September 2014 and August 2016 following DSP by OP insecticides viz., profenofos 53, phenthoate 17, diazinon 13, chlorpyrifos 5, others 12, unknown 20. SfEMG was performed every second day during hospitalization. Exposure was confirmed based on the history and red blood cell AChE assays. IMS was diagnosed in patients who demonstrated at least three out of four of the standard IMS criteria: proximal muscle weakness, bulbar muscle weakness, neck muscle weakness, respiratory paralysis between 24–96 hours post ingestion. Respiratory failure requiring intubation occurred in 73 out of 120 patients; 64 of these were clinically diagnosed with IMS. Of the 120 patients, 96 had repeated SfEMG testing, 67 of them being tested within the first 24 hours. Prolonged jitter (>33.4μs) within the first 24 hours was associated with greatly increased risk of IMS (odds ratio = 8.9, 95% confidence intervals = 2.4–29.6, p = 0.0003; sensitivity 86%, specificity 58%). The differences in jitter between IMS+ and IMS- patients remained significant for 72 hours and increased jitter was observed in some patients for up to 216 hours. For intubated patients, the median time for jitter to normalize and median time to extubate were similar, and the two variables had a moderate positive correlation (r = 0.49, P = 0.001).ConclusionsProlonged jitter recorded with SfEMG <24 hours of ingestion of an OP strongly correlates with subsequent occurrence of IMS. The time course of electrophysiological recovery of the NMJ was similar to the time course of respiratory recovery in IMS patients.

Two-Source Validation of Progressive FastICA Peel-Off for Automatic Surface EMG Decomposition in Human First Dorsal Interosseous Muscle.

This study aims to assess the accuracy of a novel high density surface electromyogram (SEMG) decomposition method, namely automatic progressive FastICA peel-off (APFP), for automatic decomposition of experimental electrode array SEMG signals. A two-source method was performed by simultaneous concentric needle EMG and electrode array SEMG recordings from the human first dorsal interosseous (FDI) muscle, using a protocol commonly applied in clinical EMG examination. The electrode array SEMG was automatically decomposed by the APFP while the motor unit action potential (MUAP) trains were also independently identified from the concentric needle EMG. The degree of agreement of the common motor unit (MU) discharge timings decomposed from the two different categories of EMG signals was assessed. A total of 861 and 217 MUs were identified from the 114 trials of simultaneous high density SEMG and concentric needle EMG recordings, respectively. Among them 168 common (MUs) were found with a high average matching rate of [Formula: see text] for the discharge timings. The outcomes of this study show that the APFP can reliably decompose at least a subset of MUs in the high density SEMG signals recorded from the human FDI muscle during low contraction levels using a protocol analog to clinical EMG examination.

Single-fiber F waves compared with conventional surface F waves, and their utility in detecting early diabetic neuropathy.

The single-fiber F-wave (SFF-wave) technique assesses the entire length of single motor fibers using a concentric needle. Herein we investigated the utility of this approach in the detection of early diabetes-related neuropathy, and compared it with the use of conventional surface F waves (CF waves). Sixteen patients with diabetes and either no neuropathy or mild neuropathy were assessed and compared with 16 age- and height-matched control participants. Both CF and SFF waves were abnormal in all 5 patients who had mild neuropathy. However, SFF waves demonstrated subclinical abnormalities in 7 of 11 patients (64%) with no neuropathy, whereas only 2 of these patients (18%) had prolonged CF waves. Minimum F-wave latency was comparable between techniques, but maximum SFF-wave latency was more frequently prolonged, as these delayed motor units were better isolated, rather than buried among summated CF-wave responses. SFF waves highlight the segmental involvement in diabetic neuropathy, and use of the SFF-wave technique detects more abnormalities than with CF waves. Muscle Nerve 58: 665-670, 2018.

Analysis of electromyograms recorded using invasive and noninvasive electrodes: a study based on entropy and Lyapunov exponents estimated using artificial neural networks

Electromyograms are electrical signals produced by the muscles. Electromyography (EMG) is an efficient technique for analyzing the normal and abnormal states of the neuromuscular system. However, many factors such as crosstalk, fatigue, type of electrodes and electrode movements, affect the quality of the acquired EMG signals. In this work, the information content of EMG signals acquired using three different electrodes namely, monopolar needle, concentric needle and high spatial resolution surface electrodes, was analyzed using Tsallis entropy and Renyi entropy. Further, Lyapunov exponents were utilized to analyze the chaotic nature of the adopted EMG signals obtained from three different electrode types. The signals were modelled using artificial neural networks (ANN) and the Lyapunov exponents were estimated using the developed ANN models. Results demonstrate that, the Tsallis entropy and Renyi entropy of EMG signals acquired using concentric needle electrodes is higher when compared to the entropy of EMG signals acquired using monopolar needle electrodes and surface electrodes. Also, the Lyapunov exponents of EMG signals measured using concentric needle electrodes is higher when compared to the EMG signals measured using monopolar needle and surface electrodes. Further, the information content of EMG signals acquired using needle electrodes is higher when compared to the surface electrodes. This work seems to be of high clinical relevance since the efficient recording of EMG signals is highly useful for development of diagnostic support tools for identification of muscle disorders.

F95. Laryngeal electromyography in patients with Amiotrophic Lateral Sclerosis (ALS): Preliminary results

Introduction Amyotrophic Lateral Sclerosis (ALS) is the most relevant motor neuron disease in adults and characterized by widespread weakness. Despite frequent bulbar involvement, little is known about clinical and electrophysiological changes in the larynx in patients with ALS. The objective of this study was to evaluate the frequency and pattern of involvement of laryngeal muscles in ALS and its functional relevance. In addition, we assessed whether laryngeal EMG (LEMG) would increase the diagnostic sensitivity for ALS. Methods Fourteen ALS patients, 13 with spinal onset and 1 with bulbar onset, underwent nasofibroscopy (NF) followed by LEMG, in which a concentric needle was used to evaluate the thyroid-arytenoid (TA), lateral crico-arytenoid (CAL), posterior crico-arytenoid (CAP) and crico-thyroid (CT) muscles, at rest and during activation. After LEMG, resting and activation of the genioglossus and masseter muscles were also studied using the same concentric needle. Results The mean age of the patients was 48.5 years and there were 6 women. The procedures were fast (30 min on average) and uneventful. Thirteen patients presented neurogenic changes in at least one laryngeal muscle. A single patient had entirely normal LEMG. We found a pattern compatible with chronic denervation (MUAPs remodeling and incomplete recruitment) with the following frequency: TA muscle in 11/14 patients (78.5%); CT in 10/14 patients (71.4%); CAP in 10/14 patients (71.4%) and CAL in 7/14 patients (50%). In 8 patients, there were fibrillations and/ or fasciculations associated with chronic neurogenic changes in the same muscle; of these, 4 had no alteration in the genioglossus muscle and 2 had only chronic alterations in the same muscle. NF revealed motor abnormalities in the larynx in 9 patients; in the remaining 5, NF was normal but LEMG identified signs of denervation in 4 of them. Conclusion LEMG is able to identify laryngeal denervation in patients with ALS. This procedure may increase diagnostic sensitivity for ALS by identifying bulbar involvement in patients without tongue denervation. Changes in LEMG may precede clinical involvement of the larynx in these patients.

F93. Probabilistic jitter characterization

Introduction Bayesian probabilistic characterization has already been used for quantitative electromyography but not for jitter analysis. Instead of classical statistical method, probabilistic characterization uses sequential cumulative probability. Our objective was to evaluate the performance of probabilistic characterization for jitter assessment. Methods We analyzed 20 controls and 20 patients with serologically confirmed Myasthenia Gravis (MG). All patients were submitted to orbicularis oculi concentric needle voluntary jitter measurements of 20 pairs of ASFAP, adding up 797 MCD measurements. Jitter was characterized in four different levels: A: μ s; B: 25–45 μ s; C: 45–65 μ s; and D: >65 μ s. We calculated the probability of an abnormal result for each jitter level. Then, we used the Bayesian sequential approach in each subject until the cumulative probability of a normal or abnormal result was >99%. Results The probability of abnormality for each jitter level was: A: 20%; B: 73%; C: 95%; and D: 99%. The cumulative probability achieved more than 99% up to the sixth potential in 77% of the subjects. However, one control subject was labeled as abnormal while four MG subjects were labeled as normal studies. Additionally, two control subjects could not be characterized up to the 20th recording. The method accuracy was 82%. Conclusion Probabilistic characterization requires fewer recordings than the statistical method. However, our study showed poor accuracy for jitter characterization. One possible reason is that MCD values in each patient are not randomly scattered during the entire exam, but rather clustered according to the sampled region.