Fasciculation potentials in foot and leg muscles of healthy young adults

EMG-Phänomene peripherer motorisch axonaler Übererregbarkeit

Bei der Nadel-Elektromyographie (EMG) besitzen Phänomene der vermehrten Erregbarkeit von Muskelfasern und von motorischen Axonen Bedeutung für die Diagnostik neuromuskulärer Erkrankungen. Zur motorisch axonalen Übererregbarkeit gehören spontane Phänomene wie Faszikulationen, spontane kontinuierliche Einzelentladungen der motorischen Einheit (SKEME), Myokymien, neuromyotone Entladungsserien und Krampi. Ferner gehören dazu reizinduzierte Phänomene wie manche A-Wellen, reizinduzierte komplex repetitive Entladungen oder tetanischen Spasmen bei Elektrolytstörungen. In der vorliegenden Übersicht wird der Kenntnisstand zu den verschiedenen Phänomenen motorisch axonaler Übererregbarkeit referiert. Ein Schwerpunkt liegt dabei auf den SKEME als neuem Mitglied der Gruppe spontaner Potenziale aus dem motorischen Axon.

Fasciculations demonstrate daytime consistency in amyotrophic lateral sclerosis

INTRODUCTION

Fasciculations represent early neuronal hyperexcitability in amyotrophic lateral sclerosis (ALS). To aid calibration as a disease biomarker, we set out to characterize the daytime variability of fasciculation firing.

METHODS

Fasciculation awareness scores were compiled from 19 ALS patients. In addition, 10 ALS patients prospectively underwent high-density surface electromyographic (HDSEMG) recordings from biceps and gastrocnemius at three time-points during a single day.

RESULTS

Daytime fasciculation awareness scores were low (mean: 0.28 muscle groups), demonstrating significant variability (coefficient of variation: 303%). Biceps HDSEMG recordings were highly consistent for fasciculation potential frequency (intraclass correlation coefficient [ICC] = 95%, n = 19) and the interquartile range of fasciculation potential amplitude (ICC = 95%, n = 19). These parameters exhibited robustness to observed fluctuations in data quality parameters. Gastrocnemius demonstrated more modest levels of consistency overall (44% to 62%, n = 20).

DISCUSSION

There was remarkable daytime consistency of fasciculation firing in the biceps of ALS patients, despite sparse and intermittent awareness among patients' accounts.

The evolving role of surface electromyography in amyotrophic lateral sclerosis: A systematic review

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease that leads to inexorable motor decline and a median survival of three years from symptom onset. Surface EMG represents a major technological advance that has been harnessed in the development of novel neurophysiological biomarkers. We have systematically reviewed the current application of surface EMG techniques in ALS.

METHODS

We searched PubMed to identify 42 studies focusing on surface EMG and its associated analytical methods in the diagnosis, prognosis and monitoring of ALS patients.

RESULTS

A wide variety of analytical techniques were identified, involving motor unit decomposition from high-density grids, motor unit number estimation and measurements of neuronal hyperexcitability or neuromuscular architecture. Some studies have proposed specific diagnostic and prognostic criteria however clinical calibration in large ALS cohorts is currently lacking. The most validated method to monitor disease is the motor unit number index (MUNIX), which has been implemented as an outcome measure in two ALS clinical trials.

CONCLUSION

Surface EMG offers significant practical and analytical flexibility compared to invasive techniques. To capitalise on this fully, emphasis must be placed upon the multi-disciplinary collaboration of clinicians, bioengineers, mathematicians and biostatisticians.

SIGNIFICANCE

Surface EMG techniques can enrich effective biomarker development in ALS.

Quantitative sonographic evaluation of muscle thickness and fasciculation prevalence in healthy subjects

BACKGROUND

In the current study, we aimed to determine normative values for muscle thickness and fasciculation prevalence in healthy subjects.

METHODS

We performed a prospective study from October to December 2018 in 65 healthy subjects. All subjects underwent quantitative sonographic evaluation of muscle thickness and fasciculation prevalence in the following 8 muscles: Biceps brachii, abductor pollicis brevis, first dorsal interosseous, abductor digiti minimi, quadriceps, tibialis anterior, extensor digitorum brevis, and abductor hallucis brevis.

RESULTS

Subject ages ranged from 21 to 82 years, with 63% women. Normative values for muscle thickness were determined using the fifth percentile. Multivariate regression analysis showed that sex, age, body mass index, and hand dominance affected muscle thickness. Fasciculations were observed frequently only in distal muscles.

CONCLUSIONS

Normal values for muscle thickness were determined, and may enhance neuromuscular ultrasound sensitivity and serve as a basis for future studies. Larger series are needed to confirm these values.

Spontaneous mechanical and electrical activities of human calf musculature at rest assessed by repetitive single-shot diffusion-weighted MRI and simultaneous surface electromyography

PURPOSE

Assessment of temporal and spatial relations between spontaneous mechanical activities in musculature (SMAM) at rest as revealed by diffusion-weighted imaging (DWI) and electrical muscular activities in surface EMG (sEMG). Potential influences of static and radiofrequency magnetic fields on muscular activity on sEMG measurements at rest were examined systematically.

METHODS

Series of diffusion-weighted stimulated echo planar imaging were recorded with concurrent sEMG measurements. Electrical activities in sEMG were analyzed by non-parametric Friedman and two-sample Kolmogorov-Smirnov test. Direct correlation of both modalities was investigated by temporal mapping of electrical activity in sEMG to DWI repetition interval.

RESULTS

Electrical activities in sEMG and number of visible SMAMs in DWI showed a strong correlation (ρ = 0.9718). High accordance between sEMG activities and visible SMAMs in DWI in a near-surface region around sEMG electrodes was achieved. Characteristics of sEMG activities were almost similar under varying magnetic field conditions.

CONCLUSION

Visible SMAMs in DWI have shown a close and direct relation to concurrent signals recorded by sEMG. MR-related magnetic fields had no significant effects on findings in sEMG. Hence, appearance of SMAMs in DWI should not be considered as imaging artifact or as effects originating from the special conditions of MR examinations. Spatial and temporal distributions of SMAMs indicate characteristics of spontaneous (microscopic) mechanical muscular action at rest. Therefore, DWI techniques should be considered as non-invasive tools for studying physiology and pathophysiology of spontaneous activities in resting muscle. Magn Reson Med 79:2784-2794, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Fasciculation in amyotrophic lateral sclerosis: origin and pathophysiological relevance

This review considers the origin and significance of fasciculations in neurological practice, with an emphasis on fasciculations in amyotrophic lateral sclerosis (ALS), and in benign fasciculation syndromes. Fasciculation represents a brief spontaneous contraction that affects a small number of muscle fibres, causing a flicker of movement under the skin. While an understanding of the role of fasciculation in ALS remains incomplete, fasciculations derive from ectopic activity generated in the motor system. A proximal origin seems likely to contribute to the generation of fasciculation in the early stages of ALS, while distal sites of origin become more prominent later in the disease, associated with distal motor axonal sprouting as part of the reinnervation response that develops secondary to loss of motor neurons. Fasciculations are distinct from the recurrent trains of axonal firing described in neuromyotonia. Fasciculation without weakness, muscle atrophy or increased tendon reflexes suggests a benign fasciculation syndrome, even when of sudden onset. Regardless of origin, fasciculations often present as the initial abnormality in ALS, an early harbinger of dysfunction and aberrant firing of motor neurons.

Identifying fasciculation potentials in motor neuron disease: A matter of probability

INTRODUCTION

Fasciculations, the spontaneous activity of single motor units (MUs) are characteristic, but nonspecific for motor neuron disease (MND). We aimed to identify MU discharge properties to optimally differentiate MND patients from healthy controls.

METHODS

High-density surface electromyography recordings were performed in the thenar muscles during 10 min of rest. MU discharges were classified as "isolated" when the interspike intervals (ISIs) before and after were > 250 ms, "continual" when both ISIs were ≤ 250 ms, or as "other".

RESULTS

In patients (n = 30) compared with controls (n = 14), more MUs were active (9 vs. 3, P < 0.001) and generated relatively more isolated discharges (35% vs. 10%, P = 0.01). Two or more MUs with isolated discharges occurred more frequently in patients compared with controls (24% vs. <1% of 10-s windows, P < 0.001).

CONCLUSIONS

More frequent occurrence of multiple MUs showing isolated discharges may improve identification of patients with MND.

The puzzling case of hyperexcitability in amyotrophic lateral sclerosis

The development of hyperexcitability in amyotrophic lateral sclerosis (ALS) is a well-known phenomenon. Despite controversy as to the underlying mechanisms, cortical hyperexcitability appears to be closely related to the interplay between excitatory corticomotoneurons and inhibitory interneurons. Hyperexcitability is not a static phenomenon but rather shows a pattern of progression in a spatiotemporal aspect. Cortical hyperexcitability may serve as a trigger to the development of anterior horn cell degeneration through a 'dying forward' process. Hyperexcitability appears to develop during the early disease stages and gradually disappears in the advanced stages of the disease, linked to the destruction of corticomotorneuronal pathways. As such, a more precise interpretation of these unique processes may provide new insight regarding the pathophysiology of ALS and its clinical features. Recently developed technologies such as threshold tracking transcranial magnetic stimulation and automated nerve excitability tests have provided some clues about underlying pathophysiological processes linked to hyperexcitability. Additionally, these novel techniques have enabled clinicians to use the specific finding of hyperexcitability as a useful diagnostic biomarker, enabling clarification of various ALS-mimic syndromes, and the prediction of disease development in pre-symptomatic carriers of familial ALS. In terms of nerve excitability tests for peripheral nerves, an increase in persistent Na⁺ conductances has been identified as a major determinant of peripheral hyperexcitability in ALS, inversely correlated with the survival in ALS. As such, the present Review will focus primarily on the puzzling theory of hyperexcitability in ALS and summarize clinical and pathophysiological implications for current and future ALS research.

Fasciculation Potentials in High-Density Surface EMG

Fasciculation potentials (FPs) are observed in healthy individuals, but also in patients with neurogenic disorders. The exact site of origin and the clinical relevance in distinguishing, for example, amyotrophic lateral sclerosis (ALS) from other neurogenic diseases based on specific characteristics of the FPs is still a matter of debate and needs further exploration. This report describes the use of high-density surface EMG (HD-sEMG), with multiple electrodes in a compact grid to noninvasively record FPs. The technique provides both temporal and spatial information of fasciculations. Examples of the FPs of a patient diagnosed with definite ALS are presented. FPs are shown in different electrode montages and the unique spatial characteristics of different FPs are presented. During 30-second recordings, 137 FPs were detected that via a decomposition algorithm could be assigned to 11 different underlying sources. It is concluded that HD-sEMG, both because of its noninvasive character and the unique spatiotemporal information, is very suitable to examine fasciculations. It allows long stable recording times and provides quantitative information. This electrophysiologic tool is expected to expand the existing knowledge of FP properties.

Needle EMG of abductor hallucis and peroneus tertius in normal subjects

Normal values for standard concentric-needle electromyography (EMG) of the abductor hallucis (AH) and peroneus tertius (PT) muscles have not been established to date, yet both are potentially useful muscles in the diagnosis of length-dependent peripheral nerve disorders. Forty-three normal asymptomatic subjects stratified by age underwent a standard set of nerve conduction studies and concentric-needle examination to exclude asymptomatic disease and develop normal values for the AH and the PT for various EMG parameters. Fibrillation potentials were observed in the AH in 21% of normal subjects (10% < 60 years old, 30% > 60 years old); 19% of subjects were unable to voluntarily activate the AH. All subjects could activate the PT regardless of age. No fibrillation potentials were observed in subjects < 60 years of age, whereas 9% of those older than 60 years had mild fibrillation potentials in the PT. The PT is a useful muscle in the evaluation of length-dependent peripheral neuropathy and other peripheral nerve disorders of the lower extremities, on the basis of ease of motor unit potential activation and analysis, and relative infrequency of fibrillation potentials in normal subjects.

Prevalence of denervation in paraspinal and foot intrinsic musculature

OBJECTIVE

The primary purpose of this investigation was to determine the prevalence of abnormal spontaneous activity (positive sharp waves (PSWs) and fibrillation potentials (FPs)) in selected lumbosacral paraspinal and foot intrinsic muscles in an asymptomatic healthy population.

DESIGN

This was a prospective assessment of 50 individuals without history or physical findings suggestive of peripheral neuromuscular disease whereby a monopolar needle electrode was located in the unilateral L4 and L5 paraspinal as well as abductor hallucis and extensor digitorum brevis muscles. These muscles were extensively evaluated for the presence of PSWs, FPs, and fasciculation potentials.

RESULTS

Ten subjects per decade from 20-59 yr and ten subjects from 60-80 yr comprised the 50 participants (28 women), resulting in a mean age of 45+/-15.9 (range, 20-76) yr. A single individual (prevalence, 2%) demonstrated fibrillation potentials in the extensor digitorum brevis, and FPs and PSWs were detected in two subjects' (4% prevalence) L4/L5 paraspinal muscles. Ninety-four percent of the subjects had fasciculation potentials in the abductor hallucis, whereas 60% had these waveforms in the extensor digitorum brevis. Only 6% of subjects had fasciculation potentials in the L4 but not L5 paraspinal muscles. All subjects demonstrated both prototypical and "atypical" appearing endplate spikes in all of the muscles examined.

CONCLUSIONS

We failed to confirm the previously reported prevalence of FPs and PSWs in both the paraspinal and foot intrinsic musculature. Atypical appearing endplate spikes, however, display configurations similar to FPs and PSWs and were present in all subjects. Failure to pay close attention to the discharge rate and rhythm of endplate spikes can lead to misinterpreting these waveforms as FPs and PSWs. It is likely that the previously reported high prevalence of spontaneous activity in healthy persons resulted from not fully appreciating the similarity between innervated and denervated spontaneous single muscle fiber discharge configurations.

Riluzole has no acute effect on motor unit parameters in ALS

Riluzole is the only drug to have been approved for the treatment of amyotrophic lateral sclerosis (ALS/MND). Its mechanism of action is complex and includes actions on NMDA and kainate receptors and modulation of voltage gated Na channels. In ALS, its effects on measurable parameters of the motor units utilising current neurophysiological techniques are unknown. In an acute randomized, double-blind, placebo-controlled, cross-over experiment, we serially assessed the effects of riluzole on motor units in muscles affected by ALS/MND using EMG. We discuss the results of our observations in the light of previous clinical trials, and their implications.

Surface EMG and myosonography in the detection of fasciculations: a comparative study

Surface electromyography (EMG) and muscle sonography both facilitate the detection of fasciculations. This study was conducted to evaluate the prevalence of fasciculations in 10 lower extremity muscles in 58 subjects 47 +/- 18 years of age without and 54 patients 52 +/- 15 years of age with various neuromuscular diseases (3 with inflammatory myopathy, 15 with lower motor neuron disease, 22 with acquired and 11 with hereditary motor and sensory neuropathy (HMSN), and 3 with adrenomyeloneuropathy). When each muscle was screened by means of myosonography for 10 seconds, fasciculations were found in up to 8 muscles in 11 control subjects (19%) and in up to 10 muscles in 41 patients (76%). Within the same recording period surface EMG revealed fasciculations in 5 control subjects (9%) and 30 patients (56%), whereas during a recording time of 20 minutes fasciculations were detected in 55 (95%) control subjects and all patients. An amplitude of 400 microV proved to be the optimum cutoff between fasciculations for healthy subjects and patients with neuromuscular disease (accuracy, 74%). Myosonography allowed differentiation of both groups with an accuracy of 79%. Surface EMG was more liable to artifacts than myosonography. The average interval between subsequent fasciculations cannot be used to differentiate patients with acquired and hereditary polyneuropathy and with lower motor neuron disease. Long-term surface EMG recording indicates fasciculations to occur in almost all patients with neuromuscular disease and the vast majority of healthy subjects. Muscle ultrasonography was more convenient and reliable than surface EMG in differentiating patients and healthy subjects.

Fasciculation potentials in healthy people

The aim of this study was to investigate the fasciculation potentials (FPs) in the small-peripheral muscles of the foot and hand and the possible associated factors, in a healthy population. One hundred-twenty-two normal individuals (65 men and 57 women), aged 17-67 years (mean 39.96, SD=12.76) participated in the study. A special questionnaire consisting of 47 questions was devised as the basic instrument of the interview, which included the Hamilton anxiety rating scale. The extensor digitorum brevis (EDB), the flexor hallucis brevis (FHB) and the first dorsal interosseous (FDI) muscles were studied bilaterally using surface electrodes. In 94 (58 men and 36 women) from 122 participants (65 men and 57 women) FPs were recorded (men 89.2%, women 63.1%, all 77%). The mean FPs per minute and muscle, in all three muscles, was 8.0 (SD=4.6). More FPs were recorded in the muscles of foot than in FDI (p<0.01) and in FHB than in EDB (p<0.001). FPs were correlated to gender, body height and weight and to the score of the Hamilton scale (r2>0.1, p<0.01). The syndrome of benign FPs was observed in 2 men (1.6% of men). These results suggest that FPs are a very common phenomenon in the peripheral muscles of healthy persons.

Fasciculations: what do we know of their significance?

Fasciculations are observed in patients with neurogenic disorders and in healthy individuals. Depending on the associated clinical symptoms and signs, they may signify the presence of a variety of disorders of the lower motor neuron. Divergent and occasionally conflicting opinions prevail regarding the aetiology, pathogenesis, clinical significance, neurophysiological characteristics and the physiological site of origin of fasciculations. In this review we examine the published literature and attempt to clarify these issues.

ECG-related fasciculation potential

We report the observation of an unusual fasciculation potential (FP). This FP was time-locked to the electrocardiogram (ECG) in 87% of the discharges. The motor unit action potential (MUAP) of the FP was also elicited as H-reflex. As mechanism we propose spindle afferent discharges mechanically triggered by the arterial pulse, i.e. a reflex fasciculation. We suggest that such a heartbeat-related mechanism could explain synchronous fasciculations described by Norris (Arch. Neurol., 1965, 13: 495-500).

Fasciculations: clinical, electromyographic, and ultrasonographic assessment

Widespread fasciculations are an important clinical sign in, for example, degenerative lower motor neuron diseases (LMND). Usually they are detected by clinical inspection and electromyography. Recently myosonography has been proposed for the detection of fasciculations. This prospective study compares the value of these three modes of examination in patients with degenerative LMND. Seventy healthy control persons and 34 patients (11 women, 23 men; aged 43-78 years; median age 60.5) with LMND were included in the study. All participants were subjected to thorough visual screening for the presence of fasciculations. Fourteen muscles were examined bilaterally by myosonography and a median of 8 muscles were screened electromyographically (only in the patients); the investigators were blinded to the other findings. Clinical inspection and ultrasonography exhibited fasciculations in up to 5 and 8 muscles, respectively, in 8 healthy persons. Ultrasonography demonstrated fasciculations in all patients, clinical inspection in all but 2, and electromyography in 26 of 33 patients (1 patient was not examined electromyographically). Comparing the three methods, clinical observation revealed fasciculations in 42%, electromyography in 39%, and ultrasonography in 67% of all muscles. Thus, ultrasonography was significantly more sensitive than the other techniques (P < 0.001). The interrater agreement (correlation coefficient) r in respect of the presence or absence of fasciculation was 0.71 for the clinical, 0.85 for the electromyographic and 0.84 for the myosonographic examinations. Ultrasonography and electromyography were more reliable than the clinical examination (P < 0.001 and P < 0.01, respectively). Our study indicates that ultrasonography is more sensitive than clinical and electromyographic examination in visualizing fasciculations in patients with LMND. Additionally, it is more reliable than clinical examination.