Detection of fasciculations in amyotrophic lateral sclerosis: The optimal ultrasound scan time

Neurophysiological and imaging biomarkers of lower motor neuron dysfunction in motor neuron diseases/amyotrophic lateral sclerosis: IFCN handbook chapter

This chapter discusses comprehensive neurophysiological biomarkers utilised in motor neuron disease (MND) and, in particular, its commonest form, amyotrophic lateral sclerosis (ALS). These encompass the conventional techniques including nerve conduction studies (NCS), needle and high-density surface electromyography (EMG) and H-reflex studies as well as novel techniques. In the last two decades, new methods of assessing the loss of motor units in a muscle have been developed, that are more convenient than earlier methods of motor unit number estimation (MUNE),and may use either electrical stimulation (e.g. MScanFit MUNE) or voluntary activation (MUNIX). Electrical impedance myography (EIM) is another novel approach for the evaluation that relies upon the application and measurement of high-frequency, low-intensity electrical current. Nerve excitability techniques (NET) also provide insights into the function of an axon and reflect the changes in resting membrane potential, ion channel dysfunction and the structural integrity of the axon and myelin sheath. Furthermore, imaging ultrasound techniques as well as magnetic resonance imaging are capable of detecting the constituents of morphological changes in the nerve and muscle. The chapter provides a critical description of the ability of each technique to provide neurophysiological insight into the complex pathophysiology of MND/ALS. However, it is important to recognise the strengths and limitations of each approach in order to clarify utility. These neurophysiological biomarkers have demonstrated reliability, specificity and provide additional information to validate and assess lower motor neuron dysfunction. Their use has expanded the knowledge about MND/ALS and enhanced our understanding of the relationship between motor units, axons, reflexes and other neural circuits in relation to clinical features of patients with MND/ALS at different stages of the disease. Taken together, the ultimate goal is to aid early diagnosis, distinguish potential disease mimics, monitor and stage disease progression, quantify response to treatment and develop potential therapeutic interventions.

Neuromuscular ultrasound changes in unilateral symptomatic subacute lumbosacral radiculopathy: A prospective simple blinded cohort study

INTRODUCTION/AIMS

Lumbosacral radiculopathy (LR) is a common disorder. Neuromuscular ultrasound (NMU) is a rapidly evolving technique for the investigation of peripheral nerve and muscle disorders, but studies using NMU in LR are lacking. The aim of the present study was to investigate ultrasonographic neuromuscular changes distant from root compression in patients with subacute to chronic compressive LR with motor impairment.

METHODS

Patients with unilateral subacute to chronic L4, L5, or S1 radiculopathy with motor impairment and confirmed by magnetic resonance imaging were included. The sciatic and femoral nerve cross-sectional areas (CSA), the CSA of lower limb muscles, and muscle fasciculation detection rate were assessed using a pre-specified neuromuscular ultrasound evaluation with blinded side-to-side comparison.

RESULTS

Of the 18 included patients, 66% were male and the mean age was 51 years. Overall, 16.7% had L4, 55.5% L5, and 27.8% S1 radiculopathy, mostly due to disc herniation (83%). Sciatic nerve CSA of the symptomatic side was increased (61.4 mm2 vs. 51.3 mm2; p = .001), and the fasciculation detection rate was higher in the affected muscles (delta = 13%, p = .007) compared to unaffected ones. Muscle CSA in affected and nonaffected muscles was decreased on the symptomatic side.

DISCUSSION

NMU evaluation in patients with symptomatic subacute to chronic LR revealed sciatic nerve enlargement distant from nerve root compression and higher fasciculation rates. These structural findings on NMU might be due to an axonal repair mechanism and an inflammatory response with endoneurial edema induced by ongoing nerve damage and potentially reflect progressive axonal loss.

Lingual fasciculation: A point of call for the diagnosis of amyotrophic lateral sclerosis

A 60-year-old female patient, with no notable medical history, was referred by the internal medicine department for a dry mouth workup. The clinical examination revealed an absence of dryness, and the presence of lingual fasciculations, associated with difficulties in mastication and phonation. These symptoms appeared spontaneously 9 months before the consultation, after leaving confinement. Given the presence of lingual fasciculations, the diagnostic hypothesis of a neurological pathology, in particular amyotrophic lateral sclerosis (ALS), was suspected. After performing an electromyogram (EMG), the diagnosis of ALS was retained. Riluzole treatment was then started, and physical therapy sessions were scheduled. Riluzole allows an average gain of 4 to 6 months of life expectancy. Speech therapy and physical therapy allow to maintain the functions as long as possible and to improve the end-of-life conditions. The interest of early detection of ALS allows delaying the progression of the disease.

Bedeutung der Muskelsonographie in der Detektion von Faszikulationen bei der ALS

Bei der amyotrophen Lateralsklerose sind Faszikulationen häufig bereits in frühen Stadien in mehreren Körperregionen vorzufinden und haben daher Eingang in die entsprechenden Leitlinien und Diagnosekriterien gefunden. Während die invasive EMG-Diagnostik unverzichtbar zum Nachweis von akut- und chronisch-neurogenen Veränderungen des elektrischen Signalverhaltens motorischer Einheiten und zur Bestätigung von Faszikulationspotenzialen bleibt, bietet die Muskelsonographie ein hochsensitives Verfahren, um schnell und nicht-invasiv Faszikulationen in den verschiedenen Muskel-Etagen zu erfassen. In dieser Übersichtsarbeit stellen wir die bisherigen Daten zum Einsatz der Muskelsonographie zur Faszikulationsdetektion dar. Durch ihren Einsatz ermöglicht die Muskelsonographie im klinischen Alltag eine zielgerichtete und hierdurch aussagekräftigere EMG-Diagnostik. Aktuelle Forschungsstudien zielen darauf ab, Faszikulationen sonomorphologisch genauer zu charakterisieren, zu quantifizieren und als Verlaufsparameter zu untersuchen.

Fasciculation differences between ALS and non-ALS patients: an ultrasound study

Background

Fasciculation is an important sign for the diagnosis of amyotrophic lateral sclerosis (ALS). Our study aimed to analyze the difference in fasciculation detected with muscle ultrasonography (MUS) between ALS patients and non-ALS patients with symptoms resembling ALS.

Methods

Eighty-eight ALS patients and fifty-four non-ALS (eight multifocal motor neuropathy, 32 chronic inflammatory demyelinating polyneuropathy/Charcot-Marie-Tooth, and 14 cervical spondylopathy or lumbar spondylopathy) patients were recruited. MUS was performed on 19 muscle groups in cervical, lumbosacral, bulbar, and thoracic regions for each patient. The intensity of fasciculation was divided into five grades based on firing frequency and number in the involved muscle groups.

Results

The overall detection rates were 72.8% in ALS and 18% in non-ALS patients. The fasciculation grades (median [IQR]) were 2 (0–3) in ALS and 0 (0–0) in non-ALS patients (P < 0.001). Fasciculations were observed in four regions for ALS patients and primarily distributed in proximal limbs. Fasciculations in non-ALS patients were primarily low-grade and mostly distributed in distal limbs.

Discussion

The fasciculation grade was higher in ALS than non-ALS patients. The distribution pattern of fasciculation was different between ALS and non-ALS patients.

Conclusions

The fasciculation grade and distribution pattern detected with MUS could help distinguish ALS from non-ALS patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12883-021-02473-5.

A model incorporating ultrasound to predict the probability of fast disease progression in amyotrophic lateral sclerosis

OBJECTIVE

We aimed to develop a model to predict amyotrophic lateral sclerosis (ALS) disease progression based on clinical and neuromuscular ultrasound (NMUS) parameters.

METHODS

ALS patients were prospectively recruited. Muscle fasciculation (≥2 over 30-seconds, examined in biceps brachii-brachialis (BB), brachioradialis, tibialis anterior and vastus medialis) and nerve cross-sectional area (CSA) (median, ulnar, tibial, fibular nerve) were evaluated through NMUS. Ultrasound parameters were correlated with clinical data, including revised ALS Functional Rating Scale (ALSFRS-R) progression at one year. A predictive model was constructed to differentiate fast progressors (ALSFRS-R decline ≥ 1/month) from non-fast progressors.

RESULTS

40 ALS patients were recruited. Three parameters emerged as strong predictors of fast progressors: (i) ALSFRS-R slope at time of NMUS (p = 0.041), (ii) BB fasciculation count (p = 0.027) and (iii) proximal to distal median nerve CSA ratio < 1.22 (p = 0.026). A predictive model (scores 0-5) was built with excellent discrimination (area under curve: 0.915). Using a score of ≥ 3, the model demonstrated good sensitivity (81.3%) and specificity (91.0%) in differentiating fast from non-fast progressors.

CONCLUSION

The current model is simple and can predict the probability of fast disease progression.

SIGNIFICANCE

This model has potential as a surrogate biomarker of ALS disease progression.

Muscle ultrasound: Present state and future opportunities

Muscle ultrasound is a valuable addition to the neuromuscular toolkit in both the clinic and research settings, with proven value and reliability. However, it is currently not fulfilling its full potential in the diagnostic care of patients with neuromuscular disease. This review highlights the possibilities and pitfalls of muscle ultrasound as a diagnostic tool and biomarker, and discusses challenges to its widespread implementation. We expect that limitations in visual image interpretation, posed by user inexperience, could be overcome with simpler scoring systems and the help of deep-learning algorithms. In addition, more information should be collected on the relation between specific neuromuscular disorders, disease stages, and expected ultrasound abnormalities, as this will enhance specificity of the technique and enable the use of muscle ultrasound as a biomarker. Quantified muscle ultrasound gives the most sensitive results but is hampered by the need for device-specific reference values. Efforts in creating dedicated muscle ultrasound systems and artificial intelligence to help with image interpretation are expected to improve usability. Finally, the standard inclusion of muscle and nerve ultrasound in neuromuscular teaching curricula and guidelines will facilitate further implementation in practice. Our hope is that this review will help in unleashing muscle ultrasound's full potential.

Fasciculation score: a sensitive biomarker in amyotrophic lateral sclerosis

OBJECTIVE

The aim of our study was to elucidate the characteristic of fasciculation distributions in amyotrophic lateral sclerosis (ALS) using a fasciculation score (FS) of muscle ultrasound (MUS) and to compare the diagnostic values of three MUS fasciculation parameters in patients.

METHODS

Thirty ALS patients, 16 ALS mimics, and 10 healthy subjects were involved. MUS of unilateral 10 muscles in each patient and needle electromyography (EMG) of total 204 muscles were performed to detect fasciculations and spontaneous activity respectively in ALS. Control groups underwent only MUS. Fasciculation was graded semiquantitatively with FS.

RESULTS

Three hundred fifty muscles in ALS and 260 in controls were examined. The fasciculation detection rates, total FS, the number of muscles with fasciculation, and the total number of fasciculations in ALS were all significantly higher than those of controls (P < 0.001). ALS patients exhibited a multifocal continuous pattern of fasciculation in limbs, whereas there were few fasciculations in controls. Compared with other parameters, total FS had the largest area under the curve (AUC) (AUC = 0.899, P < 0.001) in ALS diagnosis. The detection rates of lower motor neuron (LMN) acute lesions by MUS (70.6%) and EMG (72.1%) were nearly the same, and a positive correlation between the FS and spontaneous activity grades (P < 0.001, r = 0.359) was proved.

CONCLUSIONS

ALS patients exhibited the multifocal continuous pattern of fasciculation in limbs. FS showed high sensitivity and specificity in differentiating ALS from non-ALS patients, and the optimal cut-off value was determined as 4. The combination of MUS and EMG can provide additional information about specific muscles.

Fasciculation frequency at the biceps brachii and brachialis muscles is associated with amyotrophic lateral sclerosis disease burden and activity

INTRODUCTION

Fasciculations are most commonly seen in the biceps brachii muscle in amyotrophic lateral sclerosis (ALS). In this study we have explored the association between fasciculation frequency in a single location-biceps brachii and brachialis muscles (BB), and disease burden and activity.

METHODS

Sonographic muscle studies were performed in 90 ALS patients, 47 of whom were seen in subsequent follow-up. The association between fasciculations frequency at the BB and ALS Functional Rating Scale-Revised (ALSFRS-R) and manual muscle testing (MMT) scores was determined.

RESULTS

High fasciculation frequency at the BB, where detection rate was the highest, was associated with shorter disease duration, greater muscle thickness, higher MMT scores, and faster rate of decline in ALSFRS-R initially, and MMT subsequently.

DISCUSSION

High fasciculation frequency at the BB as determined by sonography, is associated with less impairment at time of examination, and a more active disease with a more rapid progression.

Ultrasound Detection of Vagus Nerve Atrophy in Bulbar Amyotrophic Lateral Sclerosis

BACKGROUND AND PURPOSE

Neuromuscular ultrasound in amyotrophic lateral sclerosis (ALS) is of increasing interest. As bulbar symptoms are commonly developed by most ALS patients during disease, the aim of our study was to find possible sonographic changes of vagus nerve size in bulbar affected ALS patients.

METHODS

We investigated 24 ALS patients and 19 controls without neuromuscular disorders. In ALS patients, bulbar affection was documented clinically (eg, dysarthria, dysphagia, and fasciculations) or subclinically using ultrasound and electromyography of bulbar muscles. Vagus nerve ultrasound was performed in all participants bilaterally at the level of the thyroid gland.

RESULTS

The cross-sectional area (CSA) of the vagus nerve in bulbar affected ALS patients (mean CSA right/left 1.9 ± .7 mm²/1.8 ± .6 mm²) was significantly reduced on both sides compared to controls (mean CSA right/left 2.2 ± .6 mm²/2.0 ± .3 mm²) - right: P = .0387, left: P = .0386. Receiver operating characteristic curve analysis of the vagus nerve CSA yielded a sensitivity of 66.7% and a specificity of 63.2% (cutoff value 1.85 mm²). Vagus nerve CSA did not correlate significantly with age in controls (right: P = .45, left: P = .66). In controls and ALS patients, there was no significant difference of vagus nerve CSA between the right and left sides (controls: P = .43; patients: P = .86).

CONCLUSION

Our study demonstrates vagus nerve atrophy in bulbar affected ALS patients. Further studies are warranted investigating the relevance of our finding for monitoring disease progression in ALS.

Difference in distribution of fasciculations between multifocal motor neuropathy and amyotrophic lateral sclerosis

OBJECTIVE

To examine differences in fasciculation distribution between patients with multifocal motor neuropathy (MMN) and amyotrophic lateral sclerosis (ALS) based on muscle ultrasound.

METHODS

Forty-one muscles (tongue muscle and 40 muscles of the trunk and limbs on both sides) in 5 MMN patients and 21 muscles (tongue muscle and 20 muscles on the onset side) in 21 ALS patients were subjected to muscle ultrasound individually for 60 seconds to detect the presence of fasciculations.

RESULTS

Fasciculation detection rates on the onset side were significantly higher in ALS (42.4 ± 18.3%, mean ± SD) than in MMN (21.9 ± 8.8%) patients (p < 0.05). In MMN patients, no fasciculation was detected in the tongue or truncal muscles. There was no difference in the fasciculation detection rate between the onset and non-onset sides or between upper and lower limbs in MMN patients.

CONCLUSIONS

In MMN patients, fasciculations were detected extensively in the limbs. However, the detection rate in patients with MMN was lower than in those with ALS.

SIGNIFICANCE

Demonstration of the absence of fasciculations in the tongue and truncal muscles in MMN patients by extensive muscle ultrasound examination may help distinguish MMN from ALS.

Ultrasound versus electromyography for the detection of fasciculation in amyotrophic lateral sclerosis: systematic review and meta-analysis

The objective of this study was to determine the diagnostic accuracy of ultrasound and electromyography for the detection of fasciculation in patients with amyotrophic lateral sclerosis and to compare detection rates between the two methods. By searching the Cochrane Library, MEDLINE, Excerpta Medica, and Latin-American and Caribbean Health Sciences Literature databases, we identified studies evaluating the diagnostic accuracy and fasciculation detection rates of ultrasound and electromyography. The Quality Assessment of Diagnostic Accuracy Studies, version 2, and RTI item bank tools were used for the evaluation of methodological quality. Ultrasound, for 10 s or 30 s, had a higher detection rate than did electromyography in all muscles evaluated. The overall detection rate (in patients) did not differ significantly between ultrasound for 10 s and ultrasound for 30 s. The accuracy of ultrasound for 10 s was 70% in muscles and 85% in patients. The accuracy of ultrasound for 30 s was 82% in patients. Ultrasound provided detection rates superior to those achieved with electromyography, independent of the examination time and muscles evaluated.

Primary lateral sclerosis: consensus diagnostic criteria

Primary lateral sclerosis (PLS) is a neurodegenerative disorder of the adult motor system. Characterised by a slowly progressive upper motor neuron syndrome, the diagnosis is clinical, after exclusion of structural, neurodegenerative and metabolic mimics. Differentiation of PLS from upper motor neuron-predominant forms of amyotrophic lateral sclerosis remains a significant challenge in the early symptomatic phase of both disorders, with ongoing debate as to whether they form a clinical and histopathological continuum. Current diagnostic criteria for PLS may be a barrier to therapeutic development, requiring long delays between symptom onset and formal diagnosis. While new technologies sensitive to both upper and lower motor neuron involvement may ultimately resolve controversies in the diagnosis of PLS, we present updated consensus diagnostic criteria with the aim of reducing diagnostic delay, optimising therapeutic trial design and catalysing the development of disease-modifying therapy.

Relationship between EMG-detected and ultrasound-detected fasciculations in amyotrophic lateral sclerosis: A prospective cohort study

OBJECTIVES

Fasciculation potentials (FP) are an important consideration in the electrophysiological diagnosis of ALS. Muscle ultrasonography (MUS) has a higher sensitivity in detecting fasciculations than electromyography (EMG), while in some cases, it is unable to detect EMG-detected fasciculations. We aimed to investigate the differences of FP between the muscles with and without MUS-detected fasciculations (MUS-fas).

METHODS

Thirty-one consecutive patients with sporadic ALS were prospectively recruited and in those, both needle EMG and MUS were performed. Analyses of the amplitude, duration, and number of phases of EMG-detected FPs were performed for seven muscles per patient, and results were compared between the muscles with and without MUS-fas in the total cohort.

RESULTS

The mean amplitude and phase number of FP were significantly lower in patients with EMG-detected FP alone (0.39 ± 0.25 mV and 3.21 ± 0.88, respectively) than in those with both FP and MUS-fas (1.22 ± 0.92 mV and 3.74 ± 1.39, respectively; p < 0.0001 and p = 0.017, Welch's t-test).

CONCLUSION

Small FP may be undetectable with MUS. MUS cannot replace EMG in the diagnostic approach for ALS.

SIGNIFICANCE

Clinicians should use a combination of EMG and MUS for the detection and quantitative analysis of fasciculation in ALS.

Neuromuscular Ultrasound: Clinical Applications and Diagnostic Values

Advances in high-resolution ultrasound have provided clinicians with unique opportunities to study diseases of the peripheral nervous system. Ultrasound complements the clinical and electrophysiology exam by showing the degree of abnormalities in myopathies, as well as spontaneous muscle activities in motor neuron diseases and other disorders. In experienced hands, ultrasound is more sensitive than MRI in detecting peripheral nerve pathologies. It can also guide needle placement for electromyography exam, therapeutic injections, and muscle biopsy. Ultrasound enhances the ability to detect carpal tunnel syndrome and other focal nerve entrapment, as well as pathological nerve enlargements in genetic and acquired neuropathies. Furthermore, ultrasound can potentially be used as a biomarker for muscular dystrophy and spinal muscular atrophy. The combination of electromyography and ultrasound can increase the diagnostic certainty of amyotrophic lateral sclerosis, aid in the localization of brachial plexus or peripheral nerve trauma and allow for surveillance of nerve tumor progression in neurofibromatosis. Potential limitations of ultrasound include an inability to image deeper structures, with lower sensitivities in detecting neuromuscular diseases in young children and those with mitochondrial myopathies, due to subtle changes or early phase of the disease. As well, its utility in detecting critical illness neuromyopathy remains unclear. This review will focus on the clinical applications of neuromuscular ultrasound. The diagnostic values of ultrasound for screening of myopathies, neuropathies, and motor neuron diseases will be presented.

Clinical and research applications of neuromuscular ultrasound in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disorder characterized by dysfunction at multiple levels of the neuraxis. It remains a clinical diagnosis without a definitive diagnostic investigation. Electrodiagnostic testing provides supportive information and, along with imaging and biochemical markers, can help exclude mimicking conditions. Neuromuscular ultrasound has a valuable role in the diagnosis and monitoring of ALS and provides complementary information to clinical assessment and electrodiagnostic testing as well as insights into the underlying pathophysiology of this disease. This review highlights the evidence for ultrasound in the evaluation of bulbar, limb and respiratory musculature and peripheral nerves in ALS. Further research in this evolving area is required.

Foreground Detection Analysis of Ultrasound Image Sequences Identifies Markers of Motor Neurone Disease across Diagnostically Relevant Skeletal Muscles

Diagnosis of motor neurone disease (MND) includes detection of small, involuntary muscle excitations, termed fasciculations. There is need to improve diagnosis and monitoring of MND through provision of objective markers of change. Fasciculations are visible in ultrasound image sequences. However, few approaches that objectively measure their occurrence have been proposed; their performance has been evaluated in only a few muscles; and their agreement with the clinical gold standard for fasciculation detection, intramuscular electromyography, has not been tested. We present a new application of adaptive foreground detection using a Gaussian mixture model (GMM), evaluating its accuracy across five skeletal muscles in healthy and MND-affected participants. The GMM provided good to excellent accuracy with the electromyography ground truth (80.17%-92.01%) and was robust to different ultrasound probe orientations. The GMM provides objective measurement of fasciculations in each of the body segments necessary for MND diagnosis and hence could provide a new, clinically relevant disease marker.

Functional magnetic resonance imaging of human motor unit fasciculation in amyotrophic lateral sclerosis

A novel diffusion-weighted magnetic resonance imaging protocol sensitive to contraction of individual skeletal motor units was developed. We applied this technique to the lower limb muscles of 4 patients with confirmed amyotrophic lateral sclerosis (ALS) and 6 healthy controls. A 3-minute scan revealed florid fasciculation in ALS patients, involving both superficial and deep muscles, and at a frequency higher than in healthy controls. This novel imaging technique reveals hitherto unobtainable information on human motor unit structure and function, which may allow earlier diagnosis and recruitment to clinical trials. ANN NEUROL 2019;85:455-459.

A pilot study of neuromuscular ultrasound as a biomarker for amyotrophic lateral sclerosis

INTRODUCTION

This study explores the reliability and responsiveness of neuromuscular ultrasound in amyotrophic lateral sclerosis (ALS).

METHODS

Investigations were conducted with 10 healthy controls, 10 patients with ALS (single point in time), and 10 different patients with ALS (followed over 6 months; 4 completed follow-up). Ultrasound was used to measure the thickness of the geniohyoid, bilateral biceps/brachialis, bilateral tibialis anterior, and bilateral hemidiaphragms (at inspiration and expiration). Interrater and intrarater reliability and change in muscle thickness over 6 months were measured.

RESULTS

Interrater correlation coefficients ranged between 0.80 and 0.99 in healthy controls and between 0.78 and 0.97 in patients with ALS. Intrarater correlation coefficients ranged between 0.83 and 0.98 in healthy controls. The mean percentage decline in muscle thickness over 6 months was 20.25%.

DISCUSSION

Muscle ultrasound appears to be a reliable technique for measuring important muscles in patients with ALS. Larger studies with age-matched controls should be conducted to assess further the responsiveness of this biomarker in ALS. Muscle Nerve 59:181-186, 2019.

New insights into the pathophysiology of fasciculations in amyotrophic lateral sclerosis: An ultrasound study

OBJECTIVE

To describe the fasciculation pattern in ALS and to analyse its clinical and pathophysiological significance.

METHODS

Ultrasound of 19 muscles was performed in 44 patients with a recent diagnosis (<90 days) of ALS. The number of fasciculations was recorded in each muscle and the muscle thickness and strength were additionally measured in limb muscles. A subgroup of patients were electromyographically assessed.

RESULTS

US was performed in 835 muscles and EMG was available in 263 muscles. US detected fasciculations more frequently than EMG. Fasciculations were widespread, especially in upper limbs onset patients and in the cervical region. Fasciculations' number inversely associated with ALSFR-R and body mass index (BMI) and directly with BMI loss and upper motor neuron (UMN) impairment. Our statistical model suggest that fasciculations increase with the initial lower motor neuron (LMN) degeneration, reach their peak when the muscle became mildly to moderately weak, decreasing afterwards with increasing muscle weakness and atrophy.

CONCLUSIONS

Our study suggests that both UMN and LMN degeneration trigger fasciculations causing BMI loss. The degree of LMN impairment could account for differences in fasciculations' rates within and between muscles.

SIGNIFICANCE

In ALS, fasciculations could explain the link between hyperexcitability and BMI loss.

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.