MUNIX: Reproducibility and clinical correlations in Amyotrophic Lateral Sclerosis

Could the motor unit number index be an early prognostic biomarker for amyotrophic lateral sclerosis?

OBJECTIVE

To evaluate the associations between motor unit number index (MUNIX) and disease progression and prognosis in amyotrophic lateral sclerosis (ALS) in a large-scale longitudinal study.

METHODS

MUNIX was performed at the patient's first visit, at 3, 6, and 12 months in 4 muscles. MUNIX data from the patients were compared with those from 38 age-matched healthy controls. Clinical data included the revised ALS functional rating scale (ALSFRS-R), the forced vital capacity (FVC), and the survival of the patients.

RESULTS

Eighty-two patients were included at baseline, 62 were evaluated at three months, 48 at six months, and 33 at twelve months. MUNIX score was lower in ALS patients compared to controls. At baseline, MUNIX was correlated with ALSFRS-R and FVC. Motor unit size index (MUSIX) was correlated with patient survival. Longitudinal analyses showed that MUNIX decline was greater than ALSFRS-R decline at each evaluation. A baseline MUNIX score greater than 378 predicted survival over the 12-month period with a sensitivity of 82% and a specificity of 56%.

CONCLUSIONS

This longitudinal study suggests that MUNIX could be an early quantitative marker of disease progression and prognosis in ALS.

SIGNIFICANCE

MUNIX might be considered as potential indicator for monitoring disease progression.

Biomarkers in 5q-associated spinal muscular atrophy-a narrative review

5q-associated spinal muscular atrophy (SMA) is a rare genetic disease caused by mutations in the SMN1 gene, resulting in a loss of functional SMN protein and consecutive degeneration of motor neurons in the ventral horn. The disease is clinically characterized by proximal paralysis and secondary skeletal muscle atrophy. New disease-modifying drugs driving SMN gene expression have been developed in the past decade and have revolutionized SMA treatment. The rise of treatment options led to a concomitant need of biomarkers for therapeutic guidance and an improved disease monitoring. Intensive efforts have been undertaken to develop suitable markers, and numerous candidate biomarkers for diagnostic, prognostic, and predictive values have been identified. The most promising markers include appliance-based measures such as electrophysiological and imaging-based indices as well as molecular markers including SMN-related proteins and markers of neurodegeneration and skeletal muscle integrity. However, none of the proposed biomarkers have been validated for the clinical routine yet. In this narrative review, we discuss the most promising candidate biomarkers for SMA and expand the discussion by addressing the largely unfolded potential of muscle integrity markers, especially in the context of upcoming muscle-targeting therapies. While the discussed candidate biomarkers hold potential as either diagnostic (e.g., SMN-related biomarkers), prognostic (e.g., markers of neurodegeneration, imaging-based markers), predictive (e.g., electrophysiological markers) or response markers (e.g., muscle integrity markers), no single measure seems to be suitable to cover all biomarker categories. Hence, a combination of different biomarkers and clinical assessments appears to be the most expedient solution at the time.

Prognostic Usefulness of Motor Unit Number Index (MUNIX) in Patients Newly Diagnosed with Amyotrophic Lateral Sclerosis

The MUNIX technique allows us to estimate the number and size of surviving motor units (MUs). Previous studies on ALS found correlations between MUNIX and several clinical measures, but its potential role as a predictor of disease progression rate (DPR) has not been thoroughly evaluated to date. We aimed to investigate MUNIX's ability to predict DPR at a six-month follow up.

METHODS

24 ALS patients with short disease duration (<24 months from symptoms' onset) were enrolled and divided according to their baseline DPR into two groups (normal [DPR-N] and fast [DPR-F] progressors). MUNIX values were obtained from five muscles (TA, APB, ADM, FDI, Trapezius) and averaged for each subject.

RESULTS

MUNIX was found to predict DPR at follow up in a multivariable linear regression model; namely, patients with lower MUNIX values were at risk of showing greater DPR scores at follow up. The result was replicated in a simple logistic regression analysis, with the dichotomic category "MUNIX-Low" as the independent variable and the outcome "DPR-F" as the dependent variable.

CONCLUSIONS

our results pave the way for the use of the MUNIX method as a prognostic tool in early ALS, enabling patients' stratification according to their rates of future decline.

Evaluation method of motor unit number index based on optimal muscle strength combination

Repeatability is an important attribute of motor unit number index (MUNIX) technology. This paper proposes an optimal contraction force combination for MUNIX calculation in an effort to improve the repeatability of this technology. In this study, the surface electromyography (EMG) signals of the biceps brachii muscle of eight healthy subjects were initially recorded with high-density surface electrodes, and the contraction strength was the maximum voluntary contraction force of nine progressive levels. Then, by traversing and comparing the repeatability of MUNIX under various combinations of contraction force, the optimal combination of muscle strength is determined. Finally, calculate MUNIX using the high-density optimal muscle strength weighted average method. The correlation coefficient and the coefficient of variation are utilized to assess repeatability. The results show that when the muscle strength combination is 10, 20, 50 and 70% of the maximum voluntary contraction force, the repeatability of MUNIX is greatest, and the correlation between MUNIX calculated using this combination of muscle strength and conventional methods is high (PCC > 0.99), the repeatability of the MUNIX method improved by 11.5-23.8%. The results indicate that the repeatability of MUNIX differs for various combinations of muscle strength and that MUNIX, which is measured with a smaller number and lower-level contractility, has greater repeatability.

Application Value of the Motor Unit Number Index in Patients With Kennedy Disease

The aim of this study was to evaluate the usefulness of the motor unit number index (MUNIX) technique in Kennedy disease (KD) and test the correlation between the MUNIX and other clinical parameters. The MUNIX values of the bilateral deltoid, abductor digiti minimi (ADM), quadriceps femoris (QF), and tibialis anterior (TA) were determined and compared with the course of the disease. The MUNIX sum score was calculated by adding the MUNIX values of these 8 muscles. Disability was evaluated using the spinal and bulbar muscular atrophy functional rating scale (SBMAFRS). The MUNIX scores of patients with KD were negatively correlated with the course of the disease (p < 0.05), whereas their motor unit size index (MUSIX) scores were positively correlated with the course the of disease (p < 0.05). MUNIX sum scores were correlated with SBMAFRS scores (r = 0.714, p < 0.05). MUNIX was more sensitive than compound muscle action potentials or muscle strength as an indicator of neuron loss and axonal collateral reinnervation. The MUNIX sum score is an objective and a reliable indicator of disease progression, and it is a potential choice for therapeutic clinical trials. The MUNIX can assess the functional loss of motor axons and is correlated with disability. The MUNIX sum score may be especially suitable as an objective parameter.

Assessing inter-rater reproducibility in MScanFit MUNE in a 6-subject, 12-rater "Round Robin" setup

OBJECTIVE

To assess the inter-rater reliability of MScanFit MUNE using a "Round Robin" research design.

METHODS

Twelve raters from different centres examined six healthy study participants over two days. Median, ulnar and common peroneal nerves were stimulated, and compound muscle action potential (CMAP)-scans were recorded from abductor pollicis brevis (APB), abductor digiti minimi (ADM) and anterior tibial (TA) muscles respectively. From this we calculated the Motor Unit Number Estimation (MUNE) and "A50", a motor unit size parameter. As statistical analysis we used the measures Limits of Agreement (LOA) and Coefficient of Variation (COV). Study participants scored their perception of pain from the examinations on a rating scale from 0 (no pain) to 10 (unbearable pain).

RESULTS

Before this study, 41.6% of the raters had performed MScanFit less than five times. The mean MUNE-values were: 99.6 (APB), 131.4 (ADM) and 126.2 (TA), with LOA: 19.5 (APB), 29.8 (ADM) and 20.7 (TA), and COV: 13.4 (APB), 6.3 (ADM) and 5.6 (TA). MUNE-values correlated to CMAP max amplitudes (R²-values were: 0.463 (APB) (p<0.001), 0.421 (ADM) (p<0.001) and 0.645 (TA) (p<0.001)). The average perception of pain was 4.

DISCUSSION

MScanFit indicates a high level of inter-rater reliability, even with only limited rater experience and is overall reasonably well tolerated by patients. These results may indicate MScanFit as a reliable MUNE method with potential as a biomarker in drug trials.

Motor unit number index (MUNIX) in children and adults with 5q-spinal muscular atrophy: Variability and clinical correlations

Spinal muscular atrophy (SMA) is a motor neuron disease associated with progressive muscle weakness and motor disability. The motor unit number index (MUNIX) is a biomarker used to assess loss of motor units in later-onset SMA patients. Twenty SMA patients (SMA types 3 and 4), aged between 7 and 41 years, were clinically evaluated through the Hammersmith Motor Functional Scale Expanded and the Spinal Muscular Atrophy-Functional Rating Scale. The patients underwent compound motor action potential (CMAP) and MUNIX studies of the right abductor pollicis brevis, abductor digiti minimi and tibialis anterior (TA) muscles. Age-matched healthy controls (n = 20) were enrolled to obtain normative CMAP and MUNIX values from the same muscles. Compared to healthy controls, SMA patients showed significant reductions in MUNIX values among all muscles studied, whereas CMAP showed reductions only in the weaker muscles (abductor digiti minimi and TA). MUNIX variability was significantly higher in the SMA group than in the control group. MUNIX variability in TA correlated with CMAP variability. Motor functional scores correlated with TA MUNIX. The MUNIX study is feasible in later-onset SMA patients, and TA MUNIX values correlate with disease severity in patients with mild motor impairment.

Brain Stimulation as a Therapeutic Tool in Amyotrophic Lateral Sclerosis: Current Status and Interaction With Mechanisms of Altered Cortical Excitability

In the last 20 years, several modalities of neuromodulation, mainly based on non-invasive brain stimulation (NIBS) techniques, have been tested as a non-pharmacological therapeutic approach to slow disease progression in amyotrophic lateral sclerosis (ALS). In both sporadic and familial ALS cases, neurophysiological studies point to motor cortical hyperexcitability as a possible priming factor in neurodegeneration, likely related to dysfunction of both excitatory and inhibitory mechanisms. A trans-synaptic anterograde mechanism of excitotoxicity is thus postulated, causing upper and lower motor neuron degeneration. Specifically, motor neuron hyperexcitability and hyperactivity are attributed to intrinsic cell abnormalities related to altered ion homeostasis and to impaired glutamate and gamma aminobutyric acid gamma-aminobutyric acid (GABA) signaling. Several neuropathological mechanisms support excitatory and synaptic dysfunction in ALS; additionally, hyperexcitability seems to drive DNA-binding protein 43-kDA (TDP-43) pathology, through the upregulation of unusual isoforms directly contributing to ASL pathophysiology. Corticospinal excitability can be suppressed or enhanced using NIBS techniques, namely, repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), as well as invasive brain and spinal stimulation. Experimental evidence supports the hypothesis that the after-effects of NIBS are mediated by long-term potentiation (LTP)-/long-term depression (LTD)-like mechanisms of modulation of synaptic activity, with different biological and physiological mechanisms underlying the effects of tDCS and rTMS and, possibly, of different rTMS protocols. This potential has led to several small trials testing different stimulation interventions to antagonize excitotoxicity in ALS. Overall, these studies suggest a possible efficacy of neuromodulation in determining a slight reduction of disease progression, related to the type, duration, and frequency of treatment, but current evidence remains preliminary. Main limitations are the small number and heterogeneity of recruited patients, the limited "dosage" of brain stimulation that can be delivered in the hospital setting, the lack of a sufficient knowledge on the excitatory and inhibitory mechanisms targeted by specific stimulation interventions, and the persistent uncertainty on the key pathophysiological processes leading to motor neuron loss. The present review article provides an update on the state of the art of neuromodulation in ALS and a critical appraisal of the rationale for the application/optimization of brain stimulation interventions, in the light of their interaction with ALS pathophysiological mechanisms.

Use of CMAP, MScan fit-MUNE, and MUNIX in understanding neurodegeneration pattern of ALS and detection of early motor neuron loss in daily practice

BACKGROUND

The pattern of lower motor neuron (LMN) degeneration in amyotrophic lateral sclerosis (ALS), i.e., dying-back (from the nerve ending to cell body) or dying-forward (from the cell body to nerve ending), has been widely discussed. In this study, we aimed to evaluate LMN loss using compound muscle action potential (CMAP), motor unit number index (MUNIX), and MScan-fit-based motor unit number estimation (MUNE) to understand the pattern of neurodegeneration in ALS.

METHODS

Twenty-five patients were compared with 25 controls using CMAP amplitude and area, MUNIX, and MScan-fit MUNE in three proximal and distal muscles innervated by the ulnar nerve.

RESULTS

Unlike the controls, the CMAP area, MScan-fit MUNE, and MUNIX recorded in ALS patients showed more neurodegeneration in distal muscles than proximal muscles. In ALS patients with unaffected CMAP amplitudes (n = 13), the CMAP area, MScan-fit MUNE, and MUNIX showed subtle motor unit loss of 30.7 %, 53.8 %, and 38.4 %, respectively.

CONCLUSION

The CMAP area, MScan-fit MUNE, and MUNIX showed neurodegeneration earlier than the reduction in CMAP amplitude. These tests confirmed dying-back neurodegeneration, while only MUSIX showed re-innervation in ALS.

Motor unit number index detects the effectiveness of surgical treatment in improving distal motor neuron loss in patients with incomplete cervical spinal cord injury

BACKGROUND

Recovery of motor dysfunction is important for patients with incomplete cervical spinal cord injury (SCI). To enhance the recovery of muscle strength, both research and treatments mainly focus on injury of upper motor neurons at the direct injury site. However, accumulating evidences have suggested that SCI has a downstream effect on the peripheral nervous system, which may contribute to the poor improvement of the muscle strength after operation. The aim of this study is to investigate the impact of early vs. delayed surgical intervention on the lower motor neurons (LMNs) distal to the injury site in patients with incomplete cervical SCI.

METHODS

Motor unit number index (MUNIX) was performed on the tibialis anterior (TA), extensor digitorum brevis (EDB) and abductor hallucis (AH) in 47 patients with incomplete cervical SCI (early vs. delayed surgical-treatment: 17 vs. 30) and 34 healthy subjects approximately 12 months after operation. All patients were further assessed by American spinal injury association (ASIA) motor scales and Medical Research Council (MRC) scales.

RESULTS

There are no difference of both ASIA motor scores and MRC scales between the patients who accepted early and delayed surgical treatment (P > 0.05). In contrast, the patients undergoing early surgical treatment showed lower MUSIX values in both bilateral EDB and bilateral TA, along with greater MUNIX values in both right-side EDB and right-side TA, compared to the patients who accepted delayed surgical treatment (P < 0.05).

CONCLUSIONS

Cervical SCI has a negative effect on the LMNs distal to the injury site. Early surgical intervention in Cervical SCI patients may improve the dysfunction of LMNs distal to the injury site, reducing secondary motor neuron loss, and eventually improving clinical prognosis.

Head-down tilt bed rest with or without artificial gravity is not associated with motor unit remodeling

PURPOSE

The objective of this study was to assess whether artificial gravity attenuates any long-duration head-down 6⁰ bed rest (HDBR)-induced alterations in motor unit (MU) properties.

METHODS

Twenty-four healthy participants (16 men; 8 women; 26-54 years) underwent 60-day HDBR with (n = 16) or without (n = 8) 30 min artificial gravity daily induced by whole-body centrifugation. Compound muscle action potential (CMAP), MU number (MUNIX) and MU size (MUSIX) were estimated using the method of Motor Unit Number Index in the Abductor digiti minimi and tibialis anterior muscles 5 days before (BDC-5), and during day 4 (HDT4) and 59 (HDT59) of HDBR.

RESULTS

The CMAP, MUNIX, and MUSIX at baseline did not change significantly in either muscle, irrespective of the intervention (p > 0.05). Across groups, there were no significant differences in any variable during HDBR, compared to BDC-5.

CONCLUSION

Sixty days of HDBR with or without artificial gravity does not induce alterations in motor unit number and size in the ADM or TA muscles in healthy individuals.

Motor unit number index in children with later-onset spinal muscular atrophy

BACKGROUND

Motor unit number index (MUNIX) is a validated electrophysiological biomarker in amyotrophic lateral sclerosis. MUNIX studies in spinal muscular atrophy (SMA) are limited.

METHODS

Later-onset SMA children (n = 13; three SMN2 copy number) were evaluated for Hammersmith Motor Function Scale Expanded (HMFSE) and MUNIX of right abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles. Age-matched healthy controls (n = 8) were enrolled to obtain normative APB and ADM MUNIX values.

RESULTS

Mean APB and ADM MUNIX values in SMA subjects were significantly reduced (P < .001) compared with controls. HMFSE scores strongly correlated with ADM MUNIX (r 0.63).

CONCLUSIONS

APB and ADM muscle MUNIX studies are feasible in SMA type 2 children. ADM MUNIX correlated with disease severity on motor function testing. MUNIX studies in later-onset SMA could be a potential biomarker of motor neuron loss.

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.

Reference values for the motor unit number index and the motor unit size index in five muscles

INTRODUCTION

Few reference values have been established for the motor unit number index (MUNIX) and motor unit size index (MUSIX). In this study we aimed to investigate the features of MUNIX in healthy individuals for five muscles.

METHODS

We measured the MUNIX in the right abductor pollicis brevis (APB), abductor digiti minimi (ADM), biceps brachii (BB), tibialis anterior (TA), and trapezius (TR) muscles.

RESULTS

The study enrolled 76 male and 74 female participants. The mean MUNIX and mean MUSIX of the right APB, ADM, BB, TA, and TR muscles were 191.0 ± 43.6, 179.1 ± 38.8, 179.7 ± 36.2, 152.1 ± 38.8, and 166.1 ± 40.7; and 60.4 ± 12.5, 59.3 ± 13.7, 43.8 ± 11.5, 41.3 ± 10.7, and 49.1 ± 15.2, respectively. MUNIX in these five muscles was inversely related to age.

DISCUSSION

The establishment of reference values for MUNIX and MUSIX in five muscles may help in monitoring the progression of neuromuscular diseases.

Cell-based therapies for amyotrophic lateral sclerosis/motor neuron disease

BACKGROUND

Amyotrophic lateral sclerosis (ALS), which is also known as motor neuron disease (MND), is a fatal disease associated with rapidly progressive disability, for which no definitive treatment exists. Current treatment approaches largely focus on relieving symptoms to improve the quality of life of those affected. The therapeutic potential of cell-based therapies in ALS/MND has not been fully evaluated, given the paucity of high-quality clinical trials. Based on data from preclinical studies, cell-based therapy is a promising treatment for ALS/MND. This review was first published in 2015 when the first clinical trials of cell-based therapies were still in progress. We undertook this update to incorporate evidence now available from randomised controlled trials (RCTs).

OBJECTIVES

To assess the effects of cell-based therapy for people with ALS/MND, compared with placebo or no treatment.

SEARCH METHODS

On 31 July 2019, we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, and Embase. We also searched two clinical trials registries for ongoing or unpublished studies.

SELECTION CRITERIA

We included RCTs that assigned people with ALS/MND to receive cell-based therapy versus a placebo or no additional treatment. Co-interventions were allowed, provided that they were given to each group equally.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methodology.

MAIN RESULTS

Two RCTs involving 112 participants were eligible for inclusion in this review. One study compared autologous bone marrow-mesenchymal stem cells (BM-MSC) plus riluzole versus control (riluzole only), while the other study compared combined intramuscular and intrathecal administration of autologous mesenchymal stem cells secreting neurotrophic factors (MSC-NTF) to placebo. The latter study was reported as an abstract and provided no numerical data. Both studies were funded by biotechnology companies. The only study that contributed to the outcome data in the review involved 64 participants, comparing BM-MSC plus riluzole versus control (riluzole only). It reported outcomes after four to six months. It had a low risk of selection bias, detection bias and reporting bias, but a high risk of performance bias and attrition bias. The certainty of evidence was low for all major efficacy outcomes, with imprecision as the main downgrading factor, because the range of plausible estimates, as shown by the 95% confidence intervals (CIs), encompassed a range that would likely result in different clinical decisions. Functional impairment, expressed as the mean change in the Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) score from baseline to six months after cell injection was slightly reduced (better) in the BM-MSC group compared to the control group (mean difference (MD) 3.38, 95% CI 1.22 to 5.54; 1 RCT, 56 participants; low-certainty evidence). ALSFRS-R has a range from 48 (normal) to 0 (maximally impaired); a change of 4 or more points is considered clinically important. The trial did not report outcomes at 12 months. There was no clear difference between the BM-MSC and the no treatment group in change in respiratory function (per cent predicted forced vital capacity; FVC%; MD -0.53, 95% CI -5.37 to 4.31; 1 RCT, 56 participants; low-certainty evidence); overall survival at six months (risk ratio (RR) 1.07, 95% CI 0.94 to 1.22; 1 RCT, 64 participants; low-certainty evidence); risk of total adverse events (RR 0.86, 95% CI 0.62 to 1.19; 1 RCT, 64 participants; low-certainty evidence) or serious adverse events (RR 0.47, 95% CI 0.13 to 1.72; 1 RCT, 64 participants; low-certainty evidence). The study did not measure muscle strength.

AUTHORS' CONCLUSIONS

Currently, there is a lack of high-certainty evidence to guide practice on the use of cell-based therapy to treat ALS/MND. Uncertainties remain as to whether this mode of therapy is capable of restoring muscle function, slowing disease progression, and improving survival in people with ALS/MND. Although one RCT provided low-certainty evidence that BM-MSC may slightly reduce functional impairment measured on the ALSFRS-R after four to six months, this was a small phase II trial that cannot be used to establish efficacy. We need large, prospective RCTs with long-term follow-up to establish the efficacy and safety of cellular therapy and to determine patient-, disease- and cell treatment-related factors that may influence the outcome of cell-based therapy. The major goals of future research are to determine the appropriate cell source, phenotype, dose and method of delivery, as these will be key elements in designing an optimal cell-based therapy programme for people with ALS/MND. Future research should also explore novel treatment strategies, including combinations of cellular therapy and standard or novel neuroprotective agents, to find the best possible approach to prevent or reverse the neurological deficit in ALS/MND, and to prolong survival in this debilitating and fatal condition.

Motor unit number index (MUNIX) in myopathic disorders: Clinical correlations and potential pitfalls

Our aim was to study motor unit number index (MUNIX) in myopathic disorders. We studied 11 patients with myopathy, and healthy controls. We obtained MUNIX, compound muscle action potential (CMAP), motor unit size index (MUSIX) and alpha (α, power exponent from MUNIX equation) measurements from three different muscles. MUNIX and CMAP were significantly lower in one muscle. This MUNIX decrease may not be related to motor neuron loss, but rather to muscle fiber atrophy. MUSIX and α did not change and may be useful in determining whether the MUNIX decrease is indeed due to motor unit loss.

Biomarkers in Motor Neuron Disease: A State of the Art Review

Motor neuron disease can be viewed as an umbrella term describing a heterogeneous group of conditions, all of which are relentlessly progressive and ultimately fatal. The average life expectancy is 2 years, but with a broad range of months to decades. Biomarker research deepens disease understanding through exploration of pathophysiological mechanisms which, in turn, highlights targets for novel therapies. It also allows differentiation of the disease population into sub-groups, which serves two general purposes: (a) provides clinicians with information to better guide their patients in terms of disease progression, and (b) guides clinical trial design so that an intervention may be shown to be effective if population variation is controlled for. Biomarkers also have the potential to provide monitoring during clinical trials to ensure target engagement. This review highlights biomarkers that have emerged from the fields of systemic measurements including biochemistry (blood, cerebrospinal fluid, and urine analysis); imaging and electrophysiology, and gives examples of how a combinatorial approach may yield the best results. We emphasize the importance of systematic sample collection and analysis, and the need to correlate biomarker findings with detailed phenotype and genotype data.

Assessment of the reliability of the motor unit size index (MUSIX) in single subject "round-robin" and multi-centre settings

OBJECTIVE

The motor unit size index (MUSIX) is incorporated into the motor unit number index (MUNIX). Our objective was to assess the intra-/inter-rater reliability of MUSIX in healthy volunteers across single subject "round robin" and multi-centre settings.

METHODS

Data were obtained from (i) a round-robin assessment in which 12 raters (6 with prior experience and 6 without) assessed six muscles (abductor pollicis brevis, abductor digiti minimi, biceps brachii, tibialis anterior, extensor digitorum brevis and abductor hallucis) and (ii) a multi-centre study with 6 centres studying the same muscles in 66 healthy volunteers. Intra/inter-rater data were provided by 5 centres, 1 centre provided only intra-rater data. Intra/inter-rater variability was assessed using the coefficient of variation (COV), Bland-Altman plots, bias and 95% limits of agreement.

RESULTS

In the round-robin assessment intra-rater COVs for MUSIX ranged from 7.8% to 28.4%. Inter-rater variability was between 7.8% and 16.2%. Prior experience did not impact on MUSIX values. In the multi-centre study MUSIX was more consistent than the MUNIX. Abductor hallucis was the least reliable muscle.

CONCLUSIONS

The MUSIX is a reliable neurophysiological biomarker of reinnervation.

SIGNIFICANCE

MUSIX could provide insights into the pathophysiology of a range of neuromuscular disorders, providing a quantitative biomarker of reinnervation.

Functional Biomarkers for Amyotrophic Lateral Sclerosis

The clinical diagnosis of amyotrophic lateral sclerosis (ALS) relies on determination of progressive dysfunction of both cortical as well as spinal and bulbar motor neurons. However, the variable mix of upper and lower motor neuron signs result in the clinical heterogeneity of patients with ALS, resulting frequently in delay of diagnosis as well as difficulty in monitoring disease progression and treatment outcomes particularly in a clinical trial setting. As such, the present review provides an overview of recently developed novel non-invasive electrophysiological techniques that may serve as biomarkers to assess UMN and LMN dysfunction in ALS patients.

Clinical neurophysiology of anterior horn cell disorders

The development of neurophysiological techniques for clinical assessment in the 20th century is closely related to the study of anterior horn cell diseases. The effects of motor axon loss on nerve conduction velocity and compound motor amplitude were elucidated first in amyotrophic lateral sclerosis (ALS), as was the characterization of reinnervation as detected by needle electromyography. The same changes noted in early studies still play a major role in the diagnosis of anterior horn cell diseases. In addition, much of modern neurophysiological assessment of motor axon quantitation, ion channel changes in neurogenic disease, and cortical physiology studies to assess both network and excitability abnormalities have all been applied to ALS. In this chapter, we summarize the clinical attributes of ALS and Spinal Muscular Atrophy, and review how clinical neurophysiology is employed in the clinical and the research setting.

Optimal E2 (reference) electrode placement in fibular motor nerve conduction studies recording from the tibialis anterior muscle

INTRODUCTION

In this study we aimed to determine the contribution of the E2 (reference electrode) to the compound muscle action potential (CMAP) amplitude during fibular motor recording to the tibialis anterior (TA) when E2 is placed over routine referential vs. alternative sites.

METHODS

The CMAP was obtained from 10 healthy subjects, using the active electrode (E1) over sites routinely used as E2 for the TA, whereas the E2 was over the contralateral knee. The same procedure was performed with the E1 over alternative E2 sites.

RESULTS

Significant electrical signal was captured over routine E2 placement sites. Among the tested alternative E2 sites, the ipsilateral patella (especially its medial aspect) was the most electrically silent.

DISCUSSION

Using alternative E2 sites with near isoelectric recordings can optimize near-field potential measurement in the fibular motor recording to the TA and represents a more accurate way of measuring nerve and muscle function. Muscle Nerve 59:249-253, 2019.

The utility of motor unit number index: A systematic review

The need for a valid biomarker for assessing disease progression and for use in clinical trials on amyotrophic lateral sclerosis (ALS) has stimulated the study of methods that could measure the number of motor units. Motor unit number index (MUNIX) is a newly developed neurophysiological technique that was demonstrated to have a good correlation with the number of motor units in a given muscle, even though it does not necessarily accurately express the actual number of viable motor neurons. Several studies demonstrated the technique is reproducible and capable of following motor neuron loss in patients with ALS and peripheral polyneuropathies. The main goal of this review was to conduct an extensive review of the literature using MUNIX. We conducted a systematic search in English medical literature published in two databases (PubMed and SCOPUS). In this review, we aimed to answer the following queries: Comparison of MUNIX with other MUNE techniques; the reproducibility of MUNIX; the utility of MUNIX in ALS and preclinical muscles, peripheral neuropathies, and other neurological disorders.

Modified motor unit number index (MUNIX) algorithm for assessing excitability of alpha motor neuron in spasticity

Objective

The understanding of the spasticity mechanism is still a problem in the literature, as its definition can be made on the basis of more than one parameter. Therefore, we studied alpha motor neuron excitability, dynamic changes based on force production, and patellar tendon (T) reflex in spasticity and healthy control groups.

Methods

Alpha motor neuron excitability, force production, and patellar T reflex were evaluated through three different test protocols. Motor Unit Number Index (MUNIX) measurement was applied for understanding motor neuron pool properties in the first protocol. Voluntary force production and patellar T reflex parameters were evaluated by voluntary force production and triggering patellar T reflex. Twenty spasticity and 20 healthy volunteers participated in the study.

Results

In the spasticity group, both MUNIX numbers and Motor Unit Size Index (MUSIX) numbers were lower than those in the control group. The results for the Ideal Case Motor Unit Count (ICMUC) parameter show that there is no significant difference between spasticity and healthy individuals for low-level contractions, whereas there is a significant difference for high-level contractions (p < 0.05). In the spasticity group, an increase was observed in the ratio of maximal voluntary force to the T reflex triggered force production (Tf/Vf).

Conclusion

Spasticity and healthy subjects can be distinguished easily and clearly by evaluating the changes in both kinesiological and electrophysiological findings and the decreasing threshold in the alpha motor neuron pool.

Significance

This study shows that such combined methods, which allow the evaluation of the alpha motor neuron pool, as well as kinesiological and electrophysiological parameters, are tools that cannot be overlooked in understanding spasticity.

Combinatory Biomarker Use of Cortical Thickness, MUNIX, and ALSFRS-R at Baseline and in Longitudinal Courses of Individual Patients With Amyotrophic Lateral Sclerosis

Objective: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative process affecting upper and lower motor neurons as well as non-motor systems. In this study, precentral and postcentral cortical thinning detected by structural magnetic resonance imaging (MRI) were combined with clinical (ALS-specific functional rating scale revised, ALSFRS-R) and neurophysiological (motor unit number index, MUNIX) biomarkers in both cross-sectional and longitudinal analyses. Methods: The unicenter sample included 20 limb-onset classical ALS patients compared to 30 age-related healthy controls. ALS patients were treated with standard Riluzole and additional long-term G-CSF (Filgrastim) on a named patient basis after written informed consent. Combinatory biomarker use included cortical thickness of atlas-based dorsal and ventral subdivisions of the precentral and postcentral cortex, ALSFRS-R, and MUNIX for the musculus abductor digiti minimi (ADM) bilaterally. Individual cross-sectional analysis investigated individual cortical thinning in ALS patients compared to age-related healthy controls in the context of state of disease at initial MRI scan. Beyond correlation analysis of biomarkers at cross-sectional group level (n = 20), longitudinal monitoring in a subset of slow progressive ALS patients (n = 4) explored within-subject temporal dynamics of repeatedly assessed biomarkers in time courses over at least 18 months. Results: Cross-sectional analysis demonstrated individually variable states of cortical thinning, which was most pronounced in the ventral section of the precentral cortex. Correlations of ALSFRS-R with cortical thickness and MUNIX were detected. Individual longitudinal biomarker monitoring in four slow progressive ALS patients revealed evident differences in individual disease courses and temporal dynamics of the biomarkers. Conclusion: A combinatory use of structural MRI, neurophysiological and clinical biomarkers allows for an appropriate and detailed assessment of clinical state and course of disease of ALS.

Motor unit number index correlates with disability in Charcot-Marie-Tooth disease

OBJECTIVE

The aim of this study was to assess the usefulness of motor unit number index (MUNIX) technique in Charcot-Marie-Tooth disease and test the correlation between MUNIX and clinical impairment.

METHODS

MUNIX technique was performed in the abductor pollicis brevis (APB), the abductor digiti minimi (ADM) and the tibialis anterior (TA) muscles in the nondominant side. A MUNIX sum score was calculated by adding the MUNIX of these 3 muscles. Muscle strength was measured using the MRC (medical research council) scale. Disability was evaluated using several functional scales, including CMT neuropathy score version 2 (CMTNSv2) and overall neuropathy limitation scale (ONLS).

RESULTS

A total of 56 CMT patients were enrolled. The MUNIX scores of the ADM, APB and TA muscles correlated with the MRC score of the corresponding muscle (p < 0.01). The MUNIX sum score correlated with the clinical scales CMTNSv2 (r  =  -0.65, p < 0.01) and ONLS (r  =  -0.57, p < 0.01).

CONCLUSION

MUNIX correlates with muscle strength and clinical measurements of disability in patients with CMT disease.

SIGNIFICANCE

The MUNIX technique evaluates motor axonal loss and correlates with disability. The MUNIX sum score may be a useful outcome measure of disease progression in CMT.

Motor unit number index (MUNIX) derivation from the relationship between the area and power of surface electromyogram: a computer simulation and clinical study

OBJECTIVE

The motor unit number index (MUNIX) is a technique based on the surface electromyogram (sEMG) that is gaining acceptance as a method for monitoring motor neuron loss, because it is reliable and produces less discomfort than other electrodiagnostic techniques having the same intended purpose. MUNIX assumes that the relationship between the area of sEMG obtained at increasing levels of muscle activation and the values of a variable called 'ideal case motor unit count' (ICMUC), defined as the product of the ratio between area and power of the compound muscle action potential (CMAP) by that of the sEMG, is described by a decreasing power function. Nevertheless, the reason for this comportment is unknown. The objective of this work is to investigate if the definition of MUNIX could derive from more basic properties of the sEMG.

APPROACH

The CMAP and sEMG epochs obtained at different levels of muscle activation from (1) the abductor pollicis brevis (APB) muscle of persons with and without a carpal tunnel syndrome (CTS) and (2) from a computer model of sEMG generation previously published were analysed.

MAIN RESULTS

MUNIX reflects the power relationship existing between the area and power of a sEMG. The exponent of this function was smaller in patients with motor CTS than in the rest of the subjects. The analysis of the relationship between the area and power of a sEMG could aid in distinguishing a MUNIX reduction due to a motoneuron loss from that due to a loss of muscle fibre.

SIGNIFICANCE

MUNIX is derived from the relationship between the area and power of a sEMG. This relationship changes when there is a loss of motor units (MUs), which partially explains the diagnostic sensibility of MUNIX. Although the reasons for this change are unknown, it could reflect an increase in the proportion of MUs of great amplitude.

Why averaging multiple MUNIX measures in the longitudinal assessment of patients with ALS?

OBJECTIVE

To assess the impact of averaging multiple MUNIX trials on the follow-up of patients with amyotrophic lateral sclerosis (ALS).

METHODS

We determined the percent relative change (%RC) of MUNIX, in healthy subjects and patients with ALS, by subtracting the MUNIX value in the second visit from the first. Both the mean of a set of three MUNIX (mean-MUNIX) and the first MUNIX sample (single-MUNIX) were evaluated. Then, we studied the sensitivity to detect relative changes over time and the statistical dispersion of the %RC from these two parameters.

RESULTS

We found that the mean-MUNIX %RC has lower mean coefficient of variation than the single-MUNIX %RC in all muscles. The mean-MUNIX also resulted in more ALS patients with significant %RC, i.e., outside reference limits.

CONCLUSION

The mean-MUNIX resulted in less dispersed values of %RC in patients with ALS and thus, increased the precision of the technique. The mean-MUNIX resulted also in an increase in the sensitivity to track changes over time in these patients.

SIGNIFICANCE

The mean-MUNIX should be considered in any ALS follow-up study as a more reliable approach and as a way of potentially reducing the sample size needed for the study.

Global motor unit number index sum score for assessing the loss of lower motor neurons in amyotrophic lateral sclerosis

INTRODUCTION

We propose a motor unit number index (MUNIX) global sum score in amyotrophic lateral sclerosis (ALS) to estimate the loss of functional motor units.

METHODS

MUNIX was assessed for 18 ALS patients and 17 healthy controls in 7 muscles: the abductor pollicis brevis (APB), abductor digiti minimi (ADM), tibialis anterior (TA), deltoid, trapezius, submental complex, and orbicularis oris.

RESULTS

MUNIX was significantly lower in ALS patients than in healthy controls for the APB, ADM, TA, and trapezius muscles. The MUNIX sum score of 4 muscles (ADM + APB + trapezius + TA) was lower in ALS patients (P = 0.01) and was correlated with clinical scores.

DISCUSSION

The global MUNIX sum score proposed in this study estimates the loss of lower motor neurons in several body regions, including the trapezius, and is correlated with clinical impairment in ALS patients. Muscle Nerve 56: 202-206, 2017.

Cell-based therapies for amyotrophic lateral sclerosis/motor neuron disease

BACKGROUND

Amyotrophic lateral sclerosis (ALS), which is also known as motor neuron disease (MND) is a fatal disease associated with rapidly progressive disability, for which no definitive treatment as yet exists. Current treatment regimens largely focus on relieving symptoms to improve the quality of life of those affected. Based on data from preclinical studies, cell-based therapy is a promising treatment for ALS/MND.

OBJECTIVES

To assess the effects of cell-based therapy for people with ALS/MND, compared with placebo or no additional treatment.

SEARCH METHODS

On 21 June 2016, we searched the Cochrane Neuromuscular Specialised Register, CENTRAL, MEDLINE, and Embase. We also searched two clinical trials' registries for ongoing or unpublished studies.

SELECTION CRITERIA

We planned to include randomised controlled trials (RCTs), quasi-RCTs and cluster RCTs that assigned people with ALS/MND to receive cell-based therapy versus a placebo or no additional treatment. Co-interventions were allowable, provided that they were given to each group equally.

DATA COLLECTION AND ANALYSIS

We followed standard Cochrane methodology.

MAIN RESULTS

No studies were eligible for inclusion in the review. We identified four ongoing trials.

AUTHORS' CONCLUSIONS

Currently, there is a lack of high-quality evidence to guide practice on the use of cell-based therapy to treat ALS/MND.We need large, prospective RCTs to establish the efficacy of cellular therapy and to determine patient-, disease- and cell treatment-related factors that may influence the outcome of cell-based therapy. The major goals of future research should be to determine the appropriate cell source, phenotype, dose, and route of delivery, as these will be key elements in designing an optimal cell-based therapy programme for people with ALS/MND. Future research should also explore novel treatment strategies, including combinations of cellular therapy and standard or novel neuroprotective agents, to find the best possible approach to prevent or reverse the neurological deficit in ALS/MND, and to prolong survival in this debilitating and fatal condition.