UNASSIGNED: MScanFit is a model-based algorithm for motor unit number estimation (MUNE) from compound muscle action potential (CMAP) scan data. It is a clinically applicable tool because of its quick and automatic implementation. Electrodes with different recording areas were employed to record CMAP scan data in existing studies. However, the effect of electrode recording area on MScanFit MUNE and other CMAP scan parameters has not been studied.
UNASSIGNED: CMAP scan was performed on the abductor pollicis brevis muscle of both hands on 14 healthy subjects using three different electrodes with recording areas of 10 mm × 10 mm, 11 mm × 14 mm, and 22 mm × 26 mm, respectively. Motor unit number was estimated using MScanFit for each CMAP scan. Two motor unit number index parameters, i.e., D50 and step index (STEPIX), were also derived from the CMAP scan data.
UNASSIGNED: No significant difference in D50, STEPIX, and MScanFit MUNE was observed across three different electrode recording areas, although the amplitude of CMAP decreased significantly when a larger electrode was used. Intraclass correlation coefficients of 0.792 and 0.782 were obtained for MScanFit MUNE and STEPIX, respectively.
UNASSIGNED: Compared with CMAP amplitude, D50, STEPIX, and MScanFit MUNE are less sensitive to variation in electrode recording area. However, the repeatability of MScanFit MUNE could be compromised by the inconsistency in the electrode recording area.

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.

OBJECTIVE: MScanFit MUNE (MScanFit) is a novel tool to derive motor unit number estimates (MUNEs) from compound muscle action potential (CMAP) scans. Few studies have explored its utility in 5q spinal muscular atrophy (SMA5q) patients, assessing only the abductor pollicis brevis (APB) muscle. We aimed to assess different distal muscles in pediatric and adult SMA5q patients, further evaluating clinical-electrophysiological correlations.
METHODS: We analyzed MScanFit parameters reflecting the extent of denervation (MUNE; N50) and parameters of collateral reinnervation in APB, abductor digiti minimi (ADM), and tibialis anterior (TA) muscles. SMA patients were clinically evaluated using standardized motor function clinical scales, including the Hammersmith Functional Motor Scale - Expanded and the Revised Upper Limb Module.
RESULTS: A total of 23 SMA5q (9 SMA type 2 and 14 SMA type 3) and 12 age-matched healthy controls (HCs) were enrolled. SMA patients showed lower MUNE and N50 values and higher parameters of collateral sprouting in all muscles compared to HC (p < .001). SMA type 2 patients demonstrated lower MUNE and higher collateral reinnervation values in APB and TA compared to SMA type 3 (p < .05). Walker patients showed higher values of MUNE and N50, and lower parameters of reinnervation in all muscles compared to sitters (p < .05). MScanFit parameters showed strong correlations (Rho-values ranging from .72 to .83) with clinical measurements. MUNE values were abnormal in muscles that were not clinically affected.
CONCLUSIONS: MScanFit parameters showed promise as an outcome measure. Further studies, particularly longitudinal ones, are needed to evaluate MScanFit in measuring response to treatments.

OBJECTIVE: Some patients with Hirayama disease (HD) may have generalized joint hypermobility (GJH), which may excessively increase cervical range of motion (ROM) and then worsen the HD. The purpose of this study was to identify the frequency of GJH in HD patients and to analyze the effect of GJH on cervical ROM and the severity of HD.
METHODS: The Beighton scoring system (≥4) was used to diagnose GJH in 84 HD patients. All patients underwent assessments of cervical-flexion/extension ROM; motor unit number estimation in bilateral abductor pollicis brevis (APB) muscles; handgrip strength; and the disabilities of the arm, shoulder, and hand assessments.
RESULTS: Concomitant GJH was identified in 20 (23.8%) HD patients. The HD patients with GJH exhibited greater cervical-flexion (P < .001) and cervical-extension (P = .033) ROM than those without GJH. Both greater single motor unit potential amplitudes (symptomatic side: P = .005; less-symptomatic side: P = .011) and lower motor unit numbers (symptomatic side: P = .008; less-symptomatic side: P = .013) in bilateral APB, along with lower compound muscle action potential amplitudes on the symptomatic-side APB (P = .039), were observed in patients with GJH than those without GJH. There was a mild negative correlation between motor unit number and cervical-flexion ROM in HD patients (symptomatic side: r = -0.239, P = .028; less-symptomatic side: r = -0.242, P = .027).
CONCLUSIONS: The frequency of GJH in HD patients may be higher than in the general population. Importantly, GJH may exacerbate excessive cervical-flexion ROM, thereby worsening motor unit loss in HD patients. A cautious approach should be taken when treating HD due to possible comorbid GJH.

To assess the repeatability and suitability for multicentre studies of MScanFit motor unit number estimation (MUNE), which involves modelling compound muscle action potential (CMAP) scans.
Fifteen groups in 9 countries recorded CMAP scans twice, 1-2 weeks apart in healthy subjects from abductor pollicis brevis (APB), abductor digiti minimi (ADM) and tibialis anterior (TA) muscles. The original MScanFit program (MScanFit-1) was compared with a revised version (MScanFit-2), designed to accommodate different muscles and recording conditions by setting the minimal motor unit size as a function of maximum CMAP.
Complete sets of 6 recordings were obtained from 148 subjects. CMAP amplitudes differed significantly between centres for all muscles, and the same was true for MScanFit-1 MUNE. With MScanFit-2, MUNE differed less between centres but remained significantly different for APB. Coefficients of variation between repeats were 18.0% for ADM, 16.8% for APB, and 12.1% for TA.
It is recommended for multicentre studies to use MScanFit-2 for analysis. TA provided the least variable MUNE values between subjects and the most repeatable within subjects.
MScanFit was primarily devised to model the discontinuities in CMAP scans in patients and is less suitable for healthy subjects with smooth scans.

Nonsystemic vasculitic neuropathy (NSVN) is characterized by a predominant lower limb involvement in many patients. Motor unit changes in upper extremity muscles have not been investigated in this subgroup but may be of interest for improving our understanding of the multifocal nature of the disease and counseling of patients about potential future symptoms. In this study we aimed to better understand subclinical motor involvement in the upper extremity muscles of patients with lower limb-predominant NSVN using the new motor unit number estimation (MUNE) method MScanFit.
In this single-center, cross-sectional study, 14 patients with biopsy-proven NSVN, with no clinical signs of upper extremity motor involvement, were investigated and compared with 14 age-matched healthy controls. All participants were assessed clinically and by the MUNE method MScanFit to the abductor pollicis brevis muscle.
The number of motor units and peak CMAP amplitudes were significantly reduced in patients with NSVN (P = .003 and P = .004, respectively). Absolute median motor unit amplitudes and CMAP discontinuities were not significantly different (P = .246 and P = .1, respectively). CMAP discontinuities were not significantly correlated with motor unit loss (P = .15, rho = 0.4). The number of motor units did not correlate with clinical scores (P = .77, rho = 0.082).
Both MUNE and CMAP amplitudes showed motor involvement in upper extremity muscles in lower limb-predominant NSVN. Overall, there was no evidence of significant reinnervation. Investigations of the abductor pollicis brevis muscle did not show a correlation with overall functional disability of the patients.

OBJECTIVE: To quantify the cervical sagittal alignment in patients with Hirayama disease (HD) and to investigate the effect of loss of cervical sagittal alignment upon the cervical spinal lesions in HD.
METHODS: Cervical sagittal alignments were measured in 253 HD patients and 63 healthy subjects by C2-C7 Cobb and a modified method of Toyama et al. Motor unit number estimation (MUNE) was performed in bilateral abductor pollicis brevis (APB) in all HD patients, and 31 patients further underwent cervical diffusion tensor imaging (DTI).
RESULTS: Compared with healthy subjects, HD patients showed lower C2-C7 Cobb (P < 0.05), and 83.4% patients showed loss of cervical lordosis (cervical straight or kyphosis), which was greater than healthy subjects (55.6%, P < 0.05). Compared with lordotic/straight group, patients with cervical kyphosis showed lower MUNE values and greater single motor unit potential (SMUP) in bilateral APB, and higher apparent dispersion coefficient (ADC) and lower fractional anisotropy were observed at C4/C5 level in the latter than the former (P < 0.05). C2-C7 Cobb was associated with both C4/C5 ADC and bilateral SMUP (P < 0.05).
CONCLUSIONS: Most HD patients showed loss of cervical sagittal alignments, and both MUNE and DTI detections demonstrated a positive correlation between loss of cervical sagittal alignments and cervical spinal lesions in HD. These findings supported that loss of cervical sagittal alignments may worsen motor impairments in HD. Therefore, it is necessary for clinicians to be aware of restoring cervical sagittal alignments during HD treatment.

OBJECTIVE: Rapid-stretch nerve injuries represent a substantial treatment challenge. No study has examined motor neuron connection after rapid-stretch injury. Our objective in this study was to characterize the electrophysiological properties of graded rapid-stretch nerve injury and assess motor neuron health using retrograde labeling and muscle adenosine triphosphatase (ATPase) histology.
METHODS: Male C57BL/6 mice (n = 6 per group) were rapid-stretch injured at four levels of severity: sham injury, stretch within elastic modulus, inelastic deformation, and stretch rupture. Serial compound muscle action potential (CMAP) and motor unit number estimation (MUNE) measurements were made for 48 days, followed by retrograde labeling and muscle ATPase histology.
RESULTS: Elastic injuries showed no durable abnormalities. Inelastic injury demonstrated profound initial reduction in CMAP and MUNE (P < .036) on day 2, with partial recovery by day 14 after injury (CMAP: 40% baseline, P = .003; MUNE: 55% baseline, P = .033). However, at the experimental endpoint, CMAP had recovered to baseline with only limited improvement in MUNE. Inelastic injury led to reduced retrograde-labeled neurons and grouped fiber type histology. Rupture injury had severe and nonrecovering electrophysiological impairment, dramatically reducing labeled neurons (P = .005), and atrophic or type 1 muscle fibers. There was an excellent correlation between MUNE and retrograde-labeled tibial motor neurons across injury severities (R2  = 0.96).
CONCLUSIONS: There was no significant electrophysiological derangement in low-severity injuries but there was recoverable conduction block in inelastic injury with slow recovery, potentially due to collateral sprouting. Rupture injuries yielded permanent failure of injured axons to reinnervate. These results provide insight into the pathophysiology of clinical injuries and recovery.

The compound muscle action potential (CMAP) scan is useful to study motor unit (MU) loss. It is of interest to develop simple measurements of the scan.
CMAP scan recordings were performed in the abductor pollicis brevis muscle of 20 control subjects and 26 patients with amyotrophic lateral sclerosis (ALS). They were analyzed using two new measurements called Step index (STEPIX) reflecting the number of steps, and Amplitude index (AMPIX) for amplitude of these steps.
In control subjects, STEPIX ranged from 71 to 172 while AMPIX was 78-158 µV. In ALS patients STEPIX was reduced and AMPIX was increased. The degree of change in STEPIX and AMPIX varied among patients reflecting the success or failure of reinnervation. Follow up studies in 9 muscles demonstrated reduced STEPIX and increased AMPIX despite minimal change in the CMAP.
STEPIX and AMPIX are deterministic measurements of the CMAP scan made using a spreadsheet program. STEPIX and AMPIX can be inferred as indices for the number of motor units and their size, and demonstrate the expected pattern in ALS patients.
The new algorithm for CMAP scan analysis may be useful to study disease progression in patients with ALS.

We collated all interventional clinical trials in amyotrophic lateral sclerosis (ALS), which utilised at least one neurophysiological technique as a primary or secondary outcome measure. By identifying the strengths and limitations of these studies, we aim to guide study design in future trials.
We conducted and reported this systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Eight databases were searched from inception. In total, 703 studies were retrieved for screening and eligibility assessment.
Dating back to 1986, 32 eligible interventional clinical trials were identified, recruiting a median of 30 patients per completed trial. The most widely employed neurophysiological techniques were electromyography, motor unit number estimation (including motor unit number index), neurophysiological index and transcranial magnetic stimulation (including resting motor threshold and short-interval intracortical inhibition). Almost 40% of trials reported a positive outcome with respect to at least one neurophysiological measure. The interventions targeted either ion channels, immune mechanisms or neuronal metabolic pathways.
Neurophysiology offers many promising biomarkers that can be utilised as outcome measures in interventional clinical trials in ALS. When selecting the most appropriate technique, key considerations include methodological standardisation, target engagement and logistical burden.
Future trial design in ALS would benefit from a standardised, updated and easily accessible repository of neurophysiological outcome measures.