Motor Unit Number Index Technique Research Articles

Motor unit number index: A potential electrophysiological biomarker for pediatric spinal muscular atrophy.

In adult spinal muscular atrophy (SMA), the motor unit number index (MUNIX) has been shown to be an useful electrophysiological biomarker. This study evaluated the feasibility and the clinical relevance of using the MUNIX technique for patients with pediatric SMA (Ped-SMA) and correlated MUNIX results with clinical scores. Fourteen patients with type II Ped-SMA (11 females; median age 11 y [interquartile range (IQR), 4.8-17 y]) and 14 controls (nine females; median age 10.75 y [IQR, 6.5-13.4y]) were enrolled and matched by sex, age, height, weight, and body mass index. Clinical examination included manual muscle testing, dynamometry (grasp and pinch), and motor function measure (MFM). The MUNIX technique was evaluated in the abductor digiti minimi (ADM) and abductor pollicis brevis (APB) on two sides when possible. In the patients with Ped-SMA, the MUNIX and compound muscle action potential (CMAP) amplitudes were significantly decreased and the motor size unit index (MUSIX) was significantly increased in the ADM and APB when compared to controls. The intraclass correlation coefficient was good for the intrarater variability of the CMAP amplitude, MUNIX, and MUSIX in the ADM (0.95, 0.83, and 0.89, respectively) and the APB (0.98, 0.96, and 0.94, respectively). The total CMAP amplitude correlated with the grasp and pinch scores (P< .05), and the MUNIX measurements correlated with the MFM scores. The MUNIX technique, which accurately estimated lower motor neuron loss and the number of remaining functional motor units, was shown to be a useful electrophysiological biomarker for disease progression and a potential biomarker for treatment response.

Application value of motor unit number index in patients with amyotrophic lateral sclerosis

Objective: To investigate the application value of motor unit number index (MUNIX) for diagnosis and assessment progress in patients with amyotrophic lateral sclerosis (ALS). Method: Sixty healthy controls and 60 ALS patients in the clinic were enrolled from May 2017 to December 2018. The bilateral deltoid, abductor digiti minimi, quadriceps femoris and tibialis anterior muscles of the subjects were detected by MUNIX method, and the negative peak amplitude of compound muscle action potential (CMAP) of ulnar nerve, femoral nerve, peroneal nerve, axillary nerve in bilateral was collected. MUNIX and motor unit size index (MUSIX) of muscles were compared between ALS group and control group. The difference between the MUNIX abnormal rate of muscles and abnormal rate of the corresponding CMAP negative peak amplitude in ALS patients was further compared. Meanwhile, the correlation between the disease course of ALS patients and MUNIX and MUSIX was analyzed. Results: Compared with the control group, the MUNIX values of the deltoid, abductor digiti minimi, quadriceps femoris and tibialis anterior decreased significantly (97±24 vs 183±38, 48±17 vs 191±39, 54±15 vs 159±22, 49±16 vs 147±25, all P<0.05). MUSIX values increased ((175±32) μV vs (47±15) μV, (189±34) μV vs (54±16) μV, (170±30) μV vs (49±13) μV, (190± 36) μV vs (48± 14) μV, all P<0.05)). In ALS patients, the abnormal rate of MUNIX was respectively 81%, 87%, 75% and 89%. The negative peak amplitude abnormal rate of corresponding neuralCMAP was 35%, 40%, 31% and 36%, respectively, with a significant difference (P<0.05). There was a negative correlation between MUNIX value and the course of disease in ALS patients (P<0.05), and a positive correlation between MUSIX value and the course of disease (P<0.05). Conclusion: The MUNIX technique exhibits the features of quantifying the proximal upper and lower limb muscles and assessing the loss of motor units in motor neuron degeneration.

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

ObjectiveThe 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. MethodsMUNIX 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). ResultsA 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). ConclusionMUNIX correlates with muscle strength and clinical measurements of disability in patients with CMT disease. SignificanceThe 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) in patients with anti-MAG neuropathy.

To investigate the relationship between Motor Unit Number Index (MUNIX) and functional scales in patients with anti-Myelin Associated Glycoprotein (MAG) neuropathy and to know if MUNIX is modify after rituximab (RTX) therapy. 17 patients were enrolled, of whom 6 were prospectively evaluated during one year after RTX treatment. MUNIX technique was assessed in abductor digiti mini (ADM), abductor pollicis brevi (APB) and tibialis anterior (TA) muscles. MUNIX sum score was calculated by adding the results of ADM, APB and TA muscles. MUNIX sum score was correlated with overall neuropathy limitation scale (ONLS) (r=-0.55, p=0.02), grip strength in dominant hand (r=0.63, p=0.01) MRC testing (r=0.71, p<0.001) and CMAP sum score (r=0.71, p=0.001). Twelve months after RTX, four patients improved their disability measured on the ONLS score, five patients had improved MUNIX sum score with a median increase of 37% compared to initial evaluation. MUNIX is related to motor impairment and disability in anti-MAG neuropathy and MUNIX is modified after immunosuppressive treatment. Considering its advantages, MUNIX may be a suitable test to evaluate anti-MAG neuropathy in clinical trials.

Improving the repeatability of Motor Unit Number Index (MUNIX) by introducing additional epochs at low contraction levels.

To evaluate the repeatability of (Motor Unit Number Index) MUNIX under repeatability conditions, specify the origin of variations and provide strategies for quality control. MUNIX calculations were performed on the bicep brachii muscles of eight healthy subjects. Negative effect of suboptimal electrode positions on MUNIX accuracy was eliminated by employing the high-density surface electromyography technique. MUNIX procedures that utilized a variety of surface interferential pattern (SIP) epoch recruitment strategies (including the original MUNIX procedure, two proposed improvement strategies and their combinations) were described. For each MUNIX procedure, ten thousands of different SIP pools were constructed by randomly recruiting necessary SIP epochs from a large SIP epoch pool (3 datasets, 9 independent electromyography recordings at different contraction levels per dataset and 10 SIP epochs per recording) and implemented for MUNIX calculation. The repeatability of each MUNIX procedure was assessed by summarizing the resulting MUNIX distribution and compared to investigate the effect of SIP epoch selection strategy on repeatability performance. SIP epochs selected at lower contraction levels have a stronger influence on the repeatability of MUNIX than those selected at higher contraction levels. MUNIX under repeatability conditions follows a normal distribution and the standard deviation can be significantly reduced by introducing more epochs near the MUNIX definition line. The MUNIX technique shows an inherent variation attributable to SIP epochs at low contraction levels. It is recommended that more epochs should be sampled at these low contraction levels to improve the repeatability. The present study thoroughly documented the inherent variation of MUNIX and the causes, and offered practical solutions to improve the repeatability of MUNIX.

Motor unit number index (MUNIX): Is it relevant in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP)?

ObjectiveTo determine the test–retest reliability of motor unit number index (MUNIX) technique and to explore if the MUNIX sumscore could be related with disability in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). MethodsThe MUNIX technique was unilaterally assessed in the abductor digiti mini (ADM), the abductor pollicis brevi (APB) and the tibialis anterior (TA) muscles two different times by two blinded examiners. The MUNIX sumscore was calculated by adding the results of the ADM, APB and TA muscles. Results14 CIDP patients were enrolled. The intraclass correlation coefficient (ICC) was great for inter and intra variability for ADM muscles (0.8 and 0.81), TA muscles (0.86 and 0.89) and MUNIX sumscore (0.76 and 0.83). The MUNIX sumscores from the first and second evaluations were strongly correlated (r=0.83, p<0.001). The MUNIX sumscore was significantly correlated with MRC testing (r=0.71, p<0.01), overall neuropathy limitation scale (ONLS) (r=−0.70, p<0.001), rasch-built overall disability scale (R-ODS) (r=0.71, p<0.001). ConclusionsThe MUNIX technique has a good reproducibility and the MUNIX sumscore is related to the disability. SignificanceThe MUNIX technique estimates the axonal loss and the number of functional motor units. The MUNIX sumscore may be a good instrument to evaluate the CIDP patients during their follow-up.

Modified motor unit number index: A simulation study of the first dorsal interosseous muscle

The motor unit number index (MUNIX) technique has provided a quick and convenient approach to estimating motor unit population changes in a muscle. Reduction in motor unit action potential (MUAP) amplitude can lead to underestimation of motor unit numbers using the standard MUNIX technique. This study aims to overcome this limitation by developing a modified MUNIX (mMUNIX) technique. The mMUNIX uses a variable that is associated with the area of compound muscle action potential (CMAP) rather than an arbitrary fixed value (20 mV ms) as used in the standard MUNIX to define the output. The performance of the mMUNIX was evaluated using motoneuron pool and surface electromyography (EMG) models. With a fixed motor unit number, the mMUNIX output remained relatively constant with varying degrees of MUAP amplitude changes, while the standard MUNIX substantially underestimated the motor unit number in such cases. However, when MUAP amplitude remained unchanged, the mMUNIX showed less sensitivity than the standard MUNIX in tracking motor unit loss. The current simulation study demonstrated both the advantages and limitations of the standard and modified MUNIX techniques, which can help guide appropriate application and interpretation of MUNIX measurements.

Voluntary Contraction Direction Dependence of Motor Unit Number Index in Patients with Amyotrophic Lateral Sclerosis

We investigated the voluntary contraction direction dependence of motor unit number index (MUNIX) for multifunctional muscles in patients with amyotrophic lateral sclerosis (ALS). The MUNIX technique was applied in nine first dorsal interosseous muscles of eight ALS subjects, using surface electromyography (EMG) signals from index finger abduction and flexion, respectively. In seven examined muscles, the MUNIX derived from the index finger abduction mode was smaller than that from the flexion mode. For the remaining two muscles, one had the same MUNIX; the other showed an abduction mode MUNIX much higher than the flexion mode MNUIX. Across all muscles, the median MUNIX was 96 for the index finger abduction mode and 161 for the flexion mode. The findings reveal the dependence of multifunctional muscle MUNIX on voluntary contraction directions in ALS patients. Based on this analysis, we further explored the concept of "multidimensional MUNIX" for an appropriate performance or interpretation of MUNIX in multifunctional muscles of ALS patients. An effort towards such a development was presented using both abduction and flexion mode surface EMG for MUNIX calculation.

Interrelationship between muscle strength, motor units, and aging

The interrelationship between muscle strength, motor unit (MU) number, and age is poorly understood, and in this study we sought to determine whether age-related differences in muscle strength are moderated by estimates of functioning MU number and size. Eighteen older adults (OA; 67±1.20years) and 24 young adults (YA; 22±0.74years) participated in this study. Maximum voluntary pinch–grip strength of the nondominant hand was determined and estimates of MU number were obtained from the abductor pollicis brevis muscle using the noninvasive motor unit number index (MUNIX) technique. The MUNIX technique was also utilized to derive a motor unit size index (MUSIX). An analysis of covariance (Age Group×MUNIX or MUSIX) was used to test heterogeneity of regression slopes, with body mass and gender serving as covariates. We observed that the slope of pinch–grip strength on the estimated number of MUs between YA and OA differed, indicated by an Age Group×MUNIX interaction (p=0.04). Specifically, after controlling for the effect of body mass and gender, the slope in OA was significantly positive (0.14±0.06N/MUs, p=0.03), whereas no such relationship was found in YA (−0.08±0.09N/MUs, p=0.35). A significant Age Group×MUSIX interaction was also observed for strength (p<0.01). In contrast to MUNIX, the slope in younger adults was significantly positive (0.48±0.11N/μV, p<0.01), whereas no such relationship was found in older adults (−0.30±0.22N/μV, p=0.18). These findings indicate that there is an interrelationship between muscle strength, MU numbers, and aging, which suggests that a portion of muscle weakness in seniors may be attributable to the loss of functioning motor units.

Computing motor unit number index of the first dorsal interosseous muscle with two different contraction tasks

Motor unit number index (MUNIX) is a recently developed novel neurophysiological technique providing an index proportional to the number of motor units in a muscle. The MUNIX is derived from maximum M wave and voluntary surface electromyogram (EMG) recordings. The objective of this study was to address a practical question for computing MUNIX in the first dorsal interosseous (FDI), a multifunctional muscle that generates torque about the second metacarpophalangeal joint, i.e., how will different lines of muscle activation influence its MUNIX estimates? To address this question, the MUNIX technique was applied in the FDI muscle of 15 neurologically intact subjects, using surface EMG signals from index finger abduction and flexion, respectively, while the maximum M wave remained the same. Across all subjects, the average MUNIX value of the FDI muscle was 228±45 for index finger abduction, slightly smaller than the MUNIX estimate of 251±56 for index finger flexion. Different FDI muscle activation patterns resulted in an approximately 10% difference in MUNIX estimates. The findings from this study suggest that appropriate definition of voluntary activation of the FDI muscle should be kept to ensure consistency in measurements and avoid source of error. The current study is limited by only assessing neurologically intact muscles. It is important to perform a similar analysis for patients with amyotrophic lateral sclerosis (ALS), given that ALS is the primary intention of the MUNIX method as a potential follow-up measurement for motor unit loss.

A simulation-based analysis of motor unit number index (MUNIX) technique using motoneuron pool and surface electromyogram models.

Motor unit number index (MUNIX) measurement has recently achieved increasing attention as a tool to evaluate the progression of motoneuron diseases. In our current study, the sensitivity of the MUNIX technique to changes in motoneuron and muscle properties was explored by a simulation approach utilizing variations on published motoneuron pool and surface electromyogram (EMG) models. Our simulation results indicate that, when keeping motoneuron pool and muscle parameters unchanged and varying the input motor unit numbers to the model, then MUNIX estimates can appropriately characterize changes in motor unit numbers. Such MUNIX estimates are not sensitive to different motor unit recruitment and rate coding strategies used in the model. Furthermore, alterations in motor unit control properties do not have a significant effect on the MUNIX estimates. Neither adjustment of the motor unit recruitment range nor reduction of the motor unit firing rates jeopardizes the MUNIX estimates. The MUNIX estimates closely correlate with the maximum M-wave amplitude. However, if we reduce the amplitude of each motor unit action potential rather than simply reduce motor unit number, then MUNIX estimates substantially underestimate the motor unit numbers in the muscle. These findings suggest that the current MUNIX definition is most suitable for motoneuron diseases that demonstrate secondary evidence of muscle fiber reinnervation. In this regard, when MUNIX is applied, it is of much importance to examine a parallel measurement of motor unit size index (MUSIX), defined as the ratio of the maximum M-wave amplitude to the MUNIX. However, there are potential limitations in the application of the MUNIX methods in atrophied muscle, where it is unclear whether the atrophy is accompanied by loss of motor units or loss of muscle fiber size.

An Examination of the Motor Unit Number Index (MUNIX) in Muscles Paralyzed by Spinal Cord Injury

The objective of this study was to assess whether there is evidence of motor unit loss in muscles paralyzed by spinal cord injury (SCI), using a measurement called motor unit number index (MUNIX). The MUNIX technique was applied in SCI (n=12) and neurologically intact (n=12) subjects. The maximum M waves and voluntary surface electromyography (EMG) signals at different muscle contraction levels were recorded from the first dorsal interosseous (FDI) muscle in each subject. The MUNIX values were estimated using a mathematical model describing the relation between the surface EMG signal and the ideal motor unit number count derived from the M wave and surface EMG measurements. We recorded a significant decrease in both maximum M wave amplitude and in estimated MUNIX values in paralyzed FDI muscles, as compared with neurologically intact muscles. Across all subjects, the maximum M wave amplitude was 8.3 ± 4.4 mV for the paralyzed muscles and 14.4 ± 2.0 mV for the neurologically intact muscles (p<0.0001). These measurements, when combined with voluntary EMG recordings, resulted in a mean MUNIX value of 112 ± 71 for the paralyzed muscles, much lower than the mean MUNIX value of 228 ± 49 for the neurologically intact muscles (p<0.00001). A motor unit size index was also calculated, using the maximum M wave recording and the MUNIX values. We found that paralyzed muscles showed a mean motor unit size index value of 80.7 ± 17.7 ìV, significantly higher than the mean value of 64.9 ± 10.1 ìV obtained from neurologically intact muscles (p<0.001). The MUNIX method used in this study offers several practical benefits compared with the traditional motor unit number estimation technique because it is noninvasive, induces minimal discomfort due to electrical nerve stimulation, and can be performed quickly. The findings from this study help understand the complicated determinants of SCI induced muscle weakness and provide further evidence of motoneuron degeneration after a spinal injury.

Motor Unit Number Reductions in Paretic Muscles of Stroke Survivors

The objective of this study is to assess whether there is evidence of spinal motoneuron loss in paretic muscles of stroke survivors, using an index measurement called motor unit number index (MUNIX). MUNIX, a recently developed novel neurophysiological technique, provides an index proportional to the number of motor units in a muscle, but not necessarily an accurate absolute count. The MUNIX technique was applied to the first dorsal interosseous (FDI) muscle bilaterally in nine stroke subjects. The area and power of the maximum M-wave and the interference pattern electromyogram (EMG) at different contraction levels were used to calculate the MUNIX. A motor unit size index (MUSizeIndex) was also calculated using maximum M-wave recording and the MUNIX values. We observed a significant decrease in both maximum M-wave amplitude and MUNIX values in the paretic FDI muscles, as compared with the contralateral muscles. Across all subjects, the maximum M-wave amplitude was 6.4 ± 2.3 mV for the paretic muscles and 9.7 ± 2.0 mV for the contralateral muscles (p < 0.001). These measurements, in combination with voluntary EMG recordings, resulted in the MUNIX value of 109 ± 53 for the paretic muscles, much lower than the MUNIX value of 153 ± 38 for the contralateral muscles ( p < 0.01). No significant difference was found in MUSizeIndex values between the paretic and contralateral muscles. However, the range of MUSizeIndex values was slightly wider for paretic muscles (48.8-93.3 μV) than the contralateral muscles (51.7-84.4 μV). The findings from the index measurements provide further evidence of spinal motoneuron loss after a hemispheric brain lesion.

Motor Unit Number Index (MUNIX): A novel neurophysiological marker for neuromuscular disorders; test–retest reliability in healthy volunteers

Objective To investigate the intra-rater and inter-rater test–retest reliability of the Motor Unit Number Index (MUNIX) in healthy subjects in a multicentre setting. Methods Six study centres applied the MUNIX technique in 66 healthy subjects. Five to six muscles (biceps brachii, BB; abductor digiti minimi, ADM; abductor pollicis brevis, APB; tibialis anterior, TA; extensor digitorum brevis, EDB and abductor hallucis, AH) were measured in each volunteer four times by two independent examiners. Results The method was easy to perform and well tolerated. The intraclass correlation coefficient (ICC) varied between centres and muscles. Intra-rater reliability was greatest for the AH (ICC 0.83) and EDB (ICC 0.81). Inter-rater reliability was greatest for the AH (ICC 0.69) and ADM muscles (ICC 0.69). The most critical muscle was the APB muscle (ICC 0.52, total variability). This was mostly due to variability in the compound muscle action potential (CMAP) measurements. MUNIX values of the APB, ADM and TA fell into the same range as in other motor unit number estimation (MUNE) studies. Conclusion MUNIX measurements in multiple muscles show good inter- and intra-rater reliability in healthy subjects. CMAP amplitude must be controlled to optimize reliability. Significance Results suggest that MUNIX could serve as a reliable marker for motor neuron loss in diseases like amyotrophic lateral sclerosis.

CONTRIBUTIONS OF THE COMT AND MTHFR GENES TO DEFICITS IN ADAPTIVE REAL-WORLD COMPREHENSION IN SCHIZOPHRENIA

Motor unit number index (MUNIX) is a recently developed novel neurophysiological technique providing an index proportional to the number of motor units in a muscle. The MUNIX is derived from maximum M wave and voluntary surface electromyogram (EMG) recordings. The objective of this study was to address a practical question for computing MUNIX in the first dorsal interosseous (FDI), a multifunctional muscle that generates torque about the second metacarpophalangeal joint, i.e., how will different lines of muscle activation influence its MUNIX estimates? To address this question, the MUNIX technique was applied in the FDI muscle of 15 neurologically intact subjects, using surface EMG signals from index finger abduction and flexion, respectively, while the maximum M wave remained the same. Across all subjects, the average MUNIX value of the FDI muscle was 228 ± 45 for index finger abduction, slightly smaller than the MUNIX estimate of 251 ± 56 for index finger flexion. Different FDI muscle activation patterns resulted in an approximately 10% difference in MUNIX estimates. The findings from this study suggest that appropriate definition of voluntary activation of the FDI muscle should be kept to ensure consistency in measurements and avoid source of error. The current study is limited by only assessing neurologically intact muscles. It is important to perform a similar analysis for patients with amyotrophic lateral sclerosis (ALS), given that ALS is the primary intention of the MUNIX method as a potential follow-up measurement for motor unit loss.

Distal dorsal ulnar cutaneous nerve conduction technique: normative data

To investigate the intra-rater and inter-rater test–retest reliability of the Motor Unit Number Index (MUNIX) in healthy subjects in a multicentre setting.Six study centres applied the MUNIX technique in 66 healthy subjects. Five to six muscles (biceps brachii, BB; abductor digiti minimi, ADM; abductor pollicis brevis, APB; tibialis anterior, TA; extensor digitorum brevis, EDB and abductor hallucis, AH) were measured in each volunteer four times by two independent examiners.The method was easy to perform and well tolerated. The intraclass correlation coefficient (ICC) varied between centres and muscles. Intra-rater reliability was greatest for the AH (ICC 0.83) and EDB (ICC 0.81). Inter-rater reliability was greatest for the AH (ICC 0.69) and ADM muscles (ICC 0.69). The most critical muscle was the APB muscle (ICC 0.52, total variability). This was mostly due to variability in the compound muscle action potential (CMAP) measurements. MUNIX values of the APB, ADM and TA fell into the same range as in other motor unit number estimation (MUNE) studies.MUNIX measurements in multiple muscles show good inter- and intra-rater reliability in healthy subjects. CMAP amplitude must be controlled to optimize reliability.Results suggest that MUNIX could serve as a reliable marker for motor neuron loss in diseases like amyotrophic lateral sclerosis.

PS-56-9 The duration of the therapeutic effect of botulinum toxin in the treatment of cervical dystonia varies in different neck-muscles

To investigate the intra-rater and inter-rater test–retest reliability of the Motor Unit Number Index (MUNIX) in healthy subjects in a multicentre setting.Six study centres applied the MUNIX technique in 66 healthy subjects. Five to six muscles (biceps brachii, BB; abductor digiti minimi, ADM; abductor pollicis brevis, APB; tibialis anterior, TA; extensor digitorum brevis, EDB and abductor hallucis, AH) were measured in each volunteer four times by two independent examiners.The method was easy to perform and well tolerated. The intraclass correlation coefficient (ICC) varied between centres and muscles. Intra-rater reliability was greatest for the AH (ICC 0.83) and EDB (ICC 0.81). Inter-rater reliability was greatest for the AH (ICC 0.69) and ADM muscles (ICC 0.69). The most critical muscle was the APB muscle (ICC 0.52, total variability). This was mostly due to variability in the compound muscle action potential (CMAP) measurements. MUNIX values of the APB, ADM and TA fell into the same range as in other motor unit number estimation (MUNE) studies.MUNIX measurements in multiple muscles show good inter- and intra-rater reliability in healthy subjects. CMAP amplitude must be controlled to optimize reliability.Results suggest that MUNIX could serve as a reliable marker for motor neuron loss in diseases like amyotrophic lateral sclerosis.