Effects of differences in age and body height on normal values of central motor conduction time determined by F-waves

Factors associated with improvement in tibialis anterior weakness due to lumbar degenerative disease

BACKGROUND

The weakness of the tibialis anterior remains to be a controversial topic. There has been no study that used electrophysiological assessment of the function of the lumbar and sacral peripheral motor nerves. The aim is to evaluate surgical outcomes in patients with weakness of the tibialis anterior using neurological and electrophysiological assessments.

METHODS

We enrolled 53 patients. Tibialis anterior weakness was quantified by muscle strength, as assessed using a manual muscle test on a scale of 1 through 5, with scores <5 indicating weakness. Postoperative improvement in muscle strength was classified as excellent (5 grades recovered), good (more than one grade recovered), or fair (less than one grade recovered).

RESULTS

Surgical outcomes for tibialis anterior function were categorized as "excellent" in 31, "good" in 8, "fair" in 14 patients. Significant difference in outcomes were observed depending on diabetes mellitus status, type of surgery, and the compound muscle action potentials amplitudes of the abductor hallucis and extensor digitorum brevis (p < 0.05). Surgical outcomes were classified into two groups, patients with excellent and good outcomes (Group 1) and patients with fair outcome (Group 2). Using the forward selection stepwise method, sex and the compound muscle action potentials amplitudes of the extensor digitorum brevis were identified as significant factors for their positive association with Group 1 status. The diagnostic power of the predicted probability was as high as 0.87 in terms of area under curve of the receiver operating characteristic curve.

CONCLUSIONS

There was a significant correlation between the prognosis of tibialis anterior weakness and sex and the compound muscle action potentials amplitude of extensor digitorum brevis, suggesting that recording the compound muscle action potentials amplitude of extensor digitorum brevis will aid the outcome assessment of future surgical interventions for tibialis anterior weakness.

Differentiation Between Compressive Cervical and Thoracic Myelopathy Using the Central Motor Conduction Time Ratio

PURPOSE

Thoracic myelopathy is a rare condition whose diagnosis is often missed or delayed. This study aimed to differentiate between cervical and thoracic myelopathy using motor-evoked potential testing.

METHODS

The authors included 835 patients with compressive cervical myelopathy and 94 patients with compressive thoracic myelopathy. Myelopathy using motor-evoked potentials were recorded from the bilateral abductor digiti minimi and abductor hallucis muscles through transcranial magnetic stimulation. The peripheral conduction time was measured through electrical stimulation of the ulnar and tibial nerves; moreover, the central motor conduction time (CMCT) was calculated by subtracting the peripheral conduction time from the myelopathy using motor-evoked potential latency.

RESULTS

The most accurate differentiation between compressive cervical myelopathy and compressive thoracic myelopathy was achieved by the CMCT ratios (CMCT-ADM:CMCT-AH; cutoff value of 0.490, sensitivity of 83.0%, and specificity of 80.5%). After excluding patients with compressive cervical myelopathy who had spinal cord compression at C6-7, the cutoff value was 0.490, with a sensitivity of 83.0% and specificity of 87.3%.

CONCLUSIONS

Determining the CMCT ratio (cutoff value of 0.490) through motor-evoked potential testing could facilitate differentiation between compressive cervical myelopathy and compressive thoracic myelopathy.

Normal Values of Central, Peripheral, and Root Motor Conduction Times in a Healthy Korean Population

PURPOSE

Central, peripheral, and root motor conduction times (CMCTs, PMCTs, and RMCTs, respectively) are valuable diagnostic tools for spinal cord and motor nerve root lesions. We investigated the normal values and the effects of age and height on each motor conduction time.

METHODS

This study included 190 healthy Korean subjects who underwent magnetic stimulation of the cortex and spinous processes at the C7 and L1 levels. Recording muscles were abductor pollicis brevis and abductor digiti minimi in the unilateral upper limb and extensor digitorum brevis and abductor hallucis in the contralateral lower limb. F-wave and compound motor nerve action potentials were also recorded. Central motor conduction time was evaluated as the difference between cortical motor evoked potential onset latency and PMCT using calculation and spinal stimulation methods. Root motor conduction time was computed as the difference between spinal stimulated and calculated CMCTs.

RESULTS

The average age and height of the participants were 41.21 ± 14.39 years and 164.64 ± 8.27 cm, respectively; 39.5% (75/190) patients were men. In the linear regression analyses, upper limb CMCTs showed a significant and weak positive relationship with height. Lower limb CMCTs demonstrated a significant and weak positive relationship with age and height. Peripheral motor conduction times were significantly and positively correlated with age and height. Root motor conduction times showed no significant relationship with age and height, except for abductor pollicis brevis-RMCT, which had a weak negative correlation with height.

CONCLUSIONS

This study provides normal values of CMCTs, PMCTs, and RCMTs, which have potential clinical applications. When interpreting CMCTs, age and height should be considered.

Resting-state functional magnetic resonance imaging indices are related to electrophysiological dysfunction in degenerative cervical myelopathy

The age-related degenerative pathologies of the cervical spinal column that comprise degenerative cervical myelopathy (DCM) cause myelopathy due spinal cord compression. Functional neurological assessment of DCM can potentially reveal the severity and pathological mechanism of DCM. However, functional assessment by conventional MRI remains difficult. This study used resting-state functional MRI (rs-fMRI) to investigate the relationship between functional connectivity (FC) strength and neurophysiological indices and examined the feasibility of functional assessment by FC for DCM. Preoperatively, 34 patients with DCM underwent rs-fMRI scans. Preoperative central motor conduction time (CMCT) reflecting motor functional disability and intraoperative somatosensory evoked potentials (SEP) reflecting sensory functional disability were recorded as electrophysiological indices of severity of the cervical spinal cord impairment. We performed seed-to-voxel FC analysis and correlation analyses between FC strength and the two electrophysiological indices. We found that FC strength between the primary motor cortex and the precuneus correlated significantly positively with CMCT, and that between the lateral part of the sensorimotor cortex and the lateral occipital cortex also showed a significantly positive correlation with SEP amplitudes. These results suggest that we can evaluate neurological and electrophysiological severity in patients with DCM by analyzing FC strengths between certain brain regions.

DiSCIoser: unlocking recovery potential of arm sensorimotor functions after spinal cord injury by promoting activity-dependent brain plasticity by means of brain-computer interface technology: a randomized controlled trial to test efficacy

BACKGROUND

Traumatic cervical spinal cord injury (SCI) results in reduced sensorimotor abilities that strongly impact on the achievement of daily living activities involving hand/arm function. Among several technology-based rehabilitative approaches, Brain-Computer Interfaces (BCIs) which enable the modulation of electroencephalographic sensorimotor rhythms, are promising tools to promote the recovery of hand function after SCI. The "DiSCIoser" study proposes a BCI-supported motor imagery (MI) training to engage the sensorimotor system and thus facilitate the neuroplasticity to eventually optimize upper limb sensorimotor functional recovery in patients with SCI during the subacute phase, at the peak of brain and spinal plasticity. To this purpose, we have designed a BCI system fully compatible with a clinical setting whose efficacy in improving hand sensorimotor function outcomes in patients with traumatic cervical SCI will be assessed and compared to the hand MI training not supported by BCI.

METHODS

This randomized controlled trial will include 30 participants with traumatic cervical SCI in the subacute phase randomly assigned to 2 intervention groups: the BCI-assisted hand MI training and the hand MI training not supported by BCI. Both interventions are delivered (3 weekly sessions; 12 weeks) as add-on to standard rehabilitation care. A multidimensional assessment will be performed at: randomization/pre-intervention and post-intervention. Primary outcome measure is the Graded Redefined Assessment of Strength, Sensibility and Prehension (GRASSP) somatosensory sub-score. Secondary outcome measures include the motor and functional scores of the GRASSP and other clinical, neuropsychological, neurophysiological and neuroimaging measures.

DISCUSSION

We expect the BCI-based intervention to promote meaningful cortical sensorimotor plasticity and eventually maximize recovery of arm functions in traumatic cervical subacute SCI. This study will generate a body of knowledge that is fundamental to drive optimization of BCI application in SCI as a top-down therapeutic intervention, thus beyond the canonical use of BCI as assistive tool.

TRIAL REGISTRATION

Name of registry: DiSCIoser: improving arm sensorimotor functions after spinal cord injury via brain-computer interface training (DiSCIoser).

TRIAL REGISTRATION NUMBER

NCT05637775; registration date on the ClinicalTrial.gov platform: 05-12-2022.

Characterization of the central motor conduction time in a large cohort of spinocerebellar ataxia type 3 patients

INTRODUCTION

Spinocerebellar ataxia type 3 (SCA3) is the most common subtype of hereditary ataxia. Few studies reported the CMCT features in SCA3, but with inconsistent findings. So far, CMCT in SCA3 remains largely unknown.

METHODS

This study included 86 SCA3 patients and 80 healthy controls. Motor-evoked potentials were recorded bilaterally from upper and lower limbs muscles by TMS using a double-cone coil attached to CCY-IA magnetic stimulator. CMCT was determined using F wave and paravertebral magnetic stimulation (PMS). The statistical analyses were performed using R software.

RESULTS

In our study, 36.5% of SCA3 patients had a slight prolongation of CMCT in lower limbs, but not upper limbs, uncorrelated with disease severity. Moreover, SCA3 patients with Babinski signs did not necessarily have abnormal CMCT, and vice versa. Our study demonstrated that PMS is a reliable method as F wave for detecting CMCT in SCA3. Additionally, CMCT to lower limbs was positively correlated with height, but not with age, sex, or weight in healthy controls.

CONCLUSIONS

A small proportion of SCA3 patients had a slight prolongation of CMCT in lower limbs, but not upper limbs, uncorrelated with disease severity. Furthermore, CMCT measures were observed irrespective of pyramidal sign in SCA3; however, patients with abnormal CMCT had a higher incidence of the pyramidal sign.

Comparison of the electrophysiological characteristics of tight filum terminale and tethered cord syndrome

PURPOSE

This study aims to characterize tight filum terminale (TFT) in motor evoked potential (MEP) testing by comparing TFT patients with both tethered cord syndrome (TCS) patients and healthy subjects.

METHODS

Fifty TFT patients, 18 TCS patients, and 35 healthy volunteers participated in this study. We recorded MEPs following transcranial magnetic stimulation from the bilateral abductor hallucis muscles as well as compound muscle action potentials and F-waves evoked by electrical stimulation of the tibial nerve from the bilateral abductor pollicis brevis muscles. The peripheral conduction time (PCT) was calculated from the latency of the compound action potential and F-wave. Furthermore, the central motor conduction time (CMCT) was calculated by subtracting PCT from MEP latency.

RESULTS

TFT and TCS patients had a significantly longer MEP latency than healthy subjects. PCT in TFT patients was significantly longer than those in TCS patients or healthy subjects. Using the cutoff values for PCT, we were able to diagnose patients with TFT patients with a sensitivity of 72.0% and a specificity of 91.4%.

CONCLUSION

Prolonged PCT in the MEP test may be a useful indicator for TFT and suggests that MEP may be used as an adjunct diagnostic tool for TFT.

Factors associated with an excellent outcome after conservative treatment for patients with proximal cervical spondylotic amyotrophy using electrophysiological, neurological and radiological findings

Objective: To investigate factors associated with excellent outcomes after conservative treatment in patients with proximal cervical spondylotic amyotrophy (CSA) using electrophysiological, radiological, and neurological findings. Design: Retrospective study. Setting: Yamaguchi University Hospital. Participants: Seventy-seven patients. Interventions: Erb-point-stimulated compound muscle action potentials (CMAP) were recorded in deltoid and biceps. The percentages of CMAP amplitudes on the affected side compared to the normal side in deltoid (PD) and biceps brachii (PB) were calculated. Central motor conduction time was calculated by subtracting peripheral motor conduction time from the onset latency of motor evoked potentials. Cervical lordotic angles, the diameter of C5 canal, and the intervertebral range at C4-C5 and C5-C6 levels were assessed on plain radiographs. Magnetic resonance imaging was used to assess the width of the intervertebral foramen (WIF) at C4-C5 and C5-C6 levels in the axial views. First visit and final follow-up strengths of most atrophic muscles were evaluated using manual muscle testing (MMT). Improvements in strength were classified as excellent (five grades recovered), good (more than one grade recovered), unchanged (no improvement), or poor (worsened). Results: The outcomes were excellent in 27 patients (35.1%), good in 22 (28.6%), unchanged in 26 (33.8%), and poor in two (2.5%). Factors associated with excellent outcomes were WIF at C4-C5 and C5-C6 on the normal side, PB, and CMAP amplitudes of the deltoid on the normal side. Conclusions: Patients with excellent outcomes originally had wide WIF at C4-C5 and C5-C6 levels and the absence of symptomatic spinal cord compression at C3-C4 and C4-C5 levels.

The Promotoer, a brain-computer interface-assisted intervention to promote upper limb functional motor recovery after stroke: a study protocol for a randomized controlled trial to test early and long-term efficacy and to identify determinants of response

BACKGROUND

Stroke is a leading cause of long-term disability. Cost-effective post-stroke rehabilitation programs for upper limb are critically needed. Brain-Computer Interfaces (BCIs) which enable the modulation of Electroencephalography (EEG) sensorimotor rhythms are promising tools to promote post-stroke recovery of upper limb motor function. The "Promotoer" study intends to boost the application of the EEG-based BCIs in clinical practice providing evidence for a short/long-term efficacy in enhancing post-stroke hand functional motor recovery and quantifiable indices of the participants response to a BCI-based intervention. To these aims, a longitudinal study will be performed in which subacute stroke participants will undergo a hand motor imagery (MI) training assisted by the Promotoer system, an EEG-based BCI system fully compliant with rehabilitation requirements.

METHODS

This longitudinal 2-arm randomized controlled superiority trial will include 48 first ever, unilateral, subacute stroke participants, randomly assigned to 2 intervention groups: the BCI-assisted hand MI training and a hand MI training not supported by BCI. Both interventions are delivered (3 weekly session; 6 weeks) as add-on regimen to standard intensive rehabilitation. A multidimensional assessment will be performed at: randomization/pre-intervention, 48 h post-intervention, and at 1, 3 and 6 month/s after end of intervention. Primary outcome measure is the Fugl-Meyer Assessment (FMA, upper extremity) at 48 h post-intervention. Secondary outcome measures include: the upper extremity FMA at follow-up, the Modified Ashworth Scale, the Numeric Rating Scale for pain, the Action Research Arm Test, the National Institute of Health Stroke Scale, the Manual Muscle Test, all collected at the different timepoints as well as neurophysiological and neuroimaging measures.

DISCUSSION

We expect the BCI-based rewarding of hand MI practice to promote long-lasting retention of the early induced improvement in hand motor outcome and also, this clinical improvement to be sustained by a long-lasting neuroplasticity changes harnessed by the BCI-based intervention. Furthermore, the longitudinal multidimensional assessment will address the selection of those stroke participants who best benefit of a BCI-assisted therapy, consistently advancing the transfer of BCIs to a best clinical practice.

TRIAL REGISTRATION

Name of registry: BCI-assisted MI Intervention in Subacute Stroke (Promotoer).

TRIAL REGISTRATION NUMBER

NCT04353297 ; registration date on the ClinicalTrial.gov platform: April, 15/2020.

Diversity of Cortico-descending Projections: Histological and Diffusion MRI Characterization in the Monkey

The axonal composition of cortical projections originating in premotor, supplementary motor (SMA), primary motor (a4), somatosensory and parietal areas and descending towards the brain stem and spinal cord was characterized in the monkey with histological tract tracing, electron microscopy (EM) and diffusion MRI (dMRI). These 3 approaches provided complementary information. Histology provided accurate assessment of axonal diameters and size of synaptic boutons. dMRI revealed the topography of the projections (tractography), notably in the internal capsule. From measurements of axon diameters axonal conduction velocities were computed. Each area communicates with different diameter axons and this generates a hierarchy of conduction delays in this order: a4 (the shortest), SMA, premotor (F7), parietal, somatosensory, premotor F4 (the longest). We provide new interpretations for i) the well-known different anatomical and electrophysiological estimates of conduction velocity; ii) why conduction delays are probably an essential component of the cortical motor command; and iii) how histological and dMRI tractography can be integrated.

Preoperative factors that predict fair outcomes following surgery in patients with proximal cervical spondylotic amyotrophy. A retrospective study

STUDY DESIGN

Observational cohort study OBJECTIVES: To investigate preoperative factors that predict fair outcomes following surgery in patients with proximal cervical spondylotic amyotrophy (CSA) using electrophysiological and neurological findings.

SETTING

Yamaguchi University METHODS: 54 patients with proximal CSA who underwent surgical treatment of the cervical spine were enrolled. Erb-point stimulated compound muscle action potentials (CMAP) were recorded from the deltoid and biceps brachii muscles. We computed the ratio of affected to normal side CMAP amplitudes in two muscles (deltoid and biceps brachii) and regarded the mean ratio (CMAP-R) as representing the severity of neural involvement. Pre- and postoperative strengths of the most atrophic muscles were evaluated using manual muscle testing. Improvements in strength were classified as excellent (5 grades recovered), good (more than one grade recovered), fair (no improvement), or poor (worsened).

RESULTS

Surgical outcomes were excellent in 26 patients, good in five, fair in 16, poor in seven. Patients with fair outcomes had lower CMAP-R than those patients with excellent and good outcomes [P = 0.0099, odds ratio = 0.89 (95% confidence interval, 0.81-0.97; for a change of 10%)]. Eight patients (15%) had a C5 palsy.

CONCLUSIONS

CMAP-R could be used as a reliable predictive factor related to a fair surgical outcome. We must pay attention to the incidence of C5 palsy after surgery.

Utility of the central motor conduction time recorded from the abductor pollicis brevis and the abductor digiti minimi muscles in patients with C6-7 myelopathy

OBJECTIVE

Central motor conduction time (CMCT) recorded from the abductor pollicis brevis (CMCT-APB) and abductor digiti minimi (CMCT-ADM) muscles may enable the evaluation of patients with C6-7 myelopathy. CMCT is more useful for the evaluation of the function of spinal cord than magnetic resonance imaging (MRI) findings. CMCT may be associated with age and height. However, there are few reports regarding CMCT-APB in normal subjects. This study aimed to investigate the relationships between age, height, and conduction parameters in normal subjects to assess the effectiveness of using CMCT-APB and CMCT-ADM for the evaluation of patients with C6-7 and C7-T1 myelopathy.

DESIGN

Retrospective study.

METHODS

Fifteen patients with cervical compressive myelopathy at C6-7 (11 patients) or C7-T1 (4 patients) level were enrolled. The control group consisted of 150 normal subjects (mean age 45.8±17.0 years; mean height 163.6±8.9 cm). Motor evoked potentials induced by transcranial magnetic stimulation and F-waves were used to determine CMCT.

OUTCOME MEASURES

CMCT-APB, CMCT-ADM.

RESULTS

The normative values of CMCT-APB and CMCT-ADM were 5.3±0.7 ms and 5.2±0.8 ms, respectively. CMCT-APB was significantly longer than CMCT-ADM for patients with C6-7 myelopathy (P < 0.05). Neither of the CMCTs for those with C7-T1 myelopathy were significantly different from those of controls, but CMCT-APB was more prolonged than CMCT-ADM in patients with C6-C7 myelopathy.

CONCLUSIONS

CMCTs improve the accuracy of the diagnosis of myelopathy by pinpointing the lesion in combination with MRI imaging. Selective CMCT-APB prolongation may be seen in patients with C6-7 myelopathy but not C7-T1 myelopathy.

Clinical Factors Underlying the Inter-individual Variability of the Resting Motor Threshold in Navigated Transcranial Magnetic Stimulation Motor Mapping

Correctly determining individual's resting motor threshold (rMT) is crucial for accurate and reliable mapping by navigated transcranial magnetic stimulation (nTMS), which is especially true for preoperative motor mapping in brain tumor patients. However, systematic data analysis on clinical factors underlying inter-individual rMT variability in neurosurgical motor mapping is sparse. The present study examined 14 preselected clinical factors that may underlie inter-individual rMT variability by performing multiple regression analysis (backward, followed by forward model comparisons) on the nTMS motor mapping data of 100 brain tumor patients. Data were collected from preoperative motor mapping of abductor pollicis brevis (APB), abductor digiti minimi (ADM), and flexor carpi radialis (FCR) muscle representations among these patients. While edema and age at exam in the ADM model only jointly reduced the unexplained variance significantly, the other factors kept in the ADM model (gender, antiepileptic drug intake, and motor deficit) and each of the factors kept in the APB and FCR models independently significantly reduced the unexplained variance. Hence, several clinical parameters contribute to inter-individual rMT variability and should be taken into account during initial and follow-up motor mappings. Thus, the present study adds basic evidence on inter-individual rMT variability, whereby some of the parameters are specific to brain tumor patients.

Paired Stimulation to Promote Lasting Augmentation of Corticospinal Circuits

After injury, electrical stimulation of the nervous system can augment plasticity of spared or latent circuits through focal modulation. Pairing stimulation of two parts of a spared circuit can target modulation more specifically to the intended circuit. We discuss 3 kinds of paired stimulation in the context of the corticospinal system, because of its importance in clinical neurorehabilitation. The first uses principles of Hebbian plasticity: by altering the stimulation timing of presynaptic neurons and their postsynaptic targets, synapse function can be modulated up or down. The second form uses synchronized presynaptic inputs onto a common synaptic target. We dub this a “convergent” mechanism, because stimuli have to converge on a common target with coordinated timing. The third form induces focal modulation by tonic excitation of one region (e.g., the spinal cord) during phasic stimulation of another (e.g., motor cortex). Additionally, endogenous neural activity may be paired with exogenous electrical stimulation. This review addresses what is known about paired stimulation of the corticospinal system of both humans and animal models, emphasizes how it qualitatively differs from single-site stimulation, and discusses the gaps in knowledge that must be addressed to maximize its use and efficacy in neurorehabilitation.