Denervation due to lesions of the central nervous system. An EMG study in cases of cerebral contusion and cerebrovascular accidents

Adaptation in the spinal cord after stroke: Implications for restoring cortical control over the final common pathway

Control of voluntary movement is predicated on integration between circuits in the brain and spinal cord. Although damage is often restricted to supraspinal or spinal circuits in cases of neurological injury, both spinal motor neurons and axons linking these cells to the cortical origins of descending motor commands begin showing changes soon after the brain is injured by stroke. The concept of 'transneuronal degeneration' is not new and has been documented in histological, imaging and electrophysiological studies dating back over a century. Taken together, evidence from these studies comports more with a system attempting to survive rather than one passively surrendering to degeneration. There tends to be at least some preservation of fibres at the brainstem origin and along the spinal course of the descending white matter tracts, even in severe cases. Myelin-associated proteins are observed in the spinal cord years after stroke onset. Spinal motor neurons remain morphometrically unaltered. Skeletal muscle fibres once innervated by neurons that lose their source of trophic input receive collaterals from adjacent neurons, causing spinal motor units to consolidate and increase in size. Although some level of excitability within the distributed brain network mediating voluntary movement is needed to facilitate recovery, minimal structural connectivity between cortical and spinal motor neurons can support meaningful distal limb function. Restoring access to the final common pathway via the descending input that remains in the spinal cord therefore represents a viable target for directed plasticity, particularly in light of recent advances in rehabilitation medicine.

Early histopathological changes of secondary degeneration in the spinal cord after total MCA territory stroke

Previous research has not demonstrated secondary degeneration of the spinal cord (SpC) motoneurons after cerebral infarct. The aim of the present study is to investigate the involvement of the anterior horn cells (AHC) in the early post-stroke period using histomorphological and immunohistochemical methods. Post-mortem analysis of the 6th cervical segment was performed in 7 patients who had total MCA stroke within 1 month before death. Nissl-stained sections were used for morphometry, while CD68 and synaptophysin (SYP) immunohistochemistry to monitor microglial activation and synaptic changes in the anterior horn (AH), respectively. Contralateral to the cerebral lesion (contralesional side), cells were smaller after 3 days and larger after 1 week of stroke, especially regarding the large alpha motoneurons. CD68 density increased mainly on the contralesional Rexed's IX lamina of the SpC. SYP coverage of the large motoneurons was reduced on the contralesional side. Early microglial activation in the AH and electrophysiological signs has suggested the possibility of impairment of anterior horn cells (AHC-s). Our study supported that early microglial activation in the contralesional side of the SpC may primarily affect the area corresponding to the location of large motoneurons, and is accompanied by a transient shrinkage followed by increase in size of the large AHC-s with a reduction of their synaptic coverage. After MCA stroke, early involvement of the SpC motoneurons may be suspected by their morphological and synaptic changes and by the pattern of microglial activation.

Contribution of Single-Fiber Evaluation on Monitoring Outcomes Following Injection of Botulinum Toxin-A: A Narrative Review of the Literature

Botulinum toxin-A (BoNT-A) blocks acetylcholine release at the neuromuscular junction (NMJ) and is widely used for neuromuscular disorders (involuntary spasms, dystonic disorders and spasticity). However, its therapeutic effects are usually measured by clinical scales of questionable validity. Single-fiber electromyography (SFEMG) is a sensitive, validated diagnostic technique for NMJ impairment such as myasthenia. The jitter parameter (µs) represents the variability of interpotential intervals of two muscle fibers from the same motor unit. This narrative review reports SFEMG use in BoNT-A treatment. Twenty-four articles were selected from 175 eligible articles searched in Medline/Pubmed and Cochrane Library from their creation until May 2020. The results showed that jitter is sensitive to early NMJ modifications following BoNT-A injection, with an increase in the early days’ post-injection and a peak between Day 15 and 30, when symptoms diminish or disappear. The reappearance of symptoms accompanies a tendency for a decrease in jitter, but always precedes its normalization, either delayed or nonexistent. Increased jitter is observed in distant muscles from the injection site. No dose effect relationship was demonstrated. SFEMG could help physicians in their therapeutic evaluation according to the pathology considered. More data are needed to consider jitter as a predictor of BoNT-A clinical efficacy.

Impact of shoulder subluxation on peripheral nerve conduction and function of hemiplegic upper extremity in stroke patients: A retrospective, matched-pair study

Purpose: To investigate the impact of shoulder subluxation (SS) on peripheral nerve conduction and function of the hemiplegic upper extremity (HUE) in poststroke patients.Methods: Thirty post-stroke patients were selected (SS group: 15 patients, non-SS group: 15 patients, respectively). Evaluation of nerve conduction in upper limbs: the compound muscle action potential (CMAP) amplitude and latency of suprascapular, axillary, musculocutaneous, radial, median, and ulnar nerves; the motor and sensory conduction velocity and the sensory nerve action potential (SNAP) amplitude of median, ulnar, and radial nerves. The Brunnstrom stage scale was used to evaluate the HUE motor function.Results: Compared with the healthy side, the CMAP and SNAP amplitudes of tested nerves on the HUE in both groups were lower, and the CMAP latency of the suprascapular, axillary and musculocutaneous nerves on the HUE in the SS group was longer (P < 0.05). Compared with the HUE in non-SS group, the CMAP amplitude of tested nerves (except ulnar) was decreased more (P < 0.05), the motor conduction velocity of the median nerve was lower (P < 0.05), and the Brunnstrom stage of the HUE was lower in SS group (P < 0.05).Conclusions: Stroke may lead to extensive abnormal nerve conduction on the HUE, and SS may aggravate the abnormality, which may disturb the recovery of upper limb function.

Long-term use of implanted peroneal functional electrical stimulation for stroke-affected gait: the effects on muscle and motor nerve

BACKGROUND

Peripheral changes to muscle and motor nerves occur following stroke, which may further impair functional capacity. We investigated whether a year-long use of an implanted peroneal FES system reverses stroke-related changes in muscles and motor nerves in people with foot drop in the chronic phase after supratentorial stroke.

METHODS

Thirteen persons with a chronic stroke (mean age 56.1 years, median Fugl-Meyer Assessment leg score 71%) were included and received an implanted peroneal FES system (ActiGait®). Quantitative muscle ultrasound (QMUS) images were obtained bilaterally from three leg muscles (i.e. tibialis anterior, rectus femoris, gastrocnemius). Echogenicity (muscle ultrasound gray value) and muscle thickness were assessed over a one-year follow-up and compared to age-, sex-, height- and weight-corrected reference values. Compound motor action potentials (CMAPs) and motor evoked potentials (MEPs) were obtained from the tibialis anterior muscle. Generalized estimated equation modeling was used to assess changes in QMUS, CMAPs and MEPs outcomes over the follow-up period.

RESULTS

Echogenicity of the tibialis anterior decreased significantly during the follow-up on the paretic side. Z-scores changed from 0.88 at baseline to - 0.15 after 52 weeks. This was accompanied by a significant increase in muscle thickness on the paretic side, where z-scores changed from - 0.32 at baseline to 0.48 after 52 weeks. Echogenicity of the rectus femoris normalized on both the paretic and non-paretic side (z-scores changed from - 1.09 and - 1.51 to 0.14 and - 0.49, respectively). Amplitudes of CMAP and MEP (normalized to CMAP) were reduced during follow-up, particularly on the paretic side (ΔCMAP = 20% and ΔMEP = 14%).

CONCLUSIONS

We show that the structural changes to muscles following stroke are reversible with FES and that these changes might not be limited to electrically stimulated muscles. No evidence for improvement of the motor nerves was found.

Motor Unit Properties of the First Dorsal Interosseous in Chronic Stroke Subjects: Concentric Needle and Single Fiber EMG Analysis

The purpose of this study was to better understand changes in motor unit electrophysiological properties in people with chronic stroke based on concentric needle electromyography (EMG) and single fiber EMG recordings. The first dorsal interosseous (FDI) muscle was studied bilaterally in eleven hemiparetic stroke subjects. A significant increase in mean fiber density (FD) was found in the paretic muscle compared with the contralateral side based on single fiber EMG (1.6 ± 0.2 vs. 1.3 ± 0.1, respectively, P = 0.003). There was no statistically significant difference between the paretic and contralateral sides in most concentric needle motor unit action potential (MUAP) parameters, such as amplitude (768.7 ± 441.7 vs. 855.0 ± 289.9 μV), duration (8.9 ± 1.8 vs. 8.68 ± 0.9 ms) and size index (1.2 ± 0.5 vs. 1.1 ± 0.3) (P > 0.18), nor was there a significant difference in single fiber EMG recorded jitter (37.0 ± 9.6 vs. 39.9 ± 10.6 μs, P = 0.45). The increase in FD suggests motor units of the paretic FDI have enlarged due to collateral reinnervation. However, sprouting might be insufficient to result in a statistically significant change in the concentric needle MUAP parameters. Single fiber EMG appears more sensitive than concentric needle EMG to reflect electrophysiological changes in motor units after stroke. Both single fiber and concentric needle EMG recordings may be necessary to better understand muscle changes after stroke, which is important for development of appropriate rehabilitation strategies. The results provide further evidence that motor units are remodeled after stroke, possibly in response to a loss of motoneurons.

Surface Electromyographic Examination of Poststroke Neuromuscular Changes in Proximal and Distal Muscles Using Clustering Index Analysis

Whether stroke-induced paretic muscle changes vary across different distal and proximal muscles remains unclear. The objective of this study was to compare paretic muscle changes between a relatively proximal muscle (the biceps brachii muscle) and two distal muscles (the first dorsal interosseous muscle and the abductor pollicis brevis muscle) following hemisphere stroke using clustering index (CI) analysis of surface electromyograms (EMGs). For each muscle, surface EMG signals were recorded from the paretic and contralateral sides of 12 stroke subjects versus the dominant side of eight control subjects during isometric muscle contractions to measure the consequence of graded levels of contraction (from a mild level to the maximal voluntary contraction). Across all examined muscles, it was found that partial paretic muscles had abnormally higher or lower CI values than those of the healthy control muscles, which exhibited a significantly larger variance in the CI via a series of homogeneity of variance tests (p < 0.05). This finding indicated that both neurogenic and myopathic changes were likely to take place in paretic muscles. When examining two distal muscles of individual stroke subjects, relatively consistent CI abnormalities (toward neuropathy or myopathy) were observed. By contrast, consistency in CI abnormalities were not found when comparing proximal and distal muscles, indicating differences in motor unit alternation between the proximal and distal muscles on the paretic sides of stroke survivors. Furthermore, CI abnormalities were also observed for all three muscles on the contralateral side. Our findings help elucidate the pathological mechanisms underlying stroke sequels, which might prove useful in developing improved stroke rehabilitation protocols.

Complex Neuromuscular Changes Post-Stroke Revealed by Clustering Index Analysis of Surface Electromyogram

The objective of this paperwas to characterize complex neuromuscular changes induced by a hemisphere stroke through a novel clustering index (CI) analysis of surface electromyogram (EMG). The CI analysis was performed using surface EMG signals collected bilaterally from the thenar muscles of 17 subjects with stroke and 12 age-matched healthy controls during their performance of varying levels of isometric muscle contractions. Compared with the neurologically intact or contralateral muscles, mixed CI patterns were observed in the paretic muscles. Two paretic muscles showed significantly increased CI implying dominant neurogenic changes, whereas three paretic muscles had significantly reduced CI indicating dominantmyopathic changes; the other paretic muscles did not demonstrate a significant CI alternation, likely due to a deficit of descending central drive or a combined effect of neuromuscular factors. Such discrimination of paretic muscles was further highlighted using a modified CI method that emphasizes between-side comparison for each individual subject. The CI findings suggest that there appears to be different central and peripheral processes at work in varying degrees after stroke. This paper provides a convenient and quantitative analysis to assess the nature of neuromuscular changes after stroke, without using any special equipment but conventional surface EMG recording. Such assessment is helpful for the development of appropriate rehabilitation strategies for recovery of motor function.

The effect of mild traumatic brain injury on peripheral nervous system pathology in wild-type mice and the G93A mutant mouse model of motor neuron disease

Traumatic brain injury (TBI) is associated with a risk of neurodegenerative disease. Some suggest a link between TBI and motor neuron disease (MND), including amyotrophic lateral sclerosis (ALS). To investigate the potential mechanisms linking TBI to MND, we measured motor function and neuropathology following mild-TBI in wild-type and a transgenic model of ALS, G93A mutant mice. Mild-TBI did not alter the lifespan of G93A mice or age of onset; however, rotarod performance was impaired in G93A verses wild-type mice. Grip strength was reduced only in G93A mice after mild-TBI. Increased electromyography (EMG) abnormalities and markers of denervation (AchR, Runx1) indicate that mild-TBI may result in peripheral effects that are exaggerated in G93A mice. Markers of inflammation (cell edema, astrogliosis and microgliosis) were detected at 24 and 72h in the brain and spinal cord in wild-type and G93A mice. Levels of F2-isoprostanes, a marker of oxidative stress, were increased in the spinal cord 24h post mild-TBI in wild-type mice but were not affected by TBI in G93A mice. In summary, our data demonstrate that mild-TBI induces inflammation and oxidative stress and negatively impacts muscle denervation and motor performance, suggesting mild-TBI can potentiate motor neuron pathology and influence the development of MND in mice.

Examination of Poststroke Alteration in Motor Unit Firing Behavior Using High-Density Surface EMG Decomposition

Recent advances in high-density surface electromyogram (EMG) decomposition have made it a feasible task to discriminate single motor unit activity from surface EMG interference patterns, thus providing a noninvasive approach for examination of motor unit control properties. In the current study, we applied high-density surface EMG recording and decomposition techniques to assess motor unit firing behavior alterations poststroke. Surface EMG signals were collected using a 64-channel 2-D electrode array from the paretic and contralateral first dorsal interosseous (FDI) muscles of nine hemiparetic stroke subjects at different isometric discrete contraction levels between 2 to 10 N with a 2 N increment step. Motor unit firing rates were extracted through decomposition of the high-density surface EMG signals and compared between paretic and contralateral muscles. Across the nine tested subjects, paretic FDI muscles showed decreased motor unit firing rates compared with contralateral muscles at different contraction levels. Regression analysis indicated a linear relation between the mean motor unit firing rate and the muscle contraction level for both paretic and contralateral muscles (p < 0.001), with the former demonstrating a lower increment rate (0.32 pulses per second (pps)/N) compared with the latter (0.67 pps/N). The coefficient of variation (averaged over the contraction levels) of the motor unit firing rates for the paretic muscles (0.21 ± 0.012) was significantly higher than for the contralateral muscles (0.17 ± 0.014) (p < 0.05). This study provides direct evidence of motor unit firing behavior alterations poststroke using surface EMG, which can be an important factor contributing to hemiparetic muscle weakness.

Changes in motoneuron afterhyperpolarization duration in stroke survivors

Hemispheric brain injury resulting from a stroke is often accompanied by muscle weakness in limbs contralateral to the lesion. In the present study, we investigated whether weakness in contralesional hand muscle in stroke survivors is partially attributable to alterations in motor unit activation, including alterations in firing rate modulation range. The afterhyperpolarization (AHP) potential of a motoneuron is a primary determinant of motoneuron firing rate. We examined differences in AHP duration in motoneurons innervating paretic and less impaired (contralateral) limb muscles of hemiparetic stroke survivors as well as in control subjects. A novel surface EMG (sEMG) electrode was used to record motor units from the first dorsal interosseous muscle. The sEMG data were subsequently decomposed to derive single-motor unit events, which were then utilized to produce interval (ISI) histograms of the motoneuron discharges. A modified version of interval death rate (IDR) analysis was used to estimate AHP duration. Results from data analyses performed on both arms of 11 stroke subjects and in 7 age-matched control subjects suggest that AHP duration is significantly longer for motor units innervating paretic muscle compared with units in contralateral muscles and in units of intact subjects. These results were supported by a coefficient of variation (CV) analysis showing that paretic motor unit discharges have a lower CV than either contralateral or control units. This study suggests that after stroke biophysical changes occur at the motoneuron level, potentially contributing to lower firing rates and potentially leading to less efficient force production in paretic muscles.

Examination of afterhyperpolarization duration changes in motoneurons innervating paretic muscles in stroke survivors

The after hyperpolarization (AHP) of a motoneuron is a primary determinant of motoneuron firing rate. Any increase in its duration or amplitude could alter normal motor unit (MU) firing rate properties in stroke, and potentially impact muscle force generation. The objective of this preliminary study was to examine potential differences in afterhyperpolarization (AHP) duration of motoneurons innervating paretic and contralateral limb muscles of hemiparetic stroke survivors. A novel surface EMG (sEMG) electrode was used to record from the first dorsal interosseous muscle (FDI) of three hemiparetic stroke survivors. sEMG data was decomposed to derive single motor unit (SMU) events, which were subsequently utilized to produce interval (ISI) histograms of the motor unit discharge. Interval Death Rate (IDR) analysis was then used to transform ISI histograms into death rate plots. [1] The prescribed IDR analysis method [1] involves a final transformation of death rate plots into an estimated AHP time course. The present study uses a modified method of interpreting death rate plots in order to determine AHP duration. AHP durations from this analysis are similar to durations obtained from ISI variability analysis. [2] Results from three subjects indicate that on average, motor units on the paretic side have a longer AHP duration than the contralateral side, potentially contributing to lower firing rates, and to less efficient force production in paretic muscles.

Alterations in the peak amplitude distribution of the surface electromyogram poststroke

We introduce a new method to examine the spinal motoneuron involvement after stroke using a surface electromyography (EMG) recording system. Fourteen chronic stroke survivors with mild to severe muscle weakness participated in the study. Surface EMG signals were collected from the first dorsal interosseous muscle while subjects performed isometric index finger abduction with paretic or contralateral hand at different matched force levels. Compared with the contralateral muscles, different patterns of peak amplitude distribution were observed at the paretic muscles, which could be induced by motor unit pathological alterations following a stroke. Compared with the conventional electrophysiological methods, the peak amplitude distribution analysis proposed in this study provides a convenient approach to help identify specific mechanisms of muscle weakness and other symptoms after stroke.

The effects of notch filtering on electrically evoked myoelectric signals and associated motor unit index estimates

Background

Notch filtering is the most commonly used technique for suppression of power line and harmonic interference that often contaminate surface electromyogram (EMG) signals. Notch filters are routinely included in EMG recording instrumentation, and are used very often during clinical recording sessions. The objective of this study was to quantitatively assess the effects of notch filtering on electrically evoked myoelectric signals and on the related motor unit index measurements.

Methods

The study was primarily based on an experimental comparison of M wave recordings and index estimates of motor unit number and size, with the notch filter function of the EMG machine (Sierra Wave EMG system, Cadwell Lab Inc, Kennewick, WA, USA) turned on and off, respectively. The comparison was implemented in the first dorsal interosseous (FDI) muscle from the dominant hand of 15 neurologically intact subjects and bilaterally in 15 hemiparetic stroke subjects.

Results

On average, for intact subjects, the maximum M wave amplitude and the motor unit number index (MUNIX) estimate were reduced by approximately 22% and 18%, respectively, with application of the built-in notch filter function in the EMG machine. This trend held true when examining the paretic and contralateral muscles of the stroke subjects. With the notch filter on vs. off, across stroke subjects, we observed a significant decrease in both maximum M wave amplitude and MUNIX values in the paretic muscles, as compared with the contralateral muscles. However, similar reduction ratios were obtained for both maximum M wave amplitude and MUNIX estimate. Across muscles of both intact and stroke subjects, it was observed that notch filtering does not have significant effects on motor unit size index (MUSIX) estimate. No significant difference was found in MUSIX values between the paretic and contralateral muscles of the stroke subjects.

Conclusions

The notch filter function built in the EMG machine may significantly reduce the M wave amplitude and the MUNIX measurement. However, the notch filtering does not jeopardize the evaluation of the reduction ratio in maximum M wave amplitude and MUNIX estimate of the paretic muscles of stroke subjects when compared with the contralateral muscles.

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.

Alterations in spike amplitude distribution of the surface electromyogram post-stroke

We examined surface electromyogram (EMG) characteristics during voluntary isometric activation of the first dorsal interosseous (FDI) muscle in stroke survivors. Five stroke subjects participated in the study. They were instructed to generate isometric contraction at different force levels. The recording was performed in both paretic and contralateral muscles using a matched force protocol. Comparisons of the spike amplitude distribution of the surface EMG signals were made between paretic and contralateral muscles. For a given contraction level, a widened or narrowed spike amplitude distribution was observed in paretic muscles of stroke subjects. Such differences may be induced by degeneration of some spinal motoneurons and/or disorganization of motor unit control properties after stroke.

Changes in muscle fiber density following a stroke

OBJECTIVES

Previous studies have revealed a selective functional loss of the large, high-threshold motor units in the paretic muscles after lesion of the upper motor neuron. We set out to study the degree and the time course of the reorganization of the motor units following a stroke.

METHODS

Examinations were performed on 59 patients with a unilateral ischemic stroke in the territory of the middle cerebral artery, and on 42 healthy controls. The duration of hemiparesis ranged from 2 weeks to 48 months. The fiber density (FD) in the abductor digiti minimi muscle was determined by means of single-fiber electromyography on both the hemiparetic and the unaffected side in the patients, and unilaterally in the control subjects.

RESULTS

The FD was increased on the hemiparetic side relative to the unaffected side and the control group. This change correlated with the severity of the clinical signs. The FD increased during the first 10 months following the stroke and subsequently remained stable.

CONCLUSIONS

The process of reinnervation in the muscles takes place in the acute phase after stroke. These changes are related to the severity of the symptoms.

SIGNIFICANCE

Our findings suggest that trans-synaptic degeneration of the spinal motor neurons occurs shortly after the lesion of the upper motor neurons.

Large motor units are selectively affected following a stroke

OBJECTIVE

Previous studies have revealed a loss of functioning motor units in stroke patients. However, it remained unclear whether the motor units are affected randomly or in some specific pattern. We assessed whether there is a selective loss of the large (high recruitment threshold) or the small (low recruitment threshold) motor units following a stroke.

METHODS

Forty-five stroke patients and 40 healthy controls participated in the study. Macro-EMG was recorded from the abductor digiti minimi muscle at two levels of force output (low and high). The median macro motor unit potential (macro-MUP) amplitude on the paretic side was compared with those on the unaffected side and in the controls.

RESULTS

In the control group and on the unaffected side, the macro-MUPs were significantly larger at the high force output than at the low one. However, on the paretic side the macro-MUPs at the high force output had the same amplitude as those recorded at the low force output. These changes correlated with the severity of the paresis.

CONCLUSIONS

Following a stroke, there is a selective functional loss of the large, high-threshold motor units. These changes are related to the severity of the symptoms.

SIGNIFICANCE

Our findings furnish further insight into the pathophysiology of the motor deficit following a stroke.

Up-regulation of slow K(+) channels in peripheral motor axons: a transcriptional channelopathy in multiple sclerosis

Spinal lesions produce plastic changes in motoneuron properties. We have documented the excitability of motor axons in the median nerve of 12 patients with multiple sclerosis and 50 normal subjects, hypothesizing that plastic changes in the properties of spinal motoneurons might be reflected in the properties of peripheral motor axons and be demonstrable in vivo. In the patients, there were changes in physiological measures of axonal excitability attributable to increased slow K(+) channel activity. Other measures were within control limits. These changes could be modelled by an 11% increase in slow K(+) current, with compensatory changes in membrane potential, suggesting increased expression of the responsible channels. The changes cannot be explained solely by changes in membrane potential and are not those expected if peripheral nerve axons were involved in the inflammatory process of multiple sclerosis. They probably represent a transcriptional channelopathy, due to up-regulation of channel expression. The abnormalities do not imply that peripheral nerve function has been significantly compromised, but they do suggest that the properties of the parent motoneurons have changed. This study thus provides evidence for plasticity in motoneuronal properties at a molecular level, the first such evidence for intact human subjects.

Supratentorial ischemic stroke: more than an upper motor neuron disorder

The primary goal of this study was to identify secondary functional changes in the peripheral motor units of the paretic upper extremity (UE) in patients with severe ischemic stroke and to determine how these changes develop during the first weeks after stroke. An inception cohort of 27 consecutive patients with an acute ischemic supratentorial stroke and an initial UE paralysis was compared with 10 healthy control subjects. The ulnar nerve was electrically stimulated proximal to the wrist and electromyographic recordings were obtained from the abductor digiti minimi muscle. Hemiparetic side mean values of the compound muscle action potential (CMAP) 1 and 3 weeks after stroke were compared with the nonparetic side and with CMAP values obtained from healthy control subjects. The mean CMAP amplitude in patients was significantly lower on the paretic side compared with the nonparetic side and with control subjects. Decrease in CMAP amplitude was observed in more than half of the stroke patients, sometimes as early as 4 days after stroke, and persisted in most cases. Whenever present, it was accompanied by absence of motor recovery at that specific time after stroke. Decreased CMAP amplitude in the abductor digiti minimi muscle can be seen already in the very acute phases after stroke unrelated to peripheral neuropathy, radiculopathy, or plexopathy, and it is accompanied by absence of UMN recovery. This knowledge is important for interpreting electrophysiological data in stroke patients.

The correlation between F-wave motor unit number estimation (F-MUNE) and functional recovery in stroke patients

The aim of this study was to follow up the changes in the number of motor units according to the Brunnstrom stage through a motor unit number estimation of the Fwave (F-MUNE) after a stroke, and to identify the functional significance of F-MUNE. Twenty-five patients (15 men, 10 women) with a first unilateral stroke were recruited. The maximal M-potential was evoked by the supramaximal stimulation of the median nerve at the wrist, and the maximal stimulation intensity was determined on both hemiplegic and unaffected hands. The reproducible all-or-none F-wave was evoked in 30% of the maximal stimulation intensity and was constantly stimulated at that level. The prototypes of the F-wave were chosen, and the values of F-MUNE were calculated by dividing the amplitude of the maximal M-potential by the mean amplitude of the F-prototype. The changes in F-MUNE were compared according to the progression of the Brunnstrom stage and correlated with those of the functional scales. The mean motor unit numbers decreased significantly in the hemiplegic side compared with the unaffected side. According to the progression of the Brunnstrom stage, the values of F-MUNE were reduced significantly by increasing the amplitude and recruitment of the F-prototype, and the functional scores also improved. These results show that the F-MUNE equation did not show a functional recovery related increase in stroke patients.

Electrophysiological signs of changes in motor units after ischaemic stroke

OBJECTIVE

To study changes in motor units on the hemiparetic side, and the relationship between these changes and time after stroke onset and hemiparetic severity.

METHODS

Neurography and concentric needle EMG were performed, and hemiparetic side mean and extreme parameter values were compared with the unaffected side mean and extreme parameter values using non-parametric tests.

RESULTS

The mean M wave amplitude was significantly lower, while the spontaneous activity and the mean number of motor unit potential (MUAP) phases and turns were significantly higher on the hemiparetic side. The outliers above maximum for MUAP duration and amplitude on the hemiparetic side were significantly higher than those on the unaffected side. Correlations were found between the hemiparetic side parameter values and time after stroke onset and hemiparetic severity.

CONCLUSIONS

Axonal or neuronal lesion occurs and collateral reinnervation starts in the acute phase after stroke, while enlarged motor units are found in the chronic state. These changes correlate with hemiparetic severity.

SIGNIFICANCE

This work confirms the controversial concept about lower motor neuron injury with stroke, and provides some information about its time course.

The physiological functional loss of single thenar motor units in the stroke patients: when does it occur? Does it progress?

OBJECTIVE

We examined the time at which loss of functioning motor units occurs on the hemiparetic side, the relationship between that loss and hemiparetic severity, and how long that loss continues.

METHODS

Sample surface motor unit action potentials (S-MUAPs) were evoked in F-waves. They entirely represent the activity of the relative numbers of different shape S-MUAPs for each abductor pollicis brevis muscle. S-MUAPs from selected population of F-waves were averaged after aligning onset latency. Motor unit number was obtained by dividing the maximum M-potential negative peak amplitude by the averaged S-MUAP one.

RESULTS

The motor unit number on the hemiparetic side was significantly lower than that on the unaffected side in stroke patients who had suffered hemiparesis for more than 9 days. This motor unit loss was greater in patients with severe hemiparesis. One year after onset, the chronic stroke patients showed the same motor unit loss on hemiparetic side as they had 3-4 months after onset.

CONCLUSIONS

Motor unit loss on the hemiparetic side is present as early as the second week after onset and is correlated with hemiparesis severity, and this loss continues out to 1 year. This may be due to trans-synaptic degeneration that occurs secondarily to upper motor neuron lesion.

Muscular Atrophy in the Hemiplegic Thigh in Patients After Stroke

OBJECTIVES

This study evaluated muscular atrophy in the hemiplegic limbs by assessing the muscle volume of the thighs in stroke patients.

DESIGN

Muscle volume of the bilateral thighs was determined by computed tomographic scanning in 50 hemiplegic patients after stroke.

RESULTS

The average muscle volume in the hemiplegic side was significantly lower than that in the nonhemiplegic side. When the patients were divided into the two groups aged <65 yr old and >/=65 yr, age-dependent reduction in the muscle volume was significant only in the nonhemiplegic side. In addition, the ratio of the muscle volume in hemiplegic side to that in non-hemiplegic side was lower in the younger group than in the older group, with close to significance (P = 0.07). Muscle volume in both hemiplegic and nonhemiplegic sides correlated positively with Barthel index and negatively with patient age.

CONCLUSION

Muscle volume decreases in the hemiplegic side in stroke patients.

[Spontaneous electromyographic activity. Practical importance]

Spontaneous activities are a major semeiologic sign in electromyography. The present article deals with the different aspects recorded in practice in normal and pathological cases. There are two types of spontaneous activities, those related to motor unit hyperactivity (fasciculations and myokymia) and those related to the hyperactivity of one or more muscle fibers: fibrillations, positive sharp waves, myotonic discharges and complex repetitive discharges. In the first case the lesion is located in the axone and in the second in the membrane of the muscle fibers; All theories related to the cells' abnormalities share a common feature: spontaneous activities result from abnormal firing of the membrane action potential of muscular fibers. This functional abnormality may results from different types of lesions within the cells' membrane and determines the aspects of spontaneous activities. Impaired function of muscular cells' membranes can be produced by denervation or lesion of the membrane structure itself. The latter can be multiple and linked with the membrane proteins (such as laminine or dystrophin as in AIDS diseases) or with ion channel disturbances. Multiple membrane cell alterations may produce the same kind of spontaneous activity; for instance, myotonic discharges have the same morphology in Thomsen and Steinert's disease despite their different mechanisms and fibrillations seen in denervations and myopathies. The practical consequences are discussed and a new classification of these spontaneous activities is proposed.

Physiologic decrease of single thenar motor units in the F-response in stroke patients

OBJECTIVE

To investigate the left-right difference and the reproducibility by the F-wave motor unit number estimation and to compare the motor unit number between the hemiplegic and unaffected side in stroke patients.

SETTING

A referral center and institutional practice providing outpatient care.

SUBJECTS

Seven healthy volunteers and 15 consecutive stroke patients.

DESIGN

Diagnostic statistical test and correlational study.

METHOD

Submaximal stimuli were used to evoke a sample of surface motor unit action potentials (S-MUAPs) in the F-waves that are entirely representative of the relative numbers of detected S-MUAPs of different sizes. The average S-MUAP amplitude was calculated from a selected population of F-wave responses for each abductor pollicis brevis (APB) muscle. The motor unit number was calculated by dividing the maximum M-potential negative peak amplitude by the average S-MUAP negative peak amplitude.

RESULT

There was no statistical difference between motor unit numbers on either side and between test and retest in this motor unit number estimation method among normal subjects. The motor unit number on the hemiplegic side was significantly lower than on the unaffected side (p < .05, Mann-Whitney test) among stroke patients.

CONCLUSION

The motor unit could decrease in the hemiplegic side after a moderate-to-severe hemiplegic stroke and this decrement might be due to the transsynaptic degeneration secondary to an upper motor neuron lesion.

Deficits in the coordination of agonist and antagonist muscles in stroke patients: implications for normal motor control

Movement impairments about a single joint in stroke patients may be related to deficits in the central regulation of stretch reflex (SR) thresholds of agonist and antagonist muscles. One boundary of the SR threshold range for elbow flexor and extensor muscles was measured in hemiparetic subjects by analysing electromyographic activity during stretching of relaxed muscles at seven different velocities. For each velocity, dynamic SR thresholds were measured as angles at which electromyographic activity appeared. These data were used to determine the sensitivity of the threshold to velocity and the static SR thresholds for flexors and extensors. In contrast to relaxed muscles in healthy subjects, static flexor and extensor thresholds lay within the physiological range in 11/12 and 4/12 subjects, respectively. This implies that, in the range between the static SR threshold and one of the physiological joint limits, relaxation of the muscle was impossible. Subjects then made slow movements against different loads to determine their ranges of active movement. Maximal flexor and extensor torques were lower in hemiparetic subjects throughout the angular range. In some subjects, ranges were found in which no active torque could be produced in either extensor or both muscle groups. These ranges were related to the boundary values of SR thresholds found during passive muscle stretch. The range in which reciprocally organized agonist and antagonist muscle activity could be generated was limited in all but one subject. When attempting to produce torque from positions outside their measured range of movement, excessive muscle coactivation occurred, typically producing no or paradoxical motion in the opposite direction. Results suggest a relationship between spasticity measured at rest and the movement deficit in stroke by demonstrating a link between motor deficits and control deficits in the central regulation of individual SR thresholds.

Effects of dantrolene sodium on fibrillation potentials in denervated rat muscles

To examine whether a decrease in cytosolic Ca2+ affects fibrillation potentials, we studied effects of dantolene on these potentials in denervated rat muscle. Administered intraperitoneally, dantrolene sodium (12-22 mg/kg) abolished fibrillation potentials and subthreshold oscillating potentials over 2.5-6 h without affecting excitability of the muscle to electrical stimulation. Fibrillation potentials reappeared 36-96 h after administration of dantrolene. We suggest that cytosolic Ca2+ has a specific role in generating fibrillations.

Evident trans-synaptic degeneration of motor neurons after stroke: a study of neuromuscular jitter by axonal microstimulation

Neuronal degradation accompanied by axonal degeneration has been known to occur in lower motor neurons following a stroke. In the present study, the functional integrity of neuromuscular transmission was assessed, utilizing a sensitive electrodiagnostic method consisting of stimulated single-fiber electromyography (SFEMG), along with axonal microstimulation, in paralytic muscles of stroke patients. Neuromuscular jitter was measured in the hemiplegic side extensor digitorum communis (EDC) as well as in anterior tibial (AT) muscles for 28 stroke patients and also for 13 age-matched controls. The disease duration, i.e. from the onset of stroke until the stimulated SFEMG examination, extended from 2 months to 8 years. Mean jitters obtained in EDC and AT muscles of stroke patients were found to be significantly greater than those in normal controls. Mean jitters obtained in severely weak muscles of stroke patients were greater than those in moderately weak muscles. Positive correlations were noted between the increased jitter and the disease duration from the onset of stroke until the time of the stimulated SFEMG test. These findings demonstrate a dysfunction of neuromuscular transmission in the paralytic muscles of stroke patients and suggests that trans-synaptic degeneration of motor neurons may occur in stroke. Furthermore, the neuronal degradation in stroke was positively correlated with the course duration of the disease.

Enzyme-histochemical and morphological characteristics of fast- and slow-twitch skeletal muscle after brain infarction in the rat

The right middle cerebral artery was permanently occluded in 12-week-old male spontaneously hypertensive rats. After the surgery the rats were subjected to repeated behavioural tests during the observation period. Fourteen weeks after surgery the fast-twitch extensor digitorum longus (EDL) and the slow-twitch soleus muscle of both sides were removed and examined with regard to muscle fibre characteristics obtained by histochemical and morphometrical methods. Comparisons were made with age-matched controls. Limb placement and the ability to traverse a beam or a rotating pole were repeatedly tested 2-13 weeks after the operation. In spite of permanent sensorimotor deficits in limb placement and when traversing a rotating pole or beam, no increase in pathological changes was noted in either EDL or soleus. The number and proportion of fibre types remained unchanged in both muscles. There was no difference in muscle fibre size in either EDL or soleus. It is concluded that brain infarction in the rat, although causing marked impairment of contralateral motor function, does not have a major influence on the muscle-fibre morphology or fibre-type composition, irrespective of muscle type.

Prediction of Reflex Sympathetic Dystrophy in Hemiplegic Patients by Electromyographic Study

Background and Purpose This study was designed to investigate the correlation between reflex sympathetic dystrophy syndrome (RSDS) in hemiplegic patients and spontaneous electromyographic (EMG) activity, as well as to determine the predictive value of spontaneous EMG activity in early diagnosis of RSDS.

Methods An EMG and nerve conduction velocity study of the weak upper limb was conducted on 70 hemiplegic patients at 3 to 4 weeks after cerebrovascular disease (either cerebral hemorrhage or infarction). Clinical assessment for development of the RSDS was done during the following 6 months. The correlation of RSDS development with the presence of spontaneous EMG activity and certain clinical parameters (including sex, age, side affected, cause of stroke, sensory impairment, spasticity, and shoulder subluxation) was analyzed statistically.

Results Of the 46 patients who exhibited spontaneous activity, 30 (65%) developed clinical RSDS in their hemiplegic upper extremity, whereas only 1 (4%) of the other 24 patients with no spontaneous EMG activity developed clinical RSDS within 6 months after the onset of hemiplegia ( P <.001). The correlation of RSDS development with the presence of shoulder subluxation and sensory impairment in the hemiplegic side was statistically significant. Neither age, sex, severity of spasticity, nor etiology of stroke had a significant correlation with the development of clinical RSDS.

Conclusions There is significant correlation between the presence of spontaneous EMG activity and the development of clinical RSDS in the hemiplegic upper extremity after stroke. It is concluded that spontaneous EMG activity in the hemiplegic hands of stroke patients might be a good predictor of the future development of clinical RSDS.

Denervation in hemiplegic muscles

This study examined the frequency of denervation activity in hemiplegic muscles in relation to the size and location of the central lesion. We studied 20 patients, 14 with major unilateral cerebral infarctions in the middle cerebral or internal carotid territories; four with a single lacune in the pons, internal capsule, or thalamus; and two with precentral infarcts. Using somatosensory evoked potentials, motor conduction studies, and assessments of conduction across the plexus and roots, we detected no conduction abnormalities on the affected side. Fibrillation was common in both groups, especially in distal and intermediate muscles. The distribution of the fibrillation and the normal conduction studies suggested that trauma of peripheral nerves was not a factor. Although the normal conduction studies and pattern of fibrillation activity do not exclude peripheral nerve trauma as the cause of the fibrillation, we suggest that transsynaptic degeneration is a reasonable alternative explanation.

Abnormal EMG and SSEP in a young child with an ependymoma

We report our findings on a case of ependymoma in a one-year-old boy. A partial paresis of the left arm was found but the EEG and BAEP were normal. The EMG showed fibrillations and positive sharp waves in the paretic muscles and the SSEP showed a far field negativity. After removal of the cerebral process all neurophysiologic findings normalized. We discuss a hypothesis for the established clinical neurophysiological findings.

Peripheral nerve morphometry in stroke patients

Sural nerve biopsy specimens from affected and non-affected limbs of stroke patients were examined morphometrically. Two principle abnormalities of peripheral nerve were found in hemiparetic and hemiplegic limbs. First, the frequency of abnormal teased nerve fibers was significantly increased with abnormal internodes frequently "clustered" and showing a 50% or more reduction in myelin thickness. Second, the mean diameter of myelinated nerve fibers was reduced. These results suggest a primary atrophy of peripheral nerve fibers in the affected limbs of stroke patients with secondary demyelination. Possible aetiological factors include disuse, transynaptic degeneration, ischemia, pressure effect, and decreased axoplasmic flow. It would seem that the structural integrity of peripheral nerve is frequently compromised following a cerebral lesion.