F-waves: neurophysiology and clinical value

F wave analysis based on the compound muscle action potential scan

INTRODUCTION/AIMS

Conventional F wave analysis involves a relatively uniform physiological environment induced by supramaximal stimulations. The F wave characteristics in a dynamic physiological condition, however, are rarely investigated. This study aimed to improve understanding of F wave properties in the more dynamic process by introducing a novel method to analyze F waves based on the compound muscle action potential (CMAP) scan technique.

METHODS

Twenty four healthy subjects participated in the study. The CMAP scan was applied to record muscle responses in the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles, respectively. F wave characteristics including mean F wave amplitude and latency (F-M latency), persistence and activating threshold were quantified.

RESULTS

An average of 200 F waves per muscle were obtained from the CMAP scan recording. Weak to moderate correlations between F wave amplitude and stimulating intensity were observed in most of the APB (19 muscles; r = 0.33 ± 0.14, all p < .05) and ADM (23 muscles, r = 0.46 ± 0.16, all p < .05) muscles. Significantly longer mean F latency and lower activating F-threshold were found in the ADM muscles (F-M latency: APB: 25.43 ± 2.39 ms, ADM: 26.15 ± 2.32 ms, p < .05; F-threshold: APB: 7.68 ± 8.96% CMAP, ADM: 2.35 ± 2.42% CMAP, p < .05).

DISCUSSION

This study introduces new features of F waves using the CMAP scan technique and identifies differences of F wave characteristics between the hand muscles. The CMAP scan based F waves analysis can be combined with the motor unit number estimation to assess functional alterations in motor neurons in neurological disorders.

On the origin of F-wave: involvement of central synaptic mechanisms

Neurophysiological methods are used widely to gain information about motor neuron excitability and axon conduction in neurodegenerative diseases. The F-wave is a common biomarker used to test motor neuron properties in the diagnosis of neurological diseases. Although the origin of the F-wave is a subject of debate, the most widely accepted mechanism posits that the F-wave is generated by the backfiring of motor neurons stimulated antidromically from the periphery. In this study, we developed an ex vivo mouse sciatic nerve-attached spinal cord preparation with sensory axons severed. In this preparation, stimulation of the whole sciatic nerve or its tibial branch evoked responses with the electrophysiological signatures of F-waves. Manipulations of synaptic transmission by either removal of extracellular calcium or block of post-synaptic glutamate receptors abolished these responses. These results suggest that F-waves are mediated by spinal microcircuits activated by recurrent motor axon collaterals via glutamatergic synapses.

Serotonergic and noradrenergic contributions to motor cortical and spinal motoneuronal excitability in humans

Animal models indicate that motor behaviour is shaped by monoamine neuromodulators released diffusely throughout the brain and spinal cord. As an alternative to conducting a single study to explore the effects of neuromodulators on the human motor system, we have identified and collated human experiments investigating motor effects of well-characterised drugs that act on serotonergic and noradrenergic networks. In doing so, we present strong neuropharmacology evidence that human motor pathways are affected by neuromodulators across both healthy and clinical populations, insight that cannot be determined from a single reductionist experiment. We have focused our review on the effects that monoaminergic drugs have on muscle responses to non-invasive stimulation of the motor cortex and peripheral nerves, and other closely related tests of motoneuron excitability, and discuss how these measurement techniques elucidate the effects of neuromodulators at motor cortical and spinal motoneuronal levels. Although there is some heterogeneity in study methods, we find drugs acting to enhance extracellular concentrations of serotonin tend to reduce the excitability of the human motor cortex, and enhanced extracellular concentrations of noradrenaline increases motor cortical excitability by enhancing intracortical facilitation and reducing inhibition. Both monoamines tend to enhance the excitability of spinal motoneurons. Overall, this review details the importance of neuromodulators for the output of human motor pathways and suggests that commonly prescribed monoaminergic drugs target the motor system in addition to their typical psychiatric/neurological indications.

Fully automated F-wave corridor extraction and analysis algorithm for F-wave analyses and MUNE studies

F-waves are used in motor unit number estimation (MUNE) studies, which require rapid dedicated software to perform calculations. The aim of this study is to define a mathematical method for a fully automated F-wave extraction algorithm to perform F-wave and MUNE studies while performing baseline corrections without distorting traces. Ten recordings from each class, such as healthy controls, polio patients and ALS patients, were included. Submaximal stimuli were applied to the median and ulnar nerves to record 300 traces from the abductor pollicis brevis and abductor digiti minimi muscles. The autocorrelation function and the signal of sum of all traces were used to find the location for the maximum amplitude of the F-waves. F-waves were revealed by using a cutting window. Linear line estimation was preferred for baseline corrections because it did not cause any distortion in the traces. The algorithm automatically revealed F-waves from all 30 recordings in accordance with the locations marked by a neurophysiologist. The execution of the algorithm was less than 2 (usually < 1) minutes when 300 traces were analyzed. Mean sMUP amplitudes and MUNE values are important for differentiating healthy controls from patients. Moreover, F-wave parameters belonging to polio patients on whom there was a relatively low number of studies conducted were also evaluated.

Paired corticomotoneuronal stimulation of the preactivated ankle dorsiflexor: an open-label study of magnetic and electrical painless protocols

Paired corticomotoneuronal stimulation (or electrical PCMS: ePCMS) is the repetitive pairing of an electrical stimulus to a nerve with a transcranial magnetic stimulation of the primary motor cortex (TMS-of-M1) to noninvasively influence spinal plasticity. We compared ePCMS with the new painless PCMS protocol pairing a magnetic stimulus to the nerve with TMS-of-M1 (mPCMS) in the preactivated tibial anterior muscle (TA). Sixteen healthy adults participated in two sessions (mPCMS, ePCMS), each with 180 pairs of [low-intensity TMS-of-M1 + nerve stimulation] at 0.2 Hz. TA motor-evoked potentials (MEP) to single-pulse TMS at pre-PCMS, immediately and 30 min after PCMS, were cluster-analyzed to discriminate responders and non-responders. Paired-pulse TMS-of-M1 and F-waves were also tested and BDNF polymorphism influence was explored. Both PCMS protocols significantly increased MEP amplitudes (n = 9 responders each), but the time-course differed with mPCMS inducing larger MEP increase over time. The number of BDNF-methionine carriers tended to be larger than Val66Val in mPCMS and the reverse in ePCMS, thus warranting further investigations. The MEP changes of the preactivated TA likely occurred at the pre-motoneuronal level and larger mPCMS after-effects over time may be related to the afferents recruited. mPCMS seems relevant to be tested in future studies as a painless noninvasive approach to induce sustained pre-motoneuronal plasticity in spinal cord injury.

F-waves induced by motor point stimulation are facilitated during handgrip and motor imagery tasks

The F-wave is a motor response elicited via the antidromic firings of motor nerves by the electrical stimulation of peripheral nerves, which reflects the motoneuron pool excitability. However, the F-wave generally has low robustness i.e., low persistence and small amplitude. We recently found that motor point stimulation (MPS), which provides the muscle belly with electrical stimulation, shows different neural responses compared to nerve stimulation, e.g., MPS elicits F-waves more robustly than nerve stimulation. Here, we investigated whether F-waves induced by MPS can identify changes in motoneuron pool excitability during handgrip and motor imagery. Twelve participants participated in the present study. We applied MPS on their soleus muscle and recorded F-waves during eyes-open (EO), eyes-closed (EC), handgrip (HG), and motor imagery (MI) conditions. In the EO and EC conditions, participants relaxed with their eyes open and closed, respectively. In the HG, participants matched the handgrip force level to 30% of the maximum voluntary force with visual feedback. In the MI, they performed kinesthetic MI of plantarflexion at the maximal strength with closed eyes. In the HG and MI, the amplitudes of the F-waves induced by MPS were increased compared with those in the EO and EC, respectively. These results indicate that the motoneuron pool excitability was facilitated during the HG and MI conditions, consistent with findings in previous studies. Our findings suggest that F-waves elicited by MPS can be a good tool in human neurophysiology to assess the motoneuron pool excitability during cognitive and motor tasks.

Long-term outcomes of plasma exchange versus intravenous immunoglobulin for the treatment of Guillain-Barré Syndrome: A double-blind, randomized clinical trial

Background

Most previous studies comparing the effectiveness of Plasma Exchange (PE) or intravenous immunoglobulin (IVIG) in treating Guillain-Barre syndrome (GBS) have focused on the short-term outcome at around 1 month.

Objective

To compare the long-term efficacy of PE and IVIG at one year in adult patients with GBS.

Methods

Eighty-one adult patients with acute GBS were randomized into two groups with a ratio of 2 : 1: PE (N = 54) and IVIG (N = 27). Patients were assessed with the Medical Research Council sum score (MRC sum score), GBS Disability Scale (GDS), and Functional assessment of acute inflammatory neuropathy (FAAIN) at baseline, ten days, one month, three months, and one year. Neurophysiological examinations were performed at baseline and three months following treatment.

Results

There were no significant differences between groups in demographic, clinical, and laboratory data. Both treatments produced a significant improvement in all clinical rating scales in both groups that continued up to one year. There were significant differences in the time course of recovery in the MRC and FAAIN scales, with significantly more improvement in the IVIG group at 1 and 3 months, although there was no significant difference in outcome at one year. However the effect size showed measurable differences between the PE and IVIG groups across the different measures at one-year. Electrophysiological studies showed equal improvement in most measures in both groups at three months, with a slightly greater effect in the IVIG group.

Conclusion

long term outcomes of IVIG and PE were equivalent. However the effect size showed measurable differences between the PE and IVIG groups across the different measures at one-year follow-up that indicate the superiorty of IVIG. There was also a tendency for improvement to be slightly faster in the IVIG group.

Traumatic injury to peripheral nerves

This article reviews the epidemiology, classification, localization, prognosis, and mechanisms of recovery of traumatic peripheral nerve injuries (PNIs). Electrodiagnostic (EDx) assessments are critical components of treating patients with PNIs. In particular, motor and sensory nerve conduction studies, needle electromyography, and other electrophysiological methods are useful for localizing peripheral nerve injuries, detecting and quantifying the degree of axon loss, and contributing toward treatment decisions as well as prognostication. It is critical that EDx medical consultants are aware of the timing of these changes as well as limitations in interpretations. Mechanisms of recovery may include recovery from conduction block, muscle fiber hypertrophy, distal axonal sprouting, and axon regrowth from the site of injury. Motor recovery generally reaches a plateau at 18 to 24 months postinjury. When patients have complete or severe nerve injuries they should be referred to surgical colleagues early after injury, as outcomes are best when nerve transfers are performed within the first 3 to 6 months after onset.

Optimal peripheral nerve stimulation intensity for paired associative stimulation with high-frequency peripheral component in healthy subjects

Paired associative stimulation (PAS) with high-frequency peripheral nerve stimulation (PNS), called “high-PAS”, induces motor-evoked potential (MEP) potentiation in healthy subjects and improves muscle activity and independence in incomplete spinal cord injury patients. Data on optimal PNS intensity in PAS are scarce. In a high-PAS protocol, PNS intensity is defined as “minimal intensity required to produce F-responses”. We sought to further refine this definition and to investigate how PNS intensity affects PAS outcome. Two experiments were performed on 10 healthy subjects where MEP amplitude change was measured 0, 30, and 60 min after PAS. In the first experiment, the intensity required to achieve 7/10 persistence of F-responses was used to define PNS intensity level. In the second experiment, we used the intensity required to achieve 1/10 persistence (“baseline”). In addition, we applied this intensity at + 25%, − 25%, and − 50% levels. In the first experiment, PAS did not produce significant MEP potentiation. In the second experiment, PAS produced statistically significant MEP potentiation, with PNS intensity of “baseline” and “baseline − 25%” levels but not at + 25% or − 50% levels. In conclusion, for PAS utilizing high-frequency PNS, the intensity required to achieve 1/10 F-response persistence or the intensity 25% lower produces significant MEP potentiation in healthy subjects.

5-HT2 receptor antagonism reduces human motoneuron output to antidromic activation but not to stimulation of corticospinal axons

The intrinsic electrical properties of motoneurons strongly affect motoneuron excitability to fast-acting excitatory ionotropic inputs. Serotonin (5-HT) is a neurochemical that alters the intrinsic properties of motoneurons, whereby animal models and in vitro experiments indicate that 5-HT increases motoneuron excitability by activating 5-HT₂ receptors on the somato-dendritic compartment. In the current study, we examined how antagonism of the 5-HT₂ receptor affects motoneuron excitability in humans. We hypothesised that motoneuron excitability would be reduced. The 5-HT₂ antagonist cyproheptadine was administered to ten healthy participants in a double-blinded, placebo-controlled, crossover trial. Electrical cervicomedullary stimulation was used to deliver a synchronised excitatory volley to motoneurons to elicit cervicomedullary motor evoked potentials (CMEPs) in the surface electromyography (EMG) signal of the resting biceps brachii. Likewise, electrical peripheral nerve stimulation was used to generate antidromic spikes in motoneurons and cause recurrent discharges, which were recorded with surface EMG as F-waves in a resting hand muscle. Compared to placebo, we found that 5-HT₂ antagonism reduced the amplitude and persistence of F-waves but did not affect CMEP amplitude. 5-HT₂ antagonism also reduced maximal contraction strength. The reduced recurrent discharge of motoneurons with 5-HT₂ antagonism suggests that 5-HT₂ receptors modulate the electrical properties of the initial segment or soma to promote excitability. Conversely, as cyproheptadine did not affect motoneuron excitability to brief synaptic input, but affected maximal contractions requiring sustained input, it seems likely that the 5-HT₂ mediated amplification of synaptic input at motoneuron dendrites is functionally significant only when excitatory input activates persistent inward currents.

Motor point stimulation induces more robust F-waves than peripheral nerve stimulation

The F-wave is a motor response induced by electrical stimulation of peripheral nerves via the antidromic firing of motor nerves, which reflects the motoneuron excitability. To induce F-waves, transcutaneous peripheral nerve stimulation (PNS) is used, which activates nerve branches via transcutaneous electrodes over the nerve branches. An alternative method to activate peripheral nerves, i.e., motor point stimulation (MPS) which delivers electrical stimulation over the muscle belly, has not been used to induce F-waves. In our previous studies, we observed that MPS induced F-wave like responses, i.e., motor responses at the latency of F-waves at a supramaximal stimulation. Here we further investigated the F-wave like responses induced by MPS in comparison to PNS in the soleus muscle. Thirteen individuals participated in this study. We applied MPS and PNS on the participant's left soleus muscle. Using a monopolar double-pulse stimulation, the amplitude of the second H-reflex induced by PNS decreased, while the amplitude of the motor response at the F-wave latency induced by MPS did not decrease. These results suggest that the motor response at the F-wave latency induced by MPS was not an H-reflex but an F-wave. We also found that the F-wave induced by MPS had a greater amplitude, higher persistence, and caused less pain when compared to the F-waves induced using PNS. We conclude that MPS evokes antidromic firing inducing F-waves more consistently compared to PNS.

Thenar Muscle Motor Imagery Increases Spinal Motor Neuron Excitability of the Abductor Digiti Minimi Muscle

When a person attempts intended finger movements, unintended finger movement also occur, a phenomenon called “enslaving”. Given that motor imagery (MI) and motor execution (ME) share a common neural foundation, we hypothesized that the enslaving effect on the spinal motor neuron excitability occurs during MI. To investigate this hypothesis, electromyography (EMG) and F-wave analysis were conducted in 11 healthy male volunteers. Initially, the EMG activity of the left abductor digiti minimi (ADM) muscle during isometric opposition pinch movement by the left thumb and index finger at 50% maximal effort was compared with EMG activity during the Rest condition. Next, the F-wave and background EMG recordings were performed under the Rest condition, followed by the MI condition. Specifically, in the Rest condition, subjects maintained relaxation. In the MI condition, they imagined isometric left thenar muscle activity at 50% maximal voluntary contraction (MVC). During ME, ADM muscle activity was confirmed. During the MI condition, both F-wave persistence and the F-wave/M-wave amplitude ratio obtained from the ADM muscle were significantly increased compared with that obtained during the Rest condition. No difference was observed in the background EMG between the Rest and MI conditions. These results suggest that MI of isometric intended finger muscle activity at 50% MVC facilitates spinal motor neuron excitability corresponding to unintended finger muscle. Furthermore, MI may induce similar modulation of spinal motor neuron excitability as actual movement.

Electrophysiological findings in patients with restless legs syndrome

BACKGROUND

Restless legs syndrome (RLS) manifests as an urge to move the body to relieve the discomfortable sensations, primarily when resting, sitting, laying down, or sleeping. Diagnosis of RLS relies on clinical criteria, and the immobilization test was the only instrumental tool with equivocal results.

OBJECTIVES

To assess different electrophysiological findings in patients with RLS, and compare the diagnostic values of these parameters in the diagnosis of RLS.

METHODS

30 patients with primary RLS and 30 controls who were matched for age and gender were studied. Participant's demographics, laboratory findings, and electrophysiological test, namely nerve conduction studies (NCS), cutaneous silent period (CSP), H reflex and sympathetic skin response (SSR), F-wave latency, amplitude, F-wave duration (FWD), and the ratio between FWD and duration of the corresponding compound muscle action potential (FWD/CMAPD) were analyzed.

RESULTS

None of the patients showed altered NCS data. FWD of upper (12.37 ± 2.77 ms) and lower limb (21.71 ± 5.24 ms) were significantly longer in patients. Also, FWD/CMAP duration of the upper (1.03 ± 0.2) and lower limb (2.02 ± 0.55) was longer in patients. Likewise, they exhibited delayed CSP latency from TA (110.62 ± 13.73 ms) and APB (77.35 ± 12.16 ms) whereas the CSP duration from TA and APB was decreased (37.36 ± 11.59 ms; 42.55 ± 7.97 ms, respectively). The SSR latency was not different, and right-sided H reflex amplitude (5.07 ± 3.98 mV) and H/M ratio (0.65 ± 1.81) were significantly increased in the patient group.

CONCLUSION

The data suggest that there may be a dysfunction of the inhibitory/excitatory circuits at a spinal level; and no pathology in the peripheral nerves. The unilateral difference of H reflex amplitude and H/M ratio may suggest asymmetrical central inhibitory dysfunction. Further prospective studies with larger cohorts are now needed to evaluate the pathophysiology of RLS with different neurophysiological assessment tools.

Reasons for Diagnostic Delay of Foot Drop Caused by Parasagittal Meningioma: Two Case Reports

Foot drop is defined as an impaired ability or inability of dorsiflexion. Peripheral nervous system injuries are commonly considered as the cause of this condition. The central causes including parasagittal meningioma are also described in the literature but very rarely and commonly not recognized early. In this article, we report 2 patients with isolated unilateral foot drop as the first symptom of a parasagittal meningioma and discuss several reasons for delayed diagnosis. Two patients were treated with decompressive craniotomy. The histopathological findings demonstrated a fibroblastic meningioma and a meningothelial meningioma. During postoperative follow-up, the woman patient showed nearly complete recovery and the second case regained total muscle power over a period of 12 months. The rarity of the disease, the absence of upper motor neuron signs, the occurrence of peripheral pathologies and misinterpretation of F wave on nerve conduction study, and motor unit recruitment on electromyography lead to delay in diagnosis and treatment of the central foot drop due to parasagittal meningioma.

A novel paired associative stimulation protocol with a high-frequency peripheral component: A review on results in spinal cord injury rehabilitation

In recent decades, a multitude of therapeutic approaches has been developed for spinal cord injury (SCI), but few have progressed to regular clinical practice. Novel non-invasive, cost-effective, and feasible approaches to treat this challenging condition are needed. A novel variant of paired associative stimulation (PAS), high-PAS, consists of non-invasive high-intensity transcranial magnetic stimulation (TMS) and non-invasive high-frequency electrical peripheral nerve stimulation (PNS). We observed a therapeutic effect of high-PAS in 20 patients with incomplete SCI with wide range of injury severity, age, and time since injury. Tetraplegic and paraplegic, traumatic, and neurological SCI patients benefited from upper- or lower-limb high-PAS. We observed increases in manual motor scores (MMT) of upper and lower limbs, functional hand tests, walking tests, and measures of functional independence. We also optimized PAS settings in several studies in healthy subjects and began elucidating the mechanisms of therapeutic action. The scope of this review is to describe the clinical experience gained with this novel PAS approach. This review is focused on the summary of our results and observations and the methodological considerations for researchers and clinicians interested in adopting and further developing this new method.

Tetanic stimulation of the peripheral nerve augments motor evoked potentials by re-exciting spinal anterior horn cells

Tetanic stimulation of the peripheral nerve, immediately prior to conducting transcranial electrical stimulation motor evoked potential (TES-MEP), increases MEP amplitudes in both innervated and uninnervated muscles by the stimulated peripheral nerve; this is known as the remote augmentation of MEPs. Nevertheless, the mechanisms underlying the remote augmentation of MEPs remain unclear. Although one hypothesis was that remote augmentation of MEPs results from increased motoneuronal excitability at the spinal cord level, the effect of spinal anterior horn cells has not yet been investigated. We aimed to investigate the effect of tetanic stimulation of the peripheral nerve on spinal cord anterior horn cells by analyzing the F-wave. We included 34 patients who underwent elective spinal surgeries and compared the changes in F-waves and TES-MEPs pre- and post-tetanic stimulation of the median nerve. F-wave analyses were recorded by stimulating the median and tibial nerves. TES-MEPs and F-wave analyses were compared between baseline and post-tetanic stimulation time periods using Wilcoxon signed-rank tests. A significant augmentation of MEPs, independent of the level corresponding to the median nerve, was demonstrated. Furthermore, F-wave persistence was significantly increased not only in the median nerve but also in the tibial nerve after tetanic stimulation of the median nerve. The increased F-wave persistence indicates an increase of re-excited motor units in spinal anterior horn cells. These results confirm the hypothesis that tetanic stimulation of the peripheral nerve may cause remote augmentation of MEPs, primarily by increasing the excitability of the anterior horn cells.

Cervical Electrical Neuromodulation Effectively Enhances Hand Motor Output in Healthy Subjects by Engaging a Use-Dependent Intervention

Electrical enabling motor control (eEmc) through transcutaneous spinal cord stimulation is a non-invasive method that can modify the functional state of the sensory-motor system. We hypothesize that eEmc delivery, together with hand training, improves hand function in healthy subjects more than either intervention alone by inducing plastic changes at spinal and cortical levels. Ten voluntary participants were included in the following three interventions: (i) hand grip training, (ii) eEmc, and (iii) eEmc with hand training. Functional evaluation included the box and blocks test (BBT) and hand grip maximum voluntary contraction (MVC), spinal and cortical motor evoked potential (sMEP and cMEP), and resting motor thresholds (RMT), short interval intracortical inhibition (SICI), and F wave in the abductor pollicis brevis muscle. eEmc combined with hand training retained MVC and increased F wave amplitude and persistency, reduced cortical RMT and facilitated cMEP amplitude. In contrast, eEmc alone only increased F wave amplitude, whereas hand training alone reduced MVC and increased cortical RMT and SICI. In conclusion, eEmc combined with hand grip training enhanced hand motor output and induced plastic changes at spinal and cortical level in healthy subjects when compared to either intervention alone. These data suggest that electrical neuromodulation changes spinal and, perhaps, supraspinal networks to a more malleable state, while a concomitant use-dependent mechanism drives these networks to a higher functional state.

Evaluation of F wave and split hand index in patients with amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is characterized by gradual disturbance of both upper and lower motor neurons (LMN). In ALS, muscle wasting favors the abductor pollicis brevis (APB) and first dorsal interosseous (FDI), with relative preservation of abductor digiti minimi (ADM).

Objectives

To interpret F wave changes in the context of upper and LMN dysfunction and the differences in dysfunction between spinal motoneurons innervating the APB and ADM.

Patients and methods

Forty-four subjects were studied (22 patients with ALS and 22 controls). F wave was elicited by 50 electrical stimuli from the median and ulnar nerves, and the split hand index (SHI) was measured.

Results

F latency mean, median, and maximum and F amplitude mean, median, and maximum F/M amplitude ratio were increased in patients with versus those without pyramidal signs. Limb-onset ALS patients showed the biggest reduction in SHI. The APB muscle of patients with no detectable wasting and upper MN (UMN) signs showed reduced F wave persistence, mean F wave latency and amplitudes, increased index repeater neuron and index F repeater, and mean F/M amplitude ratio.

Conclusion

There is enhanced segmental motoneuronal excitability following UMN dysfunctions. SHI appears to be a diagnostic biomarker for ALS. Abnormal F parameters recorded from APB muscle can distinct patients with ALS from the normal controls to a greater extent than do the APB/ADM and FDI/ADM compound muscle action potential amplitude ratios.

Differential Changed Excitability of Spinal Motor Neurons Innervating Tibialis Anterior and Peroneus Muscles Cause Foot Inversion After Stroke

Objective: To study differential post-stroke changes of excitability of spinal motor neurons innervating a group of antagonist muscles of ankle and their effects on foot inversion.

Methods: F waves in tibialis anterior (TA) and peroneus muscles (PN) were recorded. The condition of spasticity and foot inversion in stroke patients were also evaluated. The differences of F wave parameters between patients and healthy controls (HC), as well as TA and PN, were investigated.

Results: There were natural differences in the persistence of the F waves (Fp) and F/M amplitude ratio (F/M) between TA and PN in HC. Stroke patients showed significantly higher F/M in TA and PN, while there was no difference in Fp comparing to HC. The natural differences in F wave parameters between TA and PN were differentially retained after stroke. The natural difference of the two muscles in Fp remained unchanged and the F/M difference disappeared in those without spasticity or foot inversion, while the Fp difference disappeared and the F/M difference remained in those with spasticity or foot inversion.

Conclusion: Based on the natural difference of the number and size of spinal motor neurons innervating TA and PN, their excitability may change differently according to the severity of the stroke, which may be the reason of foot inversion.

Clinical and Physiological Significance of F-Wave in Spinocerebellar Ataxia Type 3

Objective: To evaluate the characteristics of F-wave in spinocerebellar ataxia type 3 (SCA3) patients and preclinical carriers of SCA3 gene mutation (PreSCA3), and explore the relationship between disease severity and F-wave parameters and evaluate F-wave parameters as potential biomarkers for monitoring of disease progression in SCA3. Methods: We performed F-wave recordings in median, ulnar and tibial nerves of 39 SCA3 patients, 20 PreSCA3, and 27 healthy controls, and compared F-wave parameters between them. Results: In all nerves studied, the mean F-wave amplitude, maximum F-wave amplitude, and F/M amplitude ratio were significantly increased in the SCA3 patients in comparison with the normal controls. And the minimal F-wave latency of SCA3 patients was significantly prolonged and the F-wave persistence (%) was significantly decreased in the median nerve. For the PreSCA3, the maximum F-wave amplitude was significantly higher than normal controls for both median, ulnar, and tibial nerves. The mean F-wave amplitude and F/M amplitude ratio in all nerves were comparable between PreSCA3 and normal controls. The frequency of giant F-wave and frequency of patients with giant F-wave were similar between PreSCA3 and SCA3. The values of F/M amplitude ratio in both median, ulnar, and tibial nerves were correlated positively with disease severity and disease duration. Conclusion: Significant F-wave abnormalities occur in patients with SCA3, even in PreSCA3. F-wave may therefore reveal subclinical alterations and provide objective parameters for evaluating the progression of SCA3.

F-wave parameters for the tibial nerve in Miniature Dachshunds with and without naturally acquired thoracolumbar intervertebral disk herniation

OBJECTIVE

To determine values of F-wave parameters for the tibial nerve in clinically normal Miniature Dachshunds and those with thoracolumbar intervertebral disk herniation (IVDH).

ANIMALS

53 Miniature Dachshunds (10 clinically normal and 43 with various clinical grades of thoracolumbar IVDH).

PROCEDURES

F-waves were elicited in the interosseous muscles of 1 hind limb in each dog by stimulation of the tibial nerve. F-wave parameters were measured for 32 stimuli/dog, and mean values were calculated. Linear regression was performed to assess correlations between F-wave parameters and clinical severity of IVDH.

RESULTS

For clinically normal dogs, mean ± SD values of shortest F-wave latency, mean F-wave conduction velocity, mean F-wave duration, and ratio of the mean F-wave amplitude to M response amplitude were 8.6 ± 0.6 milliseconds, 83.7 ± 6.1 m/s, 6.6 ± 1.5 milliseconds, and 9.8 ± 8.5%, respectively. F-wave persistence was 100%. Mean F-wave duration was positively correlated with clinical grade of IVDH. Linear regression yielded the following regression equation: F-wave duration (milliseconds) = 6.0 + 2.7 × IVDH grade. One dog with grade 2 IVDH had a mean F-wave duration shorter than that of all 5 dogs with grade 1 IVDH; 1 dog with grade 3 IVDH had a longer duration than that of all 10 dogs with grade 4 IVDH.

CONCLUSIONS AND CLINICAL RELEVANCE

Mean F-wave duration was correlated with the severity of inhibitory motor tract dysfunction in the spinal cord of dogs. F-wave examination may be useful for objective functional evaluation of upper motor neurons in the spinal cord.

Immune-Mediated Neuropathies

The immune-mediated neuropathies are a broad category of diseases differentiated by time course, affected nerve fibers, and disease associations. This article spans the common, well-defined inflammatory demyelinating polyradiculoneuropathies (Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy) to the rarer, acquired demyelinating neuropathy variants (Miller-Fisher syndrome and multifocal motor neuropathy), vasculitic neuropathies, and sensory neuronopathies (dorsal root ganglionopathies). These case studies illustrate the characteristic clinical patterns of the immune-mediated neuropathies encountered in neurologic practice. Recommendations for diagnostic evaluation and treatment approach accompany each case. Prompt recognition of these disorders is imperative; delays in treatment may result in prolonged morbidity and permanent disability.

Electrodiagnostic Abnormalities Associated with Fibromyalgia

PURPOSE

Increasing evidence suggests that fibromyalgia most likely represents a neurological dysfunction. We previously hypothesized that at least some fibromyalgia cases may be caused by irritation of nerve root fibers and sensory neurons due to moderately increased cerebrospinal pressure. Because of the rostro-caudal hydrostatic pressure gradient, neurogenic abnormalities are expected to be most pronounced in sacral nerve roots. The purpose was to review electrodiagnostic tests of patients with fibromyalgia.

METHODS

A retrospective review of electrodiagnostic test results, including the lumbar and sacral nerve root myotomes of patients diagnosed with fibromyalgia according to the 1990 criteria of the American College of Rheumatology was done.

RESULTS

All 17 patients were female. Sural nerve responses could not be elicited in 12% and S1-Hoffmann reflex latencies were increased in 41%. In 12% of the patients, fibular motor nerve distal latency and conduction velocity were outside normal limits. Needle-EMG revealed neurogenic motor unit potentials in 0% of L2, 6% of L3, 29% of L4, 71% of L5, 47% of S1, 94% of S2, and 76% of S3-S4 myotomes. S3-S4 nerve-supplied anal reflexes were delayed in 94%.

CONCLUSION

This is the first time that electrodiagnostic data of both lumbar and sacral nerve root myotomes in fibromyalgia patients are presented. All patients showed neurogenic abnormalities that were more pronounced in the sacral than in the lumbar myotomes with a rather patchy distribution pattern. We propose that, in addition to skin punch biopsies to assess small fiber neuropathy, assessment of the anal reflex may be a useful part of the diagnostic pathway in patients with fibromyalgia.

The evolving role of surface electromyography in amyotrophic lateral sclerosis: A systematic review

OBJECTIVE

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease that leads to inexorable motor decline and a median survival of three years from symptom onset. Surface EMG represents a major technological advance that has been harnessed in the development of novel neurophysiological biomarkers. We have systematically reviewed the current application of surface EMG techniques in ALS.

METHODS

We searched PubMed to identify 42 studies focusing on surface EMG and its associated analytical methods in the diagnosis, prognosis and monitoring of ALS patients.

RESULTS

A wide variety of analytical techniques were identified, involving motor unit decomposition from high-density grids, motor unit number estimation and measurements of neuronal hyperexcitability or neuromuscular architecture. Some studies have proposed specific diagnostic and prognostic criteria however clinical calibration in large ALS cohorts is currently lacking. The most validated method to monitor disease is the motor unit number index (MUNIX), which has been implemented as an outcome measure in two ALS clinical trials.

CONCLUSION

Surface EMG offers significant practical and analytical flexibility compared to invasive techniques. To capitalise on this fully, emphasis must be placed upon the multi-disciplinary collaboration of clinicians, bioengineers, mathematicians and biostatisticians.

SIGNIFICANCE

Surface EMG techniques can enrich effective biomarker development in ALS.

Unpleasant visual stimuli increase the excitability of spinal motor neurons

Purpose: In physical therapy for post-stroke patients, we often experience cases in which unpleasant emotions cause abnormal muscle tonus. Previously, we suggested that the magnitude of spinal motor neuron excitability was correlated with the grade of muscle tonus. Therefore, spinal motor neuron excitability was considered to be a useful index to evaluate the influence of unpleasant emotions on muscle tonus. In this study, we investigated whether unpleasant emotions evoked by visual stimuli affected the excitability of spinal motor neurons.Materials and Methods: The F-waves, an indicator of spinal motor neuron excitability, were measured in 19 healthy adult volunteers. Firstly, for the rest trial, F-waves were measured during relaxation to determine the baseline of spinal motor neuron excitability. Following the rest trial, the unpleasant trial was conducted in which F-waves were measured while the subjects viewed an unpleasant picture for 1 min. After the unpleasant trial, F-waves were measured during relaxation. For the control condition, F-waves were measured while the subjects viewed a neutral picture instead of the unpleasant picture. The recorded F-wave data were analysed for persistence and the F/M amplitude ratio.Results: Persistence and the F/M amplitude ratio were significantly greater during the unpleasant trial than during the rest trial. In the control condition, there was no significant difference in persistence and the F/M amplitude ratio compared with the three trials.Conclusions: Our findings indicate that unpleasant emotions may affect spinal motor neuron excitability. Therefore, learning how to control emotions should be important aspect of physical therapy.

Zika virus infection causes temporary paralysis in adult mice with motor neuron synaptic retraction and evidence for proximal peripheral neuropathy

Clinical evidence is mounting that Zika virus can contribute to Guillain-Barré syndrome which causes temporary paralysis, yet the mechanism is unknown. We investigated the mechanism of temporary acute flaccid paralysis caused by Zika virus infection in aged interferon αβ-receptor knockout mice used for their susceptibility to infection. Twenty-five to thirty-five percent of mice infected subcutaneously with Zika virus developed motor deficits including acute flaccid paralysis that peaked 8-10 days after viral challenge. These mice recovered within a week. Despite Zika virus infection in the spinal cord, motor neurons were not destroyed. We examined ultrastructures of motor neurons and synapses by transmission electron microscopy. The percent coverage of motor neurons by boutons was reduced by 20%; more specifically, flattened-vesicle boutons were reduced by 46%, and were normalized in recovering mice. Using electromyographic procedures employed in people to help diagnose Guillain-Barré syndrome, we determined that nerve conduction velocities between the sciatic notch and the gastrocnemius muscle were unchanged in paralyzed mice. However, F-wave latencies were increased in paralyzed mice, which suggests that neuropathy may exist between the sciatic notch to the nerve rootlets. Reversible synaptic retraction may be a previously unrecognized cofactor along with peripheral neuropathy for the development of Guillain-Barré syndrome during Zika virus outbreaks.

F Wave Analyzer, a system for repeater F-waves detection: Application in patients with amyotrophic lateral sclerosis

OBJECTIVES

We assessed the clinical usefulness of repeater F-waves (Freps) analysis in amyotrophic lateral sclerosis (ALS), using an automated computerized system (F Wave Analyzer).

METHODS

Forty consecutive F-waves were recorded from the ulnar and peroneal nerve in 52 patients with ALS and 52 healthy control subjects. Data were imported into the F Wave Analyzer which identifies Freps and groups them. Parameters of Freps and non repeater F-waves (Fnonreps) were compared.

RESULTS

Total number of repeating neurons, Freps persistence (100xFreps/40stimuli) and Index Total Freps (100xFreps/total number of F-waves) were significantly higher in the ALS compared to the control group (P ≤ 0.005). There were no consistent differences of F-wave latency or amplitude measurements between Freps and Fnonreps for both studied groups, with the exception of prolonged Freps minimum latency in ALS.

CONCLUSION

In ALS, the high numbers of Freps, reduced overall F-wave persistence and increased F-wave amplitude measurements in a relatively unaffected nerve-muscle complex reflects excitability alterations of the corresponding motor neuron pool. Overall, automatic analysis facilitates accurate and fast detection of Freps and could be useful in other clinical settings.

SIGNIFICANCE

Analysis of repeater F-waves is expected to provide new insight regarding ALS pathophysiology and utilized for monitoring in clinical drug trials.

Imagery strategy affects spinal motor neuron excitability: using kinesthetic and somatosensory imagery

Motor imagery is the mental rehearsal of a movement within working memory. Reduction of spinal motor neuron excitability has been demonstrated after stroke, and motor imagery may increase spinal motor neuron excitability in patients with a motor deficit. However, spinal motor neuron excitability varies depending on the imagery strategy used. In this study, we examined spinal motor neuron excitability during kinesthetic, somatosensory, and combined imagery. Healthy adult volunteers (n=14) were recruited for F-wave recording. The F-wave was measured during relaxation to determine baseline levels, followed by measurement during the three imagery trials performed in a random order. In the somatosensory imagery (SI) trial, participants imagined tactile and pressure perception of the thumb finger pulp during holding a pinch meter. In the kinesthetic imagery (KI) trial, participants imagined muscle contraction during isometric thenar muscle activity at 50% maximal voluntary contraction. In the combined KI and SI trial, participants performed the KI and SI simultaneously. After F-wave recording, participants evaluated the difficulty of each imagery trial using a five-point Likert scale. Persistence during SI and KI was significantly higher than that at rest. The F/M amplitude ratio during KI was significantly higher than that at rest. The five-point Likert scale score of the combined KI and SI was significantly lower than that of KI. KI may increase spinal motor neuron excitability over that of SI. Thus, it is important to consider the sensory modality chosen for imagery during rehabilitation.

Does the duration of motor imagery affect the excitability of spinal anterior horn cells?

PURPOSE

Motor imagery, the process of imagining a physical action, has been shown to facilitate the excitability of spinal anterior horn cells. In the acute phase after a stroke, the excitability of spinal anterior horn cells is significantly reduced, which leads to motor deficits. This loss of movement can be prevented by increasing the excitability of spinal anterior horn cells immediately following an injury. Motor imagery is an effective method for facilitating the excitability of spinal anterior horn cells in patients with impaired movement; however, the optimal duration for motor imagery is unclear.

MATERIALS AND METHODS

To investigate time-dependent changes in spinal anterior horn cell excitability during motor imagery, healthy adult participants were recruited to measure the F-wave, an indicator of anterior horn cell excitability. F-waves were measured from participants at baseline, during motor imagery, and post-motor imagery. During motor imagery, participants imagined isometric thenar muscle activity at 50% maximum voluntary contraction for 5 min. F-waves were measured at 1, 3, and 5 min after beginning motor imagery and analysed for persistence and F/M amplitude ratio.

RESULTS

Persistence and F/M amplitude ratios at 1- and 3-min after motor imagery initiation were significantly greater than at baseline. The persistence and F/M amplitude ratio at 5-min after motor imagery initiation, however, was comparable to baseline levels.

CONCLUSION

Therefore, 1 to 3 min of motor imagery is likely sufficient to facilitate the excitability of spinal anterior horn cells.

Reversible conduction failure on the deep tendon reflex response recording in early Guillain-Barré syndrome

Objective

To describe the case of a patient with Guillain-Barré syndrome (GBS) showing early reversible conduction failure (RCF) detected by means of serial deep tendon reflex response (T-reflex) study.

Methods

A 36-year-old woman had a 5-day history of foot and hand paresthesias ascending to thighs and arms, throbbing interscapular and neck pain, mild to moderate tetraparesis, and areflexia. Nerve conduction studies (NCS) were performed on days 7 and 33 after onset.

Results

NCS showed an equivocal electrophysiologic pattern, just an isolated distal RCF being detected on the right radial nerve at initial examination. Motor latency on deltoid muscle after Erb's point stimulation was preserved. Sensory conduction velocities were normal or slightly slowed. Somatosensory evoked potentials from median and tibial nerves were normal. Initially, F-wave study demonstrated reversible abnormalities, consisting of multiple A waves and low F-wave persistence, minimal F-wave latencies being preserved. Biceps brachii T-reflex was normal, whereas Achilles T-reflex was absent bilaterally, appearing on the second study with normal T-wave morphology and latency, thus conforming to the requirements for RCF diagnosis. Soleus H-reflex was also initially absent.

Conclusions

Serial T-reflex study is a useful technique for detecting early RCF of proximal nerve trunks in early GBS.

Significance

T-reflex is useful tool for GBS in association with NCS.

Reduced GABAergic cortical inhibition in aging and depression

The neurobiology underlying depression in older adults is less extensively evaluated than in younger adults, despite the putative influence of aging on depression neuropathology. Studies using transcranial magnetic stimulation (TMS), a neurophysiological tool capable of probing inhibitory and excitatory cortical neurotransmission, have identified dysfunctional GABAergic inhibitory activity in younger adults with depression. However, GABAergic and glutamatergic cortical neurotransmission have not yet been studied in late-life depression (LLD). Here, we used single- and paired-pulse TMS to measure cortical inhibition and excitation in 92 LLD patients and 41 age-matched healthy controls. To differentiate the influence of age and depression, we also compared these TMS indices to those of 30 younger depressed adults and 30 age- and sex-matched younger healthy adults. LLD patients, older healthy adults, and younger depressed adults demonstrated significantly lower GABA_A receptor-mediated cortical inhibition than younger healthy controls. By contrast, no significant differences in cortical inhibition were observed between older adults with and without depression. No significant differences in GABA_B receptor-mediated inhibition or cortical excitation were found between the groups. Altogether, these findings suggest that reduced cortical inhibition may be associated with both advancing age and depression, which (i) supports the model of depression as a disease of accelerated aging, and (ii) prompts future investigation into diminished GABAergic neurotransmission in late-life as a biological predisposing factor to the development of depression. Given that cortical neurophysiology was similar in depressed and healthy older adults, future prospective studies need to establish the relative influence of age and depression on cortical inhibition deficits.

Assessment of neuroplasticity in late-life depression with transcranial magnetic stimulation

BACKGROUND

Studies using Transcranial Magnetic Stimulation (TMS), a non-invasive method of brain stimulation, have implicated impaired neuroplasticity in the pathophysiology of depression in younger adults. The role of neuroplasticity in late-life depression (LLD) has not yet been explored using TMS.

OBJECTIVE

This study aimed at evaluating motor cortical neuroplasticity using paired associative stimulation (PAS). Single-pulse TMS was used to induce motor-evoked potentials (MEP) in the contralateral hand muscle before and after PAS. The potentiation of MEP amplitudes after PAS was used as an indirect index of associative plasticity and long-term potentiation (LTP) (i.e. PAS-LTP).

RESULTS

48 older adults with depression and 34 age-matched healthy controls (HC) were compared. PAS- LTP was successfully induced in 68.8% of older adults with depression and 47.1% of HC. At the group level, older adults with depression failed to show statistically significant induction of neuroplasticity, which was observed in HC. However, no significant differences were observed between the two groups for PAS-LTP.

CONCLUSION

Our results suggest that associative plasticity does not differ substantially between older adults with depression and age-matched HC. Continued research is needed to more comprehensively understand the role of neuroplasticity in the pathophysiology of LLD.

Radial Nerve F-wave reference values with surface electrodes from the anconeus muscle

INTRODUCTION

We sought to obtain normative values for radial nerve F-wave variables, recording with surface electrodes from the anconeus muscle.

METHODS

We tested 30 healthy participants (17 women, 13 men) and measured the following variables: number of F waves/40 traces (F%); minimum, maximum, and mean F-wave latency (FMIN, FMAX, FMED, respectively); F-wave chronodispersion (FCHR); interside differences of F% and FMIN (DF% and DFMIN, respectively).

RESULTS

The mean F% was 41.3%; the normative values of FMIN, FMED, FMAX, and FCHR were < 21.2, <22.1, <23.3, and < 4.0 ms, respectively; and normative values of DF% and DFMIN were < 16.6% and < 1.1 ms, respectively. Height was the sole independent predictor in a regression model of FMIN, FMED, and FMAX; this explained 37%-44% of the variability.

DISCUSSION

We identified a feasible and useful technique to record radial nerve F waves from the anconeus muscle and obtained normative values of F-wave variables. Muscle Nerve 59:244-246, 2019.

Electrical nerve stimulation modulates motor unit activity in contralateral biceps brachii during steady isometric contractions

The purpose of our study was to compare the influence of five types of electrical nerve stimulation delivered through electrodes placed over the right biceps brachii on motor unit activity in the left biceps brachii during an ongoing steady isometric contraction. The electrical stimulation protocols comprised different combinations of pulse duration (0.2 and 1.0 ms), stimulus frequency (50 and 90 Hz), and stimulus current (greater or less than motor threshold). The electrical nerve stimulation protocols were applied over the muscle of the right elbow flexors of 13 participants (26 ± 3 yr) while they performed voluntary contractions with the left elbow flexors to match a target force set at 10% of maximum. All five types of electrical nerve stimulation increased the absolute amplitude of the electromyographic (EMG) signal recorded from the left biceps brachii with high-density electrodes. Moreover, one stimulation condition (1 ms, 90 Hz) had a consistent influence on the centroid location of the EMG amplitude distribution and the average force exerted by the left elbow flexors. Another stimulation condition (0.2 ms, 90 Hz) reduced the coefficient of variation for force during the voluntary contraction, and both low-frequency conditions (50 Hz) increased the duration of the mean interspike interval of motor unit action potentials after the stimulation had ended. The findings indicate that the contralateral effects of electrical nerve stimulation on the motor neuron pool innervating the homologous muscle can be influenced by both stimulus pulse duration and stimulus frequency. NEW & NOTEWORTHY Different types of electrical nerve stimulation delivered through electrodes placed over the right biceps brachii modulated the ongoing motor unit activity in the left biceps brachii. Although the effects varied with stimulus pulse duration, frequency, and current, all five types of electrical nerve stimulation increased the amplitude of the electromyographic activity in the left biceps brachii. Moreover, most of the effects in the left arm occurred after the electrical nerve stimulation of the right arm had been terminated.

Cortical involvement in celiac disease before and after long-term gluten-free diet: A Transcranial Magnetic Stimulation study

OBJECTIVE

Transcranial Magnetic Stimulation in de novo patients with Celiac Disease previously revealed an imbalance in the excitability of cortical facilitatory and inhibitory circuits. After a median period of 16 months of gluten-free diet, a global increase of cortical excitability was reported, suggesting a glutamate-mediated compensation for disease progression. We have now evaluated cross-sectionally the changes of cortical excitability to TMS after a much longer gluten-free diet.

METHODS

Twenty patients on adequate gluten-free diet for a mean period of 8.35 years were enrolled and compared with 20 de novo patients and 20 healthy controls. Transcranial Magnetic Stimulation measures, recorded from the first dorsal interosseous muscle of the dominant hand, consisted of: resting motor threshold, cortical silent period, motor evoked potentials, central motor conduction time, mean short-latency intracortical inhibition and intracortical facilitation.

RESULTS

The cortical silent period was shorter in de novo patients, whereas in gluten-free diet participants it was similar to controls. The amplitude of motor responses was significantly smaller in all patients than in controls, regardless of the dietary regimen. Notwithstanding the diet, all patients exhibited a statistically significant decrease of mean short-latency intracortical inhibition and enhancement of intracortical facilitation with respect to controls; more intracortical facilitation in gluten-restricted compared to non-restricted patients was also observed. Neurological examination and celiac disease-related antibodies were negative.

CONCLUSIONS

In this new investigation, the length of dietary regimen was able to modulate the electrocortical changes in celiac disease. Nevertheless, an intracortical synaptic dysfunction, mostly involving excitatory and inhibitory interneurons within the motor cortex, may persist. The clinical significance of subtle neurophysiological changes in celiac disease needs to be further investigated.

F-Wave Duration as a Specific and Sensitive Tool for the Diagnosis of Restless Legs Syndrome/Willis-Ekbom Disease

STUDY OBJECTIVES

Restless legs syndrome, also known as Willis-Ekbom disease (RLS/WED), is a frequent condition, though its pathophysiology is not completely understood. The diagnosis of RLS/WED relies on clinical criteria, and the only instrumental tool, the suggested immobilization test, may lead to equivocal results. Recently, neurophysiological parameters related to F-wave duration have been proposed as a diagnostic aid. The aim of this study is to assess and compare the diagnostic values of these parameters in diagnosis of RLS/WED.

METHODS

Fifteen women affected by primary RLS/WED and 17 age- and sex- matched healthy subjects. A complete electroneurographic evaluation, including nerve conduction studies (NCS), cutaneous silent period (CSP), and F-wave parameters, namely amplitude, F-wave duration (FWD), and the ratio between FWD and duration of the corresponding compound muscle action potential (FWD/CMAPD).

RESULTS

No subject showed alterations of the NCS. However, FWD and FWD/CMAPD of both upper and lower limbs were significantly longer in patients than controls. Tibial FWD/CMAPD best discriminated RLS/WED patients from controls. A cutoff of 2.06 yielded a sensitivity of 69.2%, a specificity of 94.1%, a positive predictive power of 90%, and a negative predictive power of 80% (area under the curve = 0.817; 95% confidence interval = 0.674-0.959). The combination of ulnar or tibial FWD/CMAPD increases the sensitivity (85.7%) while slightly decreasing the specificity (87.5%, positive predictive value: 85.7%, negative predictive value: 87.5%).

CONCLUSIONS

Lower limb FWD/CMAPD ratio may represent a supportive diagnostic tool, especially in cases of evening lower leg discomfort of unclear interpretation.

Cortical involvement in celiac disease before and after long-term gluten-free diet: A Transcranial Magnetic Stimulation study

OBJECTIVE

Transcranial Magnetic Stimulation in de novo patients with Celiac Disease previously revealed an imbalance in the excitability of cortical facilitatory and inhibitory circuits. After a median period of 16 months of gluten-free diet, a global increase of cortical excitability was reported, suggesting a glutamate-mediated compensation for disease progression. We have now evaluated cross-sectionally the changes of cortical excitability to TMS after a much longer gluten-free diet.

METHODS

Twenty patients on adequate gluten-free diet for a mean period of 8.35 years were enrolled and compared with 20 de novo patients and 20 healthy controls. Transcranial Magnetic Stimulation measures, recorded from the first dorsal interosseous muscle of the dominant hand, consisted of: resting motor threshold, cortical silent period, motor evoked potentials, central motor conduction time, mean short-latency intracortical inhibition and intracortical facilitation.

RESULTS

The cortical silent period was shorter in de novo patients, whereas in gluten-free diet participants it was similar to controls. The amplitude of motor responses was significantly smaller in all patients than in controls, regardless of the dietary regimen. Notwithstanding the diet, all patients exhibited a statistically significant decrease of mean short-latency intracortical inhibition and enhancement of intracortical facilitation with respect to controls; more intracortical facilitation in gluten-restricted compared to non-restricted patients was also observed. Neurological examination and celiac disease-related antibodies were negative.

CONCLUSIONS

In this new investigation, the length of dietary regimen was able to modulate the electrocortical changes in celiac disease. Nevertheless, an intracortical synaptic dysfunction, mostly involving excitatory and inhibitory interneurons within the motor cortex, may persist. The clinical significance of subtle neurophysiological changes in celiac disease needs to be further investigated.

Generation of Repeater F Waves in Healthy Subjects

PURPOSE

F waves identical in latency, size, and shape, known as repeater F waves, have been observed occasionally in normal motor conduction recordings. The purpose of this study was to examine the occurrence and characteristics of repeater F waves in healthy subjects under different testing conditions, aiming to selectively excite lower and higher threshold motor fibers.

METHODS

Sessions of 40 traces were recorded from the ulnar nerve in 12 volunteers, applying/using supramaximal, submaximal stimuli (intensity able to elicit 30% and 60% of the maximum compound muscle action potential amplitude), and a collision technique. Repeater F waves were identified and their numbers and relative frequency were estimated. For this purpose, a custom-designed software program was developed, to avoid misjudgments of simple visual inspection.

RESULTS

Repeater occurrence was significantly higher using 30% submaximal intensity compared with the standard supramaximal stimulation. There was an inverse significant association between repeater index and overall F wave quantity. Repeaters' latency, amplitude, and duration measurements were within the ranges of the nonrepeaters.

CONCLUSIONS

We herein showed that in healthy subjects the presence of repeater F waves might increase, when stimulation conditions other than standard single, supramaximal impulses were used. The frequency of repeaters was dependent on the overall F wave persistence, but there was no evidence to support a relationship with the type of motoneurons that was preferentially stimulated.

Clinical importance of F-waves as a prognostic factor in Guillain-Barré syndrome in children

PURPOSE

A limited number of studies have examined the link between F-wave abnormalities and clinical presentation in pediatric Guillain-Barré syndrome (GBS). Therefore, this study examined the importance of F-wave abnormalities as a prognostic factor in pediatric GBS patients.

METHODS

The records and electrodiagnostic studies (EDS) of 70 GBS patients were retrospectively evaluated, and divided into 2 groups according to the results of EDS. Group A (n=33) presented with F-wave abnormalities, and group B (n=26) exhibited normal findings. We compared laboratory reports, clinical features, response to treatment, and prognosis between the 2 groups.

RESULTS

Motor weakness was the most frequently observed symptom for either group. Clinically, the incidence of fever and upper respiratory symptoms differed between the 2 groups, while the prevalence of abnormal deep tendon reflex (DTR) was significantly higher in group A than B (P<0.05). Patients diagnosed with GBS had received intravenous immunoglobulin treatment: 94% in group A and 58% in group B. Furthermore, significantly greater numbers of patients in group A showed H-reflex abnormalities and poor prognosis compared with group B (P<0.05).

CONCLUSION

This study demonstrated that F-waves are a clinically important prognostic factor in GBS. F-wave abnormalities were associated with abnormal DTR and poor prognosis in patients. Limited studies have examined the link between F-wave abnormalities and clinical results; therefore, further randomized controlled studies are needed to confirm the clinical characteristics and efficacy of treatments.

A meta-analysis of the effects of aging on motor cortex neurophysiology assessed by transcranial magnetic stimulation

OBJECTIVE

Transcranial magnetic stimulation (TMS) is a non-invasive tool used for studying cortical excitability and plasticity in the human brain. This review aims to quantitatively synthesize the literature on age-related differences in cortical excitability and plasticity, examined by TMS.

METHODS

A literature search was conducted using MEDLINE, Embase, and PsycINFO from 1980 to December 2015. We extracted studies with healthy old (50-89years) versus young (16-49years) individuals that utilized the following TMS measures: resting motor threshold (RMT), short-interval cortical inhibition (SICI), short-latency afferent inhibition (SAI), cortical silent period (CSP), intracortical facilitation (ICF), and paired associative stimulation (PAS).

RESULTS

We found a significant increase in RMT (g=0.414, 95% confidence interval (CI) [0.284, 0.544], p<0.001), a significant decrease in SAI (g=0.778, 95% CI [0.478, 1.078], p<0.001), and a trending decrease in LTP-like plasticity (g=-0.528, 95% CI [-1.157, 0.100] p<0.1) with age.

CONCLUSIONS

Our findings suggest an age-dependent reduction in cortical excitability and sensorimotor integration within the human motor cortex.

SIGNIFICANCE

Alterations in the ability to regulate cortical excitability, sensorimotor integration and plasticity may underlie several age-related motor deficits.

Motor imagery muscle contraction strength influences spinal motor neuron excitability and cardiac sympathetic nerve activity

[Purpose] The aim of this study was to investigate the changes in spinal motor neuron excitability and autonomic nervous system activity during motor imagery of isometric thenar muscle activity at 10% and 50% maximal voluntary contraction (MVC). [Methods] The F-waves and low frequency/high frequency (LF/HF) ratio were recorded at rest, during motor imagery, and post-trial. For motor imagery trials, subjects were instructed to imagine thenar muscle activity at 10% and 50% MVC while holding the sensor of a pinch meter for 5 min. [Results] The F-waves and LF/HF ratio during motor imagery at 50% MVC were significantly increased compared with those at rest, whereas those during motor imagery at 10% MVC were not significantly different from those at rest. The relative values of the F/M amplitude ratio during motor imagery at 50% MVC were significantly higher than those at 10% MVC. The relative values of persistence and the LF/HF ratio during motor imagery were similar during motor imagery at the two muscle contraction strengths. [Conclusion] Motor imagery can increase the spinal motor neuron excitability and cardiac sympathetic nerve activity. Motor imagery at 50% MVC may be more effective than motor imagery at 10% MVC.

Excitability of spinal motor neurons during motor imagery of thenar muscle activity under maximal voluntary contractions of 50% and 100

[Purpose] We often perform physical therapy using motor imagery of muscle contraction to improve motor function for healthy subjects and central nerve disorders. This study aimed to determine the differences in the excitability of spinal motor neurons during motor imagery of a muscle contraction at different contraction strengths. [Subjects] We recorded the F-wave in 15 healthy subjects. [Methods] In resting trial, the muscle was relaxed during F-wave recording. For motor imagery trial, subjects were instructed to imagine maximal voluntary contractions of 50% and 100% while holding the sensor of a pinch meter, and F-waves were recorded for each contraction. The F-wave was recorded immediately after motor imagery. [Results] Persistence and F/M amplitude ratio during motor imagery under maximal voluntary contractions of 50% and 100% were significantly higher than that at rest. In addition, the relative values of persistence, F/M amplitude ratio, and latency were similar during motor imagery under the two muscle contraction strengths. [Conclusion] Motor imagery under maximal voluntary contractions of 50% and 100% can increase the excitability of spinal motor neurons. Differences in the imagined muscle contraction strengths are not involved in changes in the excitability of spinal motor neurons.

Inflammation in the pathogenesis of lyme neuroborreliosis

Lyme neuroborreliosis, caused by the spirochete Borrelia burgdorferi, affects both peripheral and central nervous systems. We assessed a causal role for inflammation in Lyme neuroborreliosis pathogenesis by evaluating the induced inflammatory changes in the central nervous system, spinal nerves, and dorsal root ganglia (DRG) of rhesus macaques that were inoculated intrathecally with live B. burgdorferi and either treated with dexamethasone or meloxicam (anti-inflammatory drugs) or left untreated. ELISA of cerebrospinal fluid showed significantly elevated levels of IL-6, IL-8, chemokine ligand 2, and CXCL13 and pleocytosis in all infected animals, except dexamethasone-treated animals. Cerebrospinal fluid and central nervous system tissues of infected animals were culture positive for B. burgdorferi regardless of treatment. B. burgdorferi antigen was detected in the DRG and dorsal roots by immunofluorescence staining and confocal microscopy. Histopathology revealed leptomeningitis, vasculitis, and focal inflammation in the central nervous system; necrotizing focal myelitis in the cervical spinal cord; radiculitis; neuritis and demyelination in the spinal roots; and inflammation with neurodegeneration in the DRG that was concomitant with significant neuronal and satellite glial cell apoptosis. These changes were absent in the dexamethasone-treated animals. Electromyography revealed persistent abnormalities in F-wave chronodispersion in nerve roots of a few infected animals; which were absent in dexamethasone-treated animals. These results suggest that inflammation has a causal role in the pathogenesis of acute Lyme neuroborreliosis.