Analysis of F response in upper motoneurone lesions

A prospective study on split-hand index as a biomarker for the diagnosis of amyotrophic lateral sclerosis

OBJECTIVE

To determine the practical diagnostic utility of split-hand index (SI) values calculated from F-wave persistence (SI_FP) and the F/M amplitude ratio (SI_F/M) for differentiating patients with amyotrophic lateral sclerosis (ALS) from other conditions. Methods: This prospective study recruited consecutive patients from Peking Union Medical College Hospital, China, between June 2019 and December 2019. Patients 18-80 years old who had clinical neuromuscular symptoms affecting the upper limbs and required electrophysiological examinations to aid diagnosis were eligible. Compound muscle action potentials (CMAPs) and F-waves recorded from the abductor pollicis brevis (APB), first dorsal interosseous muscle (FDI), and abductor digiti minimi (ADM) were examined. SI_FP and SI_F/M were calculated as: SI = (APB × FDI)/ADM. The sensitivity and specificity of SI_FP and SI_F/M in differentiating ALS from non-ALS conditions were derived using receiver operating characteristic (ROC) curves. Results: A total of 309 participants, comprising 91 (29.4%) with ALS and 218 (70.6%) with other neuromuscular disorders, were enrolled after 54 were excluded. SI_FP was significantly reduced and SI_F/M increased in the ALS group compared with the non-ALS group (p < 0.001). By ROC curve analysis, an SI_FP cutoff of 73.3 showed 85.7% sensitivity and 80.7% specificity for differentiating ALS from non-ALS. SI_F/M and SI_CMAP showed lower sensitivity (67% and 75.8%, respectively, p < 0.001) than SI_FP for ALS diagnosis. SI_FP and SI_F/M combined did not outperform SI_FP alone. Conclusion: SI_FP could be a sensitive, noninvasive neurophysiological diagnostic marker for ALS patients with affected upper limbs. In particular, an SI_FP value of 73.3 might be the optimal cutoff for diagnosing ALS.

Application of the F-Response for Estimating Motor Unit Number and Amplitude Distribution in Hand Muscles of Stroke Survivors

The F-response was used in this study to assess changes in the first dorsal interosseous (FDI) muscle after a hemispheric stroke. The number of motor units and their sizes were estimated bilaterally in 12 stroke survivors by recording both the compound muscle action potential (CMAP) and F wave responses. These F waves were induced by applying a large number of electrical stimuli to the ulnar nerve. The amplitude distribution of individual motor unit action potentials (MUAPs) was also compared between paretic and contralateral muscles. When averaged across all the subjects, a significantly lower motor unit number estimate was obtained for the paretic FDI muscle ( 88 ±13) compared with the contralateral side ( 139 ±11) ( ). Pooled surface MUAP amplitude analysis demonstrated a right-skewed distribution for both paretic (kurtosis 3.0) and contralateral (kurtosis 8.52) muscles. When normalized to each individual muscle's CMAP, the surface MUAP amplitude ranged from 0.22% to 4.94% (median 1.17%) of CMAP amplitude for the paretic muscle, and from 0.13% to 3.2% (median 0.62%) of CMAP amplitude for the contralateral muscle. A significant difference in MUAP outliers was also observed between the paretic and contralateral muscles. The findings of this study suggest significant motor unit loss and muscle structural reorganization after stroke.

The effect of electrical passive cycling on spasticity in war veterans with spinal cord injury

Introduction: Muscle atrophy, spasticity, and deformity are among long term complication of spinal cord injury (SCI) veterans. There are numerous studies evaluating effect of functional electrical stimulation on muscle properties of SCI people, but less research has focused on the benefits of passive cycling in the management of spasticity and improving ROM of lower limbs in individuals with SCI. Aims: To evaluate the effect of electrical passive cycling on passive range of movement spasticity and electrodiagnostic parameters in SCI veterans. Methods: Sixty-four SCI veterans referred to two clinical and research center in Tehran were recruited in this prospective clinical trial. The subjects were divided into two groups according to electrical passive cycling usage: (1) patients who did not use pedal exercise (control group), (2) patients used Electrical passive cycling up to optimal level (intervention group). Main outcome measures included hip, knee, and ankle range of motion, spasticity scale, and electrodiagnostic parameters including F-Wave Consistency, F-Wave Amplitude, H/M Ratio, F/M Ratio, H-Reflex Onset Latency, and H-Reflex Amplitude. Data were recorded at the time of receiving and 1 year after pedal exercise usage. Results: Sixty-four SCI patients including 95.3% male, 4.7% female with mean age 43 years old were included in this study. All patients except one suffered from complete SCI. The involved spinal levels were cervical (17.2%), upper thoracic (34.4%), lower thoracic (45.3%), and lumbar (3.1%). Spasticity scale decreased significantly after passive cycling in group 2. Also hip, knee, and ankle ROM in group 2 were significantly improved after pedal exercise. There was a significant difference in H max/M max (RT&LT) and F/M ratio after versus before electric passive cycling system in group 2. Conclusion: These findings suggest that passive rhythmic leg exercise can lead to decrease in spasticity, increase in passive ROM of lower limbs and improvement in electrodiagnostic parameters of spasticity in patients with SCI.

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.

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.

Evaluation of parameters of serially monitored F-wave in acute cervical spinal cord injury

OBJECTIVE

In this study, we aimed to determine how physicians can evaluate the severity of acute traumatic spinal cord injury (SCI) and predict the prognosis of this injury using the relationships of changes in clinical features and electrophysiological examination results.

MATERIALS AND METHODS

Serial recordings of F-waves were performed on 20 consecutive cervical SCI patients. In 12 of the patients, changes in several parameters of F-waves which were elicited by median and ulnar nerve stimulations were examined by analyzing their relationships to clinical symptoms.

RESULTS

The maximum amplitude of the F-waves (F-max) elicited by median nerve stimulation was found to be the most reliable (statistically significant) parameter for distinguishing clinically improved patients from nonimproved patients for the prognosis in the early stages after trauma. Other parameters, including the incidence of F-waves and the mean F-wave amplitude both of which were elicited by median nerve stimulation, were somewhat helpful for predicting the prognosis. These parameters of F-waves evoked by ulnar nerve stimulation could be useful for several weeks post-trauma.

Nitrous oxide can enhance the hypnotic effect, but not the suppression of spinal motor neuron excitability by propofol in humans

PURPOSE

We investigated whether nitrous oxide can enhance the suppressive effect of propofol on spinal motor neuron excitability in humans.

METHODS

Sixteen adult patients were prospectively randomly assigned to be given either propofol alone (group P; n = 8) or a supplement of 66% nitrous oxide with propofol (group PN; n = 8) for intraoperative sedation. Propofol was administered by a target-controlled infusion system to maintain sequentially increasing plasma propofol concentrations (Cpt) of 0.5, 0.8, 1.0, 1.3, 1.5 and 1.8 microg x ml(-1) in all patients. Assessment of the patient's level of sedation in both groups was performed with the Wilson Sedation Scale (WSS). F-wave analysis on the left abductor pollicis brevis muscle was carried out for the assessment of spinal motor neuron excitability at each plasma propofol concentration.

RESULTS

Significant differences in the WSS scores between group P and group PN were observed at 0.8, 1.0, 1.3, and 1.5 microg x ml(-1) of Cpt (group P < group PN; P < 0.01). Cpt greater than 1.0 microg x ml(-1) significantly reduced F-wave persistence in a concentration-dependent manner, and the ICpt 50 and ICpt 95 values for plasma propofol concentration (plasma propofol concentrations that produced 50% and 95% inhibition of the baseline, respectively) were 1.05 and 1.95 microg x ml(-1) in group P, and 1.07 and 2.14 microg x ml(-1) in group PN, respectively.

CONCLUSION

These results suggest that nitrous oxide can enhance the hypnotic effect, but not the suppression of spinal motoneuron excitability by propofol in humans at clinical levels of Cpt.

Ulnar F wave generation assessed within 3 days after the onset of stroke in patients with relatively preserved level of consciousness

OBJECTIVE

The present study aimed to detect any significant changes of F wave variables associated with acute hemiparesis in a group of stroke patients with relatively preserved consciousness (Glascow Coma Scale (GCS) score 8 or higher) and to detect the possible clinical significance of F wave recording in acute stroke patients for diagnostic purposes.

PATIENTS AND METHODS

Thirty-two consecutive patients with mean age 65+/-10.6 years admitted with a diagnosis of acute ischemic or primary hemorrhagic stroke were studied. A series of 40 electrical stimuli were delivered to the ulnar nerve bilaterally in order to obtain F waves. F wave studies were performed within 3 days from stroke's onset. The following variables were estimated and then compared between affected and unaffected side: F persistence, F wave latency, amplitude, duration and chronodispersion. A group of 30 healthy age-matched subjects served as control.

RESULTS

F persistence was significantly lower in both affected and unaffected sides as compared to controls. There was no statistical differences of latency values between control and either side of the stroke' patients. A significant decrease of maximum F wave amplitude was detected in both affected and unaffected side as opposed to controls. Separate analysis of the subgroup of 15 patients with stroke and completely normal level of consciousness (GCS score 15) did not showed any significant differences of F wave variables in the affected or unaffected side compared with controls.

CONCLUSION

The F wave persistence is not expected to be suppressed in the first few days after stroke unless the level of consciousness is reduced. The routine F wave studies are not appropriate to evaluate the severity of motor deficit, at least in the immediate period after a stroke incident.

Level of consciousness as a conditioning factor of F wave generation in stroke patients

OBJECTIVE

The current study aimed to investigate whether the level of consciousness influenced the F wave generation, as an independent factor.

METHODS

Forty three patients with acute stroke were divided according to their level of consciousness in two groups; to those with Glasgow scale (GCS) score 3-7 indicating coma (group I) and those with GCS score 8-15 (group II). A series of 40 electrical stimuli were delivered to the ulnar nerve bilaterally in order to obtain F waves. The following variables were estimated and then compared between groups: F persistence, F wave latency, amplitude and duration. All studies were performed within 3 days from the onset of the stroke symptoms.

RESULTS

The main finding to emerge was the significantly reduced F wave persistence in the group of patients with low GCS score as opposed to patients allocated in the group with GCS score 8-15. This result is referred to F waves obtained from both the affected and unaffected limb. F wave minimum latency was also prolonged in the group with low GCS score, whilst the comparison of all other F wave variables revealed no significant differences between groups I and II. F wave persistence measurements did not differ between the affected and unaffected sides. Stroke location and type (ischemic or hemorrhagic) were not associated with alterations of F wave measurements.

CONCLUSIONS

Our results on stroke patients suggest that generation of F waves, expressed by the F wave persistence is associated with the level of consciousness.

SIGNIFICANCE

F wave study may be useful as an objective measure in documenting the severity of consciousness impairment.

Motor neuron firing dysfunction in spastic patients with primary lateral sclerosis

Patients with corticospinal tract dysfunction have slow voluntary movements with brisk stretch reflexes and spasticity. Previous studies reported reduced firing rates of motor units during voluntary contraction. To assess whether this firing behavior occurs because motor neurons do not respond normally to excitatory inputs, we studied motor units in patients with primary lateral sclerosis, a degenerative syndrome of progressive spasticity. Firing rates were measured from motor units in the wrist extensor muscles at varying levels of voluntary contraction < or =10% maximal force. At each force level, the firing rate was measured with and without added muscle vibration, a maneuver that repetitively activates muscle spindles. In motor units from age-matched control subjects, the firing rate increased with successively stronger contractions as well as with the addition of vibration at each force level. In patients with primary lateral sclerosis, motor-unit firing rates remained stable, or in some cases declined, with progressively stronger contractions or with muscle vibration. We conclude that excitatory inputs produce a blunted response in motor neurons in patients with primary lateral sclerosis compared with age-matched controls. The potential explanations include abnormal activation of voltage-activated channels that produce stable membrane plateaus at low voltages, abnormal recruitment of the motor pool, or tonic inhibition of motor neurons.

F-waves: neurophysiology and clinical value

This review deals with F responses, which are late responses obtained by supramaximal stimulation of virtually all the motor and mixed peripheral nerves. They are recorded over a muscle innervated by the stimulated nerve. The first description of F-waves was published in the fifties. Their neurophysiological mechanisms have been abundantly discussed in the literature leading to a current consensus, whereby F-waves are considered as antidromic responses produced by a pool of motoneurons activated by peripheral nerve stimulation. In the first part of this review, the neurophysiological mechanisms of F-waves as well as the distinction between these and H reflexes are described from a historical point of view. Other late responses are intentionally not reported; nevertheless A-waves are discussed since they are frequently ill-described in a number of conditions. Stimulation and recording procedures as well as F-wave parameters analysis are detailed, with emphasis on measures most useful for clinical purposes. A rigorous F-wave recording method is mandatory for reliable and meaningful analyses. Physiological factors, which influence F-waves such as ageing, drugs and sleep, must be known and their effects discussed. Also, as maturation is an important factor in clinical neurophysiology, data on F-wave ontogenesis are reviewed and discussed. Finally, the different F-wave alterations described so far in the literature, in either peripheral or central disorders, are listed and commented. It is emphasised that F-waves are particularly useful for the diagnosis of polyneuropathies at a very early stage and for the diagnosis of proximal nerve lesions. F-wave recording is indeed one of the rare methods in routine examination allowing at the same time the functional assessment of motor fibres on their proximal segment, and contributing to the evaluation of motoneuronal excitability.

Neurophysiologic evaluation of spastic hypertonia: implications for management of the patient with the intrathecal baclofen pump

A number of techniques attempt to objectively quantify various clinical characteristics associated with spastic hypertonia and related motor disorders. These range in cost, complexity, physiologic basis of measured response, and invasiveness. With a greater range of treatment options for spasticity and an increase in the number of centers participating in studies of interventions for spasticity, published reports reflect increasing use of objective quantification techniques. We review studies that highlight the potential utility of neurophysiologic techniques, including the H-reflex, F-wave, and flexion withdrawal reflex, in the objective evaluation of response to intrathecal baclofen administration. The accumulated knowledge suggests that neurophysiologic evaluation is useful for assessing spinal cord responsiveness, and we recommend it as an adjunct to clinical evaluation when judging the overall effectiveness of intrathecal baclofen administration.

Lumbar repetitive magnetic stimulation reduces spastic tone increase of the lower limbs

STUDY DESIGN

Comparison of spinal lesion subjects and normal subjects.

OBJECTIVE

To investigate the effects of a paravertebral repetitive magnetic stimulation on spastic tone increase of the lower limbs.

SETTING

Munich, Germany.

METHODS

We compared the effects in 15 patients with different spinal lesions and in 16 healthy subjects. The spastic tone increase was evaluated clinically with the Ashworth scale and apparatively with the pendulum test, both at fixed times before and after stimulation. Unilateral stimulation was applied to the lumbar nerve roots L3 and L4 of the clinically more spastic leg.

RESULTS

The spastic tone decreased significantly in the interval between 4 and 24 h after stimulation. This effect was slightly more pronounced in the contralateral extremity. Furthermore, the stimulation motor threshold of the patients was significantly raised.

CONCLUSION

Repetitive magnetic unilateral stimulation has a positive effect on spastic tone increase due to spinal lesions, causing a decrease that lasts for about 1 day not only on the ipsilateral but also on the contralateral side.

Do F-wave measurements detect changes in motor neuron excitability?

The use of F waves to assess motor neuron excitability in experimental paradigms has never been validated. Our objective was to determine whether F-wave area, amplitude, and persistence measurements change in response to manipulations known to alter the excitability of motor neurons. The effects of muscle vibration, contraction of a remote muscle, and high-intensity stimulation of ipsilateral or contralateral fingers were assessed in 12 healthy volunteers. F-wave area, amplitude, and persistence all declined with ipsilateral cutaneous stimulation. The other maneuvers facilitated some, but not all, of the F-wave measurements. Changes in F-wave area and amplitude were correlated, but neither correlated with changes in persistence. A sample size of 50-75 F waves was needed to approximate amplitude and area results from 100 F waves with an accuracy of +/- 25%. We conclude that changes in F waves are better at detecting inhibition than facilitation of motor neurons. F waves reflect motor neuron excitability in a general way but do not allow for accurate measures of short-term changes in excitability.

Correlation between the M and F wave characteristics and the innervated muscle strength in spinal muscular atrophy

The purpose of this study is to elucidate the interrelation between the M and F wave characteristics of the median nerve and the grip power in patients with spinal muscular atrophy (SMA). The SMA patients showed decreased amplitudes of the M and F waves, decreased frequency of the F wave, and an increase of the F/M ratio as compared with the normative values. The F wave frequency and the amplitudes of M and F waves, which showed a significant linear correlation with each other, became lower in accordance with the decrease of grip power. The properties of M and F waves strongly correlated with the number of surviving motor neurons which would be fewer in those severely affected by SMA.

Clinical value of F-wave recordings in traumatic cervical spinal cord injury

F-waves and motor/sensory nerve conduction (NCS) of the median and ulnar nerves were examined in 66 patients with traumatic motoneurone lesion due to acute and chronic cervical spinal cord injury (SCI). The examinations were performed in parallel in chronic tetraplegics once and in acute tetraplegic patients monthly for the first 3 months, after 6 months and 1 year post-trauma. A pathological reduction of the compound muscle action potential (CMAP) (in 10% even a complete loss of the CMAP) was present in about 50% of the patients. The mean CMAP values of tetraplegic patients with either acute or chronic SCI were significantly (P < 0.001) reduced compared to normal subjects. Because sensory nerve conduction in these patients was normal, the reduction of CMAP should be due to damage of intramedullar motoneurones or anterior nerve roots. While in all chronic SCI patients with preserved CMAP F-waves could be elicited, 50% of the acute SCI patients showed a complete loss of F-waves of both nerves during the initial examination due to spinal shock. After 6 months all acute SCI patients with preserved motor potentials regained F-waves. Therefore, the excitability of F-waves is influenced by spinal shock in acute SCI. The mean F-wave latencies (Fmin-response, Fmin-M response) revealed no significant difference between healthy subjects and SCI patients. However, the frequency of F-wave production was related to the severity of the motoneurone lesion. Furthermore, while the F-wave latencies and CMAP values did not change significantly with time after acute SCI, the frequency of F-wave production increased, but remained reduced compared to normal subjects.

Cortical modulation of spinal excitability: an F-wave study

F-waves are known to be highly sensitive to changes in the excitatory state of the spinal cord. This paper describes the effects of subthreshold transcranial magnetic stimulation on the F-waves evoked in hand and foot muscles. In the abductor pollicis brevis muscle, the F-wave was significantly enhanced when the cortical stimulus was given with a delay corresponding approximately to the expected time of collision, i.e., the difference between the mean latency of the F-wave and the mean latency of the motor evoked potential. A second, usually larger facilitatory phase follows the first phase after 2-3 msec, and later peaks of enhancement often occurred. After the enhancement periods, a significant inhibition of the F-wave was usually observed. In the extensor digitorum brevis muscle, the first facilitatory phase was observed some milliseconds earlier than expected in 4 of 5 subjects, and the inhibitory phase was less pronounced. We argue that the sequential arrival of I-waves at the spinal segment could be responsible for the changes observed in the F-wave recorded from the small hand muscle. In the foot muscle, anatomical and technical factors could contribute to the generation of a D-wave. The strong inhibition observed in the F-wave recorded from the hand muscle is likely to be due to the arrival on alpha-motoneurons of inhibitory postsynaptic potentials (IPSPs) generated by the cortical stimulus. Our data show that the F-wave ia a probe for changes in the spinal cord excitatory state.

F wave in acute cerebellar damage

Studies of occurrence of the F wave can be considered as a method of assessment of excitability of the spinal cord motoneurones. So far it has been analyzed in relation to the damage to the pyramidal and extrapyramidal systems. In the present paper, various parameters of the F response (maximal and mean amplitude-absolute and in relation to the M response, frequency of occurrence of all and identical F waves, minimal latency and chronodyspersion) were given analysis in 15 patients with hypotonia after acute cerebellar damage, and in 35 healthy subjects. In the patients, the F response was found to be decreased in amplitude (mean-absolute and ratio to M) and in frequency. Therefore, a conclusion can be drawn that it confirms the decrease of segmental motoneurone excitability after cerebellar damage.

Influence of baclofen upon the alpha-motoneuron in spasticity by means of F-wave analysis

Intrathecal baclofen dramatically improves severe spastic syndromes. This improvement is likely related to reduced excitability of alpha-motoneurons. To investigate the influence of baclofen upon the alpha-motoneuron, we analyzed F-waves before and after intrathecal baclofen bolus injection (usually 50 micrograms) as well as after administration of different, constantly delivered doses (60-200 micrograms/day). Intrathecal baclofen bolus decreased the maximum F-wave amplitude (Fp) from an initial value of 9% of the maximum M amplitude (Mmax) (= F/M-ratio) to 2.4% of the Mmax after 130-180 min, reduced the mean F-wave amplitude 60% within 150 min, and shortened the mean duration by 40-60% after 130-180 min. Constantly delivered baclofen of 100 micrograms/day reduced the F/M-ratio from 5% to 2%, the mean F-wave amplitude by 40-80%, and the F-wave mean duration by 40-80%. The minimum F-wave latency did not change after bolus or during steady state administration. The findings indicate that the F-wave mean and maximum amplitude as well as the mean duration are altered in a quantifiable manner following intrathecal baclofen application.

Absent F-waves early in a case of transverse myelitis

A 29-year-old female presented with acute onset of interscapular pain, followed by weakness of both legs and both hands, and a thoracic sensory level. F-waves in her legs and arms were absent initially, but other conduction studies were normal. An initial spine MRI was normal but a second study 10 days later revealed an enlarged spinal cord with areas of enhancement. Repeat neurophysiologic studies showed return of F-waves in the legs and absent compound muscle action potential (CMAP) in the hands with early denervation on needle examination. An acute intraxial lesion needs to be included in the differential diagnosis of absent F-waves.