F-Wave Characteristics as Surrogate Markers of Spasticity in Patients With Secondary Progressive Multiple Sclerosis

Application of new waveform analysis methods reflecting F-wave diversity -classification of F-wave diversity according to differences in the derived muscles

Background

The F wave waveforms show diversity according to the number and size of re-firing cells, but there is still no analytical method that reflects this feature. We previously reported that five classifications of F waves are obtained from the ulnar nerve. However, the diversity of F waves derived from the lower extremities may not be similar. We therefore compared the diversity of F waves in the upper and lower extremities in healthy subjects.

New method

F waves were measured during tibial nerve stimulation in 26 healthy subjects. The amount of amplitude decrease was calculated from the amplitude value after the additive averaging process and based on the average amplitude value of each stimulus, and the relationship between the peak latency and density was examined.

Results

The amount of amplitude decrease due to the additive averaging process was negatively correlated with the density of negative peaks. The diversity of F waves could be categorized into four class based on the histograms.

Comparison with existing method

The new method uses a novel additive average method that reflects the diversity of F waves. Furthermore, it uses a histogram to visualize the cancellation between waveforms.

Conclusion

We developed an analysis method that reflects the diversity of F waves in a novel manner, which visualizes cancellation between waveforms using a histogram.

Excitability of anterior horn cells after periodic or discrete repetitive movements

INTRODUCTION/AIMS

It has been well established that spasticity interferes with smooth joint movements. Although the degree of spasticity is related to the excitability of anterior horn cells and is thought to improve after repetitive movements, the effect of the rhythm of repetitive movements on the excitability of anterior horn cells remains unknown. Therefore, we investigated the excitability of anterior horn cells after periodic and discrete repetitive movements using F waves.

METHODS

Right-handed, healthy subjects were recruited for this study. Subjects then performed periodic or discrete repetitive thumb abduction movements for 10 seconds, measuring the F waves before, immediately after, and then 2 and 4 minutes after performing these movements. Specifically, the F waves were recorded from the abductor pollicis brevis muscle, after median nerve stimulation at the wrist. Next, the F/M amplitude ratio, which was used to evaluate the excitability of anterior horn cells, was compared before, immediately after, and 2 and 4 minutes after each task.

RESULTS

A total of 12 subjects participated in this study. In the periodic task, the F/M amplitude ratio was found to be significantly decreased immediately after the task compared with before the task, but there was no significant difference between the other trials. Conversely, in the discrete task, there was no significant difference in the F/M amplitude ratio between trials.

DISCUSSION

Periodic repetitive movements were found to temporarily reduce the excitability of anterior horn cells.

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.

Repeater F-waves in amyotrophic lateral sclerosis: Electrophysiologic indicators of upper or lower motor neuron involvement?

OBJECTIVE

To extract insight about the mechanism of repeater F-waves (Frep) by exploring their correlation with electrophysiologic markers of upper and lower motor neuron dysfunction in amyotrophic lateral sclerosis (ALS).

METHODS

The correlations of Frep parameters with clinical scores and the results of neurophysiological index (NI), MScanfit MUNE, F/M amplitude ratio (F/M%), single and paired-pulse transcranial magnetic stimulation (TMS), and triple stimulation technique (TST) studies, recorded from abductor digiti minimi (ADM) and abductor pollicis brevis (APB) muscles of 35 patients with ALS were investigated.

RESULTS

Frep parameters were correlated with NI and MScanfit MUNE in ADM muscle and F/M% in both muscles. None of the Frep parameters were correlated with clinical scores or TST and TMS measures. While the CMAP amplitudes were similar in the two recording muscles, there was a more pronounced decrease of F-wave persistence in APB, probably heralding the subsequent split hand phenomenon.

CONCLUSION

Our findings suggest that the presence and density of Freps are primarily related to the degree of lower motor neuron loss and show no correlation with any of the relatively extensive set of parameters for upper motor neuron dysfunction.

SIGNIFICANCE

Freps are primarily related to lower motor neuron loss in ALS.

Assessing muscle compliance in stroke with the Myotonometer

BACKGROUND

This study explores changes of the intrinsic biomechanical property in the biceps brachii muscle after a hemispheric stroke using the Myotonometry technique.

METHODS

Nineteen subjects with chronic hemiplegia participated in the study. Myotonometer was used to measure tissue displacement when compression force was applied at 8 levels from 2.45N to 19.6N. Muscle displacement and compliance were determined and averaged over multiple trials.

FINDINGS

Statistical analysis indicated a significant decrease in muscle displacement and compliance in the spastic muscles compared with the contralateral side (muscle displacements: spastic: 4.51 (0.31) mm, contralateral: 5.74 (0.37) mm, p<0.005; compliance: spastic: 0.17 (0.011) mm/N, contralateral: 0.22 (0.014) mm/N, p<0.005). Correlation analysis, however, did not show any association between clinical assessments and myotonometric measurement (p>0.1).

INTERPRETATION

Alterations of muscle compliance in the spastic side reflect changes in the contractile or intrinsic mechanical properties after a stroke. Findings of the study have demonstrated high sensitivity and effectiveness of the Myotonometer in assessing muscle compliance changes.

Importance of sample size for the estimation of repeater F waves in amyotrophic lateral sclerosis

BACKGROUND

In amyotrophic lateral sclerosis (ALS), repeater F waves are increased. Accurate assessment of repeater F waves requires an adequate sample size.

METHODS

We studied the F waves of left ulnar nerves in ALS patients. Based on the presence or absence of pyramidal signs in the left upper limb, the ALS patients were divided into two groups: One group with pyramidal signs designated as P group and the other without pyramidal signs designated as NP group. The Index repeating neurons (RN) and Index repeater F waves (Freps) were compared among the P, NP and control groups following 20 and 100 stimuli respectively. For each group, the Index RN and Index Freps obtained from 20 and 100 stimuli were compared.

RESULTS

In the P group, the Index RN (P = 0.004) and Index Freps (P = 0.001) obtained from 100 stimuli were significantly higher than from 20 stimuli. For F waves obtained from 20 stimuli, no significant differences were identified between the P and NP groups for Index RN (P = 0.052) and Index Freps (P = 0.079); The Index RN (P < 0.001) and Index Freps (P < 0.001) of the P group were significantly higher than the control group; The Index RN (P = 0.002) of the NP group was significantly higher than the control group. For F waves obtained from 100 stimuli, the Index RN (P < 0.001) and Index Freps (P < 0.001) of the P group were significantly higher than the NP group; The Index RN (P < 0.001) and Index Freps (P < 0.001) of the P and NP groups were significantly higher than the control group.

CONCLUSIONS

Increased repeater F waves reflect increased excitability of motor neuron pool and indicate upper motor neuron dysfunction in ALS. For an accurate evaluation of repeater F waves in ALS patients especially those with moderate to severe muscle atrophy, 100 stimuli would be required.

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.

F Wave Study in Amyotrophic Lateral Sclerosis: Assessment of Segmental Motoneuronal Dysfunction

Background:

Dysfunctional spinal circuit may play a role in the pathophysiology of amyotrophic lateral sclerosis (ALS). The purpose of this study was to use F waves for assessment of segmental motoneuronal excitability following upper motor neuron (UMN) dysfunctions in ALS.

Methods:

We studied the F waves of 152 ulnar nerves recorded from abductor digiti minimi in 82 patients with ALS. Two groups of hands were defined based on the presence or absence of pyramidal signs in the same upper limb. The group with pyramidal signs in the upper limbs was designated as the P group, and the group without pyramidal signs in the upper limbs was designated as the NP group.

Results:

The mean (P < 0.001), median (P < 0.001) and maximum (P = 0.035) F wave amplitudes, mean (P < 0.001), median (P < 0.001) and maximum (P = 0.003) F/M amplitude ratio, index repeating neuron (P < 0.001) and index repeater F waves (P < 0.001) of the P group were significantly increased compared with the NP group. No significant differences were identified for F wave chronodispersion (P = 0.628), mean F wave latency (P = 0.151), minimum F wave latency (P = 0.211), maximum F wave latency (P = 0.199), F wave persistence (P = 0.738), F wave duration (P = 0.152), F wave conduction velocity (P = 0.813) and number of giant F waves (P = 0.072) between the two groups.

Conclusions:

In this study, increased F wave amplitude, F/M amplitude ratio and number of repeater F waves reflected enhanced segmental motoneuronal excitability following UMN dysfunctions in ALS.

Activity-dependent depression of the recurrent discharge of human motoneurones after maximal voluntary contractions

Despite maximal voluntary effort, the output of human motoneurone pools diminishes during fatigue. To assess motoneurone behaviour, we measured recurrent discharges evoked antidromically by supramaximal nerve stimulation after isometric maximal voluntary contractions (MVCs).They were measured as F-waves in the electromyographic activity (EMG). Supramaximal stimuli to the common peroneal and ulnar nerves evoked F-waves at rest before and after MVCs in tibialis anterior (TA) and abductor digit minimi (ADM), respectively. F-waves were depressed immediately after a sustained MVC. For TA, the size and time course of depression of the F-wave area (26 ± 13%; mean ± SD; P =0.007) and persistence (∼20%) were similar after a 10-s or 1-min MVC. For ADM, the decline in F-wave area (39.8 ± 19.6%; P <0.01) was similar after the two contractions but the decline in persistence (probability of occurrence) of the F-wave differed (14.6 ± 10.5% and 32.5 ± 17.1% after 10-s and 1-min MVCs respectively). Comparison of a very long (2-min) with a very short (2-s)MVC in ADM showed that the depression of F-wave area, as well as persistence, was greater after the longer contraction. This suggests, at least for ADM, that the depression is related to the duration of voluntary activity and that the decrease in F-waves could contribute to central fatigue. To examine whether changes in motor axon excitability caused the depression, we measured compound muscle action potentials (M-waves) to submaximal stimulation of the ulnar nerve after a 2-s and 2-min MVC. Submaximal M-waves were not depressed after a 2-s MVC. They were depressed by a 2-min MVC, but the time course of depression of the F- and M-waves differed. Thus, depression of F-waves does not simply reflect reduced excitability of peripheral motor axons.Hence, we propose that activity-dependent changes at the soma or the initial segment depress the recurrent discharge of human motoneurones and that this may contribute to central fatigue.