Repeater F-waves Research Articles

Repeater F-waves: Clinical Importance and Distinction from A-waves

ABSTRACT Aim: The aim of this study was to distinguish repeater F-waves (Frep) from A-waves by measuring the amplitude and ratio and investigating their relationship with neuromuscular diseases (NMDs). Materials and Methods: We retrospectively reviewed and compared the Frep records of 414 patients with different NMDs and 162 control subjects with normal electrophysiologic findings. Optimal cutoff points were determined using receiver operating characteristic curves, yielding >99% specificity versus A-waves. Results: The sensitivity at each derived cutoff point for the median, ulnar, peroneal, and tibial nerves were 58.5% for ≥340 uV, 46.2% for ≥350 μV, 13.1% for ≥560 μV, and 50.1% for ≥410 μV, respectively. However, the Frep/M-response amplitude ratio demonstrated very low sensitivity. The occurrence of repeater F-waves (Freps) was similar in patients with primary demyelination and axonal degeneration (P > 0.05); however, it was higher than that in control subjects (P < 0.017). The Frep amplitudes in patients with primary demyelination were significantly lower than in patients with axonal degeneration and control subjects (P < 0.017). The M-response amplitude negatively correlated with the occurrence of Freps and positively correlated with the F-wave persistence (P < 0.001). Discussion: The amplitude parameter appears to be an essential criterion for assessing late potentials, which may help differentiate Freps from A-waves, thereby facilitating the accurate detection of Freps. The increased occurrence of Freps indicates dysfunction of lower motor neurons, independent of the pathophysiologic process.

Unique clinical and electrophysiological features in the peripheral nerve system in patients with sialidosis – a case series study

BackgroundTo investigate the peripheral nervous system involvement in S sialidosis with typical features of myoclonus, seizure, and giant waves in somatosensory evoked potentials suggesting hyperexcitability in the central nervous system.MethodsThe clinical presentation of patients with genetically confirmed sialidosis was recorded. Neurophysiological studies, including nerve conduction studies (NCSs), F-wave studies, and needle electromyography (EMG), were performed on these patients.ResultsSix patients (M/F: 2:4) were recruited. In addition to the classical presentation, intermittent painful paresthesia was noted in four patients, and three of whom reported it as the earliest symptom. In the NCSs, one patient had reduced compound muscle action potential amplitudes in the right ulnar nerve, while another patient had prolonged distal motor latency in the bilateral tibial and peroneal nerves. Prolonged F-wave latency (83.3%), repeater F-waves (50%), and neurogenic polyphasic waves in EMG (in 2 out of 3 examined patients) were also noted. Interestingly, a very late response was noted in the F-wave study of all patients, probably indicating lesions involving the proximal peripheral nerve or spinal cord.ConclusionIn addition to the central nervous system, the peripheral nervous system is also involved in sialidosis, with corresponding clinical symptoms. Further study on these phenomena is indicated.

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

ObjectiveTo 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). MethodsThe 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. ResultsFrep 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. ConclusionOur 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. SignificanceFreps are primarily related to lower motor neuron loss in ALS.

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

ObjectivesWe assessed the clinical usefulness of repeater F-waves (Freps) analysis in amyotrophic lateral sclerosis (ALS), using an automated computerized system (F Wave Analyzer). MethodsForty 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. ResultsTotal 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. ConclusionIn 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. SignificanceAnalysis of repeater F-waves is expected to provide new insight regarding ALS pathophysiology and utilized for monitoring in clinical drug trials.

An algorithm for automatic detection of repeater F-waves and MUNE studies

The present study aims to develop an algorithm and software that automatically detects repeater F-waves which are very difficult to analyze when elicited as high number of recordings in motor unit number estimation studies. The main strategy of the study was to take the repeater F waves discriminated by the neurologist, from limited number of recordings, as the gold standard and to test the conformity of the results of the new automated method.Ten patients with ALS and ten healthy controls were evaluated. 90 F-waves with supramaximal stimuli and 300 F-waves with submaximal stimuli were recorded. Supramaximal recordings were evaluated both manually by an expert neurologist and automatically by the developed software to test the performance of the algorithm. The results both acquired from the neurologist and from the software were found compatible. Therefore, the main expected impact of the present study is to make the analysis of repeater F waves easier primarily in motor unit number estimation studies, since there is currently a continuing need for such automated programs in clinical neurophysiology.Submaximal recordings were examined only by the developed software. The extracted features were: maximum M response amplitude, mean power of M response, mean of sMUP values, MUNE value, number of baskets, persistence of F-waves, persistence of repeater F-waves, mean of F-waves’ powers, median of F-waves’ powers. Feature selection methods were also applied to determine the most valuable features. Various classifiers such as multi-layer perceptron (MLP), radial basis function network (RBF), support vector machines (SVM) and k nearest neighbors (k-NN) were tested to differentiate two classes. Initially all features, then decreased numbers of features after feature selection process were applied to the aforementioned classifiers. The classification performance usually increased when decreased features were applied to intelligent systems. Ulnar recordings under submaximal stimulation showed better performance when compared with supramaximal equivalents or median nerve equivalents. The highest performance was obtained as 90% with k-NN algorithm which was a committee decision based classifier. This result was achieved with only two features, namely mean of sMUP amplitude and MUNE value.

F52. Repeater F-waves: Electrophysiologic manifestations of upper or lower motor neuron involvement?

The aim of this study is to compare repeater F-wave parameters with CMAP amplitudes recorded from the hand muscles (as indicators of the amount of lower motor neuron [LMN] loss) and with the triple stimulation technique (TST) ratios in the same muscles (as indicators of upper motor neuron [UMN] involvement) in 19 patients with amyotrophic lateral sclerosis (ALS). Ninety F-waves were recorded from thenar and hypothenar muscles by supramaximal stimuli applied to the relevant nerves at the wrist level. Repeater F-waves (Frep) were visually defined as those presented with the same amplitude, latency and shapes. Repeater neuron (RN) index, Frep index, persistances of F-waves, F/M amplitude ratio and the neurophysiologic index (NI) were calculated. By depending our laboratory normals, TST ratio values lower than 82% and 86% were accepted as abnormal showing UMN involvement in thenar and hypothenar muscles respectively. TST ratios were abnormal in 13 thenar and 11 hypothenar muscles. None of the Frep parameters showed any significant relationship with the abnormal TST ratios, except the lower Frep index in thenar muscles, in patients with UMN involvement according to low TST ratios. However, there was a strong negative correlation with the CMAP amplitudes and Frep index and RN index values in hypothenar muscle (Spearman’s rho, p < 0.001). These findings imply that repeater F waves might be a manifestation of LMN loss more than being a result of UMN involvement.

S101. A novel automatized F-wave MUNE method: A preliminary analysis

Introduction The aim of this study was to test a novel automatized F-wave MUNE method by comparing its results with those elicited with the manual method performed in patients with amyotrophic lateral sclerosis (ALS) and healthy controls. Methods Ninety F-waves elicited with supramaximal stimuli were recorded from thenar and hypothenar muscles in 10 ALS patients and 4 healthy controls. For manual analysis, F-waves with the same amplitude, latency and shape were selected visually by the same examiner. For automatized analysis, similar signals were grouped according to latencies of negative and positive peaks and peak-to-peak amplitudes in MATLAB by using the original software developed for this study. The mean amplitudes of F-waves repeating more than once were defined as sMUPs and MUNE value for each case was calculated by dividing the CMAP amplitude by mean sMUP amplitude. Results Data of two healthy controls and 1 ALS patient were excluded from the analysis since no repeater F-waves were detected by one of the methods. sMUP and F-wave MUNE values calculated by both methods were found to be highly correlated (Spearman’s rho, p μ V and 406.55 μ V, respectively in thenar muscles and 412.53 μ V and 332.77 μ V in hypothenar muscles). Similar F-wave MUNE values were also calculated by using both methods (26.00 and 28.58, respectively in thenar muscles and 36.04 and 30.18 in hypothenar muscles). Conclusion Our automatized F-wave MUNE method seems to be promising in reflecting motor unit numbers in the hand muscles in patients with ALS and healthy controls.

P351 The assessment of repeater F-waves in patients with amyotrophic lateral sclerosis

Objectives Repeater F-waves (Freps) were seen in patients with amyotrophic lateral sclerosis (ALS). The factors implicated for the presence and frequency of Freps were loss of the motor neurons and the changes in their excitability. The aim of this study was to assess the Freps in ALS patients and to compare their frequencies in thenar and hypothenar muscles. Methods Sixteen ALS patients and 11 healthy controls were recruited to the study. All patients had ⩾2 mV CMAPs recorded from the hand muscles. Ninety F-waves were recorded from abductor digiti minimi (ADM) and abductor pollicis brevis (APB). The index of repeater neurons (RN) and Freps were calculated. Results Mean index RN and index Freps values of ADM and APB muscles in ALS group (17.1 and 42.6 for ADM and 16.3 and 41.9 for APB) were significantly higher than those of healthy controls (4.7 and 13.9 for APB and 1.5 and 3.6 for ADM). ALS group had a lower persistence of F-waves for both muscles than healthy controls (56.4 and 94.6 for APB and 83.4 and 97.0 for ADM). Freps parameters were not different between thenar and hypothenar muscles, whereas persistence of F-waves was lower in the thenar (56.4%) as compared to the hypothenar (83.4%) muscles. Discussion Similar Freps parameters in the thenar and hypothenar muscles might be caused by the inclusion criteria. Lower F-persistence in the thenar muscles was in accordance with the split-hand phenomenon. Conclusion The assessment of Freps and F persistence may be useful in understanding of the electrophysiological changes in ALS.

A study of dynamic F-waves in juvenile spinal muscular atrophy of the distal upper extremity (Hirayama disease)

ObjectiveThe study aimed to analyse changes in the upper limb F-waves during neck flexion in patients with Hirayama disease (HD). Material and methodsThis study included 41 healthy subjects, 38 HD patients and 24 patients with amyotrophic lateral sclerosis (ALS). Bilateral F-waves were consecutively recorded 20 times with the neck both in the standard position and after persistent neck flexion for 30min. The persistence, minimal latencies, chronodispersion, F/M ratios and amplitudes of the F-waves and repeater F-waves were compared between the standard neck and neck flexion positions. ResultsDuring neck flexion, repeater F-waves were found in more HD patients, the percentage of both the ulnar and median repeater F-waves increased significantly, and higher F/M ratios were observed on the symptomatic side (P<0.05). No differences in the F-waves were observed in the healthy subjects or the ALS patients during neck flexion (P>0.05). DiscussionHD might be more likely to present as a position-related dysfunction rather than a spinal cord-intrinsic disease. Thus, HD patients could be counselled to avoid neck flexion for long periods of time to prevent further damage, especially in the progressive stage of the disease.

Differences in Dysfunction of Thenar and Hypothenar Motoneurons in Amyotrophic Lateral Sclerosis.

This study aimed to determine differences in spinal motoneuron dysfunction between the abductor pollicis brevis (APB) and the abductor digiti minimi (ADM) in amyotrophic lateral sclerosis (ALS) patients based on studying F-waves. Forty ALS patients and 20 normal controls (NCs) underwent motor nerve conduction studies on both median and ulnar nerves, including F-waves elicited by 100 electrical stimuli. The F-wave persistence (P < 0.05), index repeating neuron (RN; P < 0.001), and index repeater F-waves (Freps; P < 0.001) significantly differed between the APB and the ADM in the NC participants. For the hands of the ALS patients that lacked detectable wasting or weakness and exhibited either no or mild impairment of discrete finger movements, significantly reduced F-wave persistence (P < 0.001), increased index RN (P < 0.001), and increased index Freps (P < 0.001) were observed in APB in comparison with the normal participants, with relatively normal ADM F-wave parameters. For the hands of ALS patients that exhibited wasting and weakness, the mean F-wave amplitude (P < 0.05), the F/M amplitude ratio (P < 0.05), F-wave persistence (P < 0.001), index RN (P < 0.05), and index Freps (P < 0.05) significantly differed between APB and ADM. The differences in the dysfunction of motoneurons innervating APB and ADM are unique manifestations in ALS patients. The F-wave persistence (P = 0.002), index RN (P < 0.001), and index Freps (P < 0.001) in the APB seemed to differentiate ALS from the NCs more robustly than the ADM/APB Compound muscle action potential (CMAP) amplitude ratio. Thus, F-waves may reveal subclinical alterations in anterior horn cells, and may potentially help to distinguish ALS from mimic disorders.

1-A-D-13. Repeater F-waves may be derived from the reinnervated type I motor unit in polio survivors

Despite our previous report that repeater F-waves are characteristic findings in polio survivors, the origin of these repeater F-waves remains to be clarified. In this study, 43 polio survivors (polio group) and 20 healthy age- and height-matched volunteers (control group) underwent motor conduction studies of their bilateral median and tibial nerves, including F-waves elicited by 100 stimuli. The polio group showed significantly prolonged F-wave minimal latency in the median nerve compared to the controls. The mean F-wave amplitude was not significantly different between the groups. Concerning the repeater F-waves in the polio group, minimal latencies were significantly prolonged, and their mean amplitudes were significantly higher than for the non-repeater F-waves of both nerves. According to publications on muscle pathology, polio survivors show a characteristic predominance of type I muscle fibers. Therefore, these repeater F-waves, with a prolonged minimal latency and high amplitude, might be derived from the reinnervated type I motor unit. These findings suggest that repeater F-waves could indicate motor unit pathophysiology in polio survivors.

Repeater F-waves are signs of motor unit pathology in polio survivors.

ABSTRACTIntroductionThe purpose of this study was to determine whether F‐waves reveal electrophysiological features of anterior horn cells in polio survivors.MethodsForty‐three polio survivors and 20 healthy controls underwent motor nerve conduction studies of the median and tibial nerves bilaterally, including sampling of F‐waves elicited by 100 stimuli and the determination of motor unit number estimation (MUNE).ResultsA significant increase in abnormally stereotyped (“repeater”) F–waves and a reduction of F‐wave persistence were observed in both nerves in the polio group as compared with the control group. Repeater F‐waves had a negative correlation with MUNE.ConclusionsThese trends in F‐wave persistence and repeater F‐waves after motor unit loss are characteristic findings in polio survivors. Repeater F‐waves are a sign of motor unit pathology. Muscle Nerve 51:680–685, 2015

P533: Repeater F-waves are early signs of motor unit pathology in polio survivors

P533: Repeater F-waves are early signs of motor unit pathology in polio survivors

Usefulness of assessing repeater F‐waves in routine studies

Repeater F-waves are sometimes seen in routine studies. We retrospectively reviewed the clinical significance of repeater F-waves in median, ulnar, and fibular nerve recordings in 50 healthy subjects and groups of 50 patients each with diabetic polyneuropathy, amyotrophic lateral sclerosis, carpal tunnel syndrome, ulnar mononeuropathy, and L5 root lesion. The number of identical F-waves and their repetitions in samples of 20 stimuli were estimated. Repeater F-waves occurred significantly more frequently in all nerves and patient groups than in healthy individuals. Their persistence was negatively correlated with that of non-repeater F-waves. Based on the presented material and recording condition it appears that repeater F-waves differentiate between health and disease but not between different types of pathology of motor neurons or their axons. Even in routinely recorded samples of 20 traces, the index of repeater all F-waves could be used as a sign of nerve pathology.

Presence of repeater F‐waves in the early stage of Guillain‐Barré syndrome

The absence or a prolonged latency of late responses, like F-waves, is a common neurophysiological finding with diagnostic utility in the early Guillain-Barré syndrome. However, the presence and the number of repeater F-waves have not been studied in this disease. In four patients, we report the transient presence of repeater F-waves in nerves of the lower limbs shortly after the onset of the disease. In each patient, the initial (diagnostic) nerve conduction study showed a high incidence of repeater F-waves in the tibial or in the peroneal nerves of one side, with normal distal motor latencies; in the other nerves explored the F-waves were fully abolished and the motor potentials were abnormal. In a second study, done 2-6 weeks later, we observed the abolition of the F-waves or a significant increase of its minimal latency in those nerves in which we had detected the repeaters. The presence of a high number of repeater F-waves with normal latencies in some nerves may be a transient and initial electrophysiological sign useful in the early diagnosis of this disease.

A study of F‐waves in patients with unilateral lumbosacral radiculopathy

The F wave, a late response of low amplitude, is widely used in the study of peripheral nerve lesions, and its persistence and latencies are the main parameters that are usually considered. The analysis of repeater F-waves, which are commonly observed in association with focal or generalized motor neuropathy, is not always performed as a standard electrodiagnostic protocol. We recorded and quantified the F waves from 13 healthy subjects and 22 patients with unilateral lumbosacral radiculopathy (ULSR) affecting the L5 or S1 roots. We found differences between the injured and normal sides of patients with ULSR in several F-wave parameters. Taking into consideration the normalized and pooled values of tibial and peroneal nerves in the injured side of patients with ULSR, the minimum and mean latencies were higher (1.05 and 1.04 with respect to 1.00; P < 0.01), the relative amplitude of the F waves was higher (1.95 with respect to 1.00; P < 0.001), and the percentage of repeater F-waves was also higher (4.19 with respect to 1.00; P < 0.001). This latter parameter was the most sensitive to detect lateral differences as indicated by the percentage of change and its high z score. Our results show that the use of F-waves may improve the electrodiagnosis of the ULSR if the number of repeater waves is evaluated given the clear and consistent increase of this variable in patients with lumbosacral root injury.