Is Video-Oculography a Predictive Test for Myasthenia Gravis with Ocular Symptoms?

Background and Objective: The aim of this study was to evaluate the contribution of extraocular muscle function testing with video-oculography (VOG), which is a noninvasive and easily applicable method of recording eye movement with digital cameras, to the diagnosis of myasthenia gravis (MG) in patients without any clinical eye movement abnormalities. Methods and Materials: The study included 18 patients prediagnosed with ocular MG: MG Group (N = 7) with abnormal, and non-MG Group (N = 11) with normal single-fiber electromyography. Control group included 50 healthy volunteers. Ocular movements were recorded with the EyeSeeCam VOG device. Results: The inward latency of the 10° horizontal saccade and the downward latency of the 10° vertical saccade were significantly delayed; and the downward amplitude of the 10° vertical saccade was significantly lower in the MG group. Receiver operating characteristic curve analyses showed high specificity values for the discrimination of MG patients. Conclusions: This study supports the usefulness of the VOG device in revealing subclinical extraocular muscle involvement in MG.

Parameters derived from compound muscle action potential scan for discriminating amyotrophic lateral sclerosis-related denervation.

INTRODUCTION: The objective of this study was to determine compound muscle action potential (CMAP) scan parameters and MScanFit motor unit number estimation (MUNE) in patients with amyotrophic lateral sclerosis (ALS) and to compare the results in the abductor pollicis brevis (APB) to those in the abductor digiti minimi (ADM). METHODS: CMAP scans were recorded from the APB and ADM in 35 patients with ALS and 21 controls. MScanFit MUNE, neurophysiological index (NI), step%, returner%, and D50 were calculated. RESULTS: CMAP scan parameters including the returner%, MScanFit MUNE, and NI can distinguish ALS with high sensitivity and specificity. The electrophysiological parameters, with the exception of D50 (the number of largest consecutive differences of recorded responses generating 50% of maximum CMAP), showed more pronounced changes in the APB than in the ADM, even though most of the patients had normal APB/ADM amplitude ratios. DISCUSSION: CMAP scan parameters and MScanFit MUNE can be used in the evaluation of denervation and reinnervation and may herald the "split hand" in ALS.

Analysis of motor unit firing characteristics in patients with motor neuron diseases.

This study was designed to evaluate firing rate variability in patients with upper/lower motor neuron disorders. Twenty healthy subjects and 19 patients with motor neuron disorders participated in the study. Consecutive motor unit action potential pairs from extensor digitorum communis (EDC) muscle were recorded from each subject with trigger-delay line mode. Patients with motor neuron disorders (17.7 ± 10.8 ms) showed significantly higher mean time variability of interpotential interval value than healthy volunteers (10.3 ± 0.1 ms) (p < 0.001).

The effect of recording site on extracted features of motor unit action potential.

Motor unit action potential (MUAP), which consists of individual muscle fiber action potentials (MFAPs), represents the electrical activity of the motor unit. The values of the MUAP features are changed by denervation and reinnervation in neurogenic involvement as well as muscle fiber loss with increased diameter variability in myopathic diseases. The present study is designed to investigate how increased muscle fiber diameter variability affects MUAP parameters in simulated motor units. In order to detect this variation, simulated MUAPs were calculated both at the innervation zone where the MFAPs are more synchronized, and near the tendon, where they show increased temporal dispersion. Reinnervation in neurogenic state increases MUAP amplitude for the recordings at both the innervation zone and near the tendon. However, MUAP duration and the number of peaks significantly increased in a case of myopathy for recordings near the tendon. Furthermore, of the new features, "number of peaks×spike duration" was found as the strongest indicator of MFAP dispersion in myopathy. MUAPs were also recorded from healthy participants in order to investigate the biological counterpart of the simulation data. MUAPs which were recorded near to tendon revealed significantly prolonged duration and decreased amplitude. Although the number of peaks was increased by moving the needle near to tendon, this was not significant.

Does vitamin B alter the efficacy of botulinum toxin?

Botulinum toxin prevents acetylcholine release at motor nerve terminals. Group B vitamins (B-vit) are essential for proper nerve function. The present study addresses the question of whether B-vit accelerate recovery in rat skeletal muscle after botulinum toxin A (Btx-A) injection. Forty-four adult male Wistar albino rats were used in this experimental study. Rats were divided into three groups: group 1 rats were given Btx-A injection only, group 2 rats were given B-vit supplementation before Btx-A injection, and group 3 rats were given Btx-A and B-vit injections together. During the experiment, compound muscle action potential (CMAP) of the gastrocnemius muscle was recorded before Btx-A injection and sequentially ten times after toxin injection. The statistical significance of the CMAP amplitude change among the groups was analyzed. All groups showed similar amplitude change between consecutive measurement points. In conclusion, combining Btx-A injection with B-vit supplement does not decrease the efficacy of the toxin.

Classification of juvenile myoclonic epilepsy data acquired through scanning electromyography with machine learning algorithms.

In this paper, classification of Juvenile Myoclonic Epilepsy (JME) patients and healthy volunteers included into Normal Control (NC) groups was established using Feed-Forward Neural Networks (NN), Support Vector Machines (SVM), Decision Trees (DT), and Naïve Bayes (NB) methods by utilizing the data obtained through the scanning EMG method used in a clinical study. An experimental setup was built for this purpose. 105 motor units were measured. 44 of them belonged to JME group consisting of 9 patients and 61 of them belonged to NC group comprising ten healthy volunteers. k-fold cross validation was applied to train and test the models. ROC curves were drawn for k values of 4, 6, 8 and 10. 100% of detection sensitivity was obtained for DT, NN, and NB classification methods. The lowest FP number, which was obtained by NN, was 5.

Excitability changes at brainstem and cortical levels in blind subjects.

OBJECTIVES: This study was designed to search potential changes in trigemino-facial system in blind subjects by the use of relatively well-established electrophysiological methods. Excitability changes in the motor cortex were also investigated by transcranial magnetic stimulation studies (TMS) with the expectation of finding some abnormal interactions between the cortex and brainstem. METHODS: Twenty blind (BS) and 13 control subjects (CoS) were included in the study. Blink reflex and its recovery with paired electrical stimulation were studied at 150, 200, 300, 400 and 500 ms interstimulus intervals (ISI). Facial F waves elicited by buccal branch stimulation were recorded from nasalis muscles. Motor cortex excitability with recordings from left first dorsal interosseus muscle was studied by using magnetically elicited silent periods and paired magnetic stimuli, subthreshold conditioning and suprathreshold test, given at ISIs of 2, 3, 4, 10, 12, 15 and 20 ms. RESULTS: Blink reflex recovery was significantly reduced in BS group comparing to CoS at 400 and 500 ms ISIs. This difference between the groups was more prominent for the responses evoked by the initial stimulation side and faded away with stimulations on the contralateral side. Facial F wave amplitudes and F/M amplitude ratios were higher in BS group. In TMS studies, the early inhibitions at 2 and 4 ms were found to be significantly less in BS as compared to that of CoS. CONCLUSIONS: The reduced blink reflex recovery and its fast restoration with continuing stimulation might be explained by conditioning and extinction processes which have been shown to be mainly carried out by cerebellar-brainstem pathways. Our TMS studies showed reduced intracortical inhibition in the motor cortices of BS cases and facial F wave studies revealed the possible effect of this altered excitability on the facial motor nuclei. SIGNIFICANCE: Firing probabilities of facial motor neurons in BS are probably determined by the equilibrium between the low-set excitability of blink reflex interneurons and the enhanced excitability brought on by the descending motor pathways.

Decrement pattern in Lambert-Eaton myasthenic syndrome is different from myasthenia gravis.

The decrement pattern at low rates of repetitive nerve stimulation in myasthenia gravis (MG) is characterized by a decrease of compound muscle action potential size within the first 4-5 responses. With subsequent stimuli, compound muscle action potential size either increases or does not change. Following an observation that the pattern of decrement might be different in patients with Lambert-Eaton myasthenic syndrome (LEMS), we retrospectively studied traces from eight LEMS patients and 14 patients with seropositive generalized MG, calculating decrement percent from first to fourth and from first to ninth compound muscle action potential. In the LEMS patients, compound muscle action potential amplitude decreased progressively from first to ninth stimulus at 2, 3 or 5Hz in all traces but one. In contrast, MG patients demonstrated the expected improvement after the initial decrement in all traces except one. In the evaluation of patients suspected of having myasthenia gravis, the finding of progressive decrement pattern at low rates of repetitive nerve stimulation may alert the electromyographer to the possibility of Lambert-Eaton syndrome and prompt the performance of further electrodiagnostic tests.

Abnormal neuromuscular transmission in cluster headache.

OBJECTIVE: To identify and investigate any dysfunction of neuromuscular transmission in episodic cluster headache. BACKGROUND: Abnormal neuromuscular transmission has been shown in migraine with aura and in migraine without aura by using single fiber electromyography. Especially for migraine with aura, a genetic cause has been postulated. Episodic cluster headache is a primary headache disorder in which genetic factors may, at times, play a strong role. METHODS: Single fiber electromyography during voluntary contraction of the extensor digitorum communis muscle, nerve conduction studies of upper and lower extremities, and concentric needle electromyography of the extensor digitorum communis were performed on 6 patients with episodic cluster headache and 6 age-matched normal controls. Twenty potential pairs were recorded from each subject. Twenty individual jitter values and a mean jitter value were calculated for each subject. Both mean individual jitter values and numbers of abnormal individual jitter values were compared in patients with cluster headache versus normal controls. RESULTS: Three of 6 patients with episodic cluster headache showed pronounced neuromuscular transmission abnormalities by single fiber electromyography. None of the controls had any neuromuscular transmission abnormality. Another patient with episodic cluster headache had borderline dysfunction of neuromuscular transmission. Transmission was clearly normal in only 2 of 6 patients with cluster headache. CONCLUSION: These results suggest that episodic cluster headache may share the same abnormality of neuromuscular transmission observed in migraine.

Effect of triggering potential on calculations of jitter in single-fiber EMG.

Jitter values are calculated in reference to a triggering potential during single-fiber electromyography (SFEMG) performed during voluntary contraction. When there are more than two single-fiber action potentials (SFAP) and the selected triggering potential is from an abnormal end-plate, all the jitters calculated from the same trace will be affected. In this study, the effect of triggering potential on calculated jitter was investigated in myasthenic and healthy volunteers by switching the triggering potential and recalculating the jitter off-line. Selecting a triggering potential from an abnormal end-plate increased the number of abnormal individual jitters as well as the mean jitter. Therefore, if the equipment software has the capacity to change the trigger potential, the triggering potential should not be from an abnormal end-plate if all possible jitter values are to be calculated for traces having three or more single-fiber potentials. Otherwise, only one jitter value should be included from any one trace to prevent false-positive results.

Compound muscle action potential analysis in different death models: significance for the estimation of early postmortem interval.

In this experimental study, we investigated the varieties of excitability of gastrocnemius muscle via sciatic nerve as per different death models (asphyxia, abundant-bleeding and gradual-bleeding) on rats and the significance for the estimation of postmortem interval was evaluated. For this purpose, the rats were applied different stimulus intensities (5, 20, 40 mA) with 0.1 ms duration, before, during and every 5 min after death, using rectangular impulses, and the mean amplitude, onset latency and area values for each compound muscle action potential (CMAP) were elicited. It was detected that amplitude and area increased and onset latencies prolonged in the first postmortem 15 min. From the 15 min, CMAP area and amplitude showed an ever-increasing decrease and the prolongation of onset latencies became apparent. The decrease rate of area and amplitude was found to be statistically significantly different in asphyxia and abundant-bleeding models compared with in gradual-bleeding model, at 30 min measurements. However, there was not any significant difference in onset latency increase rates of three groups. Separately, any significant correlation between the agony and excitability periods among the groups could not be detected. The fact that the increase rate of onset latency did not show a significant difference as per death models indicated that onset latency ratios would be more appropriate criteria in determination of postmortem interval, regardless the reason of death.

Surface stimulation single-fiber electromyography in myasthenia gravis.

Surface stimulation for single-fiber electromyography has been proposed previously as a novel technique based on a study performed on healthy subjects. The current study was designed to determine the diagnostic value of surface stimulation single-fiber electromyography in patients with myasthenia gravis. Ten patients with myasthenia gravis were recruited for the study. Surface stimulation of the facial nerve trunk, as well as extramuscular needle stimulation of its zygomatic branch was performed. Twenty single-fiber potentials were recorded from the orbicularis oculi muscle for each stimulation type in each patient. For both stimulation techniques, mean jitter values and the total number of abnormal individual junctions were found to be abnormally high. Jitter values obtained by surface stimulation were comparable with those obtained by needle stimulation.