China
Africa
Explore chapters and articles related to this topic
Neurologic Diagnosis
Published in Philip B. Gorelick, Fernando D. Testai, Graeme J. Hankey, Joanna M. Wardlaw, Hankey's Clinical Neurology, 2020
The electrical (not mechanical) potential is recorded over a standard anatomical location of muscle, usually active electrode over end-plate region and reference electrode over the distal tendon. The recorded orthodromic compound muscle action potential (CMAP) is the summated evoked response of the muscle produced by stimulation of its motor nerve (e.g. abductor digiti minimi with ulnar stimulation) (Figure 1.44a). The CMAP is filtered, amplified, and displayed on a digital screen.
Tumours of the Facial Nerve
Published in John C Watkinson, Raymond W Clarke, Christopher P Aldren, Doris-Eva Bamiou, Raymond W Clarke, Richard M Irving, Haytham Kubba, Shakeel R Saeed, Paediatrics, The Ear, Skull Base, 2018
Patrick R. Axon, Samuel A.C. MacKeith
Electroneurography (ENoG) has been advocated as a method for calculating the proportion of facial nerve motor neurons lost to tumour compression. It measures the compound muscle action potential (CMAP) to maximal bipolar stimulation of the facial nerve at the stylomastoid foramen. The investigation is used as an aid in the management of acute facial paralysis because it indicates the severity of Wallerian degeneration in the days after onset of facial weakness. ENoG, however, does have its drawbacks. It relies on comparison of the maximal CMAP derived from the muscles of the affected and normally functioning side and has a poor test–retest reliability. It is particularly inaccurate for assessing longstanding or slowly progressive facial palsy, for two important reasons. First, it is unable to take into account terminal collateral sprouting in response to nerve injury, which increases the number of muscle fibres each motor neuron innervates. Second, it cannot differentiate between motor neurons that are functioning normally across the site of tumour compression and those in conduction block. As such, a clinical assessment of facial function using the House-Brackmann grading system provides a pragmatic assessment for guiding management decisions. Some units do advocate the use of ENoG to monitor for subclinical deterioration in nerve function as an additional factor when considering surgical intervention.11
Neuromuscular disorders
Published in Ashley W. Blom, David Warwick, Michael R. Whitehouse, Apley and Solomon’s System of Orthopaedics and Trauma, 2017
The nerve under study (usually a mixed motor and sensory nerve) is stimulated electrically at an easily accessible subcutaneous site (e.g. the forearm or wrist for the median nerve or behind the medial malleolus for the posterior tibial nerve), until it propagates an action potential which travels to the innervated muscle where a surface electrode records the response (Figure 10.7). Measurements are displayed on an oscilloscope screen, the most informative being the time it takes in milliseconds (ms) for the impulse to reach the muscle, called the latency, and the magnitude of the response evoked in millivolts (mV), called the amplitude of the evoked compound muscle action potential (CMAP). By measuring the distance from the stimulating electrode to the recording electrode, and setting this against the latency, one can deduce the nerve conduction velocity (NCV) in metres per second between those two points (Figure 10.8).
Comparison of the Effects of Extracorporeal Irradiation and Liquid Nitrogen on Nerve Recovery in a Rat Model
Published in Journal of Investigative Surgery, 2021
Hüseyin Kaya, Dündar Sabah, Burçin Keçeci, Levent Küçük, Oytun Erbaş, Fatih Oltulu, Gürkan Yiğittürk, Dilek Taskiran
Electrophysiological studies are often used for the diagnosis of neuromuscular and neuropathic disorders. The compound muscle action potential (CMAP) recording is a minimally invasive and reliable method which enables to evaluate nerve conduction both in human and animal studies. In peripheral nerve pathologies, the measurement of CMAP amplitudes and latencies provides important information about the axonal loss and demyelination. The distance between the negative and positive peaks in the CMAP curves (p–p distance) obtained by submaximal stimulation is called amplitude. The duration between the stimulus and onset of CMAP is referred as latency (Figure 3). As described in previous studies, while axonal pathologies cause a substantial reduction in the CMAP amplitude, the loss in myelin thickness results in prolonged of distal latency and reduced conduction velocity [17–20].
Phrenic nerve study as outcome in clinical trials for amyotrophic lateral sclerosis
Published in Amyotrophic Lateral Sclerosis and Frontotemporal Degeneration, 2021
Susana Pinto, Mamede De carvalho
Diaphragmatic compound muscle action potential (CMAP) was elicited bilaterally by percutaneous bipolar electrical phrenic nerve stimulation at the neck (posterior to the middle lateral border of the sternocleidomastoid muscle). Recordings used surface electrodes (with filter setting 20–10 kHz) with the active electrode (G1) positioned at the homolateral costosternal angle and the reference electrode (G2) at the costal margin 16 cm from the active electrode, as described elsewhere (10–15); responses were recorded at the end of expiration to assure diaphragm relaxation (16). Brachial plexus responses were avoided by repositioning the stimulating electrode. A minimum of three consistent motor responses were recorded from each side and the response with the highest peak-to-peak amplitude was selected. The mean peak-to-peak amplitude value (meanPhrenAmpl) of both right- and left-side responses was used for the analyses, considered as an inclusion criterion and follow-up outcome. A cutoff equal or above 0.4mV was chosen as inclusion criterion for normality, as mentioned before in the literature (10).
Mexiletine (NaMuscla) for the treatment of myotonia in non-dystrophic myotonic disorders
Published in Expert Opinion on Orphan Drugs, 2020
Karen J. Suetterlin, Dipa Raja Rayan, Emma Matthews, Michael G Hanna
There is also good evidence of mexiletine’s effect on weakness in NDM. In the RCT, the patient-reported weakness severity score reduced while on mexiletine by 1.26 (p < 0.01) while in the aggregated n-of-1 trial the probability of a clinically meaningful reduction in weakness was 87%. This effect is also supported by neurophysiological studies. The neurophysiological correlate of weakness in NDM is a drop in compound muscle action potential (CMAP) on exercise testing. CMAP drop is cold-induced and exacerbated by repetition in PMC, improved by repetition in recessive MC and tends not to alter significantly during short exercise testing in dominant MC and SCM [4]. In 1994 Jackson and Barohn demonstrated increased compound muscle action potentials (CMAP) on the short exercise test following mexiletine therapy in a patient with PMC [32]. Maintenance of CMAP amplitude has also been reported in response to repetitive stimulation in MC patients taking mexiletine [40], implying that mexiletine is effective at reducing the transient weakness that can be associated with recessive MC.