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Background: In motor nerve conduction studies (MNCS), proximal stimulation should give a longer duration and lower amplitude compound muscle action potential (CMAP) due to higher temporal dispersion. Yet the CMAP waveforms at the distal and proximal stimulation sites appear remarkably similar. The objective of this study was to confirm this anomaly and investigate its possible cause by studying the median and ulnar nerves. Methods: Recordings from 50 subjects with normal electrodiagnostic studies were reviewed. The conduction velocity (CV) was measured using different points on the negative phase of the CMAP including its peak and baseline crossing. Collision studies were performed in three healthy subjects to measure the dispersion when nerve action potentials (APs) propagated from elbow to wrist. Results: CV was relatively unaffected by the measurement point on the CMAP. The CMAP duration with elbow stimulation increased minimally compared to wrist stimulation. This was inconsistent with the dispersion of the AP from wrist to elbow measured in collision studies. Discussion: The insignificant change in the CMAP in spite of axon AP dispersion is an enigma. We hypothesize that the terminal conduction time (TCT) (i.e., conduction in terminal axon branches, neuromuscular transmission, etc.) is independent of axon CV, represents a significant portion of the latency, masks AP dispersion, and reduces CMAP dispersion. This yields similar CMAPs with distal and proximal stimulation. The onset latency at the distal stimulation site does not depend on CV. Thus, onset latency and CV may not reflect the conduction properties of the fastest conducting axons. [ABSTRACT FROM AUTHOR]

Electrical Interference (EI: radiated electromagnetic and/or power line interference) is a common problem in clinical neurophysiology with many causes and thus various conceivable solutions. Although newer digitized electrodiagnostic (EDX) systems have markedly reduced EI issues, it remains a possible impediment in achieving high quality studies. So that the electrodiagnostic medicine consultant (EMC) can problem solve EI, this monograph details the fundamental functional concepts and terminology of electronic amplification and recording electrodes from a practical perspective. This information is then utilized in a proposed standard operating protocol (SOP) to help the EMC address a wide variety of EI sources. Three major EI sources are considered: the EDX system/operator error, the environment, and the patient. The first is a thorough assessment of the recording electrodes from the perspective of clean electrodes, security of attachment, appropriate gel application, proper lead connections to both the patient and instrument, and similarity of electrode composition. Second is how adverse environmental conditions are mitigated through isolating the EDX instrument from nearby large generator sources, unplugging unnecessary equipment, keeping the amplifier close to the patient along with short and braided electrode leads, and utilize filtering (both 60 Hz and total bandwidth) with appropriate caution to avoid unwanted signal distortion. Third, the patient and EMC interaction must be considered. Specifically, all electronic devices that can be removed should be powered down and relocated as far as feasible from the EDX system, including digital watches, cell phones, TENS units, and other such devices. A systematic application of the above proposed protocol should solve the majority of EI issues., (© 2024 by the American Association of Neuromuscular & Electrodiagnostic Medicine, Inc. All rights reserved.)

Introduction/aims: To add objectivity to the routine needle electromyography examination, we describe an "Augmented Intelligence" based interference pattern (IP) analysis method that mimics the subjective assessment by quantifying IP fullness, discreteness, amplitude, pitch, and motor unit firing rate (FR)., Methods: IP recordings from 20 control subjects and other patients with neuropathy and myopathy were analyzed. The IP was divided into three groups: low, intermediate, and full to mimic visual appearance. Reference values (RVs) were defined for each group. "Fence" pattern was defined based on the discreteness and amplitude. Upper limit of FR was defined. Various technical artifacts were detected and excluded from analysis., Results: In control subjects, a total of 2435 recordings from 119 commonly tested muscles were analyzed. The single set of RVs was satisfactory across the tested muscles. Amplitude increased when the pattern changed from low to full. Pitch did not correlate with fullness and its RVs were same for all groups. In patients with neuropathy, an intermediate or low pattern, high amplitude, fence pattern, low pitch, and high FR were demonstrated. In patients with myopathy, a full pattern with low amplitude and high pitch was demonstrated., Discussion: The algorithm makes simple measurements that are readily interpreted by the electromyographer. In this respect, it augments analysis by providing quantitative data. If implemented in an "on-line" manner, it can provide guidance to the operator without adding to the procedure time or changing the recording technique. The measurements can also be included in the report to support the study's findings., (© 2025 Wiley Periodicals LLC.)

Introduction/aims: In healthy subjects, we observed high amplitude motor unit potential (MUP) waveforms that resembled the cannula potential (CP) with a positive sharp wave (PSW)-like waveform. We analyzed the source of this signal, its prevalence, and its effects on the analysis of electromyographic waveforms., Methods: Three channel recordings were performed to explore the contribution of the needle core and cannula to the MUP. In 7 control subjects with no neuromuscular disease, the EMG interference pattern was quantified for the amplitude asymmetry (AASM) of its positive and negative going peaks., Results: The large amplitude MUP resembling a CP with a PSW-type waveform is recorded by the needle core, not the cannula. With a slight change in needle position, its amplitude decreased and the waveform had a normal appearance. Thus, it is an artifact. Such potentials (AASM > 150%) are commonly encountered (frequency 7%) and occur in all muscles and subjects in this study., Discussion: The artifact is an enigma and appears related to the interaction between the needle and muscle fiber(s) similar to that in PSW signals. Failure to recognize these waveforms may result in a false impression of abnormality. AASM calculations can help confirm this artifact in automated analysis algorithms to preclude false positive neurogenic patterns., (© 2024 Wiley Periodicals LLC.)