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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]

ABSTRACT Introduction/Aims Methods Results Discussion 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.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.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.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. [ABSTRACT FROM AUTHOR]

Introduction/Aims: Conventional F wave analysis involves a relatively uniform physiological environment induced by supramaximal stimulations. The F wave characteristics in a dynamic physiological condition, however, are rarely investigated. This study aimed to improve understanding of F wave properties in the more dynamic process by introducing a novel method to analyze F waves based on the compound muscle action potential (CMAP) scan technique. Methods: Twenty four healthy subjects participated in the study. The CMAP scan was applied to record muscle responses in the abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles, respectively. F wave characteristics including mean F wave amplitude and latency (F‐M latency), persistence and activating threshold were quantified. Results: An average of 200 F waves per muscle were obtained from the CMAP scan recording. Weak to moderate correlations between F wave amplitude and stimulating intensity were observed in most of the APB (19 muscles; r = 0.33 ± 0.14, all p <.05) and ADM (23 muscles, r = 0.46 ± 0.16, all p <.05) muscles. Significantly longer mean F latency and lower activating F‐threshold were found in the ADM muscles (F‐M latency: APB: 25.43 ± 2.39 ms, ADM: 26.15 ± 2.32 ms, p <.05; F‐threshold: APB: 7.68 ± 8.96% CMAP, ADM: 2.35 ± 2.42% CMAP, p <.05). Discussion: This study introduces new features of F waves using the CMAP scan technique and identifies differences of F wave characteristics between the hand muscles. The CMAP scan based F waves analysis can be combined with the motor unit number estimation to assess functional alterations in motor neurons in neurological disorders. [ABSTRACT FROM AUTHOR]

Introduction/Aims: To date, there is minimal literature in following resolution of partial conduction block (PCB) in compression neuropathy. We investigated a case of cyclist's palsy with PCB from compression using serial nerve conduction studies to monitor recovery. Methods: Clinical recovery was monitored concomitant with compound muscle action potential (CMAP) amplitudes that were recorded from 3 ulnar‐innervated muscles (first dorsal interosseous [FDI] 6 days post‐onset, palmar interosseus [PI] 16 days post‐onset, and abductor digiti minimi [ADM]) in both limbs. Sensory nerve conduction studies and needle electromyography were also performed. Results: PCB was demonstrated in the FDI and PI with recordings done proximal and distal to the site of injury. Recovery in the FDI and PI occurred between week 2 and 3 post‐onset but continued to improve until about 14 wk post‐onset when the CMAP values on the affected side approximated the contralateral side. Sensory conduction studies were normal and symmetric. Needle EMG at 21 days post‐injury showed no active denervation and a reduced number of normal‐appearing motor unit potentials firing >16 Hz that reverted to a normal pattern on final study at 99 days post‐onset. Discussion: This study shows how rapidly PCB may initially resolve although full recovery takes longer. Criteria for defining PCB may be misleading when doing nerve conductions and comparing only the evoked responses below and above the block. To fully characterize PCB, it is important to optimize the position of the active recording electrode (E1) as well as compare results with the unaffected side. [ABSTRACT FROM AUTHOR]

Introduction/Aims: Switching between different types of electrodes during motor and sensory nerve conduction studies adds time to a study. We investigated the use of disposable disc electrodes (DDE) used for motor nerve conduction studies to record the antidromic sensory nerve action potential (SNAP) in median, ulnar and radial sensory nerve conduction studies. Methods: The SNAP was recorded using four different electrode types: reusable ring, reusable bar, disposable ring, and DDE in a random rotating order. Studies were performed in healthy subjects. Other than being an adult with no history of neuromuscular disease, there were no exclusion criteria. Results: We studied 20 subjects (11 females, 9 males; age 41.1 ± 15.7 y). The SNAP waveforms recorded by all four electrode types were similar. There was no statistically significant difference in the onset latency, peak latency (PL), negative peak amplitude (NPA), peak to peak amplitude, or conduction velocity. In individual nerve recordings, the absolute PL difference between reusable ring electrodes (our current standard) and DDE was less than 0.2 ms in 58 of 60 (97%) nerves. The mean absolute NPA difference was 3.1 μV (standard deviation = 2.85 μV). Recordings with NPA difference >5 μV also had high NPA and/or had large artifacts. Discussion: DDE may be used for performing motor and sensory nerve conduction studies. This can reduce the time required for electrodiagnostic testing. [ABSTRACT FROM AUTHOR]

ABSTRACT 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. [ABSTRACT FROM AUTHOR]