An Artifact in Concentric Needle EMG Recordings.

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.

Electrical Interference in Clinical Practice: A Conceptual and Practical Approach.

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.

The Enigma of the Motor Nerve Conduction Study.

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.

F wave analysis based on the compound muscle action potential scan.

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.

Revisiting the compound muscle action potential (CMAP).

The compound muscle action potential (CMAP) is among the first recorded waveforms in clinical neurography and one of the most common in clinical use. It is derived from the summated muscle fiber action potentials recorded from a surface electrode overlying the studied muscle following stimulation of the relevant motor nerve fibres innervating the muscle. Surface recorded motor unit potentials (SMUPs) are the fundamental units comprising the CMAP.

Neurophysiological and imaging biomarkers of lower motor neuron dysfunction in motor neuron diseases/amyotrophic lateral sclerosis: IFCN handbook chapter.

This chapter discusses comprehensive neurophysiological biomarkers utilised in motor neuron disease (MND) and, in particular, its commonest form, amyotrophic lateral sclerosis (ALS). These encompass the conventional techniques including nerve conduction studies (NCS), needle and high-density surface electromyography (EMG) and H-reflex studies as well as novel techniques. In the last two decades, new methods of assessing the loss of motor units in a muscle have been developed, that are more convenient than earlier methods of motor unit number estimation (MUNE),and may use either electrical stimulation (e.

Walter Eichler and his role in the development of electroneurography.

Walter Eichler (1904-1942) performed the first in situ nerve conduction studies in humans. Eichler's work has been largely overlooked and there have been no biographical accounts written of him. His 1937 paper, Über die Ableitung der Aktionspotentiale vom menschlichen Nerven in situ (On the recording of the action potentials from human nerves in situ) was translated and reviewed.

Serial electrodiagnostic studies in acute partial conduction block from cyclist's palsy.

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.

Recording sensory nerve action potential using different electrode types.

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.

Volume conduction: Extracellular waveform generation in theory and practice.

The extracellular waveform manifestations of the intracellular action potential are the quintessential diagnostic foundation of electrodiagnostic medicine, and clinical neurophysiology in general. Volume conduction is the extracellular current flow and associated voltage distributions in an ionic conducting media, such as occurs in the human body. Both surface and intramuscular electrodes, in association with contemporary digital electromyographic systems, permit very sensitive detection and visualization of this extracellular spontaneous, voluntary, and evoked nerve/muscle electrical activity.

Defective E2 electrode lead gives low-amplitude compound muscle action potential.

Introduction/aims: Low-amplitude compound muscle action potential (CMAP) suggests a neuromuscular pathology. Low amplitude will also result from a defective E1 electrode or its lead, that is, a technical artifact. The aim of this study was to investigate the effect of a defective E2 electrode lead on the CMAP.

Motor unit recruitment and firing rate at low force of contraction.

Introduction/aims: A prevailing concept of motor unit (MU) recruitment used for calculating recruitment ratio (RR) suggests a progressive linear increase in firing rate (FR). The objective of this study is to assess its validity.

Methods: Concentric needle electromyography (EMG) recordings were made in normal muscle and abnormal muscle of patients with neurogenic findings.

Analysis of the compound muscle action potential scan: Step index (STEPIX) and amplitude index (AMPIX).

Objective: The compound muscle action potential (CMAP) scan is useful to study motor unit (MU) loss. It is of interest to develop simple measurements of the scan.

Methods: CMAP scan recordings were performed in the abductor pollicis brevis muscle of 20 control subjects and 26 patients with amyotrophic lateral sclerosis (ALS).

Marching band model for simulating a single muscle fiber action potential.

Objective: We describe a mathematical model to calculate a single muscle fiber action potential (AP). Based on a marching band pattern, it is an enhancement to our previously described "modified line source" model.

Methods: Calculations were performed using an Excel spread sheet.

Reinnervation as measured by the motor unit size index is associated with preservation of muscle strength in amyotrophic lateral sclerosis, but not all muscles reinnervate.

Introduction/aims: The motor unit size index (MUSIX) may provide insight into reinnervation patterns in diseases such as amyotrophic lateral sclerosis (ALS). However, it is not known whether MUSIX detects clinically relevant changes in reinnervation, or if all muscles manifest changes in MUSIX in response to reinnervation after motor unit loss.

Methods: Fifty-seven patients with ALS were assessed at 3-month intervals for 12 months in four centers.

Revising nerve conduction reference limits.

Introduction/aims: Our electrodiagnostic laboratory uses reference limits (RL) that have been handed down for four decades. With changes in instrumentation and technique, we wish to know if our RL should be modified. It is also useful to have RL based on patient demographics.

Experiment for teaching virtual cathode in nerve conduction studies.

Introduction/aims: The virtual cathode (VC) is a site near the anode where the nerve can be stimulated. Costimulation of neighboring nerves via the VC can affect recording and interpretation of responses. Hence, it is important to teach trainees the concept of the VC.

MeRef: Multivariable extrapolated reference values in motor nerve conduction studies.

Introduction: In this study we describe a method called "multivariable extrapolated reference values" (MeRef) that derives reference values (RVs) using patient data and includes the dependence of these variables on multiple patient demographic variables, such as age and height.

Methods: Computer simulations were used to generate "normal" and "patient" nerve conduction data. Median, ulnar, and tibial motor nerve conduction data from 500 patients studied were tabulated.

Atypical fibrillation and fasciculation potentials: An exercise in waveform identification and analysis.

No consensus criteria exist for recording and analyzing waveforms in clinical electromyography (EMG). There have been significant technical improvements in recent decades that are under-used in both routine practice and research. In current practice, disciplined techniques in acquisition and analysis of signals are required to appropriately define them.

Quantitative laryngeal electromyography parameters may correlate with improved outcomes following botulinum toxin injection for spasmodic dysphonia.

Background: Despite use of qualitative laryngeal electromyography (LEMG) guided botulinum toxin A (BoNT-A) injection for treatment of adductor spasmodic dysphonia (AdSD), unsatisfactory injections and complete "misses" remain problematic. We aimed to determine if the quantitative LEMG measure of number of small segments (NSS) correlates with voice outcomes following (BoNT-A injection for AdSD.

Methods: Automated quantitative LEMG analysis was performed during electromyography (EMG) -guided BoNT-A injection into the thyroarytenoid-lateral cricoarytenoid muscle complex for treatment of AdSD.

Single-institutional reference values for concentric needle jitter analysis using the extrapolated reference values procedure: Comparison to published reference values.

Background: The extrapolated reference values procedure (E-Ref) was used to compare data from a single institution with the recently published reference value (RV) for concentric electrode jitter.

Methods: Data from voluntarily activated concentric needle jitter studies in the frontalis muscle were obtained using retrospective chart review. All measured signals were reviewed for acceptable quality.

Form factor analysis of the surface electromyographic interference pattern.

Introduction: In contrast to needle electromyography (EMG), surface EMG recordings are painless. It is of interest to develop methods to analyze surface EMG for diagnostic purposes.

Methods: Surface EMG interference pattern (SIP) recordings from the abductor pollicis brevis muscle of healthy subjects and subjects with amyotrophic lateral sclerosis (ALS) were analyzed by measuring root-mean-square (RMS) voltage, mean rectified voltage, form factor (FF), and the clustering index (CI).

Standards of instrumentation of EMG.

Standardization of Electromyography (EMG) instrumentation is of particular importance to ensure high quality recordings. This consensus report on "Standards of Instrumentation of EMG" is an update and extension of the earlier IFCN Guidelines published in 1999. First, a panel of experts in different fields from different geographical distributions was invited to submit a section on their particular interest and expertise.

Impact of disuse muscular atrophy on the compound muscle action potential.

Background: Disuse atrophy from immobilization is the result of decreased neural activity and muscle unloading.

Methods: We studied the impact of disuse on hand intrinsic compound muscle action potentials (CMAPs) in a cohort of 39 patients with unilateral 6-week immobilization of the hand in a cast, after distal radius fracture. We excluded patients with nerve injury.