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An Artifact in Concentric Needle EMG Recordings.

Sanjeev D Nandedkar^1,2, Paul E Barkhaus²

¹Natus Medical Inc, Hopewell Junction, New York, USA.

|December 13, 2024

Summary

A common artifact in electromyography (EMG) mimics abnormal signals. This needle-related artifact, characterized by high amplitude motor unit potential (MUP) waveforms, can be identified using amplitude asymmetry (AASM) calculations to avoid misdiagnosis.

Keywords:

amplitude asymmetry cannula potential concentric needle electromyography needle electrode artifact

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Area of Science:

Neurology
Electrophysiology
Biomedical Engineering

Background:

High amplitude motor unit potential (MUP) waveforms resembling cannula potentials (CP) with positive sharp wave (PSW)-like features are observed in healthy subjects.
The origin and impact of these waveforms on electromyographic (EMG) analysis require investigation.

Purpose of the Study:

To analyze the source of CP/PSW-like MUP waveforms in healthy subjects.
To determine the prevalence of this signal.
To assess its effect on EMG waveform analysis.

Main Methods:

Three-channel recordings were used to differentiate contributions from the needle core and cannula.
Electromyography (EMG) interference patterns in 7 healthy subjects were analyzed for amplitude asymmetry (AASM) of positive and negative peaks.

Main Results:

The CP/PSW-like MUP waveform originates from the needle core, not the cannula.
Slight needle repositioning normalizes the waveform, confirming it as an artifact.
This artifact, indicated by AASM > 150%, occurs in 7% of recordings across all muscles and subjects.

Conclusions:

The artifact, likely due to needle-muscle interaction, mimics abnormal signals like PSW.
Failure to recognize this artifact can lead to false positive neurogenic pattern diagnoses.
AASM calculations can aid automated algorithms in identifying this artifact and preventing misdiagnosis.