03 artifact-related epilepsy

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DOI 10.1212/WNL.0b013e31827973252013;80;S12Neurology

William O. TatumArtifact-related epilepsy

January 14, 2013This information is current as of

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William O. Tatum, DO,

FAAN

Correspondence to

Dr. Tatum:

[email protected]

Artifact-related epilepsy

ABSTRACT

Potentials that do not conform to an expected electrical field generated by the brain characterize an

extracerebral source or artifact. Artifact is present in virtually every EEG. It is an essential compo-

nent for routine visual analysis, yet it may beguile the interpreter into falsely identifying waveforms

that simulate epileptiform discharges (ED). The principal importance of artifact is represented by the

frequency of its occurrence in contrast to the limited frequency of normal variants that may imitate

pathologic ED. Continuous EEG monitoring has uncovered newly identified artifacts unique to pro-

longed recording. The combined use of video and EEG has revolutionized our ability to distinguish

cerebral and extracerebral influences through behavioral correlation that is time-locked to the elec-

trophysiologic features that are present on EEG. Guidelines exist to ensure minimal standards of

recording. Precise definitions are present for ED. Still, the ability to distinguish artifact from patho-

logic ED requires a human element that is to provide the essential identification of an abnormal EEG.The ramification of a misinterpreted record carries an acute risk of treatment and long-term conse-

quences for diagnosis-related harm. Neurology 2013;80 (Suppl 1):S12S25

GLOSSARY

cEEG5 continuous EEG; ED5 epileptiform discharges; EMU5 epilepsy monitoringunit; ICA5 independent componentanalysis;ICU5 intensive care unit; PNEA 5 psychogenic nonepileptic attacks; PWS5 patients with seizures; vEEG 5 video EEG.

Recording EEG is routinely performed to evaluate many different neurologic conditions thatinvolve the brain. It is most commonly utilized and most specific in the evaluation process ofpatients with suspected seizures. The clinical utility of surface-based EEG is to detect and localizeelectrocerebral activity as a helpful adjunct in the clinical care of patients. Potentials that do not

conform to an expected electrical field that is generated by the brain characterize an extracerebralsource or artifact.1 Artifacts are present in virtually every EEG and may arise from a variety ofextracerebral sources (table 1), yet they are an essential component for routine visual analysis.2

The ideal EEG represents a weighted balance that maximizes cerebral activity and minimizesextracerebral activity. Emergence of artifacts becomes increasingly evident when the sensitivityor the duration of the recording increases. Both physiologic3 and nonphysiologic4 sources ofartifact may lead to confusion and incorrect interpretation of the EEG. EEG is uniquely suitedfor neurophysiologic identification, classification, quantification, and localization of epileptiformdischarges (ED) in patients with seizures (PWS) and may be done in real time.

Artifacts are intertwined with epilepsy. Relative to epilepsy, they may beguile the interpreter

into misidentifying waveforms (false-positive) that simulate ED (figure 1). They may obscure therecording during ED or seizures to eliminate EEG detection (false-negative) from a diagnosticequation. Cerebral spikes may be difficult to separate from spikes due to artifact (figure 2). Thedefinition of a spike (or a sharp wave) refers only to duration (spike 5 2070 milliseconds; sharp

wave5 70200 milliseconds) and not the source, pathologic mechanism, or inherent epileptoge-nicity. Hence the definitions are fairly precise but not that helpful in interpreting EEG.5 Theprincipal importance of artifact is represented by the frequency of its occurrence, and in the abilityto mimic epileptiformabnormalities.1,6 The clinical impact is supported by approximately 30% ofpatients admitted to an epilepsy monitoring unit (EMU), who represent over 250,000 people in the

From the Department of Neurology, Mayo College of Medicine, Mayo Clinic, Jacksonville, FL.

Go to Neurology.org for full disclosures. Disclosures deemed relevant by the authors, if any, are provided at the end of this article.

S12 2012 American Academy of Neurology

2012 American Academy of Neurology. Unauthorized reproduction of this article is prohibited.


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United States misdiagnosed with epilepsy.7

The true prevalence that is either predicated

or promulgated by an abnormal and misin-terpreted EEG is emerging as an important

subgroup with a true incidence that is currentlyunknown. However, in one series of patientsundergoing video-EEG (vEEG) for newly diag-nosed psychogenic nonepileptic attacks (PNEA),up to 32% had epileptiform abnormalities on aprevious EEG report that upon review by a ded-icated electroencephalographer were found to benormal.8 Identifying a mismatch between poten-

tials generated by the brain from activity thatdoes not conform to a realistic head model isthe foundation for recognizing artifact. It is withthis in mind that artifact-related epilepsy is dis-cussed within the framework of common arti-facts that mimic ED on scalp EEG.

TECHNOLOGY The era of computer-based EEG has

elevated the quality of acquiring EEG by analog equip-

ment, and transcended many of the limitations previ-

ously imposed by recording electrocerebral signals onto

paper media.9 Previously, artifact introduced into the

Figure 1 Repetitive artifact from scratching simulating an electrographic seizure

Note the limited field with opposite polarity in ipsilateral temporal chain and involvement of the extracerebral EKG channel despite the apparent pseudoe-

volution. From Tatum WO, Dworetzky BA, Schomer DL. Artifact and recording concepts in EEG. J Clin Neurophysiol 2011;28:252263.4 Used with

permission.

Table 1 Common sources of EEG artifact

Nonphysiologic sources Physiologic sources

Electrodes Normal

Pop Eye movements

Impedance mismatch Cardiac

Lead wires Myogenic

Machine and connections Bone defects

Aliasing Mastication and deglutition

Jackbox Abnormal

60 Hz Tremor

Static electricity Myoclonus

Implanted electrical devices Movements

Neurology 80 (Suppl 1) January 1, 2013 S13



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tracing was unable to be separated or modified after it

was recorded. Since the advent of digital EEG, record-ing, analyzing, and storing large quantities of infor-

mation are possible with the ability to make post hoc

changes in montages, filter settings, display speed, and

quality. However, new types of artifact have become

evident as our use of continuous EEG (cEEG) monitor-

ing expands.10 cEEG and quantitative EEG have yielded

newly identified artifacts that appear during prolonged

recording. Patients in special care units, including the

EMU, intensive care unit (ICU), and operating room,

are particularly vulnerable.10,11 False conclusions may

be drawn due to artifact with power spectral analyses

or topographic displays that have been unavailable in

the past.12 The combined use of video and EEG (vEEG)

has revolutionized our ability to distinguish cerebral and

extracerebral influences through behavioral correlation

time-locked to the electrophysiologic features on EEG.13

A quiet patient, controlled setting, and a qualified

technologist are the foundation to minimizing the

amount of artifact. The responsibility of the techno-

logist during the recording is to prove whether a wave-

form is artifact or not, and act to identify or eliminate

it from the recording.14 The technologist monitors, eli-

minates, and camouflages extracerebral sources when

bioelectric fields introduce artifact. Electrode con-

tact with the scalp (figure 3), maintenance of a quietenvironment, and troubleshooting are keys to mini-

mize artifact-related diagnoses of epilepsy. Without

immediate identification of an extracerebral source,

the likelihood of subsequently misidentifying artifact

as abnormalities is greater. In that case, the principles

of electrophysiology solely govern recognition. Trou-

bleshooting artifact must be done at the time of the

recording. Post hoc filtering and montage manipu-

lation (figure 4) may help, but unless a noncephalic

source is identified, the electrocerebral field may

appear real.

The EEG recording may not be fairly represented

by the limits of the machine and misrepresent an arti-

fact. Aliasing undersamples any signal in time (sample

rate) and space (number of electrodes), recording false

signals. Environmental sources of artifact may intro-

duce 60 Hz into the recording. Electrical and magnetic

fields intrinsic to the electrode and body add linearly to

the signal and are usually recognizable. Modern isolated

grounds attenuate 60-Hz noise and like a notched filter,

help to facilitate interpretation of obscured EEG. How-

ever, the majority of artifact in the EEG appears as

extraneous noise to hamper optimal interpretation of

Figure 2 A couplet of pseudo-spike-and-slow waves in a 21-year-old with new-onset seizure suspected to be due to excessive energy drinks

Note the rapid spikes, intermixed myogenic artifact, absent cerebral field, and positive phase reversals in the frontocentral channels during eye blinks on arousal. The

tracing was otherwise normal and the patient was not treated without recurrence at 6 months.

S14 Neurology 80 (Suppl 1) January 1, 2013



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the EEG. Hence the post hoc interpretation of EEG is

often compromised if visual analysis relies solely upon

waveform or pattern recognition.15

The physical andfunctional components of EEG are represented by a

few critical parameters of recording (table 2). Guide-

lines for prolonged EEG monitoring in the EMU have

been developed to address technical features.16

SOURCES OF ARTIFACT Artifact may arise any-

where between the patientelectrode interface and the

recording device and commonly occurs due to insecureconnection between the two.17 Some areas in the hos-

pital are electrically complex and hostile to recording

and predispose to artifacts.5,7,10 Both extrinsic and

intrinsic electrical noise can result in artifact that may

Figure 4 Changing the montage may be beneficial in elucidating artifact in the EEG

Note thesuspicious frontopolar spikes(A) at theend of an electrodechainin theA-P longitudinal bipolar montage. With redesign of themontage to thetrans-

verse bipolar montage, this becomes identifiable as single electrode artifact at FP2 (B).

Figure 3 Periodic single electrode artifact mimicking periodic lateralized epileptiform discharges

Note the absence of a cerebral field and isolation to a single electrode.




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obscure the EEG and mimic IED. Common external

sources of electrical artifact are due to the 60-Hz alter-

nating current from nearby power supplies, devices, or

outlets, though this is usually recognizable. Electrical

noise produced in the environment by ventilators, feed-

ing/infusion pumps, and IV drip external to the patient

Figure 5 Electrostatic artifact during multiplexing (red square) when a laptop cable touches the telemetry cable during seizure monitoring

Note the single electrode artifact at FP1 (black arrow).

Table 2 Suspicious features of the EEG that suggest artifact

Restricted activity or waveform to only 1 channel

Artifact until proven otherwise

Activity that appears in .1 noncontiguous head region

Suggests a discontinuous generator such as artifact

Complex waveforms with alternating double and triple phase reversals

Implies a field that is not due to a cerebral generator

Activity that appears at the end of an electrode chain

May imply a source that is distant to the brain

Atypical generalized waveforms

Suggests the potential for an equipment artifact involving all channels

Periodic patterns

Precise periodicity and morphology suggests artifact

Very high or very slow frequencies ,1 Hz or .70 Hz

Most cerebral activity lies between 1 and 35 Hz

Adapted from Tatum WO, Dworetzky BA, Schomer DL. Artifact and recording concepts in EEG. J Clin Neurophysiol

2011;28:252263.4




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may create capacitance, inductance, and electrostatic

artifacts (figure 5), resulting in high-amplitude poten-

tials that mimic EDs. Interference due to biologically

active magnetic fields may also be introduced by inter-

nal generators, including cardiac pacemakers, ven-

tricular assist devices, and neurostimulators. These

contribute to a variety of artifacts that usually obscure

but occasionally mimic ED. Independent of the source,

the foundation to judge artifact is established when an

unbelievable electrophysiologic localization, polarity,

and field exist. Distribution may be diffuse, hemi-

spheric, or focal and restricted to a single channel. Non-

physiologic waveforms associated with single-electrode

artifact or movement associated with the cable may

appear suspicious. Suspicious waveforms should

always raise the possibility of artifact.10 Many nonphy-

siologic and physiologic artifacts are encountered in the

process of recording EEG.18When combinations occur

(figure 2), greater difficulty in identification is present.

INTERICTAL ARTIFACT ED are commonly mim-

icked by artifact. Artifacts may be confused with both

focal and generalized ED and arise from physiologic

and nonphysiologic sources. Ocular, myogenic, oral

and pharyngeal, cardiac, and sources that stem from

defects of the cranial bones may generate artifact that

simulates ED (figure 6). Nonphysiologic sources

including electrodes, wires, jackbox, machines, inter-

nal, and external/environmental sources are common.

This is especially true in special care units, although

these are usually able to be identified. Physiologic sour-

ces of artifact are usually the principal source4,5 of

waveforms misidentified as ED. Electrophysiologic

dipoles exist in most biological tissue produced by

electrical current gradients. Eye movement artifact on

EEG is present in virtually every conscious individual.

The biological dipole of the cornea is electropositive

relative to the retina. Eye movement generates a direct

current potential difference, which is measurable in the

horizontal by the anterior temporal electrodes (i.e., F7/

F8 positions) and the vertical plane represented by

the anterior scalp electrodes (FP1/FP2 positions). An

electro-oculogram helps differentiate cerebral potentials

that are in phase with extracerebral potentials (figure 7)

Figure 6 Right skull breach after craniotomy demonstrates a single electrode artifact that appears as repetitive F8 spikes

Note the electrode popwith a rapid spike andrecoveryto baseline without a discernible electrocerebralfield.The electrodewas later identified to be at the

edge of the craniotomy and was resecured with elimination of thespike-and-waves.




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that are out of phase.19

Due to the Bell phenomenon, aneye blink in the frontal head region produces a surface

positive sharp waveform as the cornea depolarizes the

frontopolar electrodes when it rolls upward during eyelid

closure. The peak deflection is downward and rarely

confusing in isolation. However, when photic stimula-

tion produces myogenic spikes and is coupled with eye

flutter, a combination of artifacts may mimic generalized

spike-and-waves (figure 8). Eye movement monitors

placed below the eye can verify the ocular origin. By

demonstrating out of phase deflections, the confu-

sion with a photoparoxysmal response or pseudofrontal

intermittent rhythmic delta activity can be proven.

Eye movements may generate spikes (figure 9). These

arise from the lateral rectus muscles (also known as

muscle artifact) during REM. They represent motor

unit potentials generated by muscles of the globe near

the lateral orbit (F7/F8). Higher amplitude direct cur-

rent potentials during horizontal eye movements may

also produce slow wave in a similar manner. When lat-

eral rectus spikes occur in a repetitive fashion (i.e., nys-

tagmus), focal spikes may erroneously be interpreted as

ED. The temporalis and frontalis are the principal

muscles that produce myogenic artifact on EEG.

Similar to the lateral rectus spikes, contraction ofthe frontalis muscles (figure 8) may produce myo-

genic potentials that mimic.20 Myogenic artifact asso-

ciated with the rhythmic and repetitive motion of

chewing may create burst of high-amplitude general-

ized polyspikes (figure 10) that can be confused with

ED.21 Cardiac muscle is another important source of

artifact, especially during states of impaired con-

sciousness. Babies, children, and adults with short

necks (greater cardiac proximity), double-distance elec-

trodes (i.e., brain death recordings), and reference mon-

tages predispose to EKG artifact. When waveforms

appear in succession, the periodicity of the EKG artifact

may mimic generalized periodic epileptiform discharges

and prompt unnecessary diagnostic evaluations or treat-

ment. Similarly, bipolar montages may reveal left

hemispheric diphasic waveforms in the temporal der-

ivations due to the vector created by the electrical con-

duction of the left ventricle, generating the QRS

complex to simulate periodic lateralized epileptiform

discharges. A linked ear reference will help to cancel

the EKG artifact. When artifact is frequent, bilateral,

and rhythmic, confusion with nonconvulsive status epi-

lepticus may potentially arise.

11

Figure 7 Vertical eye blink artifact demonstrates out-of-phase potentials in the eye movement monitors (oval) while horizontal eye

movements direction is identified by the positive phase reversals that lie proximate to the corneal (the conjugate negative phase

reversal closest to the retina)




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ICTAL ARTIFACTS Repetitive body movements mayproduce changing electrical fields to produce rhyth-

mic depolarization mimicking electrographic seizures

(figure 11).22 The importance of separating nonepilep-

tic behavioral sources, creating artifact from pseudoe-

pileptiform patterns produced by artifact due to

behavioral sources, is crucial and is assisted by identi-

fication of that behavior (figure 12). The difference is

essential when treatment relies solely on the interpre-

tation of EEG, such as in those patients who are

encephalopathic or comatose. PNEA may generate

rhythmic artifacts that mimic seizures. They are com-

mon and may challenge even the experienced electro-

encephalographer in the absence of historical and video

accompaniment.23 Similarly, unilateral or asymmetric

tremor (i.e., Parkinson disease or essential tremor) or

movement may produce ipsilateral artifacts that simu-

late a focal seizure. Varying frequencies can produce

pseudoevolution while varying amplitudes are cou-

pled with varying amplitudes of body movement.

Movement monitors applied to the affected limb or

body part may readily demonstrate artifact by demon-

strating time-locked potentials to the brain-EKG-

movement channels and are in-phase. When recurrent

or continuous, focal status epilepticus may be misdiag-nosed. Myoclonus associated with generalized high-

amplitude bursts of myogenic artifact, if misinterpreted,

might confirm generalized seizures. In a patient with

recurrent attacks, juvenile myoclonic epilepsy might

be misdiagnosed, translating to lifelong treatment

(Tatum, personal observation, 2010). In the absence

of a trained observer or concomitant video recording, a

variety of movements may create the appearance of a

seizure. Ambulatory EEG is especially prone to artifact

(figure 13). cEEG contains pitfalls in the ICU28 and

distinguishing artifact that mimics nonconvulsive sta-

tus epilepticus may separate holding medication from

induction of iatrogenic coma.

DETECTING AND REMOVING ARTIFACT Emerging

recognition of the impact of this problem and evolving

software availability provide the tools to overcome the

boundaries imposed by artifact. Artifact recognition is

the essential first step. The ability to define artifact is

based upon electrophysiologic cues. Visual analysis,

technologists support, and postacquisition choice in

montage design and filtration are helpful to validate

a

suspicious

waveform. Video capability is rapidly

Figure 8 Pseudo-spike-and-slow waves due to superimposition of vertical eye blink artifact (black arrow) and myogenic spikes (red arrow)

The addition of eye movement monitors was able to demonstrate out-of-phase extracerebral potentials and video-confirmed eyelid flutter.




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becoming a standard even for routine EEG recording.

It permits true clinical correlation with behavior cou-

pling to EEG, allowing recognition of potential extrac-

erebral generators. Guidelines exist to ensure minimal

standards of recording.24

Some artifact is crucial to identify stages of sleep and

level of consciousness. Whether to monitor or eliminate

artifacts depends upon the accessibility and necessity of

the source. New artifact rejection software is available.25

High linear frequency filter, automated rejection, and

automated elimination are means of eliminating arti-

fact when it exists as interference. Specialized artifact

rejection algorithms have been devised to eliminate

artifact in unique environments to combine the tem-

poral resolution of EEG with the spatial resolution of

MRI.26

The easiest means of achieving artifact reduction is

to avoid them. When they do occur, visually iden-

tifying and rejecting contaminated epochs of EEG

results in eliminating artifact, as well as useful informa-

tion. Several automated techniques exist to remove arti-

fact from the EEG. EMG artifact is usually more difficult

to remove than eye movement artifacts with automated

artifacts removal systems. One method, known as regres-

sion, has been used offline to remove ocular artifact.27

This technique is based upon time or frequency domains

and removes reference channels that contain eye move-

ment (EMG reference channels are harder to identify).

While widely utilized, some intermixed cerebral activity

is extracted as well. Independent component analysis

(ICA) is a newer method that is based upon source

separation.28 After the mixed signals from EEG are

processed, the ICA algorithm isolates one or a few

components composed of artifact and then removes

them. ICA methods have demonstrated superiority of

this method over other methods, including digital

filtration.29,30 The most recent algorithms31 attempt

to correlate a greater similarity between muscle activ-

ity and noise. Source separations are optimized and

EMG sources are isolated and eliminated by subtract-

ing the contribution of these components by auto-

correlation values less than a specified threshold for

artifact that is determined by statistical analysis.29

Many of the automatic artifact removal systems apply

to a singular type of artifact (i.e., eye movements or

EMG), though recently proposed methods may allow

Figure 9 Motor unit potentials generated by muscles of the orbit that represent spike-artifact (red arrow)

Note the lambda waves in the occipital region that are surface-positive sharp waves and a normal physiologic response (blue arrow).




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Figure 10 Repetitive polyspikes associated with chewing artifact during computer-assisted ambulatory EEG recording

Video was not available but the polyphasic morphology with a bitemporally predominant field is characteristic at 1.5 Hz.

Figure 11 Unilateral left arm tremoring in a patient in the intensive care unit

Note the similar appearance to an electrographic seizure but the adjacent triplephase reversals (black arrows) and their occurrence between noncontiguous

channels T5-O1 and FP2-F8.




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Figure 12 Artifact from wiggling a finger in an ear canal

Note the slight increase in frequency from 4 Hz to 5.5 Hz prior to abrupt cessation that mimics an electrographic seizure. This EEG might be suspicious

without a comment from the technologist if confirmatory history or video recording was not available. The consequence of misdiagnosis would include long-

term treatment with antiepileptic drugs.

Figure 13 Artifact simulating a 5-second burst of 2-Hz generalized spike-and-wave on computer-assisted ambulatory EEG in a 36-year-old

patient referred for evaluation of seizures

Note the involvement of the extracerebral channel (EKG).




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removal of more than 1 type.32 Using more than1 technique such as the canonical correlation analysis

that removes EMG and ICA to remove eye move-

ment artifacts allows more complete artifact removal

from the EEG.29

ILLUSTRATIVE CASE OF MISIDENTIFIED

ARTIFACT A 32-year-old woman was visiting friends.

She experienced an accidental slip and fall at her hotel.

She struck her head but did not lose consciousness. She

later developed an episode of dizziness, collapsed, and

briefly lost consciousness. In a local emergency department,

she was diagnosed with syncope. She was admitted over-night for cardiac monitoring and was seen by a cardiologist

and a neurologist. Her CT brain was normal. An EEG was

reported to be abnormal due to P3 and F4 sharp waves.

She was placed on carbamazepine and discharged with a

diagnosis of seizure disorder. Subsequently her spells

recurred manifest as abrupt loss of consciousness with

shaking all over. She was then placed on topiramate.

The episodes continued frequently. A second EEG dem-

onstrated T5 and T4 sharp waves. vEEG monitoring was

performed but no episodes were captured. Left temporal

Figure 14 Representative case samples of EEG illustrate the effect of narrowing the filter settings on artifact

Unfiltered artifact (A) eliminates contamination by myogenic artifact to produce sharp waves in (B) showing filtered EEG (circle). (C) Independent bursts of

bitemporal wicket waves (arrow).




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spikes were identified and she was implanted with a vagus

nerve stimulator. She sued the hotel chain for $49 million.

Later, she was directed by the defense attorney to a

university center where video-EEG captured PNEA.

Acquisition of the initial 2 EEGs demonstrated artifact

(figure 14) with filter settings of 515 Hz. Review of

the inpatient video-EEG revealed clear left temporal

wicket waves.

The case settled for $6 million out of court based

upon drug-resistant post-traumatic seizures.

This case illustrates the impact of false performance

of, reliance on, and interpretation of the EEG. The ini-

tial clinical diagnosis of syncope was correct before giv-

ing rise to PNEA. An EEG ordered for syncope had

disastrous results. It did not conform to performance

standards (filter settings of 170 Hz), which produced

artifact that mimicked sharp waves. The atypical loca-

tions and the variability in different settings was a clue

that the interpretation was misguided. While initially

nonphysiologic reasons led to incorrect medical treat-

ment, misidentification of physiologic wicket spikes,which are a benign variant of normal, as pathologic

resulted in a surgical procedure.

The litigation and sizable award settlement was

based upon overinterpreted EEG.

CONCLUSIONS Many nonphysiologic and physio-

logic artifacts are encountered in the process of record-

ing EEG.18 Some artifacts are essential to understand

functions of the brain; however, many artifacts are not

and may lead to misinterpretation of the EEG as epi-

leptiform, prompting incorrect treatment. Most physi-cian errors are diagnostic.33 Despite computerization of

EEG, artifact identification, recognition, and elimina-

tion will still be essential human tasks of EEG interpre-

tation. It is surprising that more punitive damages and

civil lawsuits have not been filed based upon misinter-

preted EEG34 given the ramifications of overtreatment

that may be life-altering or even fatal. With the unique

and complex nature imposed by the many artifacts that

exist, even seasoned technologists and electroencepha-

lographers will continue to be challenged to recognize

every artifact that may be surreptitiously identified asED and jeopardize the correct interpretation of the

EEG summarized for clinical decision-making. With

the greater emphasis on prolonged EEG recording,

newly identified artifacts will continue to become

apparent.35 It is with this in mind that artifact-related

epilepsy remains a clinical consideration during routine

interpretation of the EEG.

AUTHOR CONTRIBUTIONS

W. Tatum: drafting/revising the manuscript, contribution of vital reagents/

tools/patients, acquisition of data, study supervision.

DISCLOSURE

The author reports no disclosures relevant to the manuscript. Go to

Neurology.org for full disclosures.

Received November 16, 2011. Accepted in final form February 29, 2012.

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DOI 10.1212/WNL.0b013e31827973252013;80;S12Neurology

William O. TatumArtifact-related epilepsy

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03 artifact-related epilepsy

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