03 Artifact-Related Epilepsy

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Artifact-related epilepsy
William O. Tatum Neurology 2013;80;S12 DOI 10.1212/WNL.0b013e3182797325 This information is current as of January 14, 2013

The online version of this article, along with updated information and services, is located on the World Wide Web at: http://www.neurology.org/content/80/1_Supplement_1/S12.full.html

Neurology ® is the official journal of the American Academy of Neurology. Published continuously since 1951, it is now a weekly with 48 issues per year. Copyright © 2013 by AAN Enterprises, Inc. All rights reserved. Print ISSN: 0028-3878. Online ISSN: 1526-632X.

Artifact-related epilepsy

William O. Tatum, DO, FAAN

ABSTRACT

Correspondence to Dr. Tatum: [email protected]

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 component 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 prolonged 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 electrophysiologic 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 pathologic 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 consequences for diagnosis-related harm. Neurologyâ 2013;80 (Suppl 1):S12–S25
GLOSSARY
cEEG 5 continuous EEG; ED 5 epileptiform discharges; EMU 5 epilepsy monitoring unit; ICA 5 independent component analysis; ICU 5 intensive care unit; PNEA 5 psychogenic nonepileptic attacks; PWS 5 patients with seizures; vEEG 5 video EEG.

Recording EEG is routinely performed to evaluate many different neurologic conditions that involve the brain. It is most commonly utilized and most specific in the evaluation process of patients with suspected seizures. The clinical utility of surface-based EEG is to detect and localize electrocerebral 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 extracerebral source or artifact.1 Artifacts are present in virtually every EEG and may arise from a variety of extracerebral 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 minimizes extracerebral activity. Emergence of artifacts becomes increasingly evident when the sensitivity or the duration of the recording increases. Both physiologic3 and nonphysiologic4 sources of artifact may lead to confusion and incorrect interpretation of the EEG. EEG is uniquely suited for neurophysiologic identification, classification, quantification, and localization of epileptiform discharges (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 the recording during ED or seizures to eliminate EEG detection (false-negative) from a diagnostic equation. Cerebral spikes may be difficult to separate from spikes due to artifact (figure 2). The definition of a spike (or a sharp wave) refers only to duration (spike 5 20–70 milliseconds; sharp wave 5 70–200 milliseconds) and not the source, pathologic mechanism, or inherent epileptogenicity. Hence the definitions are fairly precise but not that helpful in interpreting EEG.5 The principal importance of artifact is represented by the frequency of its occurrence, and in the ability to mimic epileptiform “abnormalities.”1,6 The clinical impact is supported by approximately 30% of patients 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

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

Table 1

Common sources of EEG artifact
Physiologic sources Normal Eye movements Cardiac Myogenic Bone defects Mastication and deglutition Abnormal Tremor Myoclonus Movements

Nonphysiologic sources Electrodes Pop Impedance mismatch Lead wires Machine and connections Aliasing Jackbox 60 Hz Static electricity Implanted electrical devices

subgroup with a true incidence that is currently unknown. However, in one series of patients undergoing video-EEG (vEEG) for newly diagnosed psychogenic nonepileptic attacks (PNEA), up to 32% had epileptiform “abnormalities” on a previous EEG report that upon review by a dedicated electroencephalographer were found to be normal.8 Identifying a mismatch between potentials generated by the brain from activity that does not conform to a realistic head model is the foundation for recognizing artifact. It is with this in mind that artifact-related epilepsy is discussed within the framework of common artifacts that mimic ED on scalp EEG.
TECHNOLOGY The era of computer-based EEG has elevated the quality of acquiring EEG by analog equipment, and transcended many of the limitations previously imposed by recording electrocerebral signals onto paper media.9 Previously, artifact introduced into the

United States misdiagnosed with epilepsy.7 The true prevalence that is either predicated or promulgated by an “abnormal” and misinterpreted EEG is emerging as an important
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 “pseudoevolution.” From Tatum WO, Dworetzky BA, Schomer DL. Artifact and recording concepts in EEG. J Clin Neurophysiol 2011;28:252–263.4 Used with permission. Neurology 80 (Suppl 1) January 1, 2013 S13

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

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.

tracing was unable to be separated or modified after it was recorded. Since the advent of digital EEG, recording, analyzing, and storing large quantities of information 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) monitoring 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 technologist during the recording is to prove whether a waveform is artifact or not, and act to identify or eliminate it from the recording.14 The technologist monitors, eliminates, and camouflages extracerebral sources when
S14 Neurology 80 (Suppl 1) January 1, 2013

bioelectric fields introduce artifact. Electrode contact with the scalp (figure 3), maintenance of a quiet environment, and troubleshooting are keys to minimize 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. Troubleshooting artifact must be done at the time of the recording. Post hoc filtering and montage manipulation (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 artifact. Aliasing undersamples any signal in time (sample rate) and space (number of electrodes), recording false signals. Environmental sources of artifact may introduce 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. However, the majority of artifact in the EEG appears as extraneous noise to hamper optimal interpretation of

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

Figure 3

Periodic single electrode artifact mimicking periodic lateralized epileptiform discharges

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

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 and functional components of EEG are represented by a few critical parameters of recording (table 2). Guidelines for prolonged EEG monitoring in the EMU have been developed to address technical features.16
Figure 4 Changing the montage may be beneficial in elucidating artifact in the EEG

SOURCES OF ARTIFACT Artifact may arise anywhere between the patient–electrode interface and the recording device and commonly occurs due to insecure connection between the two.17 Some areas in the hospital 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

Note the suspicious frontopolar spikes (A) at the end of an electrode chain in the A-P longitudinal bipolar montage. With redesign of the montage to the transverse bipolar montage, this becomes identifiable as single electrode artifact at FP2 (B). Neurology 80 (Suppl 1) January 1, 2013 S15

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

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;28:252–263.4

obscure the EEG and mimic IED. Common external sources of electrical artifact are due to the 60-Hz alternating current from nearby power supplies, devices, or

outlets, though this is usually recognizable. Electrical noise produced in the environment by ventilators, feeding/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). S16 Neurology 80 (Suppl 1) January 1, 2013

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

Figure 6

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

Note the electrode “pop” with a rapid spike and recovery to baseline without a discernible electrocerebral field. The electrode was later identified to be at the edge of the craniotomy and was resecured with elimination of the “spike-and-waves.”

may create capacitance, inductance, and electrostatic artifacts (figure 5), resulting in high-amplitude potentials that mimic EDs. Interference due to biologically active magnetic fields may also be introduced by internal generators, including cardiac pacemakers, ventricular 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, hemispheric, or focal and restricted to a single channel. Nonphysiologic 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 nonphysiologic and physiologic artifacts are encountered in the process of recording EEG.18 When combinations occur (figure 2), greater difficulty in identification is present.
INTERICTAL ARTIFACT

ED are commonly mimicked 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, internal, and external/environmental sources are common. This is especially true in special care units, although these are usually able to be identified. Physiologic sources 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)
Neurology 80 (Suppl 1) January 1, 2013 S17

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

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)

that are out of phase.19 Due to the Bell phenomenon, an eye 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 stimulation 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 confusion 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 current potentials during horizontal eye movements may also produce slow wave in a similar manner. When lateral rectus spikes occur in a repetitive fashion (i.e., nystagmus), focal spikes may erroneously be interpreted as ED. The temporalis and frontalis are the principal muscles that produce myogenic artifact on EEG.
S18 Neurology 80 (Suppl 1) January 1, 2013

Similar to the lateral rectus “spikes,” contraction of the frontalis muscles (figure 8) may produce myogenic potentials that mimic.20 Myogenic artifact associated with the rhythmic and repetitive motion of chewing may create burst of high-amplitude generalized polyspikes (figure 10) that can be confused with ED.21 Cardiac muscle is another important source of artifact, especially during states of impaired consciousness. Babies, children, and adults with short necks (greater cardiac proximity), double-distance electrodes (i.e., brain death recordings), and reference montages 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 treatment. Similarly, bipolar montages may reveal left hemispheric diphasic waveforms in the temporal derivations due to the vector created by the electrical conduction 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 epilepticus may potentially arise.11

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

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.

ICTAL ARTIFACTS Repetitive body movements may produce changing electrical fields to produce rhythmic depolarization mimicking electrographic seizures (figure 11).22 The importance of separating nonepileptic behavioral sources, creating artifact from pseudoepileptiform patterns produced by artifact due to behavioral sources, is crucial and is assisted by identification of that behavior (figure 12). The difference is essential when treatment relies solely on the interpretation of EEG, such as in those patients who are encephalopathic or comatose. PNEA may generate rhythmic artifacts that mimic seizures. They are common and may challenge even the experienced electroencephalographer 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 simulate a focal seizure. Varying frequencies can produce “pseudoevolution” while varying amplitudes are coupled with varying amplitudes of body movement. Movement monitors applied to the affected limb or body part may readily demonstrate artifact by demonstrating time-locked potentials to the brain-EKGmovement channels and are in-phase. When recurrent

or continuous, focal status epilepticus may be misdiagnosed. Myoclonus associated with generalized highamplitude 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 status 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, technologist’s support, and postacquisition choice in montage design and filtration are helpful to validate a “suspicious” waveform. Video capability is rapidly
Neurology 80 (Suppl 1) January 1, 2013 S19

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

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).

becoming a standard even for routine EEG recording. It permits true “clinical correlation” with behavior coupling to EEG, allowing recognition of potential extracerebral 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 artifact when it exists as “interference.” Specialized artifact rejection algorithms have been devised to eliminate artifact in unique environments to combine the temporal 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 identifying and rejecting “contaminated” epochs of EEG results in eliminating artifact, as well as useful information. Several automated techniques exist to remove artifact from the EEG. EMG artifact is usually more difficult to remove than eye movement artifacts with automated
S20 Neurology 80 (Suppl 1) January 1, 2013

artifacts removal systems. One method, known as regression, 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 movement (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 activity and noise. Source separations are optimized and EMG sources are isolated and eliminated by subtracting the contribution of these components by autocorrelation 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

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

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 triple phase reversals (black arrows) and their occurrence between noncontiguous channels T5-O1 and FP2-F8. Neurology 80 (Suppl 1) January 1, 2013 S21

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

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 longterm 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). S22 Neurology 80 (Suppl 1) January 1, 2013

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

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).

removal of more than 1 type.32 Using more than 1 technique such as the canonical correlation analysis that removes EMG and ICA to remove eye movement 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 overnight 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 demonstrated T5 and T4 sharp waves. vEEG monitoring was performed but no episodes were captured. Left temporal
Neurology 80 (Suppl 1) January 1, 2013 S23

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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 5–15 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 initial clinical diagnosis of syncope was correct before giving rise to PNEA. An EEG ordered for syncope had disastrous results. It did not conform to performance standards (filter settings of 1–70 Hz), which produced artifact that mimicked sharp waves. The atypical locations and the variability in different settings was a clue that the interpretation was misguided. While initially nonphysiologic reasons led to incorrect medical treatment, 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.

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.

Many nonphysiologic and physiologic artifacts are encountered in the process of recording 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 epileptiform, prompting incorrect treatment. Most physician errors are diagnostic.33 Despite computerization of EEG, artifact identification, recognition, and elimination will still be essential human tasks of EEG interpretation. It is surprising that more punitive damages and civil lawsuits have not been filed based upon misinterpreted 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 electroencephalographers will continue to be challenged to recognize every artifact that may be surreptitiously identified as ED 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.
CONCLUSIONS

AUTHOR CONTRIBUTIONS
W. Tatum: drafting/revising the manuscript, contribution of vital reagents/ tools/patients, acquisition of data, study supervision. S24 Neurology 80 (Suppl 1) January 1, 2013

REFERENCES 1. Klass DW. The continuing challenge of artifacts in the EEG. Am J EEG Technol 1995;35:239–269. 2. Aurlien H, Gjerde IO, Aarseth JH, et al. EEG background activity described by a large computerized database. Clin Neurophysiol 2004;115:665–673. 3. Krauss GL, Abdallah A, Lesser R, Thompson RE, Niedermeyer E. Clinical and EEG features of patients with EEG wicket rhythms misdiagnosed with epilepsy. Neurology 2005;64:1879–1883. 4. Tatum WO, Dworetzky BA, Schomer DL. Artifact and recording concepts in EEG. J Clin Neurophysiol 2011;28: 252–263. 5. Maulsby RL. Guidelines for assessment of spikes and sharp waves in EEG tracings. Am J EEG Technol 1971;11:3–16. 6. Tatum WO, Husain AM, Benbadis SR, Kaplan PW. Normal adult EEG and patterns of uncertain significance. J Clin Neurophysiol 2006;23:194–207. 7. Benbadis SR, Allen Hauser W. An estimate of the prevalence of psychogenic non-epileptic seizures. Seizure 2000;9:280– 281. 8. Benbadis SR, Tatum WO. Overintepretation of EEGs and misdiagnosis of epilepsy. J Clin Neurophysiol 2003;20:42– 44. 9. Ferree TC, Luu P, Russell GS, Tucker DM. Scalp electrode impedance, infection risk, and EEG data quality. Clin Neurophysiol 2001;112:536–544. 10. Tatum WO, Dworetzky BA, Freeman WD, Schomer DL. Artifact: recording EEG in special care units. J Clin Neurophysiol 2011;28:264–277. 11. Hirsch LJ, Kull LL. Continuous EEG monitoring in the intensive care unit. Am J Electroneurodiagnostic Technol 2004;44:137–158. 12. Nuwer MR. Quantitative EEG: I: techniques and problems of frequency analysis and topographic mapping. J Clin Neurophysiol 1988;5:1–43. 13. Tatum WO. Long-term EEG monitoring: a clinical approach to electrophysiology. J Clin Neurophysiol 2001;18:442–455. 14. Sullivan L. EEG artifacts. In: American Society of Electroneurodiagnostic Technologists I. Kansas City: American Society of Electroneurodiagnostic Technologists; 2008:5. 15. Young GB, Campbell VC. EEG monitoring in the intensive care unit: pitfalls and caveats. J Clin Neurophysiol 1999;16: 40–45. 16. American Clinical Neurophysiology Society. Guideline twelve: guidelines for long-term monitoring for epilepsy. J Clin Neurophysiol 2008;25:170–180. 17. Reilly EL. EEG recording and operation of the apparatus. In: Niedermeyer E, Lopes da Silva FH, eds. Electroencephalography: Basic Principles, Clinical Applications, and Related Fields. Philadelphia: Lippincott Williams & Wilkins; 1999:122–142. 18. Stern J, Engle J. Atlas of EEG Patterns. Philadelphia: Lippincott Williams & Wilkins; 2005. 19. Bonnet M, Carley D, Carskadon M, et al. ASDA report EEG arousals: scoring rules and samples. Sleep 1992;15:173–184. 20. Dworetzky B, Herman S, Tatum WO. Niedermeyer’s Electroencephalography: Basic Principles, Clinical Application,

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

21. 22.

23. 24.

25.

26.

27.

and Related Fields, 6th ed. Philadelphia: Wolters Kluwer/ Lippincott Williams & Wilkins; 2011. Epilepsy Therapy Project. All about epilepsy [online]. Available at: www.epilepsy.com. Accessed September 15, 2011. Sethi NK, Torgovnick J, Sethi PK. Rhythmic artifact of physiotherapy in intensive care unit EEG recordings. J Clin Neurophysiol 2008;25:62. Benbadis SR. The EEG in nonepileptic seizures. J Clin Neurophysiol 2006;23:340–352. American Electroencephalographic Society. Guideline one: minimum technical requirements for performing clinical electroencephalography. J Clin Neurophysiol 1994;11:2–5. De Clercq W, Vergult A, Vanrumste B, et al. A new muscle artifact removal technique to improve the interpretation of the ictal scalp electroencephalogram. Conf Proc IEEE Eng Med Biol Soc 2005;1:944–947. Allen PJ, Polizzi G, Krakow K, Fish DR, Lemieux L. Identification of EEG events in the MR scanner: the problem of pulse artifact and a method for its subtraction. Neuroimage 1998;8:229–239. Gratton G, Coles MG, Donchin E. A new method for offline removal of ocular artifact. Electroencephalogr Clin Neurophysiol 1983;55:468–484.

28.

29.

30.

31.

32.

33. 34. 35.

Makeig S, Bell AJ, Jung T-P, Sejnowski T. Independent component analysis of electroencephalographic data. In: Advance in Neural Information Processing Systems 8. Cambridge: MIT Press; 1996:145–151. Gao J, Yang Y, Sun J, Yu G. Automatic removal of various artifacts from EEG signals using combined methods. J Clin Neurophysiol 2010;27:312–320. Urrestarazu E, Iriarte J, Alegre M, Valencia M, Viteri C, Artieda J. Independent component analysis removing artifacts in ictal recordings. Epilepsia 2004;45:1071–1078. Vergult A, De Clercq W, Palmini A, et al. Improving the interpretation of ictal scalp EEG: BSS-CCA algorithm for muscle artifact removal. Epilepsia 2007;48:950–958. Dammers J, Schiek M, Boers F, et al. Integration of amplitude and phase statistics for complete artifact removal in independent components of neuromagnetic recordings. IEEE Trans Biomed Eng 2008;55:2353–2362. Newman-Toker DE, Pronovost PJ. Diagnostic errors: the next frontier for patient safety. JAMA 2009;301:1060–1062. Dyer C. 10m pounds sterling settlement for children misdiagnosed with epilepsy. BMJ 2005;330:1466. Young B, Osvath L, Jones D, Socha E. A novel EEG artifact in the intensive care unit. J Clin Neurophysiol 2002;19:484–486.

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Artifact-related epilepsy William O. Tatum Neurology 2013;80;S12 DOI 10.1212/WNL.0b013e3182797325 This information is current as of January 14, 2013
Updated Information & Services References including high resolution figures, can be found at: http://www.neurology.org/content/80/1_Supplement_1/S12.full .html This article cites 29 articles, 2 of which can be accessed free at: http://www.neurology.org/content/80/1_Supplement_1/S12.full .html#ref-list-1 This article, along with others on similar topics, appears in the following collection(s): All Epilepsy/Seizures http://www.neurology.org/cgi/collection/all_epilepsy_seizures EEG http://www.neurology.org/cgi/collection/eeg_ Information about reproducing this article in parts (figures, tables) or in its entirety can be found online at: http://www.neurology.org/misc/about.xhtml#permissions Information about ordering reprints can be found online: http://www.neurology.org/misc/addir.xhtml#reprintsus

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