The document discusses the complexities and potential pitfalls of EEG interpretation in diagnosing epilepsy, highlighting that many misdiagnoses stem from overinterpreting normal EEG findings. It emphasizes the importance of accurate training and cautious analysis to avoid false-positive results that can lead to inappropriate treatments. The key takeaway is that while EEGs are important, their findings must always be contextualized with the patient's clinical history and symptoms, as a normal EEG does not rule out epilepsy.

1. The Philosophy of

2. EEG & Epilepsy
• In 29% - 55% of patients with epilepsy, the initial EEG will
show EDs  approximately 15% of these patients have
repeatedly “negative” studies or normal-appearing EEG.
• Approximately 30% of patients seen at epilepsy centers for
refractory seizures do not have seizures and have been
misdiagnosed
– many of them have histories not in the least suggestive of seizures
– many of them have their diagnosis based largely (and sometimes
solely) on an ‘abnormal’ EEG
ERS 2Miller & Henry, 2013; Tatum, 2013; Benbadis, 2010

3. Bad EEG may be harmful
Good EEG is invaluable
• The main consequence of EEG misinterpretation is that false-positive
reports lead to inappropriate treatments.
• Without recording a seizure, the EEG is only supportive when diagnosing
epilepsy. However, the supportive nature of an interictal EEG is only valid if
clear interictal epileptiform discharges (IED) are encountered.
• When over-identified IED are reported, the misinterpretation of the EEG
often goes unchallenged until ictal recordings are performed. A repeat
normal recording does not resolve the issue of a prior false-positive
interpretation.
Miller & Henry, 2013; Tatum, 2013 ERS 3

4. Vague Nonspecific Symptoms + an Overread EEG =
Incorrect Diagnosis of Seizure(s)
“..Routine interictal EEG recording is one of the most abused
investigations in clinical medicine and is unquestionably
responsible for great human suffering.”
Benbadis, 2013 ERS 4

5. The essence of EEG reading:
a pattern recognition skill
• EEG interpretation is a different sort of mental skill—
it takes viewing of many studies, with a variety of
findings, to begin to reliably recognize common
abnormalities.
Miller & Henry, 2013
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6. To accurately interpret an
abnormal EEG,
one must first have the
ability to identify normal
patterns
Miller & Henry, 2013 ; Tatum, 2013; Noachtar, 2018 ERS 6

7. The Stages of EEG Analysis
Stage 1
- Nothing makes sense
Stage 2
- You think you understand but you see abnormalities everywhere
Stage 3
- You gain more hindsight, you recognize a spike but wonder if it is
actually significant
Stage 4
- You are finally able to form your own opinion, even if it is different
from your teacher’s, this last stage is the sign you have matured, you
have acquired enough experience to have your own opinion and to
discuss an EEG.
ERS 7Gelisse & Crespel, 2016

8. A group of clinical neurophysiologists..
60% of the respondents were certified in clinical
neurophysiology by a national board of examiners..
>90% had encountered misread EEGs..
>95% of the misinterpretations were due to
overinterpretation:
– Of normal findings
– Of artifact
Tatum, 2013
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9. ERS 9

10. A major contributor to the misdiagnosis of epilepsy is
the tendency to overread normal EEGs as abnormal
• The wrong diagnosis of seizures is sometimes based solely on
the “abnormal” EEG.
• The vast majority of overread patterns are wicket rhythms or
“nameless variants”.
• The common and unfortunate misconception is that phase
reversals are somehow indicative of abnormalities
 Phase reversals do not indicate epileptogenicity or even abnormality,
they only indicate location.
Benbadis, 2013 ERS 10

11. Reasons for the overreading
• The “looking too hard” syndrome
the reader is “trying too hard” to find abnormalities because the patient
had a “seizure” (history bias)
• Lack of training & inexperience
i.e., not seeing enough normal tracings and the range of normal variations
• Not applying strict criteria to make sharply contoured
waveforms epileptiform
Benbadis, 2013 ERS 11

12. Differentiating normal variants from meaningful spikes
and sharp waves can at times be challenging
Guidelines for EEG interpretation available for defining and
identifying EDs do not exist
but helpful rules have been described..
Miller & Henry, 2013; Benbadis, 2013; Tatum, 2013 ERS 12

13. Epileptiform Pattern
= Interictal epileptiform discharge, epileptiform activity
: Transients distinguishable from background activity with a characteristic morphology typically,
but neither exclusively nor invariably, found in interictal EEGs of people with epilepsy.
EPs have to fulfill at least 4 of the following 6 criteria:
1. Di- or tri-phasic waves with sharp or spiky morphology (i.e. pointed peak)
2. Different wave-duration than the ongoing background activity, either
shorter or longer.
3. Asymmetry of the waveform: a sharply rising ascending phase and a more
slowly decaying descending phase, or vice versa.
4. The transient is followed by an associated slow after-wave.
5. The background activity surrounding epileptiform discharges is disrupted
by the presence of the epileptiform discharges.
6. Distribution of the negative and positive potentials on the scalp suggests a
source of the signal in the brain, corresponding to a radial, oblique or
tangential orientation of the source (see dipole). This is best assessed by
inspecting voltage maps constructed using common-average reference.
ERS 13Kane et al, 2017

14. EEG patterns which may be mistaken as epileptiform
Noachtar, 2018 ERS 14

15. Tips for diagnostic purpose when identifying EDs
2 Minutes Rule
• If 2minutes after review of the EEG, a
“discharge” is unable to be clearly categorized
as an ED, a conservative interpretation should
apply, and the waveform interpreted as
nonepileptiform.
Tatum, 2013
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16. ERS 16

17. Artifacts are intertwined with epilepsy
• Artifacts may beguile the interpreter into
misidentifying wave forms (false-positive) that
simulate ED.
• Artifacts may obscure the recording during ED or
seizures to eliminate EEG detection (false-negative)
from a diagnostic equation.
Tatum, 2013
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18. Removing Artifacts
• Artifact recognition is the essential first step
• Despite computerization of EEG, artifact
identification, recognition, and elimination
will still be essential human tasks of EEG
interpretation
• The easiest means of achieving artifact
reduction is to avoid them
Tatum, 2013
ERS 18

19. Tatum, 2013
Artifacts are present in virtually every EEG and may
arise from a variety of extracerebral sources.
• Some artifact is crucial
to identify stages of
sleep and level of
consciousness.
• Some areas in the hos-
pital are electrically
complex/hostile to
recording & predispose
to artifacts.
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20. 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 wave-form is artifact or not, and act to
identify or eliminate it from the recording  Technologist
monitors, eliminates, and camouflages extracerebral sources
bioelectric fields introduce artifact.
• Electrode contact with the scalp, maintenance of a quiet
environment, and troubleshooting are keys to minimize
artifact-related diagnoses of epilepsy.
• Troubleshooting artifact must be done at the time of the
recording. Post hoc filtering and montage manipulation may
help, but unless a noncephalic source is identified, the
electrocerebral field may appear real.
Tatum, 2013
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21. ERS 21

22. Systematic approach to EEG abnormalities
• The interpretation of EEG is associated with a poor inter-
oberserver reliability.
• Pattern recognition is inherently prone to pitfalls when rules
[of polarity] and convention are ignored.
• Problems of fluctuation in the accuracy of EEG interpretation
may vary from person to person and even in the same person
over time.
• There are guidelines available for conducting EEG studies, but
those available for defining and identifying EDs do not exist
for EEG interpretation.
• It is important to follow a systematic approach to the
classification of EEG abnormalities.
Miller & Henry, 2013; Tatum, 2013; Noachtar, 2018 ERS 22

23. EEG interpretation & report [1]
• Requires knowledge of the patient’s age, past medical and
medication history, their clinical condition during the EEG,
particularly level of consciousness and responsiveness.
• Should follow a standard format that includes a factual
description, a classification and a clinical interpretation of the
EEG record.
• EEG interpretation summarizes the results of the EEG and
gives a clinical interpretation in light of the diagnosis and the
questions posed by the referring physician.
• Terminology of the EEG interpretation should follow common
neurological and clinical practice and use terms
understandable to other physicians not specialized in EEG
Noachtar, 2018 ERS 23

24. EEG interpretation & report [2]
• All EEG phenomena should be described as precisely as
possible in terms of frequency, amplitude, phase relation,
waveform, localization, quantity, and variability of these
parameters.
• The terminology used should follow international standards
and recommendations
Noachtar, 2018 ERS 24

25. Kaplan & Benbadis, 2013 ERS 25

26. There are only few normal individuals
with epileptiform dicharges in the EEG
• Epileptiform discharges in the EEG without having
seizures:
– Children: 2-3%
– Adults: 0.5%
the epileptifom discharges occur only during photic
stimulation in half of these individuals
Noachtar, 2018 ERS 26

27. “We do not treat the EEG”
• A normal EEG does not exclude a clinical
diagnosis of epilepsy
• An abnormal EEG finding may not be related to
the provisional diagnosis or presenting
symptoms
Miller & Henry, 2013; Tatum, 2013 ERS 27

28. • The diagnosis of seizures relies mainly on a good history,
which requires skills and time.
• The importance of the EEG is [often] overemphasized, and it is
especially detrimental when it is interpreted out of clinical
context.
• Overreading is more harmful than underreading.
• Every EEG should be interpreted with care and caution to
avoid pitfalls.
• Proper training is a crucial aspect of minimizing as many of
the errors as possible.
ERS 28

29. References
• Benbadis, S.R. (2010) 'The tragedy of over-read EEGs and wrong diagnoses of epilepsy', Expert
Review of Neurotherapeutics, vol. 10, no. 3, pp. 343-346.
• Gaspard, N. and Hirsch, L.J. (2013) 'Pitfalls in ictal EEG interpretation: Critical care and intracranial
recordings', Neurology, vol. 80, p. S26.
• Gelisse, P. and Crespel, A. (2016) Atlas of Electroencephalography Volume I: Awake and Sleep EEG,
Activation Procedures and Artifact, Paris: John Libbey Eurotext.
• Kane, N., Acharya, J., Benickzy, S., Caboclo, L., Finnigan, S. and Kaplan, P.W. (2017) 'A revised glossary
of terms most commonly used by clinical electroencephalographers and updated proposal for the
report format of the EEG findings. Revision 2017', Clinical Neurophysiology Practice, vol. 2, pp. 170-
185.
• Kaplan, P.W. and Benbadis, S.R. (2013) 'How to write an EEG report: Dos and don'ts', Neurology, vol.
80, p. S43.
• Miller, J.W. and Henry, J.C. (2013) 'Solving the dilemma of EEG misinterpretation', Neurology, vol. 80,
pp. 13-14.
• Noachtar, S. (2018) 'EAN/ILAE-CEA: How to approach EEG and avoid overreading in epilepsy - Level
1: Systematic approach to EEG abnormalities', 4th Congress of the European Academy of Neurology
, Lisbon.
• Tatum, W.O. (2013) 'Artifact-related epilepsy', Neurology, vol. 80, p. S12.
• Tatum, W.O. (2013) 'How not to read an EEG: Introductory statements', Neurology, vol. 80, p. S1.
• Tatum, W.O. (2013) 'Normal "suspicious" EEG', Neurology, vol. 80, p. S4.
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30. ERS 30

31. How to identify artifacts?
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32. Gaspard, 2013
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33. Tatum, 2013
ERS 33

34. Gaspard, 2013 ERS 34

35. The role of EEG for vague cases suspected non-convulsive seizure..
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36. Gaspard, 2013 ERS 36

37. Gaspard, 2013 ERS 37

38. ICU: the most hostile environment for EEG recording..
Tips n trick?
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39. Gaspard, 2013ERS 39

40. How to write an EEG report
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41. Items to include
in EEG report
Kaplan & Benbadis, 2013ERS 41

42. Guideline..
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43. ..Updated Proposal for the Report Format
of the EEG Findings, Revision 2017
Kane et al, 2017 ERS 43

44. ..Updated Proposal for the Report Format
of the EEG Findings, Revision 2017
Kane et al, 2017
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45. ..Updated Proposal for the
Report Format
of the EEG Findings,
Revision 2017
Kane et al, 2017
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46. ..Updated Proposal for the Report Format
of the EEG Findings, Revision 2017
Kane et al, 2017
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47. Thank You
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