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IMAGE OF THE MOMENT Pract Neurol 2007; 7: 323–325
Misdiagnosis of
epilepsy due to
errors in EEG
interpretationSelim R Benbadis
CASE 1
A 33-year-old woman was evaluated for
episodes of generalised weakness, fatigue,
diffuse pain, and dizziness. Her EEG revealed
‘‘temporal sharp waves’’ (fig 1, arrow). Despite
the history, she was diagnosed with seizures
and started on antiepileptic drugs.
CASE 2
A 46-year-old woman was evaluated for a
single episode of loss of consciousness after
stepping out of her car. She recalled feeling
unwell and weak, and then came to 1–
2 minutes later with people around her.
Witnesses said that she slumped down to
the ground and was out and limp with no
abnormal movements. EEG showed left tem-
poral sharp waves ‘‘with phase reversals’’
(fig 2, arrow). Again despite the history, a
diagnosis of seizures was made and anti-
epileptic drugs recommended.
COMMENT
Both EEGs show normal temporal sharply
contoured waveforms that do not meet
criteria for significant (epileptiform) sharp
waves (see fig 3). These are benign ‘‘nameless’’
fluctuations of background and have been
described under various names.1–3
Such wave-
forms are of no clinical significance and are
likely found on most routine EEGs. They are
the most commonly over-read pattern that
results in erroneous diagnoses of epilepsy.1, 2
These two cases illustrate the serious
problem of EEG over-interpretation that
results in misdiagnoses of seizures—a very
common scenario seen later at referral
epilepsy centres.
S R Benbadis
Professor and Director
Comprehensive Epilepsy Program,
Departments of Neurology &
Neurosurgery, University of South
Florida and Tampa General
Hospital, Tampa, Florida, USA;
sbenbadi@health.usf.edu
323Benbadis
www.practical-neurology.com
The reasons for the over-interpretation of
EEGs include:
N Over-emphasis on ‘‘phase reversals’’ and
the common misconception that these
indicate abnormalities.4
Basic principles of
polarity and localisation make it clear that
phase reversals are not at all indicative of
abnormalities; they only indicate location
(maximum voltage). ‘‘Phase reversals’’ are
not even one of the criteria used to
determine if a discharge is of epileptogenic
significance, because normal waveforms
and artifacts also have phase reversals.
Figure 1
These sharp transients arise from an
ongoing rhythm of the same frequency.
They do not clearly stand out or disrupt
the background activity. Contrast this
with the sharp waves shown in figure 3.
Figure 2
See details for figure 1.
324 Practical Neurology
10.1136/jnnp.2007.124370
N Trying ‘‘too hard’’ to find abnormalities
because the patient had a suspected
‘‘seizure’’ and the EEG reader is biased
by the history.
N Inexperience—not seeing enough normal
tracings and the range of normal varia-
tions.
N Not applying strict criteria to make sharp
transients epileptiform (see fig 3).
N Taking the EEG out of clinical context.
Neither of the two cases above had a
history suggestive of seizures, yet the
diagnosis was made based on the EEG.
Some solutions:
N ‘‘Conservative’’ reading should be strongly
emphasised during EEG training; when in
doubt, report as normal, as recommended
by most epileptologists.
N Applying strict criteria to call a sharp
waveform a sharp wave (see fig 3).
N Reading EEG blind to the history (the
history should then be integrated after
the EEG is classified, resulting in a clinical
interpretation of the diagnosis).
REFERENCES
1. Benbadis SR, Tatum WO. Over-intepretation of
EEGs and misdiagnosis of epilepsy. J Clin
Neurophysiol 2003;20:42–4.
2. Krauss GL, Abdallah A, Lesser R, et al. Clinical and
EEG features of patients with EEG wicket rhythms
misdiagnosed with epilepsy. Neurology
2005;64:1879.
3. Blume WT, Kaibara M, Young GB. Atlas of adult
electroencephalography. Philadelphia: Lippincott
Williams & Wilkins, 2001:41–172.
4. Benbadis SR. The EEG in nonepileptic seizures. J Clin
Neurophysiol 2006;23:340–52.
General criteria which help characterise a sharply contoured transient as a spike or sharp
wave with epileptogenic significance:
l standing out from the ongoing background
l high amplitude
l disturbing the ongoing background, as evidenced by aftergoing slow activity or
suppression
l different frequency from the ongoing background
Figure 3
This figure shows clear right
temporal sharp waves in two
patients with right temporal lobe
epilepsy confirmed by seizure-free
outcome after temporal lobectomy.
Note the high amplitude, the clear
‘‘disruption’’ of background with
aftergoing slow wave, and the
different slope on the upgoing
versus downgoing phases. Both of
these sharp waves have a
maximum at the F8 and T2
electrodes.
325Benbadis
www.practical-neurology.com

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Misdiagnosis of epilepsy due to errors in eeg interpretation

  • 1. IMAGE OF THE MOMENT Pract Neurol 2007; 7: 323–325 Misdiagnosis of epilepsy due to errors in EEG interpretationSelim R Benbadis CASE 1 A 33-year-old woman was evaluated for episodes of generalised weakness, fatigue, diffuse pain, and dizziness. Her EEG revealed ‘‘temporal sharp waves’’ (fig 1, arrow). Despite the history, she was diagnosed with seizures and started on antiepileptic drugs. CASE 2 A 46-year-old woman was evaluated for a single episode of loss of consciousness after stepping out of her car. She recalled feeling unwell and weak, and then came to 1– 2 minutes later with people around her. Witnesses said that she slumped down to the ground and was out and limp with no abnormal movements. EEG showed left tem- poral sharp waves ‘‘with phase reversals’’ (fig 2, arrow). Again despite the history, a diagnosis of seizures was made and anti- epileptic drugs recommended. COMMENT Both EEGs show normal temporal sharply contoured waveforms that do not meet criteria for significant (epileptiform) sharp waves (see fig 3). These are benign ‘‘nameless’’ fluctuations of background and have been described under various names.1–3 Such wave- forms are of no clinical significance and are likely found on most routine EEGs. They are the most commonly over-read pattern that results in erroneous diagnoses of epilepsy.1, 2 These two cases illustrate the serious problem of EEG over-interpretation that results in misdiagnoses of seizures—a very common scenario seen later at referral epilepsy centres. S R Benbadis Professor and Director Comprehensive Epilepsy Program, Departments of Neurology & Neurosurgery, University of South Florida and Tampa General Hospital, Tampa, Florida, USA; sbenbadi@health.usf.edu 323Benbadis www.practical-neurology.com
  • 2. The reasons for the over-interpretation of EEGs include: N Over-emphasis on ‘‘phase reversals’’ and the common misconception that these indicate abnormalities.4 Basic principles of polarity and localisation make it clear that phase reversals are not at all indicative of abnormalities; they only indicate location (maximum voltage). ‘‘Phase reversals’’ are not even one of the criteria used to determine if a discharge is of epileptogenic significance, because normal waveforms and artifacts also have phase reversals. Figure 1 These sharp transients arise from an ongoing rhythm of the same frequency. They do not clearly stand out or disrupt the background activity. Contrast this with the sharp waves shown in figure 3. Figure 2 See details for figure 1. 324 Practical Neurology 10.1136/jnnp.2007.124370
  • 3. N Trying ‘‘too hard’’ to find abnormalities because the patient had a suspected ‘‘seizure’’ and the EEG reader is biased by the history. N Inexperience—not seeing enough normal tracings and the range of normal varia- tions. N Not applying strict criteria to make sharp transients epileptiform (see fig 3). N Taking the EEG out of clinical context. Neither of the two cases above had a history suggestive of seizures, yet the diagnosis was made based on the EEG. Some solutions: N ‘‘Conservative’’ reading should be strongly emphasised during EEG training; when in doubt, report as normal, as recommended by most epileptologists. N Applying strict criteria to call a sharp waveform a sharp wave (see fig 3). N Reading EEG blind to the history (the history should then be integrated after the EEG is classified, resulting in a clinical interpretation of the diagnosis). REFERENCES 1. Benbadis SR, Tatum WO. Over-intepretation of EEGs and misdiagnosis of epilepsy. J Clin Neurophysiol 2003;20:42–4. 2. Krauss GL, Abdallah A, Lesser R, et al. Clinical and EEG features of patients with EEG wicket rhythms misdiagnosed with epilepsy. Neurology 2005;64:1879. 3. Blume WT, Kaibara M, Young GB. Atlas of adult electroencephalography. Philadelphia: Lippincott Williams & Wilkins, 2001:41–172. 4. Benbadis SR. The EEG in nonepileptic seizures. J Clin Neurophysiol 2006;23:340–52. General criteria which help characterise a sharply contoured transient as a spike or sharp wave with epileptogenic significance: l standing out from the ongoing background l high amplitude l disturbing the ongoing background, as evidenced by aftergoing slow activity or suppression l different frequency from the ongoing background Figure 3 This figure shows clear right temporal sharp waves in two patients with right temporal lobe epilepsy confirmed by seizure-free outcome after temporal lobectomy. Note the high amplitude, the clear ‘‘disruption’’ of background with aftergoing slow wave, and the different slope on the upgoing versus downgoing phases. Both of these sharp waves have a maximum at the F8 and T2 electrodes. 325Benbadis www.practical-neurology.com