misdiagnosis of epilepsy due to errors in eeg interpretation
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IMAGE OF THE MOMENTPract Neurol 2007; 7: 323–325
Misdiagnosis ofepilepsy due toerrors in EEGinterpretationSelim R Benbadis
CASE 1A 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 2A 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.
COMMENTBoth 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 BenbadisProfessor 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’’ andthe common misconception that theseindicate abnormalities.4 Basic principles ofpolarity and localisation make it clear that
phase reversals are not at all indicative ofabnormalities; they only indicate location(maximum voltage). ‘‘Phase reversals’’ arenot even one of the criteria used todetermine if a discharge is of epileptogenicsignificance, because normal waveformsand artifacts also have phase reversals.
Figure 1These 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 2See details for figure 1.
324 Practical Neurology
10.1136/jnnp.2007.124370
N Trying ‘‘too hard’’ to find abnormalitiesbecause the patient had a suspected‘‘seizure’’ and the EEG reader is biasedby the history.
N Inexperience—not seeing enough normaltracings and the range of normal varia-tions.
N Not applying strict criteria to make sharptransients epileptiform (see fig 3).
N Taking the EEG out of clinical context.Neither of the two cases above had ahistory suggestive of seizures, yet thediagnosis was made based on the EEG.
Some solutions:
N ‘‘Conservative’’ reading should be stronglyemphasised during EEG training; when indoubt, report as normal, as recommendedby most epileptologists.
N Applying strict criteria to call a sharpwaveform a sharp wave (see fig 3).
N Reading EEG blind to the history (thehistory should then be integrated afterthe EEG is classified, resulting in a clinicalinterpretation of the diagnosis).
REFERENCES1. Benbadis SR, Tatum WO. Over-intepretation of
EEGs and misdiagnosis of epilepsy. J ClinNeurophysiol 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. Neurology2005;64:1879.
3. Blume WT, Kaibara M, Young GB. Atlas of adultelectroencephalography. Philadelphia: Lippincott
Williams & Wilkins, 2001:41–172.
4. Benbadis SR. The EEG in nonepileptic seizures. J ClinNeurophysiol 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 backgroundl high amplitudel disturbing the ongoing background, as evidenced by aftergoing slow activity or
suppressionl different frequency from the ongoing background
Figure 3This 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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