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