BOSTON—Between 30% and 40% of patients di- agnosed with intractable epilepsy do not have epilepsy, according to an overview presented at the 69th
Annual Meeting of the American Academy of Neurology. A combination of overreading and overemphasizing EEGs can contribute to misdiagnosis, said Selim R.
Benbadis, MD, Professor of Neurology and Director of
the Comprehensive Epilepsy Program at the University
of South Florida in Tampa.
Neurologists overread EEGs “because of the perception
that there is less risk in overdiagnosing epilepsy, as opposed to underdiagnosing [the disease], and that is not
correct,” said Dr. Benbadis.
The consequences of an epilepsy misdiagnosis can
be serious. Patients can lose driving privileges, which
may limit their employment opportunities. Epilepsy
also is associated with a stigma that can be difficult to
dispel, said Dr. Benbadis. In addition, patients misdiagnosed with epilepsy can have side effects from
Why Are EEGs Overread?
Two of the major reasons for misinterpration of EEGs
are lack of training and inexperience, said Dr. Benbadis. Currently, it is not mandatory to learn how to read
an EEG during neurology residency. Many neurology
programs do require EEG training, but many do not. “If
you are not experienced in looking at [an EEG], you will
overread and think that everything is abnormal,” said Dr.
Benbadis. Many normal variants and artifacts can look
like epileptiform discharges to neurologists who are inexperienced in reading EEG.
Commonly overread EEG patterns include normal
variants such as wicket rhythms, nonspecific temporal
fluctuations, and rhythmic midtemporal theta of drows-
iness. In addition, one study found that most patients
were misdiagnosed with epilepsy because of overread
EEGs; nonspecific fluctuations in the temporal region
were misread as sharp waves.
The idea that “phase reversals” represent EEG abnormalities is a misconception, said Dr. Benbadis. A phase
reversal, which identifies the location of maximum
voltage, does not indicate abnormalities. Every normal
waveform can have phase reversals, he said. A “history
bias” can also lead to a misdiagnosis of epilepsy. For
example, if a patient has a history of seizures or suspected seizures, a neurologist might be biased toward a
diagnosis of epilepsy, and “look too hard” when reading
the EEG, said Dr. Benbadis.
Steps to Improve EEG Interpretation
When deciding whether a discharge is epileptiform,
neurologists should look for waves with an asymmetric contour that clearly stand out from the ongoing
background of an EEG. About 98% of the time, with
clear epileptiform discharges, neurologists can be
sure that they indicate epilepsy without knowing the
patient’s history, said Dr. Benbadis. Experts should
develop consensus guidelines for EEG interpretation, and all neurology residents should be required
to train in the EEG laboratory, said Dr. Benbadis. In
addition, when there is doubt about whether an EEG
was abnormal, “we must obtain the very EEG previously read as abnormal and redo the tracing or consult a colleague,” he added. Patients who have been
diagnosed with epilepsy due to an abnormal EEG are
encouraged to get a second opinion from an epilepsy
or EEG specialist. NR
Benbadis SR. “Just like EKGs!” Should EEGs undergo a confirmatory interpretation by a clinical neurophysiologist? Neurology. 2013;80( 1 Suppl 1):
Lack of training and inexperience may contribute to misinterpretation of EEGs.