BOSTON—Between 30% and 40% of patients diagnosed 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.
Selim R. Benbadis, MD
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 seizure medications.
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 drowsiness. 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.
—Erica Tricarico
Suggested Reading
Benbadis SR. “Just like EKGs!” Should EEGs undergo a confirmatory interpretation by a clinical neurophysiologist? Neurology. 2013; 80(1 Suppl 1):S47-S51.
