Before epilepsy surgery, doctors may consider using brain imaging to locate language and memory functions in the brain instead of the more invasive procedure that is commonly used, according to a guideline published by the American Academy of Neurology in the January 11, 2017, online issue of Neurology. According to a press release, it is the first evidence-based guideline that systematically reviewed all evidence for such an evaluation.
Guideline authors noted, however, that the evidence for the recommendations is weak, since many of the studies had relatively small numbers of patients with similar types of epilepsy and were conducted at only one institution, so the results may not be generalisable to everyone with epilepsy.
For the guideline, authors compared evidence for functional magnetic risk imaging (fMRI) and the Wada test. Because the Wada test is invasive, there are risks and discomforts.
“Because fMRI is becoming more widely available, we wanted to see how it compares to the Wada test,” says lead author Jerzy Szaflarski of the University of Alabama at Birmingham, USA, and fellow of the American Academy of Neurology. “While the risks associated with the Wada test are rare, they can be serious, including stroke and injury to the carotid artery.”
The guideline found weak evidence that fMRI may be a possible alternative for the Wada test to evaluate the language functions in the brain for people with medial temporal lobe epilepsy, temporal epilepsy in general or extratemporal epilepsy. There was not enough evidence to make a recommendation for people with temporal neocortical epilepsy or temporal tumors.
There was moderate evidence that fMRI of verbal memory or language encoding should be considered for predicting verbal memory outcome for people who are being evaluated for left medial temporal lobe surgery.
The guideline found weak evidence that fMRI using nonverbal memory encoding may be considered for predicting visuospatial memory outcomes for people being evaluated for temporal lobe surgery.
“Larger studies need to be conducted to increase the quality of available evidence,” says Szaflarski. “Plus, neither fMRI nor the Wada test have standardized procedures. Doctors should carefully advise patients of the risks and benefits of fMRI versus the Wada test.”
The guideline was supported by the American Academy of Neurology and endorsed by the American College of Radiology and the American Epilepsy Society.