Study challenges reliability of EEG test for photosensitivityPosted: 07/19/2014
If the results of a recent study at SUNY at Buffalo are any indication, there are an awful lot of people vulnerable to visually induced seizures who are being told they aren’t at risk. The study showed that testing for photosensitivity using EEG with photic stimulation provides unreliable information. In the wake of these findings, ruling out photosensitive epilepsy–and ignoring the seizure risk from video games–simply on the basis of intermittent photic stimulation results would seem very unwise.
This study–not yet published–by the Buffalo research team found that the test is poorly correlated with vulnerability to visually induced seizures in everyday life. Just 6.2 percent of patients with a history of visually provoked seizures tested positive for photosensitivity.
The standard test for photosensitivity is intermittent photic stimulation—a strobe light flashing at specified frequencies—while hooked up to EEG. Abnormal waves provoked by the photic stimulation are known as the photoparoxysmal response (PPR). (To avoid triggering a seizure during the procedure, the flashing is halted as soon as any of these abnormal waves appear.)
Researchers have known for a long time that many people who test positive never actually experience photic seizures. The Buffalo study confirms this: of 86 patients whose EEG yielded a PPR, just 13 (15.11 percent) reported having experienced visually triggered seizures. What’s new here is the finding that many people who test negative do actually experience these seizures.
The investigators, led by Novreen Shahdad, MD, initiated their study after a patient with a clear history of seizures provoked by electronic screens did not test positive for photosensitivity. “With the increasing popularity of video games and parental concern of their predisposition for seizures,” the authors wrote, “there is a need to identify individuals at risk for PIS [photic induced seizures].”
Shahdad and her colleagues examined a Buffalo EEG database and found 129 patients between 1999 and 2013 who reported seizures triggered by TV, computer use, and video games. Of those patients, a total of 8 tested positive for photosensitivity. Thirty of the 129 patients had reported a history of video game seizures. Of those 30, only one showed a photosensitive response on EEG!
Photosensitivity is defined by researchers as the appearance on EEG, in response to photic stimulation, of certain spike and wave patterns characteristic of epilepspy. Note that the criterion for photosensitivity is not the occurrence of visually induced seizures in everyday life—it refers only to the strobe test.
The study concluded:
“In contrast to the general impression, our study did not find a significant association of a positive response to photic stimulation in patients with photic induced seizures (PIS). This association was seen only in 6.2% of patients with PIS. In addition, PPR on EEG was not associated with statistically significant increase of PIS. Hence we conclude that PPR cannot be used as an isolated predictor for PIS.”
I’ve previously raised questions about diagnosing vulnerability to visually induced seizures soleley on the basis of EEG response to photic stimulation. More study is certainly warranted.