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| |  Visual Habituation Helps Identify Paediatric Patients With Photosensitive Epilepsy: Presented at AES By John Otrompke BOSTON -- December 8, 2009 -- In a poster presented here at the American Epilepsy Society (AES) 63rd Annual Meeting, researchers investigated the nature of photosensitive epilepsy, a subset of the disease which has been defined as a spectrum disorder. “Many paediatric epilepsy patients have photosensitivity,” said Daniela Brazzo, MD, Astor University, Birmingham, England, on December 6. “However, at some point, they don’t suffer from photosensitivity anymore.” In photosensitive epilepsy patients, epileptic seizures are brought on by light effects, because the patients lack a normal visual gating mechanism, possibly due to genetic differences. Dr. Brazzo and colleagues looked at 60 children, 19 of whom suffered from photosensitive epilepsy, 18 of whom had idiopathic generalised epilepsy, and 23 of whom were normally developing without epilepsy. The children were exposed to visual stimuli. “However, the frequency was low, so we didn’t find any patients who had seizures during the trial,” Dr. Brazzo explained. Therefore, researchers instead examined the difference in the distance between troughs and peaks of a brain wave measured on an electroencephalogram (EEG). The measurements were taken at 75, 100, and 145 milliseconds after exposure to the stimuli, Dr. Brazzo explained. Patients were exposed to a black-and-white checkerboard pattern, for 600 consecutive trials, averaged in 6 sequential blocks, at which point researchers analysed the brain waves for evidence of habituation to the signals. “We found an increase in amplitude in the photosensitive patients, versus a decline in the other 2 groups,” said Dr. Brazzo. The researchers found the difference only in the first block, in which photosensitive patients showed lower amplitude (P < .002). It is thought that susceptibility to light in paediatric epilepsy patients has been related to 2 chromosomes. Photosensitive epilepsy is associated with an altered balance between excitatory and inhibitory impulses, but further study is needed to determine whether the lack of visual gating is merely the result of the repeated insults produced by repeated epileptiform events and ictal activity, according to the researchers. [Presentation title: Abnormal Cortical Excitability and Photosensitive Epilepsy. Abstract 2.005]
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