How to Interpret Photoparoxysmal EEG Results?

Abstract

Photosensitivity is defined as a “photoparoxysmal response” (PPR) to intermittent photic stimulation (IPS) during an electroencephalogram (EEG). The PPR consists of spikes, spike-waves, or intermittent slow waves, ranging from localised occipital spikes (Grade 1) to generalised spike and wave or polyspike and wave complexes (Grade 4). Photosensitivity alone does not represent an epileptic syndrome, as it can be present in many categories of epileptic disorders and in 4% of healthy children or adolescents. In addition, several general factors such as sleep deprivation, alcohol abuse, and drug withdrawal should be taken into account when assessing photosensitivity as they may influence the likelihood of observing photoparoxysmal EEG results. Although photosensitivity can be considered a trait occurring across various conditions, syndromes in which all, or almost all, seizures are induced by photic stimuli can be considered syndromes of reflex epilepsy. In pure photosensitive epilepsy, seizures exclusively occur in response to photic stimulation as opposed to epilepsy with photosensitivity, where seizures may be spontaneous or elicited by photic stimulation. Pure photosensitive epilepsies include idiopathic photosensitive occipital lobe epilepsy and photosensitive benign myoclonic epilepsy of infancy. Photosensitivity is also frequently observed in juvenile myoclonic epilepsy and epilepsy with GTCS on awakening and in other severe syndromes, especially when myoclonus is also present, such as Dravet syndrome and progressive myoclonus epilepsies.