Methodology of photic stimulation revisited: Updated European algorithm for visual stimulation in the EEG laboratory

Abstract

SUMMARYIntermittent photic stimulation (IPS) is a common procedure performed in the electroencephalography (EEG) laboratory in children and adults to detect abnormal epileptogenic sensitivity to flickering light (i.e., photosensitivity). In practice, substantial variability in outcome is anecdotally found due to the many different methods used per laboratory and country. We believe that standardization of procedure, based on scientific and clinical data, should permit reproducible identification and quantification of photosensitivity. We hope that the use of our new algorithm will help in standardizing the IPS procedure, which in turn may more clearly identify and assist monitoring of patients with epilepsy and photosensitivity. Our algorithm goes far beyond that published in 1999 (Epilepsia, 1999a, 40, 75; Neurophysiol Clin, 1999b, 29, 318): it has substantially increased content, detailing technical and logistical aspects of IPS testing and the rationale for many of the steps in the IPS procedure. Furthermore, our latest algorithm incorporates the consensus of repeated scientific meetings of European experts in this field over a period of 6 years with feedback from general neurologists and epileptologists to improve its validity and utility. Accordingly, our European group has provided herein updated algorithms for two different levels of methodology: (1) requirements for defining photosensitivity in patients and in family members of known photosensitive patients and (2) requirements for tailored studies in patients with a clear history of visually induced seizures or complaints, and in those already known to be photosensitive.

Reexamining the Added Value of Intermittent Photic Stimulation and Hyperventilation in Routine EEG Practice

“…Although PPRs are most frequently generalized, photic stimulation has the potential to trigger focal occipital epileptiform discharges [17,18]. Besides its importance in increasing the diagnostic yield of routine EEG and better defining the type of epilepsy, IPS has other potential benefits that were not specifically addressed in this study [3]. Quantification of the response to IPS by determining the flash frequency thresholds eliciting a PPR and personalized studies using pattern and TV testing can help identify environmental triggers [19] and, accordingly, select the most appropriate therapeutic measure [20].…”

“…They are said to significantly increase the diagnostic yield of the regular EEG [3,4]. It is well known that these procedures will enhance interictal epileptic discharges especially in patients with generalized epilepsy but also in those with partial seizures [4,5].…”

EEG in adults in the laboratory or at the patient's bedside

“…Methodology of the standard stimulation procedure [87,88]. Before starting IPS, clinical data suggesting photosensitivity must be evaluated (age range between 10-20 years, notion of antiepileptic treatment, notion of sleep deprivation, notion of seizures in front of the TV and notion of family history of photosensitivity).…”

Dose‐dependent suppression of human photoparoxysmal response with the competitive AMPA/kainate receptor antagonist BGG492: Clear PK/PD relationship

“…The trial design concept, along with the PPR model and its standardized evaluation of outcome parameters, is widely referenced in the literature. 6,8,[10][11][12][13] In photosensitive patients, epileptiform electroencephalography (EEG) discharges can be evoked repeatedly in a very controlled manner in the laboratory by standardized intermittent photic stimulation (IPS). 13 An individual PPR range is determined hourly by an upper and lower sensitivity limit.…”

“…White flashes from a PS33 photostimulator (Grass Technologies, Warwick, RI, U.S.A.) were administered at a maximum of 14 separate frequencies (2,6,8,10,13,15,18,20,23,25,30,40,50, and 60 Hz) in ascending and descending order and the photosensitivity response assessed during three eye conditions: eye closure, eyes closed, and eyes open. The corresponding established photosensitivity ranges were then translated into the SPR, which is defined as the number of frequencies that consistently elicit a PPR.…”