Clinical Significance of EEG Abnormalities During Photic Stimulation in Patients with Photosensitive Epilepsy

Abstract

Summary: Purpose: The continued presence of EEG abnormalities in patients with a history of photosensitive seizures is used to signify the persistence of photosensitive epilepsy. The extent to which this approach places patients at risk of seizures is unclear, however. We describe those EEG abnormalities that may be tolerated with low risk of further seizures, and those that are indicative of poor seizure control.Methods: Fifty patients with EEG evidence of persistent photosensitive epilepsy underwent photosensitivity testing with diffuse and patterned light; 58% of patients continued to experience seizures, and 42% were seizure free. The incidence of EEG abnormalities to diffuse and patterned intermittent photic stimulation (IPS) was analysed as a function of recent seizures.Results: All patients showed EEG abnormalities to patterned IPS; there was n o significant association between patterned IPS and poor seizure control. EEG abnormalities to diffuse IPS occurred in 58% of patients, and 76% of these patients had experienced a seizure within the previous year. These patients were more than twice as likely to be poorly controlled than those who showed abnormalities only to patterned IPS. These results were consistent for both medicated and unrnedicated patients.Conclusions: EEG abnormalities to patterned IPS can be used to signify the persistence of photosensitive epilepsy, but abnormalities to diffuse IPS are more likely to indicate the patient is poorly controlled and at risk of further seizures.

Human photosensitivity: from pathophysiology to treatment

“…Fylan et al. (1999) demonstrated that, in patients with a history of photosensitive seizures, abnormalities to patterned IPS are more common than those to diffuse IPS and, although consistent with the clinical history of VS, are not reliable predictors of the patients being poorly controlled.…”

“…, 2001). This EEG response, elicited by IPS or by other visual stimuli of daily life, is called Photo Paroxysmal Response (PPR) (Fylan et al. , 1999; Kasteleijn‐Nolst Trenité et al.…”

Topical Review: Photosensitivity and Epilepsy

“…The results of the study by Fylan et al on 50 patients with EEG evidence of persistent photosensitive epilepsy demonstrated that EEG abnormalities to patterned intermittent photic stimulation can be used to signify the persistence of photosensitive epilepsy, but abnormalities to diffuse intermittent photic stimulation indicate that the patient is poorly (1) spikes within the occipital rhythm, (2) parieto-occipital spikes with a biphasic slow wave, (3) parieto-occipital spikes with a biphasic slow wave and spread to the frontal region, and (4) generalized spikes and wave or polyspikes and wave .63 It is still unclear to what extent the finding of one of these responses is related to the risk of visually induced seizures because apart from the methodology of intermittent photic stimulation, age and duration of medication also have influences on the type of response.…”

“…Following the classification of electroclinical phenomena, patients can be classified into five types': 1. Individuals with a photoparoxysmal response on the EEG and no history of epileptic seizures.…”

Visual Sensitivity and Epilepsy: A Proposed Terminology and Classification for Clinical and EEG Phenomenology

“…There is a clear female predominance among patients with VS and IGE. The triggering role of visual stimuli tends to decrease through adulthood, although the PPR may persist on repeated EEG investigations (23,70,78).…”