Contribution of intermittent photic stimulation to routine EEG

Intermittent photic stimulation (IPS) is an activation procedure performed during electroencephalography (EEG) to detect photosensitive patients. This procedure is recommended in routine EEGs but the benefit of IPS in the general population is not clearly ascertained.

We retrospectively analyzed 7683 EEGs of patients referred for a routine EEG to the Clinical Physiology Department of Lariboisière hospital, mainly from the emergency ward and the department of neurology, not specifically involved in epilepsy. All EEGs were performed with a standardized protocol. Photic driving response, photomyoclonic response and photoparoxysmal response (PPR) were specifically collected. A correlation analysis was performed between the response induced by IPS, demographical and clinical data, and current treatment or recreational drug use.

Median age was 56.4 years (41.7-71.2); 3,042 (39.6%) of patients were female; 1,208 patients (15.7%) had a past medical history of epilepsy. Photic driving response occurred in 67 EEGs (0.9%), and PPR in 6 EEGs (0.1%), all with a known history of epilepsy. Thus 0.5% (6/1,208) of epilepsy patients had a PPR. Photomyoclonic responses were not observed. Juvenile myoclonic epilepsy was the only factor associated with the presence of PPR (RR=75.26 [11.82-479.21]). PPR was not associated with clinical symptoms or seizures. There was no correlation with the type of treatment or recreational drug use.

Our results confirm that responses to IPS are rare in adult patients and especially PPR. Moreover, all patients with a PPR had a known previous history of epilepsy. These results question the benefit of IPS in adult patients with no history of epilepsy.