Photosensitivity According to Types of Epilepsy and Epileptic Syn‐ dromes.
Authors: Shiraishi Hideaki , Fujiwara Tateki , Inoue Yushi , Yagi Kazuichi 
Published: August 2005

Purpose: Despite various reports about photo‐paroxysmal response (PPR) among patients with epilepsy, few such studies utilize the classification of epileptic syndromes defined by the International League against Epilepsy (ILAE) in 1989. We analyzed the features of patients with positive PPR according to the type of epilepsy and epileptic syn‐ dromes in Japanese patients.

Patients: We investigated 2, 187 patients with epilepsy who were treated in The National Epilepsy Center for I year between February 1997 and February 1998. The mean age was 24.2 years old, 1,226 patients were male (56%), and 961 female (44%). We diagnosed the epileptic syndrome by electroclinical analysis and investigation of seizure phenomenon. The number of patients for each epileptic syndrome was 232 (I I% of all patients) with idiopathic generalized epilepsy (ICE), 512 (23%) with symptomatic generalized epilepsy JSGE), I,199 (55%) with symptomatic partial epilepsy (SPE), 23 (I%) with idiopathic partial epilepsy (IPE), 105 (5%) with undetermined epilepsy (UDE), and 110 (5%) with unclassifiable epilepsy (UCE).

Methods: We used a Grass PS33 Plus photic stimulator to deliver intermittent photic stimulation (IPS) with the following parameters: flash intensity 8 (about 1000 lux at the nasion), placed 30 cm from the nasion in a brightly illuminated room, 18 flashes per second, and eyes open then closed. If the PPR was elicited, 6, 10, 12, 15, 33, and 20 flashes per second stimulation were executed. The stimulation period was 4 seconds for screening at first, but stimulation was stopped if a positive response was obtained. The definition of positive PPR was based upon Binnie's criteria of bilateral diffuse spike‐wave complexes or polyspike‐wave complexes outlasting the stimulus for at least 100 msec.

Results: Thirty‐seven (1.7% of all patients) patients showed a positive PPR in our analysis. The distribution was 19 male patients (1.5% of all the male patients) and I8 female patients (1.9% of all the female patients), Mean age was 17.0 years old and ranged from 4 to 44 years old. The subpopulation of patients with positive PPR findings according to the type of epilepsy was 10 with SGE (2.0% of all patients with SGE), 13 with IGE (5.6% of all patients with IGE, p < O.Ol), 9 with SPE (0.7% of all patients with SPE), and 5 with UDE (4.8% of a11 patients with UDE, p < 0.05). Juvenile myoclonic epilepsy (JME) patients with positive PPR accounted for 17.4% of all the patients with JME, p < 0.01. Positive PPRs occurred in 5 patients with GTCS on awakening (7.6% of all the patients with GTCS on awakening, p < 0.01).

The subpopulations of SPE were: 2 with TLE (0.4% of all patients with TLE), 5 with OLE (4.5% of all patients with OLE, p < 0.05) and 1 with FLE. The exact epileptic focus could not be determined in 1 patient with positive PPR findings. Incidence of positive PPR gradually increased with age to 15 years old and suddenly decreased after 20 years old. The maximum incidence was 4.3% at the age range between 11 and I5 years old and this high incidence remained until 20 years old.

Conclusions: ICE was the most characteristic type of epilepsy with positive PPR findings, and the patients with JME and GTCS on awakening elicited PPR most frequently. OLE occurred most frequently among the patients with SPE. We also confirmed that the incidence of PPR showed a characteristic dependency upon age.