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Keywords:

  • Photosensitivity;
  • Photosensitive epilepsy;
  • Epileptic syndrome;
  • Photoparoxysmal response

Abstract

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. REFERENCES

Summary:  Purpose: We examined the incidence and distribution of photosensitivity among the different age groups and different types of epilepsies and epileptic syndromes. Furthermore, we considered the influence of ethnic and geographic factors on the incidence of photoparoxysmal response (PPR) in epilepsy patients.

Methods: We analyzed the responses to intermittent photic stimulation (IPS) by using a Grass PS22 or PS33 photic stimulator for in 2,187 unselected patients with epilepsy who were treated in our center.

Results: The classic PPR was elicited in 37 (1.7%) patients. The mean age of these 37 patients was 17.0 years. The subpopulation of patients having PPR included 2.0% of all patients with symptomatic generalized epilepsy, 5.6% (p < 0.01) of those with idiopathic generalized epilepsy, 0.7% of those with symptomatic localization-related epilepsy, and 2.9% of those with undetermined epilepsy. PPR accounted for 17.4 % (p < 0.01) of the patients with juvenile myoclonic epilepsy, 7.6% (p < 0.01) of those with grand mal on awakening, and 6.1% (p < 0.01) of those with symptomatic occipital lobe epilepsy. The incidence of PPR increased in patients up to age 15 years, and suddenly decreased after age 20 years.

Conclusion: The present study presents the first report from eastern Asia, analyzing the incidence of PPR with a restricted definition comparable to the other studies, and the rate of PPR was relatively low compared with the studies performed in the European countries. We could confirm the clear relation between age and positive PPR.

Photosensitivity is detected on the EEG as a paroxysmal response to intermittent photic stimulation (IPS). This reaction is called the photoparoxysmal response (PPR). Photosensitive epilepsy is a typical example of reflex epilepsy, and numerous articles have been published on the PPR in patients with epilepsy (1–11). Especially Jeavons and Harding deeply analyzed photosensitivity of the human epilepsy patients (12). However, few of these reports are based on the classifications of seizures, epilepsies, and epileptic syndromes proposed by the International League Against Epilepsy (ILAE) (13,14). Previously we reported that the photosensitivity rate for 1,542 patients with epilepsy was 1.5%(15). Because the rate of PPR in the previous report was relatively low compared with that in the studies performed in the European countries (2–4), in the present study, we reexamined the incidence and distribution of photosensitivity among the different age groups and different types of epilepsies and epileptic syndromes. Furthermore, we tried to consider the influence of ethnic and geographic factors on the incidence of PPR in epilepsy patients.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. REFERENCES

Patients

We studied retrospectively a total of 2,187 unselected patients with epilepsy who were treated in our Center between February 1997 and February 1998. The patients, aged younger than 1–81 years (mean, 24.2 years), were 1,226 (56%) male and 961 female (44%) patients. The majority of these patients were treated with antiepileptic drugs (AEDs). We classified the epilepsies and epileptic syndromes of these patients according to the criteria of the ILAE (13,14). Analysis of the patients by type of epilepsy showed that 232 patients (11% of all patients) had an idiopathic generalized epilepsy (IGE); 512 (23%) patients, symptomatic generalized epilepsy (SGE); 1,201 (55%) patients, symptomatic localization-related epilepsy (SLRE); 23 (1%) patients, idiopathic localization-related epilepsy (ILRE); 103 (5%) patients, undetermined epilepsy (UDE); and 116 (5%) patients, unclassifiable epilepsy (UCE).

Among the patients with SLRE, there were 277 patients (23% of all SLRE patients) with frontal lobe epilepsy (FLE), 457 (38%) patients with temporal lobe epilepsy (TLE), 24 (2%) patients with parietal lobe epilepsy (PLE), and 114 (9%) patients with occipital lobe epilepsy (OLE). The localization of epileptogenic focus in 329 (27%) patients with SLRE could not be specified. Of the 232 patients with IGE, 23 (10%) patients had juvenile myoclonic epilepsy (JME), 68 patients had grand mal (GM) on awakening, and 29 patients had childhood absence epilepsy (CAE).

Methods

We used a Grass PS22 or PS33 photic stimulator (Grass INST. DIV., W. Warwick, RI, U.S.A.) for IPS under conditions based on the protocol of Binnie (16). The flash lamp was placed 30 cm from the nasion with a flash intensity level of 8. Stimulation was performed in a highly illuminated room, with 1,000 lux at the nasion. We determined this illumination as 1,000 lux, approximately equivalent to the normal daily illumination in a living room, and based on Binnie's protocol. Photic stimulation was first done at 18 flashes per second under conditions of eye closure, eyes closed, and eyes open. If the PPR was elicited under any of the three conditions, photic stimulation was then done at 6, 10, 12, 16, 33, and 20 flashes per second. The stimulus train lasted 4 s of each condition, or was stopped immediately if a PPR was elicited. The PPR was defined as bisynchronous diffuse spikes-and-waves and multiple spikes-and-waves, not frequency-locked to the stimulus and outlasting the stimulus train by ≥100 ms (16).

We examined the relationship between the frequency of the positive PPR findings and the epileptic syndrome and the patient's age.

Statistical analysis

The χ2 test and Fisher's exact test were used to evaluate the significance of the results.

RESULTS

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. REFERENCES

The PPR was elicited in 37 (1.7%) of the 2,187 patients. The patients with positive PPR were aged from 4 to 44 years (mean, 17.0 years), and there were 19 male (1.5% of all male patients) and 18 female (1.9% of all female patients) patients. Thirteen patients had IGE (5.6% of all with IGE, p < 0.01 compared with total patients with PPR), 10 patients had SGE (2.0% of all patients with SGE), 11 patients had SLRE (0.7% of all with SLRE), and three patients had UDE (2.9% of all with UDE; Table 1).

Table 1.  Photoparoxysmal response in relation to types of epilepsy
Epilepsy typeNo. of patientsNo. of patients with PPRs (%)
  • IGE, idiopathic generalized epilepsy; ILRE, idiopathic localization-related epilepsy; SGE, symptomatic generalized epilepsy; SLRE, symptomatic localization-related epilepsy; UDE, undetermined epilepsy; UCE, unclassifiable epilepsy.

  • a

     p < 0.01 compared with total patients.

SGE51210 (2.0)
IGE23213 (5.6)a
SLRE1,20111 (0.7)
ILRE230
UDE1032 (2.9)
UCE1160
Total2,18737 (1.7)

Among the IGE patients, there were four patients with JME (17.4 % of all patients with JME, p < 0.01) and five patients with GM on awakening (7.6% of all with GM on awakening, p < 0.01; Table 2).

Table 2.  Incidence of photoparoxysmal response in idiopathic generalized epilepsy
Epileptic syndromeNo. of patientsNo. of patients with PPRs (%)
  • CAE, childhood absence epilepsy; GM, grand mal; JME, juvenile myoclonic epilepsy; PPR, photoparoxysmal response.

  • a

     p < 0.01 compared with total patients.

JME234 (17.4)a
GM on awakening685 (7.6)a
CAE291 (3.4)
Others1123 (2.7)
Total23213 (5.6)

Among the patients with SLRE, there was one patient with FLE (0.4% of all patients with FLE), two patients with TLE (0.4% of all patients with TLE), and seven patients with OLE (6.1% of all with OLE, p < 0.01). The localization of epileptogenic focus in one patient could not be specified (Table 3).

Table 3.  Incidence of photoparoxysmal response in localization-related epilepsy
Epileptic syndromeNo. of patientsNo. of patients with PPRs (%)
  • FLE, frontal lobe epilepsy; OLE, occipital lobe epilepsy; PLE, parietal lobe epilepsy; TLE, temporal lobe epilepsy.

  • a

     p < 0.01 compared with total patients.

  • b

     Localization-related epilepsy with unspecified focus localization.

FLE2771 (0.4)
TLE4572 (0.4)
PLE240
OLE1147 (6.1)a
Not specifiedb3291 (0.3)
Total1,20111 (0.7)

The incidence of PPR gradually increased in patients up to age 15 years, and suddenly decreased after age 20 years. The maximal incidence was 4.3% between ages 11 and 15 years, and the incidence remained high until age 20 years (Fig. 1).

image

Figure 1. Incidence of photosensitivity in patients with epilepsy at different ages. Number of patients with epilepsy at different ages (bars). The incidence of the photoparoxysmal response (straight line) gradually increased with ages up to 15 years, and suddenly decreased after age 20 years.

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The incidence of PPR by the type of epilepsy was analyzed in different age groups (Fig. 2).

image

Figure 2. Incidence of photosensitivity in relation to types of epilepsy and age. Between ages 15 and 20 years, there was a significantly higher incidence of photoparoxysmal responses (PPRs; 20%) in IGE patients, and between ages 6 and 10 years, the incidence of PPRs was significantly higher in UDE patients. UDE, undetermined epilepsy; SLRE, symptomatic localization-related epilepsy; SGE, symptomatic generalized epilepsy; IGE, idiopathic generalized epilepsy.

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The incidence was 20% (p < 0.01) in patients with IGE aged 16–20 years, and it was 8.0% (p < 0.05) at ages 6–10 years in patients with UDE. Between the ages of 21 and 25 years, only the patients with SGE showed PPRs. Furthermore, only those with IGE showed PPR in the patients older than 31 years.

DISCUSSION

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. REFERENCES

Kasteleijn-Nolst Trenité(2) reported that 4.3% of patients with epilepsy showed PPR elicited by photic stimulation, and the ratio of male to female patients was 1:1.6. Binnie and Jeavons (3), whose analysis used the ILAE classification of epileptic syndromes, reported the incidence of PPR as 5.5% of patients with epilepsy. They also stated that the PPR incidence is 21.1% in patients with IGE, 5.1% in patients with SGE, 2.8% in patients with localization-related epilepsy, and 2.9% in patients with unclassifiable epilepsy. In the present study, 1.7% of the patients showed PPR elicited by photic stimulation, and only the patients with IGE had a significantly higher incidence of PPR compared with the total patients. The difference in the incidence of PPR between the sexes did not have statistical value in our study.

In our survey, we initially used 18 flashes per second photic stimulation as a screening test. It was thought that there might be a risk of false-negative reaction using only 18 flashes per second stimulation.

Jeavons and Harding reported that 95% of PPR-positive patients reacted to 18 flashes per second stimulation (12). They also reported 96% of all PPR-positive patients were elicited by the stimulation ranging between 15 and 20 flashes per second (12). Although we underwent another stimulation if possible when there was a subtle reaction, such as if fundamental driving on the occipital region was elicited during screening using 18 flashes per second stimulation, there were a few false negatives in our study.

The incidence of PPR was significantly higher in the epileptic syndromes of JME and GM on awakening than in CAE or other IGE syndromes in our study. This agrees with the findings of Wolf and Goosses (4). In patients with SLRE, there was a significantly higher incidence of PPR in patients with OLE. Localization-related epilepsy (LRE) has been thought to have little relation to photosensitivity, although photic-induced partial seizures have been reported among patients with OLE (5–8). Guilliam and Chiappa (17) reported that among 115 patients with positive PPR findings, 17 patients had partial seizures. We reported that 11 patients (30% of all PPR-positive patients) with LRE had positive PPR findings. This incidence was higher than that in their reports. One reason that our incidence was relatively high was possibly that there were 1,261 patients (59% of all subjects) with LRE. Because Guilliam and Chiappa did not clearly describe their subjects, it was not easy to compare their results with ours. But their report and our findings clearly suggest a close relationship between photosensitivity and OLE.

Our study showed the characteristic age dependency of photosensitivity. Wolf and Goosses (4) reported a higher incidence of PPRs in the age group of 11–15 years in German patients, and noted that the incidence suddenly decreased after age 20 years, and subsequently decreased further. Jeavons and Harding also reported the age dependency of the photosensitivity (12). They deeply and restrictedly analyzed the onset of photosensitivity among patients with epilepsy. According to their report, 76% of the age at onset of photosensitivity among patients with epilepsy ranged between ages 8 and 18 years (12). Our survey confirmed their work by another restricted PPR criterion.

Analysis of photosensitivity by the types of epilepsies in the different age groups showed that the most characteristic type of epilepsy with respect to PPR was UDE at ages 6–10 years, IGE at ages 16–20 years, SGE at ages 21–25 years, and IGE at older than age 30 years. These findings suggest that, in the presence of photosensitivity, the type of epilepsy is most likely to be UDE in childhood and IGE in the adolescent period. Although the incidence of IGE, even in patients with therapy-resistant seizures, tends to decrease with age, the incidence of photosensitivity in our IGE patients increased with age by 45 years old.

According to our study and previous reports from another researcher, IGE is the most characteristic epileptic syndrome. But because of this fact, we submit that there were risks of insufficient survey after age 20 years because the frequency and need for treatment decreased by age after adolescence.

We used a restricted definition of PPR, classic and prolonged PPR, based on the definition of Binnie et al. (16), to exclude the self-limiting responses and to include the evidence of sustained afterpotentials, even for a short time. Reilly and Peters (18) suggested that if the criteria excluded the self-limiting response, 90% of PPRs would be true positive. Puglia et al. (19) also found a significant relationship between the incidence of seizures induced by photic stimulation and classic PPR.

Our results could be compared with those of the studies on the PPR from different institutions based on the similar criteria (2,3,9,16). In our study, the PPR incidence was 1.7%, which is low compared with that of northern European and Arabian populations (2–4,10,16), and high compared with that of Indian patients with epilepsy (9). According to Danesi and Oni (11), the incidence of photosensitivity in African patients with epilepsy is 1.6%, which is similar to our result. However, because their criteria for PPR were not defined in their article, it is hard to compare their results with ours. The relatively low incidence of PPRs in our sample may relate to the source of the patients. Because our center specializes in the treatment of severe epilepsy, we have a high proportion of patients with chronic intractable epilepsy, and a low proportion of patients with newly diagnosed epilepsy. It is well known that AEDs, especially valproic acid (VPA) and lamotrigine (LTG), suppress PPRs. Among the patients with PPRs we analyzed, there were 21 patients treated with VPA and only three patients who were untreated with AEDs. Because 46.2% of all patients in our center were treated with VPA in the surveillance period, the condition of AED treatment was thought to be similar among the patients in our survey. This condition may have also contributed to the low incidence of PPR in our patients. There was no patient treated by LTG, because LTG has not been approved for use in Japan.

Because of the bias mentioned earlier, our result may not represent the photosensitivity in Japan. Animation-induced seizures (Pokemon incidents) that happened on December 16, 1997, in a large area in Japan, may suggest that photosensitivity in Japan appears to be not uncommon (20). Further studies with a careful selection of patients characterized equally by type of epilepsy or epileptic syndromes, the condition of medication, and closely matched groups for age are necessary to determine the possible geographic and ethnic differences of photosensitivity in Japan.

Acknowledgment: We thank Dr. C. Binnie and Dr. M. Seino for assistance on planning and execution of this study, and Ms. Reiko Ishihara and her colleagues for technical assistance.

REFERENCES

  1. Top of page
  2. Abstract
  3. PATIENTS AND METHODS
  4. RESULTS
  5. DISCUSSION
  6. REFERENCES
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    Guilliam FG & Chiappa KH. Significance of spontaneous epileptiform abnormalities associated with a photoparoxysmal response. Neurology 1995;45:4536.
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    Reilly EL & Peters JF. Relationship of varieties of electroencephalographic photosensitivity to clinical convulsive disorders. Neurology 1973;23:10507.
  • 19
    Puglia JF, Brenner RP, Soso MJ. Relationship between prolonged and self-limited photoparoxysmal responses and seizure incidence: study and review. J Clin Neurophysiol 1992;9:13744.
  • 20
    Yamauchi T. Clinical study on photosensitive seizures. Rapid Communication Digest of the Special Research Group of Ministry of Health and Welfare, Japan, 1998. [in Japanese]