Two different pathological conditions of photoparoxysmal responses in hereditary dentatorubral-pallidoluysian atrophy

Photosensitivity and epilepsy: Current concepts and perspectives-A narrative review

The authors review the influence of photic stimuli on the generation of epileptic seizures, addressing the first descriptions of the phenomenon and its subsequent exploration. Initially defined in the 1950's, links between intermittent photic stimulation (IPS) and seizures were well understood by the 1970. Since then the increasing exposure to photic stimuli associated with modern life (for instance through TVs, patterns, computer games and electronic instruments with flickering displays) has led to an increased interest in this issue. Diverse stimulation procedures have been described and difference in the effects of stimulation frequencies and types, colour and lighting have been recognised. Approximately 5% of patients with epilepsy have photosensitive epilepsy (PSE). PSE is commoner in younger individuals, more frequent in women, often time-limited, generally easy to treat and closely related to generalised epilepsies, especially Juvenile Myoclonic Epilepsy (JME). Structural and functional studies of PSE indicate abnormalities beyond the frontal lobes and evidence for the role of the visual cortex in human PSE. A reduction in connectivity between prefrontal and frontopolar regions and increased connectivity between occipital cortex and the supplementary motor area may be the basis for triggering motor seizures in JME. Due to the changes observed in such areas, it is hypothesised that photoparoxysmal responses (PPR) could be a final expression of pathogenic phenomena in the striato-thalamocortical system, and possibly a core feature of JME as system epilepsy. The familial transmission of epileptiform responses to IPS is well-recognised, but no clear relation between PSE and specific genes has emerged. Although the influence of ethnic factors on PSE has been widely studied, clear conclusions are still lacking. Pharmacological therapeutic approaches are beyond the scope of this review although preventive measures allowing patients to avoid PS seizure initiation and/or generalisation are discussed. Given the gender/age group most commonly affected by PSE, the risks and benefits of drug treatment need to be carefully weighed up.

The photoparoxysmal response: the probable cause of attacks during video games

Photic stimulation is part of a typical EEG in most countries, especially to check on the photoparoxysmal response (PPR). Interest in this response was enhanced in 1997 when hundreds of Japanese children had attacks while viewing a TV cartoon called "Pokemon." The overall prevalence of the PPR among patients requiring an EEG is approximately 0.8%, but 1.7% in children and 8.87% in patients with epilepsy, more often in Caucasians and females. Autosomal dominant inheritance is indicated, and this response is seen especially at the wavelength of 700 nm or at the flicker frequency of 15-18 Hz. The PPR extending beyond the stimulus carries no increased risk of seizures. Prognosis is generally good, especially after 20 years of age. Attention to PPR has been increased with the advent of video games, and the evoked seizures from these games are likely a manifestation of photosensitive epilepsy. Drug therapy has emphasized valproic acid, but Levetiracetam has also been successful in eliminating the PPR.

Photosensitivity and epilepsy

Photosensitive epilepsy is a well-known condition characterized by seizures in patients who show photoparoxysmal responses on electroencephalography (EEG) elicited by intermittent photic stimulation. Photoparoxysmal responses can be defined as epileptiform EEG responses to intermittent photic stimulation or to other visual stimuli of everyday life and are frequently found in nonepileptic children. The modern technologic environment has led to a dramatic increase in exposure to potential trigger stimuli; nowadays, television and video games are among the most common triggers in daily life. There is ample evidence for genetic transmission of photoparoxysmal responses; systematic family studies have provided data for an autosomal dominant mode of inheritance with age-dependent penetrance for photosensitivity. The age of maximum penetrance is between 5 and 15 years. The prognosis for control of seizures induced by visual stimulation is generally very good. The large majority of patients do not need anticonvulsant therapy, but, when needed, the drug of choice is valproate. Stimulus avoidance and stimulus modification can be an effective treatment in some patients and can sometimes be combined with antiepileptic drug treatment.

Long-wavelength red light emission from TV and photosensitive siezures

PURPOSE

We investigated a role of long-wavelength red light emission from TV in the induction of photosensitive seizures by an animated TV program called "Pocket Monsters".

METHODS

The luminance energy of recorded color bar was measured by a spectroradiometer in cathode-ray tubes (CRTs) of photosensitive patients with and without seizures on the program (induced patients and photosensitive controls).

RESULTS

The mean ratio of long-wavelength red light to total visible range was significantly higher in the CRTs of induced patients than in the CRTs of photosensitive controls. The ratio of luminance energy between at turn-on and at 60 min after turn-on of the CRTs indicated that luminance energy in long-wavelength red range from the CRTs of induced patients increased significantly after turn-on of CRTs.

CONCLUSIONS

High amounts of long-wavelength red light emitted from CRTs might play an important role in induction of photosensitive seizures in "Pokemon" incident.

Wavelength dependence of photoparoxysmal responses in photosensitive patients with epilepsy

PURPOSE

We tried to specify the relation between the photoparoxysmal response (PPR) and the wavelength spectra of flashing light in various photosensitive epileptic syndromes in the physiologic state.

METHODS

Intermittent photic stimulation (IPS) by a Grass PS22 photic stimulator was performed with wavelength-specific optical filters in photosensitive patients with epilepsy (idiopathic generalized epilepsy, IGE; hereditary dentatorubral-pallidoluysian atrophy, DRPLA) and photosensitive subjects without epilepsy.

RESULTS

Five of 19 normal trichromat patients with IGE and an IGE patient with deuteranomaly showed wavelength-dependent PPRs. The wavelength-dependent PPRs were elicited only by IPS containing wavelength spectra approximately 700 nm in the normal trichromat patients. Two of four patients with DRPLA showed wavelength-dependent PPRs, and two other DRPLA patients showed quantity-of-light-dependent PPRs. Quantity-of-light-dependent PPRs are elicited by IPS containing more than a certain quantity of light, independent of the wavelength composition of the flashing light. Two of five subjects without epilepsy showed wavelength-dependent PPRs.

CONCLUSIONS

There are wavelength-dependent and quantity-of-light-dependent pathophysiologic mechanisms for eliciting PPRs by low-luminance IPS. Consideration of the quantity and wavelength composition of light from electronic screens will lead to the prevention of photosensitive seizures induced by electronic screen games.

Patient background of the Pokemon phenomenon: questionnaire studies in multiple pediatric clinics

Many children in Japan developed various neuropsychological problems, including seizures, while watching the program Pocket Monster, televised on 16 December 1997. To examine the basis for this incident, we have performed a survey of volunteering children and their parents who visited our pediatric clinics for other reasons from 8 January to 28 February 1998. Children and their parents filled out questionnaires. Among the total of 662 children surveyed, the great majority (603, 91.1%) was found to have watched the Pocket Monster program and 30 individuals (5.0% of viewers) complained of variable degrees of neuropsychological abnormalities. These included seizures (two cases), headache (nine cases), nausea (eight cases), blurred vision (four cases), vertigo (two cases), dysthymia (two cases) and vomiting (one case). Nearly half (14) of these children developed symptoms during or immediately after watching the program, while the remainder did so later. Representative cases are reported and other statistical aspects are discussed.

Wavelength dependency of photoparoxysmal responses in photosensitive nonepileptic subjects

Using specially made optical filters, we analyzed the wavelength dependency of photoparoxysmal responses (PPRs) in five photosensitive nonepileptic subjects. The wavelength spectrum around 700 nm (680-700 nm) was estimated as the only visible spectrum essential for eliciting PPRs in two normal trichromat nonepileptic subjects, although the effect of some wavelength spectra (360-400 nm and 520-580 nm) was uncertain. The wavelength dependency of PPRs in two photosensitive nonepileptic subjects was the same as that found in some patients with photosensitive idiopathic generalized epilepsy.