‘Photosensitive epilepsy’ encompasses heterogeneous epileptic conditions in which seizures are triggered by photic stimulation. It is not an epilepsy syndrome. Epileptic photosensitivity, the propensity to seizures induced by light, is a genetically determined trait that may be asymptomatic throughout life or manifest with epileptic seizures. EEG photosensitivity, i.e. provocation of photoparoxysmal responses by intermittent photic stimulation (IPS), may or may not be associated with clinical photosensitivity.

Prevalence
1/4000 individuals aged 5 to 24 years (5% of patients with epileptic seizures). Clinical photosensitivity is found in 2% of patients of all ages presenting with seizures; 10% of patients presenting with seizures in the 7- to 19-year age range.

Abnormal EEG responses to light or pattern stimulation; occurs in 0.3% to 3% of the population.

Some recognized syndromes of idiopathic generalized epilepsy (IGE), such as juvenile myoclonic epilepsy (JME), show a high incidence of clinical or EEG photosensitivity. High prevalence of photosensitivity is found in certain forms of severe epilepsy, such as Dravet syndrome (>40%), Unverricht-Lundborg disease (90%), and other progressive myoclonic epilepsies.

Of 685 children affected by the TV Pokemon cartoon incident in Japan, only 24% who had a seizure during the cartoon had previously experienced a seizure.

Incidence
Newly presenting seizures and photosensitivity: 1.1/100,000 in the general population and 5.7/100,000 in the age group of 7 to 19 years.

Age at onset
Mainly 2 to 18 years; peak at 12 to 13 years.

Sex
2/3 are females.

Etiology
Genetically determined. Autosomal dominant and less often autosomal recessive inheritance. Probable linkage to chromosomes 7q32,16p13, 6p21.2 and 13q31.3. The gene encoding Nedd4-2, a ubiquitin protein ligase, has been implicated in some families.

Clinical manifestations
(1) generalized seizures are the more common: myoclonic jerks, generalized tonic-clonic seizures (GTCS), and absences, alone or in combination; (2) photically induced occipital focal seizures are not as common; and (3) extra-occipital focal seizures from onset are exceptional.

Precipitating factors
Flickering lights of artificial or natural light sources: video games, television, computer visual display units, discotheques, and natural flickering lights.

EEG
The resting EEG is usually normal but 20% to 30% of cases show eye closure-related paroxysms.

Properly applied intermittent photic stimulation (IPS) elicits abnormal photoparoxysmal responses (PPR) that may be (1) posterior PPR which are the mildest form of PPR (50% have clinical photosensitivity) and (2) generalized PPR, which are highly associated (90%) with clinical photosensitivity.

Prognosis
Usually; 3/4 become seizure free and 1/3 achieve complete remission. However, seizures in syndromes of photosensitive epilepsy such as Jeavons syndrome and JME are lifelong.

Management options*
Avoidance of precipitating factors. Valproate or levetiracetam could be considered if AED treatment is needed.

*Expert opinion, please check FDA-approved indications and prescribing information

This page was adapted from:

The educational kit on epilepsies
The epileptic syndromes
By C. P. Panayiotopoulos

Originally published by MEDICINAE
21 Cave Street, Oxford OX4 1BA
First published 2006 and reprinted in 2007