Photosensitivity and Epilepsy

Alberto Verrotti MD, PhD; Daniela Trotta, MD; Carmela Salladini, MD; Giovanna di Corcia, MD

Disclosures

J Child Neurol. 2004;19(8):571-578. 

In This Article

Classification of Photoparoxysmal Responses and Electroclinical Phenomena

A typical generalized photoparoxysmal response consists of a spike-and-wave discharge limited to the stimulus train that involves both anterior and posterior regions, bilateral and synchronous.[7] The discharge was originally defined by Bickford et al. as a photoconvulsive response.[62] Waltz et al. subclassified the photoparoxysmal response in four types of abnormal response to intermittent photic stimulation: (1) spikes within the occipital rhythm, (2) parieto-occipital spikes with a biphasic slow wave, (3) parieto-occipital spikes with a biphasic slow wave and spread to the frontal region, and (4) generalized spikes and wave or polyspikes and wave.[63] It is still unclear to what extent the finding of one of these responses is related to the risk of visually induced seizures because apart from the methodology of intermittent photic stimulation, age and duration of medication also have influences on the type of response. However, today it is accepted that among responses to intermittent photic stimulation in untreated subjects, only generalized paroxysmal epileptiform discharges (spikes, polyspikes, and spike-and-wave complexes) are clearly linked to epilepsy.[21]

Following the classification of electroclinical phenomena, patients can be classified into five types[2]:

  1. Individuals with a photoparoxysmal response on the EEG and no history of epileptic seizures. In this group of subjects, the photoparoxysmal response is generally detected by chance among individuals with headache or another complaint or because of a family member with epilepsy or photosensitivity.[20,28,29,64] Some years ago, So et al. studied a cohort of nonepileptic adults who showed a photoparoxysmal response on intermittent photic stimulation and found that the mere presence of a photoparoxysmal response did not influence the probability of developing seizures because none of the 33 individuals developed seizures over the subsequent 6- to 12-year period.[3] We studied 14 nonepileptic children who showed a photoparoxysmal response and demonstrated that this EEG change was not related to the presence of seizures and must not be considered a marker for the development of epilepsy.[4]

  2. Patients with spontaneous seizures but with a photoparoxysmal response on the EEG. In this group, there are children with different types of epilepsy. Among the idiopathic generalized epilepsies, visual sensitivity is quite frequent in benign myoclonic epilepsy in infancy and in juvenile myoclonic epilepsy; in this second type of epilepsy, the association with visual sensitivity is very frequent, up to 80% of cases.[22] Moreover, epilepsy with generalized tonic-clonic seizures on awakening is accompanied by a photoparoxysmal response in approximately 13% of patients.[65]

  3. Patients with an isolated visually induced seizure in special circumstances, with or without a photoparoxysmal response on the EEG. This group comprises patients with a single seizure while playing a computer game or watching television.

  4. Recurrent visually induced seizures and no spontaneous seizures, with or without a photoparoxysmal response on the EEG. These children show myoclonic jerks and/or epilepsy with generalized tonic-clonic seizures only in response to a visual stimulus.

  5. Visually induced and spontaneous seizures, with or without a photoparoxysmal response on the EEG.

In everyday practice, the second type is the most important; in fact, there are different forms of epilepsies with the photoparoxysmal response as a peculiar aspect, which is often useful for the diagnosis.

Pure photosensitive epilepsy, characterized by generalized seizures exclusively provoked by a flicker, is typically a disorder of adolescence, with a female predominance.[30,66,67] The seizures are reported to be typically generalized tonic-clonic, as in 84% of Jeavons and Harding's patients,[67] whereas some cases consist of absences, partial motor seizures, and myoclonic seizures.[35,68]

Among these epilepsies, progressive myoclonus epilepsies are a large group, including neuronal ceroid lipofuscinoses,[69,70] Lafora's disease,[71,72] Unverricht-Lundborg disease,[73] and myoclonus epilepsy with ragged red fibers (MERRF).[74]

Analysis of photosensitivity by types of epilepsies showed that, in the presence of photosensitivity, the type of epilepsy is most likely to be undetermined epilepsy in childhood and idiopathic generalized epilepsy in the adolescence.[33]

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