Abstracts

Rationale: Photosensitivity can occur in several different epilepsy syndromes, the most frequent association being with genetic generalized epilepsy (GGE), especially with juvenile myoclonic epilepsy (JME). Phenotypic overlap between the idiopathic photosensitive occipital epilepsy (IPOE) and GGE may occur. We describe the electro-clinical characteristics of a large consanguineous family from Turkey with idiopathic photosensitive epilepsy and a pedigree consistent with Mendelian inheritance. Methods: A family with 6 affected individual over 2 generations had idiopathic epilepsy and both clinical and electrical photosensitivity on their EEGs. They underwent extensive electro-clinical phenotyping. Photosensitive syndromes were classified as IPOE, GGE and IPOE overlap, and early onset photosensitive absence epilepsy (EOPAE). ?  Results: All of the affected family members with idiopathic photosensitive epilepsy were female. Age at seizure onset was between 4-15 years. 2 affected family members had IPOE/JME, 2 identical twin sisters with EOPAE, 1 with IPOE, and 1 with EOPAE/IPOE. The most prominent seizure types at onset were visual hallucinations, consoncious head version, and secondarily generalized tonic-clonic seizures (TCSs) in 3 patients, and photosensitive absence seizures associated with concomitant myoclonic jerks in 3 other patients. All patients had visual auras including coloured circles or bright flashes of light, 4 with conscious head version; 5 with myoclonic jerks of the arms; all had also non-photic-induced TCSs precipitated by sleep deprivation on awakening. All experienced eyelid blinking which was triggered by environmental photic stimulation during their disease course. All had migraine headache and 5 had febrile seizures. An earlier age at seizure onset was observed in 3 patients who presented with photosensitive absences seizures in the first 4 years of life. Their EEGs showed fast (>4 Hz) generalized polyspike-and wave activity and photoparoxysmal response (PPR) related to eye closure in all. 5 had focal parieto-occipital spike and waves. The monozygotic twin sisters had generalized 14 Hz fast rhythmic discharges on their EEGs. 3 unaffected family members had normal EEGs. Antiepileptic drugs eliminate visual symptoms, myoclonic seizures and TCSs in all, but with continuing brief and mild absences and characteristic EEG abnormalities in monozygotic twin.  Conclusions: The phenotyping in this family with idiopathic photosensitive epilepsy show heterogeneous patterns of epilepsy syndromes consisting of a spectrum from pure IPOE to GGE/EOPAE/IPOE. The occipital primary visual cortex appears to be necessary to trigger systems for propagation and generalization of electrical activity with associated clinical manifestations. Thus, the separation of idiopathic photosensitive epilepsies into generalized and focal groups is somewhat artificial. Idiopathic photosensitive epilepsy subsyndromes may represent a biologic continuum rather than discrete entities. Funding: No funding