Abstracts

Rationale: Idiopathic photosensitive occipital epilepsy (IPOE) is a rare focal photosensitive syndrome presenting in late childhood or adolescence. Patients present with occipital seizures manifesting as colourful visual hallucinations and illusions. Autonomic symptoms, myoclonus, absences and generalised tonic clonic seizures have also been reported. Seizures are triggered by external photic stimulation; television screens or video games. Intermittent photic stimulation causes occipital photoparoxysmal responses (PPR) and may cause generalised discharges. Photosensitivity is thought to be genetically determined as PPR is primarily associated with idiopathic generalised epilepsies and some monogenic disorders. We report on 16 year old monozygotic female twins with IPOE who presented aged 14 years old with identical occipital seizure histories associated with external photic stimulation and exhibiting similar electroencephalogram (EEG) correlates. Methods: Patient consent was obtained prior to retrospective casenotes review. Data on clinical history and investigation outcomes were extracted for each twin. Results: Focal occipital seizures characterised clinically by ‘starry eyes’ lasting 40-100 seconds and associated with bi-occipital repetitive spike discharges were reproducibly precipitated by brief photic stimulation at 16-17Hz for five seconds in each twin. Visual symptoms ceased suddenly with termination of the bi-occipital repetitive spike activity. Seizures were triggered by watching television in the dark or occurred whilst in bed with the lights out. Neurological examination and subsequent MRI brain imaging was normal in both twins. Both subjects remain free of focal occipital seizures on levetiracetam monotherapy and lamotrigine monotherapy respectively. Conclusions: This twin case study of the rare focal photosensitive epilepsy syndrome IPOE provides support for the general consensus that photosensitivity is genetically determined, and can be associated with focal onset epilepsies.