Photosensitivity in juvenile myoclonic epilepsy.

Photosensitivity is reported to occur in approximately 40% of patients with juvenile myoclonic epilepsy. Our experience suggests that the prevalence is higher and may be related to both the duration of intermittent photic stimulation and also the age at which the procedure is undertaken. A two-year retrospective review of all EEGs was undertaken on all children attending a paediatric EEG department to identify those with juvenile myoclonic epilepsy. Photosensitivity was defined as a generalized spike or spike-wave paroxysm occurring at least twice during intermittent photic stimulation. Sixty-one children with a diagnosis of juvenile myoclonic epilepsy with a median age of 13 (range 7-16) years were identified, 55 (90%) of whom were photosensitive. Eighteen of these 55 patients showed photosensitivity only after four minutes of continuous photic stimulation. The prevalence of photosensitivity in juvenile myoclonic epilepsy is likely to be higher than previously reported. When a diagnosis of juvenile myoclonic epilepsy is being considered, the initial diagnostic EEG should include intermittent photic stimulation for up to five minutes, or less if the patient shows evidence of photosensitivity. The identification of photosensitivity may have important management implications.