Diagnosing photosensitive epilepsy: fancy new versus old fashioned techniques in patients with different epileptic syndromes.

Purpose: To demonstrate the clinical importance of using a high quality photic stimulator for recording EEGs to diagnose photosensitivity.

Methods: We performed EEG examinations on 2 adult and 2 paediatric patients with a history of visually induced seizures; routinely we used a Grass PS 40 photic stimulator (rectangular Xenon lamp giving flashes of 10 μs duration, 0.7J, 1-30 Hz, width 7 cm, length 12 cm). We repeated the IPS with a Grass PS 33 plus stimulator (round Xenon lamp giving flashes of 10 μs duration, 1J, 1-60 Hz, diameter 14 cm).

Results: Patients were affected by both benign and catastrophic epilepsies. They complained about episodes of dizziness (case 1), dizziness accompanied by a sensation in the arms and fear (case 2), absences (case 3), and myoclonic jerks (case 4). These symptoms occurred when working with neon lights, computers or ironing striped clothes (case 1), while driving (case 2), whenever there was sunlight (case 3 and 4). Only IPS performed with the Grass PS 33 plus stimulator evoked PPRs accompanied by their typical complaints. In all cases, the revised diagnosis led to changes in their treatment and the disappearance or diminishment of their complaints and PPR range.

Conclusion: A PPR can occur in various types of epilepsy, can have a different meaning, and requires a different therapeutic intervention. Only an appropriate photic stimulator with diffuse white light and a flash intensity level of 1J/flash, can reliably demonstrate whether a patient is photosensitive, or equally important exclude it.