Abstracts

Rationale: The photosensitivity model is a well known human model to determine antiepileptic properties of new AEDs as proof of principle (POP). This Photosensitivity Model still has not been thoroughly explored. Methods: Photic induced EEG responses (Photoparoxysmal responses, PPRs) of 236 regular photosensitive patients (163 F; 69%), mean age = 20 + 10 yr (min 7, max 60 yrs) were analyzed. In all patients, standardized photic stimulation, 2 - 60 Hz, using a Grass PS 33plus had been performed with determination of upper and lower sensitivity ranges in 3 eye conditions. The PPRs for patients with vs. without AEDs were compared (t-test; Mann-Whitney; Anova regression analysis). Results: Of the 236 patients with a PPR, 233 had a PPR on eye closure, 206 with eyes closed and 149 with eyes open. Most patients were on stable AEDs (152; 64%) and monotherapy (104; 44%), with VPA in 62 cases, CBZ in 18 and other AEDs in 24. Forty eight patients (20%) took 2-4 AEDs, with PB as most often prescribed drug in combination (18), followed by ESM (14), LTG (10) , one of the the benzodiazepines DZP, CNZ or CLB (9), PHT (4) and VGB (1). The upper sensitivity limit had a greater spreading and at eye closure and eyes closed they were higher in women (p=0.002 and 0.018) than in man. Patients on AEDs had significant changes (lowering of) upper limit while the lower sensitivity limit did not change significantly (see Table I). Conclusions: The upper sensitivity limits of photosensitive patients are lower in patients with AEDs, compared to those without. This phenomenon is also seen in individual cases participating in POP studies, in which the same patient is investigated with and without trial medication. Determination of the upper limit may be sufficient in POP new AED trials, which reduces the total number of photic stimulations by half. This has advantages for the patient and will reduce the costs of the POP-trial.