Abstracts

Rationale: The efficacy of single doses of many AEDs has been shown in photosensitive epilepsy patients in phase IIa studies over many years (Schmidt B, Epilepsy Res 2006). The efficacy of AEDs to continuously suppress a photoparoxysmal EEG response (PPR) in epilepsy patients at steady-state or long-term in the clinic is less well known. VPA has been one of the first drugs that had a significant impact on the EEG photosensitivity ranges (Rowan, 1979) and is still considered a drug of first choice. Some anecdotal evidence exists for the continued positive clinical effects of VPA when administered at steady-state, long-term daily doses. Other AEDs with a different mechanism(s) of action (many broad spectrum), have been effective in single does in the so-called human photosensitivity model as well. However, is the suppressive effect of AEDs in steady state still different from drug naïve patients? Are there differences in size of effect between AEDs with different mechanisms of action? Methods: Standardized EEG PPR Data from 239 consecutive epilepsy patients (163 F, 73 M; mean age 20.9 (SD 10.1 ; range 7-70 yrs) treated with select AEDs for at least 6 months have been analyzed. After a standard EEG registration in wakefulness with hyperventilation during three minutes, patients have been investigated with ascending and descending flash frequencies ( 2,4,8,10,13,15,18 20 Hz and 60, 50, 40, 30, 25 and 23 Hz) using a GRASS PS 33 stimulator. Photosensitivity ranges were determined at eye closure, eyes closed and eyes open (Kasteleijn-Nolst Trenite, Epilepsia 2012). A smaller PPR range signifies a greater response to the respective AED. Results: Eighty-four (36%) were drug naïve, 104 (44%) on monotherapy and 48 (20%) on polytherapy. The majority took VPA (103;44% ) and CBZ (51;22% ) while other medications (PB, ESM, LTG, PHT, VGB) were taken by 56 (24%)of patients. Monotherapy VPA was used in 62 patients (17 males) and monotherapy CBZ in 18 (2 males). VPA median dose = 1,000 mg daily (range 100-3,000 mg); CBZ = 400 mg daily (range 100-1,500 mg). VPA-treated patients had a substantially smaller PPR range at steady-state in the eye closure condition (VPA = 14.6, compared to drug-naive patients (21.6). The %CV was much less for VPA, indicating consistency in PPR response. Steady-state CBZ-treated patients showed a slight to modest PPR effect = 20.6 compared to drug-naive patients, and greater variability. Age was not a factor. Conclusions: In patients with photosensitivity, steady-state VPA & CBZ show a continued (at least 6 months) PPR effect. CBZ's steady-state PPR effect is much more variable vs. VPA. CBZ-treated photosensitivity patients may need higher doses.