The effect of transcranial direct current stimulation on photoparoxysmal response in EEG and prognosis in patients with photosensitive idiopathic generalized epilepsy

INTRODUCTION: There are very few and outdated studies on the long-term prognosis of photosensitive epilepsies. Valproic acid (VPA), which is the first choice in the treatment of photosensitive epilepsy, creates a problem for patients, mostly women, due to its teratogenic effect. In this study, we aimed to retrospectively examine the long-term prognosis of patients with photosensitive idiopathic generalized epilepsy (IGE) and to investigate the acute effect of transcranial direct current stimulation (TDCS) on photoparoxysmal response (PPR) on EEG, which is prospectively investigated as an alternative adjunctive therapy in epilepsy patients. METHODS: Medical records and EEG data of patients with IGE, who were followed up for at least 10 years and had PPR in their EEG, were analyzed and their demographic, clinical and EEG characteristics were recorded. Prognostic data and course types and electroclinical variables were compared with appropriate statistical methods. In addition, three different applications as sham, anodal, and cathodal TDCS at one-week intervals were applied to IGE patients with PPR detected in at least 2 EEGs, by placing the active electrode in Oz, for 2 mA, 20 minutes. Spike wave indices (SWI) measured by two independent researchers were compared during intermittent photic stimulation (IPS) on EEGs before and after the application. RESULTS: The mean follow-up period of 108 IGE patients, included in the prognosis study, was 16.79 ± 6.45 (10 – 42) years; 74.1% of these patients were female. Patients with juvenile myoclonic epilepsy (JME) (37%), juvenile absence epilepsy (JAE) (15.7%), and absence epilepsy with eyelid myoclonia (EMAE) (14.8%) were the main syndromes of the cohort. In terms of the remission groups, 28% of the patients were in the relapse-remission group; 14% of the patients had never been in remission. The early remission rate was relatively low, 6%, and the remaining patients were in the late remission group. The longest seizure-free period was 6.25±5.8 years; the longest generalized tonic-clonic seizure-free (GTCS) time was 10.12±6 years. Coexistence of three seizure types, accompanying additional focal seizurefeatures, history of convulsive status epilepticus (CSE), self-induction (SI), clinical finding accompanying PPR, asynchrony and focal finding in EEG discharges, low lower and high upper frequency limits of PPR, and having a wide range of PPR frequencies were found to be statistically significant poor prognostic factors. Eleven patients, all female, were included in the TCDS study after their consents. After cathodal TCDS 3 patients; after anodal TCDS, 1 patient had an increase in SWI compared to baseline EEG and post-sham EEG. Although SWI values did not change significantly, 8 patients subjectively gave positive feedback. As a side effect, transient skin rash was reported in only one patient. CONCLUSION: Our study, which was conducted in a large group of photosensitive epilepsies and is important in terms of long-term follow-up, detected various poor prognosis markers similar to other IGE syndromes. In addition, CSE, the presence of clinical findings accompanying PPR, and the wide frequency range of PPR were reported as poor prognostic factors for this epilepsy group for the first time. In the newly proposed course types, it was found that early remission is rare in photosensitive IGEs, mostly with relapse-remission, and no remission was observed in approximately 14%. This information is important in terms of correct counseling for prognosis of these patients. In our sham-controlled TCDS study, in which both cathodal and anodal stimulation was performed using the Oz stimulation region in a limited sample, our data showed that there was no significant change in SWI, despite subjective well-being. Although we did not obtain significant data, we think that, unlike the placebo effect, the subjective positive effect should be considered in additional treatment and new studies can be planned in terms of long-term treatment.