Left hemispheric epilepsy is more frequent and has worse clinical course that right hemispheric epilepsy

Few studies demonstrated that focal epilepsy (FE) with left hemispheric (LH) seizure onset is more frequent than with right hemispheric (RH) seizure onset. In addition, patients with LH seizure onset show worse clinical course compared to those with RH seizure onset. The aim of our study was to investigate both issues in a great cohort of FE patients.

In the retrospective study, we reviewed the clinical and paraclinical data of 682 patients with exclusively LH or RH seizure onset. We ascertained the laterality of seizure onset mainly by ictal and postictal semiology and ictal EEG findings. In the absence of ictal data, the basis of lateralization was the evidence of unilateral structural brain abnormality together with a corresponding interictal EEG finding. The endpoint of analysis of the clinical course was the presence/absence of five-year remission on drug treatment in the first ten years of treatment.

Out of the 682 patients, 378 (55.4 per cent) had LH and 304 (44.6 per cent) had RH seizure onset. The difference was statistically significant (p = 0.04). Out of them, 213 LH and 156 RH patients were eligible to evaluate prognosis. Five-years-remission was attained by 71 patients (33.3 per cent) in the LH, and 65 (41.7 per cent) in the RH group. The difference was statistically significant (p = 0.05).

We demonstrated the LH dominance of seizure onset and the worse clinical course of the patients with LH seizure onset. The findings are manifestations of the lateralized epileptic propensity of the brain. The dissimilar clinical course of the patient with LH and RH seizure onset may shape the general prognostic scheme in FE patients.