Interictal regional paroxysmal fast activity on scalp EEG is common in patients with underlying gliosis

Objective: Interictal regional paroxysmal fast activity (RPFA) on scalp EEG is common in patients with focal cortical dysplasia (FCD). Little data exists regarding the presence of RPFA in other etiologies. Methods: We studied the association between RPFA and etiology on MRI in patients with drug resistant focal epilepsy undergoing presurgical evaluation in 2011. RPFA was defined as >= 3 consecutive spikes with a frequency of >= 10 Hz lasting >= 300 ms but < 4 s. Results: 626 patients fulfilled the inclusion criteria. Of these, 138 (22%) patients had RPFA while rest had other interictal epileptiform discharges (IEDs). RPFA was located at posterior head region in 52.2% patients, frontal regions in 24.6% patients and over temporal regions in 17.4% patients. Focal gliosis (61, 44%) and FCD (27, 19%) were common etiologies in patients with RPFA. Compared to patients with other IEDs, patients with RPFA were more likely to have focal gliosis (61/138 vs. 39/488; p < 0.0001) or FCD (27/138 vs 37/488; p < 0.001) as the etiology of epilepsy. Conclusion: In developing countries, focal gliosis is more common than FCD as the underlying etiology in patients with RPFA on scalp EEG. Significance: Focal gliosis should be considered as one of the common substrate for RPFA on scalp EEG. (C) 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.