Regional paroxysmal fast rhythms on scalp EEG: an observational study

Objective: It is known that interictal regional paroxysmal fast activity (RPFA) on scalp electroencephalogram (EEG) is seen in patients with focal cortical dysplasia. We aim to investigate these activities and to understand their correlation with structural lesions on magnetic resonance imaging (MRI) and other interictal epileptiform activities on scalp EEG. Methods: We searched the prevalence of RPFA in video EEG monitorized epilepsy patients between 2012-2016 years. An additional group of patients were also added to the cohort from routine EEG recordings in order to make correlations of RPFA's with the accompanying EEG features and structural lesions on MRI. RPFA was defined as frequencies above 10 Hz, on 2-5 consecutive electrodes and short lasting. Results: A total of 250 patients were screened retrospectively. The prevalence of RPFA was 5.6% (14 patients). The total group consisted of 19 patients. The frequencies of RPFA were between 20-35 Hz (mean 26.21) and the amplitudes were between 2052 mu V (mean 30.84). The duration of RPFA vary between 200-770 milisecond (mean 293.42). All patients but one had epilepsy. Nine patients had abnormal MRI. The MRI lesion and location of RPFA were concordant in three patients. Fifteen patients had also focal sharp/spike activities which were concordant with the localization of RPFA in 13 patients. Ictal activity was available in thirteen patients. The localization of the onset of ictal activities of these patients were found to be concordant with the location of RPFA in 5 patients. Conclusion: The prevalence of RPFA was 5.6%. RPFA was observed not only in patients with developmental lesions but also encephalomalacic lesions. The concordance of RPFA with interictal, ictal EEG features and MR lesions was found moderate.