Frequency, distribution and clinical significance of benign variants in electroencephalography (EEG): Possible relationships with epilepsy types and syndromes

THESIS ABSTRACT The aim of this study is to investigate the frequency and distribution of benign variants (BV) in electroencephalogram (EEG) and their possible relationships with demographic and clinical characteristics, seizure types and epilepsy syndromes. In this retrospective and cross-sectional study, data from 815 patients with EEG recordings were analyzed. Clinical, demographic and neurophysiological data of the patients were evaluated. The parameters analysed included age, gender, reason for requesting EEG, requesting unit, presence and type of seizures, presence of epilepsy diagnosis, type of epilepsy syndrome if any, use of antiepileptic drugs, presence of diseases other than epilepsy and brain magnetic resonance imaging (MRI) results. Regarding the EEG, alertness during recording, pathology, presence of epileptiform activity, presence and types of benign EEG variants were recorded. All obtained data were evaluated statistically. Benign variants were detected in 266 (32.6%) of the patients. The most common were photomyogenic response 171 (21%), positive occipital sharp sleep transitions (POSTs) 70(8.6%) and photic driving 67 (8.2%). The POSTs variant was observed more frequently especially in the 21–30 age group, and its incidence decreased with increasing age (p < 0.05). Benign variants, especially POSTs and photic driving, were detected more frequently in women. (p < 0.05). It was generally observed at a higher rate in individuals with normal MRI and EEG (p < 0.05). While a positive correlation was found between epilepsy diagnosis and POSTs, no direct significant correlation was found between other variants and epilepsy. Among epilepsy syndromes, BV and POSTs were seen more frequently in idiopathic generalized epilepsy and focal epilepsy of unknown cause groups (p < 0.05). Subclinical Rhythmic Electroencephalographic Discharges (SREDA) were never recorded in adults, and Benign Sporadic Sleep Spines (BSSS) were detected significantly less than reported in the literature. Benign variants are structures that are frequently encountered in clinical evaluations but have the potential to be confused with epileptic activity. The findings show that benign variants should be carefully evaluated during the diagnosis and management of epilepsy and can be frequently seen in all individuals with and without epilepsy, and that some variants are very rare indeed.