Comparative Aspects in Interictal, Intraictal and Postictal Electroencephalogram in Dogs with Idiopathic Epilepsy

Epilepsy is a chronic brain disease, of varied etiology, defined by the presence of the seizures of definite epileptic nature and by evolutional criteria, made of their tendencies to repeat in absence of triggering factors, known at variable intervals. The diagnosis of this disease is based on the clinical features and electrophysiology of the brain. Electroencephalogram (EEG) is the efficiently electrobiological test assessing the impact of epilepsy on activity of the brain. The aims of this study are to describe the interictal, intraictal and postictal parameters, and to evaluate the clinical usefulness of the EEG recording in dogs with idiopathic epilepsy, using induced sleep as activation method. EEG was performed on 27 dogs with idiopathic epilepsy. Electrical potentials acquisition was performed using the electroencephalograph Neurofax S, MEB 9400K Nihon Kohden. Before the test, all dogs were sedated with medetomidine hydrochloride 30 μg/kg inj. i.m. Stainless steel needle electrodes were subcutaneously placed, in an 8 channel bipolar montage, according to the model of Redding and Knecht (1984). The visual and quantitative analysis of the electroencephalographic tracks in idiopathic epilepsy revealed a background activity with a high instability and diversity of aspects, as there was more discordance between the electrical and clinical findings of the epilepsy. During interictal period, in incipient cases and onset of epilepsy, the EEG alterations were discrete, resuming to a couple of overvaulted peaks and ample lent theta waves on a normal background track. When epilepsy had a longer evolution, the background activity showed an intersection of slow waves with abnormally frequent waves, rich in epilpeptiform interictal discharges like: fast spike, slow waves, polyspike and typical or atypical spike-wave complexes. The intraictal period was characterized by electrical crisis, suddenly appeared on all derivations, then intensified by neuronal recruiting phenomenon and in 2-3 seconds the EEG anomalies spread in all brain areas, as epilpeptiform discharges became bilateral synchronous. Postictal EEG was characterized by a much flattened aspect of the tracks, almost isoelectric. In conclusion, EEG gives valuable information about parameters and the severity of changes induced by epilepsy. EEG recorded using as an induced sleep activation method is the main way which proves the presence of an epileptic focus in the absence of clinical sings.