Comparison of electroencephalographic findings with hippocampal magnetic resonance imaging volumetry in dogs with idiopathic epilepsy

Abstract

Background: In humans, temporal lobe epilepsy (TLE), is a type of focal epilepsy occurring mainly in the mesial TLE (mTLE), commonly associated with hippocampal sclerosis (HS). Objectives: According to recent studies, TLE might also occur in dogs and could be associated with hippocampal atrophy (HA)/HS. To date, hippocampal lesions have not been correlated with electroencephalographic (EEG) findings in epileptic dogs. Animals: An EEG examination, brain magnetic resonance imaging, and volumetric assessment of the hippocampus were performed in 16 nonepileptic and 41 epileptic dogs. Methods: In this retrospective study, the presence and localization of EEG‐defined epileptiform discharges (EDs) was blindly evaluated. The hippocampus was measured and assessed for unilateral atrophy. The results of EEG and volumetric findings were correlated to determine whether the functional epileptic focus is equivalent to structural changes. Results: The median hippocampal asymmetric ratio (AR) in epileptic dogs was significantly greater than in the control group (P < .001). Using a cut‐off threshold AR of >6%, 56% (23/41) of the dogs were characterized with unilateral HA. Of those animals, 35% (8/23) had EDs in the temporal leads and 26% (6/23) had no EDs. In 88% (7/8) of dogs with EDs in the temporal leads that had unilateral HA, the EDs correlated with the side of the decreased hippocampal volume. Conclusions and Clinical Importance: The results indicate an association between the presence of EDs detectable on EEG and a decrease in the unilateral hippocampal volume in some cases of canine idiopathic epilepsy that might reflect features of human mTLE.

Interictal Single-Voxel Proton Magnetic Resonance Spectroscopy of the Temporal Lobe in Dogs With Idiopathic Epilepsy

“…However, the fact that other studies documented functional or structural changes of the hippocampus (10,12,13,28) warrants further investigations limited to hippocampus formation using H1-MRS. Further detailed classification of dogs with focal seizures and focal seizures evolving to generalized seizures, as well as use of continuous long-term electroencephalography, should be considered in order to improve anatomical localization of epileptic activity.…”

“…Generally, the diagnosis of canine idiopathic epilepsy (IE) is made without evidence of MRI structural or morphological lesions or insults that secondarily influence the neuronal network (9). This concept might change in the face of growing evidence of documented structural changes in dogs with IE, like changes of apparent diffusion coefficient (ADC) parameters (10) or volumetric changes of white-to-gray matter ratio (11) or hippocampus (12,13). The main knowledge about generalized tonic-clonic seizures (GTCSs) is based on electrophysiological experiments that indicated involvement of bilateral cortical, subcortical, and brain stem networks in the seizure activity (14)(15)(16).…”

“…An increased ADC has been measured in the temporal lobe of epileptic dogs (10). Finally, abnormal activity on electroencephalography (EEG), localized within the temporal lobe in dogs with epileptic seizures, has been documented in association with hippocampal atrophy (12,32). These results warrant further investigation of the temporal region in canines with suspected idiopathic Abbreviations: ADC, apparent diffusion coefficient; ANCOVA, analysis of covariance; ANOVA, analysis of variance; ATP, adenosine triphosphate; CHESS, chemical shift-selective; Cho, choline; Cho/Cr, choline-to-creatine ratio; Cho/NAA, choline-to-N-acetylaspartate ratio; CK, creatine kinase; Cr, creatine; CSF, cerebrospinal fluid; EEG, electroencephalography; FLAIR, fluid-attenuated inversion recovery; GTCS, generalized tonic-clonic seizure; H1-MRS, proton magnetic resonance spectroscopy; IE, idiopathic epilepsy; IVETF, International Veterinary Epilepsy Task Force; LCModel, linear combination model; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; NAA, N-acetylaspartate; NAA/Cho, N-acetylaspartate-to-choline ratio; NAA/Cr, Nacetylaspartate-to-creatine ratio; NP, number of phase-encoding steps; PCr, phosphocreatine; PRESS, point resolved spectroscopy sequence; SD, standard deviation; SE, spin echo; SNR, signal intensity-to-noise ratio; STEAM, stimulated echo acquisition mode; T1-w, T1-weighted; T2-w, T2-weighted; TE, echo time; TI, inversion time; TLE, temporal lobe epilepsy; TR, repetition time.…”

Companion animal models of neurological disease

“…Several quantitative MRI and functional neuroimaging techniques have been investigated in dogs with idiopathic/genetic epilepsy. Hippocampal atrophy (HA), similar to what is described in humans with mesial temporal lobe epilepsy (TLE) and hippocampal sclerosis, has been identified in up to 56 % of epileptic dogs in which volumetric MRI analyses are performed ( Czerwick et al, 2018 ; Etsey et al, 2017 ). Studies that have obtained contemporaneous EEG on dogs with HA have also demonstrated that epileptiform discharges frequently localize to the hemisphere containing the HA ( Czerwick et al, 2018 ).…”

Vómito, sialorrea y regurgitación como signos clínicos de convulsiones epilépticas focales autonómicas en tres perros

“…El EEG muestra la función de la corteza cerebral y puede ser útil para determinar el diagnóstico de epilepsia y definir el tipo de trastorno convulsivo y la zona epileptogénica (14). Las ondas en punta, puntas en espiga, constituyen uno de los elementos patológicos más significativos del EEG.…”