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

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.