A Subset of Dogs with Presumptive Idiopathic Epilepsy Show Hippocampal Asymmetry: A Volumetric Comparison with Non-Epileptic Dogs Using MRI.

Chelsie M Estey,Joseph Sackman,Jennifer Bouma,Mark Rishniw,Erica Burkland,David M Lin,Curtis W Dewey

doi:10.3389/fvets.2017.00183

Chelsie M Estey, Joseph Sackman + Show 5 more

Open Access

https://doi.org/10.3389/fvets.2017.00183

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Abstract

MRI-acquired volumetric measurements from 100 dogs with presumptive idiopathic epilepsy (IE) and 41 non-epileptic (non-IE) dogs were used to determine if hippocampal asymmetry exists in the IE as compared to the non-IE dogs. MRI databases from three institutions were searched for dogs that underwent MRI of the brain and were determined to have IE and those that were considered non-IE dogs. Volumes of the right and left hippocampi were measured using Mimics® software. Median hippocampal volumes of IE and non-IE dogs were 0.47 and 0.53 cm3, respectively. There was no significant difference in overall hippocampal volume between IE and non-IE dogs; however, IE dogs had greater hippocampal asymmetry than non-IE dogs (P < 0.012). A threshold value of 1.16 from the hippocampal ratio had an 85% specificity for identifying IE-associated asymmetry. Thirty five percent of IE dogs had a hippocampal ratio >1.16. Asymmetry was not associated with any particular hemisphere (P = 0.67). Our study indicates that hippocampal asymmetry occurs in a subset of dogs with presumptive idiopathic/genetic epilepsy, suggesting a structural etiology to some cases of IE.

Highlights

Idiopathic epilepsy (IE) is the most commonly diagnosed canine neurologic disorder in veterinary medicine [1]
Non-idiopathic epilepsy (IE) dogs were older than IE dogs at the time of MRI (P = 0.01), but had similar distributions of sex (44% male and 56% female in each group) and proportions of purebred dogs (75 vs 82%)
Our study shows that dogs with IE have greater hippocampal asymmetry than non-IE dogs, and that a greater proportion of epileptic than non-IE dogs have hippocampal ratios indicative of asymmetry using criteria similar to those in humans

Summary

Introduction

Idiopathic epilepsy (IE) is the most commonly diagnosed canine neurologic disorder in veterinary medicine [1]. Almost half of all dogs presenting for seizures are subsequently diagnosed with IE, and in one study IE was diagnosed in 75% of dogs with an onset of seizures before 1 year of age [2, 3]. 25–30% of dogs treated for IE are refractory to treatment or are poorly controlled, often requiring multiple anticonvulsant drugs [4]. Epileptic dogs that exhibit cluster seizures or status epilepticus have shorter lifespans than those that do not experience these episodes [3, 5, 6]. Many breeds are susceptible to IE, but how epilepsy in different breeds differs is poorly understood [4]. Our understanding of epilepsy in dogs, and how many forms of epilepsy might exist, is still rudimentary. Our inability to accurately diagnose the type of epilepsy in affected

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