Grey matter volume in healthy and epileptic beagles using voxel-based morphometry – a pilot study

Frank et al. BMC Veterinary Research (2018) 14:50 https://doi.org/10.1186/s12917-018-1373-8 RESEARCH ARTICLE Open Access Grey matter volume in healthy and epileptic beagles using voxel-based morphometry – a pilot study Lisa Frank1* , Matthias Lüpke2, Draginja Kostic1, Wolfgang Löscher3 and Andrea Tipold1 Abstract Background: One of the most common chronic neurological disorders in dogs is idiopathic epilepsy (IE) diagnosed as epilepsy without structural changes in the brain. In the current study the hypothesis should be proven that subtle grey matter changes occur in epileptic dogs. Therefore, magnetic resonance (MR) images of one dog breed (Beagles) were used to obtain an approximately uniform brain shape. Local differences in grey matter volume (GMV) were compared between 5 healthy Beagles and 10 Beagles with spontaneously recurrent seizures (5 dogs with IE and 5 dogs with structural epilepsy (SE)), using voxel-based morphometry (VBM). T1W images of all dogs were prepared using Amira 6.3.0 for brain extraction, FSL 4.1.8 for registration and SPM12 for realignment. After creation of tissue probability maps of cerebrospinal fluid, grey and white matter from control images to segment all extracted brains, GM templates for each group were constructed to normalize brain images for parametric statistical analysis, which was achieved using SPM12. Results: Epileptic Beagles (IE and SE Beagles) displayed statistically significant reduced GMV in olfactory bulb, cingulate gyrus, hippocampus and cortex, especially in temporal and occipital lobes. Beagles with IE showed statistically significant decreased GMV in olfactory bulb, cortex of parietal and temporal lobe, hippocampus and cingulate gyrus, Beagles with SE mild statistically significant GMV reduction in temporal lobe (p < 0.05; family- wise error correction). Conclusion: These results suggest that, as reported in epileptic humans, focal reduction in GMV also occurs in epileptic dogs. Furthermore, the current study shows that VBM analysis represents an excellent method to detect GMV differences of the brain between a healthy dog group and dogs with epileptic syndrome, when MR images of one breed are used. Keywords: Voxel-based morphometry, Dogs, Epilepsy, Grey matter, MRI Background Dogs with epilepsy are frequent patients in veterinary practice [1]. Idiopathic epilepsy (IE) is one of the most common chronic neurological disorders in dogs, which is defined as a disorder of the brain characterized by spontaneous recurrent epileptic seizures of unknown, genetic or suspected genetic origin [1–3]. A genetic component was considered in several breeds [4], especially in Australian Shepherds [5], Beagles [6], Belgian Shepherds [7], Border Collies [8], English Springer * Correspondence: 1 Department of Small Animal Medicine and Surgery, University of Veterinary Medicine, Hannover, Germany Full list of author information is available at the end of the article Spaniels [9], Golden Retrievers [10], Keeshonds [11], Labrador Retrievers [12], Lagotto Romagnolos [13, 14], Viszlas [15] and others. Affected dogs mostly have their first epileptic seizure with an age of 6 months to 6 years, interictal general and neurological examinations are normal [16, 17]. Because IE is a diagnosis of exclusion, several diagnostic approaches have to be considered: TIER I: history, general and neurological examination, blood tests and urine analysis, TIER II: adding magnetic resonance imaging (MRI) and cerebrospinal fluid (CSF) analyses, TIER III: in addition electroencephalographic examinations [17]. Structural epilepsy (SE), caused by intracranial lesions like vascular damage, inflammation, trauma, anomalies or neoplasia of the brain, or reactive © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Frank et al. BMC Veterinary Research (2018) 14:50 seizures are further reasons for the occurrence of seizures [1, 17]. For diagnostic purposes MRI of the brain is used to detect structural changes [1] resp. to diagnose IE by exclusion of such changes [18]. However, using new techniques such as volumetric studies in human epileptic patients, a reduced or increased volume of several grey matter (GM) structures could be detected using voxel- based morphometry (VBM) [19]. VBM is an automatically computational quantitative method to analyse MR images and detect differences in brain morphologies for instance in grey matter volume (GMV), white matter volume (WMV) or other structures between two groups of subjects [19]. After several pre-processing steps MR images are normalized to a consistent space for comparing each voxel of the same region in MR images of subjects by statistical analysis [19–21]. Resulting differences in brain volumes can be displayed in statistical parametric maps (SPM) [20]. Only few volumetric studies have been performed in veterinary medicine, since the diversity of head and brain shape between dog breeds [22] limit the application of VBM in dogs. In one volumetric study differences in the ratio of ventricular system volume to brain volume between dogs with IE and a healthy dog group were detected as preliminary results, while white matter (WM) volume to GMV ratio was not different between these groups [23]. In another study abnormalities of the hippocampus were seen in 12%, an unilateral atrophy of hippocampus in 48% of dogs with IE compared to healthy dogs by measuring the surface areas of the hippocampus in each MR image plane [24]. No significant differences in hippocampus volume between dogs with IE and controls were found by Milne et al. [25]. Only after the reduction of the 95% reference interval in the chosen analysis an atrophy of hippocampus in 18 of 74 dogs with IE could be shown [25]. In the current study the VBM method was chosen because of its sensitivity in detecting subtle structural alterations, which cannot be measured by conventional MRI [26]. Aim of this study was to examine whether GMV differences exist between healthy and epileptic Beagles. This study was conducted in only one dog breed to examine an approximately uniform brain shape. The hypothesis should be proven that epileptic Beagles have reduced GMV, especially in hippocampus and basal nuclei, as well as increased GMV in frontal regions of the brain. Methods Animals Fifteen Beagles were included in this study. Five Beagles (2 male, 3 male-neutered) with an average age of 29.6 months and an average weight of (...truncated)