Investigating gray matter volumes in idiopathic epileptic Border Collies and Greater Swiss Mountain Dogs using voxel-based morphometry.

OBJECTIVE: To investigate regional gray matter volume differences in Border Collies and Greater Swiss Mountain Dogs with idiopathic epilepsy compared with healthy controls using voxel-based morphometry (VBM). METHODS: This retrospective single-center study analyzed 3D T1-weighted MRI datasets from 46 dogs, comparing dogs with idiopathic epilepsy with breed-matched healthy controls. Regional gray matter volume was assessed using an automated FSL-based voxel-based morphometry pipeline with semi-manual brain extraction and 1.5 mm smoothing kernel. To account for inter-breed anatomical variation, separate study-specific templates were created for each breed. Volumetric comparisons of gray matter, white matter, total brain and gray matter ratios were performed for both breeds and analyzed using the Mann-Whitney U test. RESULTS: A total of 46 dogs were included, of those, 18 Border Collies and 13 Greater Swiss Mountain Dogs were diagnosed with idiopathic epilepsy, while 5 Border Collies and 10 Greater Swiss Mountain Dogs served as healthy controls. Volumetric comparisons highlighted pronounced size differences between breeds. Within each breed, no significant differences in gray and white matter volumes or ratios were found between healthy controls and epileptic dogs. A statistically significant difference in the gray matter ratio was detected when both breeds were pooled (58% vs. 57%, p = 0.039). VBM did not reveal any significant differences in gray matter volume between groups. However, exploratory analysis in Border Collies suggested increased gray matter volume in limbic regions (amygdala, retrosplenial fissure) and temporal areas, whereas Greater Swiss Mountain Dogs showed increases in the cerebellum. Both breeds showed focal gray matter volume reductions in the right anterior ectolateral gyrus. CONCLUSION: VBM analysis did not identify statistically significant differences in gray matter volume between dogs with idiopathic epilepsy and healthy controls. However, exploratory analyses revealed breed-specific patterns of both focal gray matter decreases and regional increases. This mixed pattern supports the concept of canine idiopathic epilepsy as a distributed network disease.