Abstracts

Rationale: The thalamo-cortical network is impaired in patients with idiopathic generalized epilepsies (IGEs). Investigations using quantitative neuroimaging were able to depict focal abnormalities in these patients. Diffusion tensor imaging (DTI) is a technique which is able to detect white matter abnormalities. The findings on DTI probably reflects axonal integrity. From previous works we hypothesized that in patients with IGEs the abnormalities are not restricted to the thalamo-cortical network but may be related to white matter changes in other locations allowing the spreading of the epileptiform discharge. Methods: 14 patients with IGEs (8 women, mean age 28 8) and 22 controls (13 women, mean age 30 10) were investigated. All Individuals were submitted to a 3T MRI scanner. DTI images were acquired using echoplanar imaging sequence with 34 diffusion directions. Images were processed and analyzed using MRIcroN and FSL softwares. Initially images were converted into Neuroimaging Informatics Technology Initiative (NIfTI) format. Gradient directions and b-values were extracted. Images were then corrected for eddy currents and the fractional anisotropy (FA) maps were calculated. Voxelwise statistical analysis was carried out using TBSS (Tract-Based Spatial Statistics), part of FSL software. FA maps were aligned into a standard space using nonlinear registration. Next, a mean FA image was created and thinned to create a mean FA skeleton which represents the centres of all tracts common to the patients and controls. Each subject's aligned FA data was then projected onto this skeleton and the resulting data fed into voxelwise cross-subject statistics (Figure A). Statistical analysis was conducted using t-test corrected for multiple comparisons. Results: Comparison between patients and controls revealed areas of increased FA in IGE group localized mainly at the corpus callosum (data of the maximum voxel) two-sample t(34) = 5.5, p < 0.001 (MNI coordinates, x= -15mm,y= -43mm, z= 16mm), ventral mesencephalum t(34) = 6.3, p < 0.001 (x= 12, y= -17, z= -16) and at the anterior limb of the internal capsule t(34) = 4, p < 0.001 (x= -15, y= 10, z= 6). Figure B depicts the results above reported. There were no areas of reduced FA. Conclusions: Structural abnormalities were disclosed in the white matter of patients with IGE. Interestingly, in opposition to the literature, FA was increased in the patients. Increased diffusion may facilitate several mechanisms related with the seizures: the corpus callosum contribute to high interhemispheric synchronization; the anterior limb of the internal capsule is part of the thalamo-cortical circuitry which is involved in the maintenance of the generalized discharges; the mesencephalum have an important role in generalized tonic-clonic seizures which were present in all patients investigated in here. Therefore, our findings probably are drawing the whole system involved in IGE pathogenesis.