Abstracts

Rationale: Idiopathic generalized epilepsies (IGE) are diseases in which the prognosis for seizure control usually is favorable. Some subsyndromes are self-limited and the seizures may remit. Most of the patients who require treatment with antiepileptic drugs, achieve seizure freedom. However, recurrence after drug withdrawal is the rule in almost the same rate of treatment success. The mechanism of these diseases involves the extensive thalamo-cortical network. Quantitative neuroimaging disclosed mild cortical and thalamic abnormalities in these patients and few studies addressed the evolution, if any, of these findings. Since IGE probably last for the whole life, the objective of this investigation was to perform a longitudinal analysis of patients with IGE using voxel-based morphometry (VBM).Methods: 26 individuals (20 women) with IGE and 5 (2 women) controls were investigated. All subjects were submitted to 2T (first acquisition) and 3T (second acquisition) MRI scanners. A 3D T1 volumetric sequence was used for VBM analysis. Images were processed using SPM8 and VBM8 toolbox. The unified segmentation approach was used. First, images were submitted to intra-subject registration. The estimated parameters of normalization were then applied to all images. For this process the DARTEL algorithm was used. After the normalization and segmentation of gray matter, images were realigned again and smoothed with an 8mm FWHM filter. A hierarchical linear model applied with the flexible factorial design was used for statistical analysis. Statistical level selected was a p < 0.05 with correction for multiple comparisons (family-wise error). Comparisons between the first and second acquisitions were performed in patients and control groups.Results: The mean age was 28/36 years in the first and second acquisition respectively in the patients group and 25/33 in the control group. Time from first and second MRI acquisitions was 7 years (range 3-10 years) for the patients group and 8 years (3-13) for the control group. 17 patients had juvenile myoclonic epilepsy, 5 had juvenile absence epilepsy and 4 had generalized tonic-clonic seizure only. In the patients group, the region of maximal gray matter atrophy was in the thalamus (corrected p < 0.001, coordinates x = -5 y = -18 z =1, cluster extent 3071) and in the frontal regions (Figure A). In the control group, the main area of atrophy was also located in the thalamus however with a smaller cluster extent 234 (Figure B). Areas of increased gray matter volumes were also disclosed in the patients group mainly involving the basal ganglia and areas adjacent to the central sulcus. In the control group no areas of increased gray matter volumes were observed.Conclusions: The observations in here suggest that IGE are not static diseases and network plasticity exists in these patients. The thalamus and the frontal lobe were the main areas involved. This finding confirms the participation of this circuitry in the mechanisms of IGE.