Abstracts

Rationale: Juvenile myoclonic epilepsy is the most frequent form of idiopathic generalized epilepsy (IGE). Previous neuroimaging investigations showed that the thalamo-cortical circuitry play an important role in the pathogenesis of the seizures in JME patients. Both structural and functional investigations showed abnormalities in the thalamus. However, few investigations tried to combine these neuroimaging modalities. The association between structural and functional quantitative investigations may help to elucidate the mechanisms behind IGE. The aim of this study was to explore functional and structural abnormalities of the thalamus in patients with JME. Methods: Diagnosis was performed according to clinical and electroencephalographical (EEG) features following ILAE recommendations. All patients were submitted to magnetic resonance imaging (MRI) in a 2 Tesla scanner. Single voxel (2x2x2cm3) proton magnetic resonance spectroscopy (MRS) was performed. The voxel was placed at the right thalamus. Localized shimming at the region of interest (ROI) was conducted for correction of field inhomogeneities and PRESS sequence was used to acquire spectra. Using the MRI manufacturer software (Elscint, Prestige Haifa, Israel) the NAA/Cr ratios were obtained for each patient and controls. 3D volumetric T1 sequences with 1mm isotropic voxels were used for thalamic morphometry. Images were submitted to normalization and automatic segmentation using the IBASPM toolbox. The thalami were derived from the Automatic Labeling Atlas (AAL), an automated parcellation method, included in the IBASPM toolbox. The volumes in cm3 obtained for each individual were normalized based in the total intracranial volume of the controls. Since there was no side-to-side differences expected in patients and controls groups, we used the average of the right and left thalamic volumes to simplify statistical analysis. We also conducted a ROI investigation using MRIcro software. The thalamic ROIs of the patients were subtracted from the control group. The MRS NAA/Cr ratios and thalamic volumes of the patients were compared to a group of 18 controls (8 women, mean age 34 years ± 16). For the comparisons between means t-test was used. Results: We investigated 21 patients with JME (13 women, mean age 30 years ± 9). MRS revealed reduced NAA/Cr ratios (p < 0.001) and thalamic volumes (p = 0.009) in JME patients (1.44 ± 0.1, 40843 ± 3330 cm3) compared to controls (1.88 ± 0.1, 43701 ± 3220 cm3). ROI comparisons showed that the thalami of the patients were reduced mainly at the antero-inferior portion compared to controls. Conclusions: The present investigation demonstrated that the thalami of JME patients have abnormal structure and function. These findings differ from previous observations performed by our group which demonstrated increased thalamic volumes in patients with absence seizures. Clinical, EEG and genetic heterogeneity may help to explain this divergence. Acknowledgements: This study was supported by FAPESP and CAPES.