Abstracts

Rationale: The thalamus plays a pivotal role in the epileptogenic network of both idiopathic generalized epilepsy (IGE) and temporal lobe epilepsy (TLE). Our purpose was to assess the local structural changes in the thalamus in IGE and TLE in vivo. Methods: We obtained manual thalamic segmentations on MRI in 37 patients with drug-resistant TLE, 18 patients with IGE (11 epilepsy with generalized tonic-clonic seizures only, 7 juvenile myoclonic epilepsy, and 1 juvenile absence epilepsy), and 19 age-and sex-matched healthy controls. In each individual, we obtained surface-based measurements of local deformations (SPHARM-PDM, Styner et al. 2006) of the thalamus relative to a template model. We assessed differences in thalamic SPHARM-PDM in each patient group relative to controls, as well as the effects of clinical variables using linear models. Results: Relative to controls, TLE patients displayed local atrophy mainly in ipsilateral anterior, mediodorsal, and pulvinar thalamic subdivisions (Figure A and B). In TLE, atrophy intensified with a longer duration of epilepsy (-0.01 mm/year, t=-3.17, p<0.005) and a previous history of febrile convulsions (t=-1.87, p<0.08). IGE patients showed diffuse and bilateral tendencies for local thalamic atrophy (p<0.025). The only change that surpassed the threshold at FDR<0.05 was observed in the right medial division (Figure C). Although there was a slight tendency for progressive atrophy in this cluster, this effect was not significant (t=-1.31, one-tailed p=0.10). However, post-hoc power analysis on the duration effect size in the cluster (power=0.95, effect size %r%=0.56, alpha=0.05, one-tailed) indicated that we would have needed a total sample size of 26 IGE patients to detect significant progressive thalamic atrophy. We did not find any difference in local volume between patients with juvenile myoclonic epilepsy and those with generalized tonic-clonic seizures only (FDR>0.2). Conclusions: The medial thalamic division is the most affected structure in both TLE and IGE. In the former, atrophy is more widespread and ipsilateral to the seizure focus.