Abstracts

Rationale: Electrical status epilepticus in sleep (ESES) is associated with a high rate of macroscopic thalamic lesions on magnetic resonance images (MRI). However, most patients with ESES have no macroscopic lesions on MRI and the cause in these patients remains unknown. The aim of this study is to evaluate whether patients with ESES and normal macroscopic MRI have a smaller thalamic volume than controls.Methods: All consecutive patients with the electroencephalographic pattern of ESES 1) between 2 and 21 years, 2) a normal macroscopic brain MRI, and 3) at least one brain MRI of sufficient quality to perform volumetric analysis were included. Total brain volume (volume of the intracranial content) and thalamic volume were compared between these patients and a group of healthy controls of the same age range.Results: Twenty-one patients (13 males) with a median (p25-p75, range) age of 7.5 (7-10, 2.5-14) years were compared to 52 healthy controls (29 males) with a median age of 11 (7.5-12, 3-14) years. Patients with ESES had smaller median volumes than controls in the left thalamus (7.37 cm3 vs 7.75 cm3, Wilcoxon rank-sum test z= 2.632, p= 0.0085), right thalamus (7.72 cm3 vs 8 cm3, Wilcoxon rank-sum test z= 2.681, p= 0.0073), overall thalamic volume [left thalamus + right thalamus] (15.14 cm3 vs 15.83 cm3, Wilcoxon rank-sum test z= 2.669, p= 0.0076), and total brain volume (1333 cm3 vs 1392 cm3, Wilcoxon rank-sum test z= 2.181, p= 0.0292) [Figure 1]. Corrected for age using linear regression, patients had a smaller left thalamus (p= 0.027), right thalamus (p= 0.02), and overall thalamic volume (p= 0.022), but there were no differences in total brain volume (p= 0.121) [Figure 2]. Only one of the cases was treated with steroids before the completion of the MRI and, in that patient, steroid treatment was discontinued 3 years prior to MRI acquisition. Seventeen out of 21 of our patients were on antiepileptic drugs (as monotherapy or polytherapy) before and during the acquisition of the MRI. Some of these antiepileptic drugs have been associated with a reduction in brain volume. The number of patients in this study did not allow us to control for the use of antiepileptic drugs as a potential confounder of thalamic volume. In the future, comparison to patients with intractable epilepsy without ESES will be included as an additional control group.Conclusions: Our results demonstrate that patients with ESES without macroscopic lesions on MRI have a smaller thalamus than healthy controls. This difference cannot be explained by age-related differences or use of steroids. When adjusted for age, thalamic size differences were independent from overall brain volume changes.