Altered structural connectivity in epilepsy with myoclonic atonic seizures

OBJECTIVE: Epilepsy with myoclonic-atonic seizure (EMAS) is a rare generalized epilepsy in young children associated with various neurodevelopmental and epileptic outcomes. Although conventional brain imaging is usually normal, we previously identified morphometric alterations in the frontal lobes and cerebellum. We here investigated structural connectivity differences between EMAS patients and healthy subjects several years after epilepsy onset and explored their associations with epilepsy severity and cognitive performance. METHODS: Thirteen EMAS patients (4 females, 5-14 years) and 14 matched controls were included. Patients were classified into three outcome groups (good, intermediate, poor) according to seizure control and behavioral functioning. Individual structural and diffusion data (T1-weighted sequence, multi-shell diffusion MRI) were processed using the FreeSurfer and the Connectome Mapper pipelines. Number of fibers (NoF), fiber density (FD), fractional anisotropy (FA) and apparent diffusivity coefficient (ADC) were used for group comparison and linear regression analyses. RESULTS: Network-based statistics identified a subnetwork encompassing the sensorimotor cortex and brainstem with reduced fiber count and FD in EMAS patients compared with controls. No group differences were observed in FA or ADC, and neither of these measures correlated with the NoF. In contrast, lower NoF and FD were associated with reduced frontal lobe volume (p = 0.002 and p = 0.001, respectively) and with poorer clinical outcomes (p < 0.001). CONCLUSIONS: A specific altered cortico-subcortical network including pericentral motor areas and probably reticular formation, was identified in our EMAS sample. This supports the Doose's original hypothesis of a brainstem-cortical network involvement in EMAS. These changes were not explained by differences in FA or ADC but decrease in the NoF. The role of sustained seizure activity, antiseizure medication and genetics remains to be clarified through prospective longitudinal studies.