Is ictal dystonia associated with an inhibitory effect on seizure propagation in focal epilepsies?

Abstract

In focal epilepsy, ictal version and ictal dystonia are thought to reflect seizure spread into the frontal eye field and the basal ganglia, respectively. Here we investigated whether the occurrence of dystonia during seizure evolution reflects mechanisms preventing secondary generalization. To this aim, the evolution of seizures in patients with focal epilepsies was compared as to whether concomitant (1) dystonia, (2) dystonia and version, or (3) version occurred. Seizure evolutions of 79 patients characterized by either dystonia (n=29; 232 seizures), dystonia and head version in the same seizure evolution (n=9; 83 seizures) or head version (n=41; 330 seizures), were included in the study. The rate of secondary generalization was significant lower in seizures with ictal dystonia (8%, 6 of 72 seizures) compared to seizures with ictal dystonia and version (62%, 13 of 21 seizures, p<0.0001) or compared to seizures with version (95%, 82 of 86 seizures, p<0.0001). This study shows that seizures with unilateral ictal dystonia are less likely to generalize as compared to seizures associated with version. This effect is likely to reflect the involvement of inhibitory mechanisms related to the basal ganglia, which exert an inhibiting effect on secondary seizure generalization.