Differential electrographic seizure patterns in malformations of cortical development, early life brain injury, and later life brain injury

Structural epilepsy is a chronic neurologic condition that may be caused by in utero malformations of cortical development (MCD) or post-natal brain injuries resulting in encephalomalacia. We hypothesized that the timing of epileptogenic insult would lead to distinct electrographic seizure patterns. Specifically, we predicted that later life insults would lead to longer duration seizures with higher proportion of focal: focal to bilateral tonic-clonic (FBTC) seizures and low rates of bihemispheric onset seizures, as compared to early life insults. We performed a retrospective chart review of 70 adult patients – 33 with epilepsy secondary to brain injury (9 with injury occurring before 16 years and 24 with injury occurring at or after 16 years) with resultant encephalomalacia on MR imaging and 37 with epilepsy secondary to MCD – admitted to the University of Pittsburgh Epilepsy Monitoring Unit for presurgical evaluation. There were no significant differences in duration of epilepsy or number of trialed seizure medications between the groups. We examined scalp EEG data for all patients, as well as intracranial EEG data in a subset. We analyzed seizure duration, seizure frequency, and seizure type (focal, FBTC, and bihemispheric onset) in three cohorts: MCD patients, patients with brain injury occurring in early life (<16 years old), and patients with brain injury occurring in later life (≥16 years old). Patients with later life brain injury had significantly longer and less frequent seizures as compared to MCD cohorts. There were no differences between MCD and early life brain injury cohorts. Seizure duration findings were corroborated in a subset of patients who additionally underwent intracranial EEG monitoring. Additionally, later life brain injury patients had significantly different seizure types as compared to MCD cohorts, with high rates of FBTC and low rates of bihemispheric onset. Again, there was no significant differences in seizure type between early life brain injury and MCD cohorts. These novel findings indicate the relevance of timing of epileptogenic insult on the electrophysiological characteristics of structural epilepsies.