Abstracts

Rationale: Impaired consciousness in epilepsy has a significant negative impact on patient quality of life, yet the mechanisms for loss of consciousness during seizures are poorly understood. In this study, we explore whether impaired consciousness during partial seizures can usually be attributed to specific deficits in the content of consciousness or to a more general decrease in the overall level of consciousness. Prior studies concerning loss of consciousness during seizures have relied on retrospective and subjective methods. We recently developed a prospective tool for assessing ictal behavior called the responsiveness in epilepsy scale (RES) that provides objective data about specific deficits in cognition and sensorimotor function. Methods: We examined the results of RES testing in 83 partial seizures captured in 30 patients. All patients were recruited during admission to Yale New Haven Hospital, and were undergoing continuous video/EEG (cVEEG) for seizure evaluation at the time of enrollment. All seizures were scored on a scale from 0 to 4, and performance for partial seizures was analyzed based on the initial cycle of ictal testing. To determine whether the distribution of RES scores might be related to bias intrinsic to the scale, we also examined results of standardized testing in a cohort of brain-injured patients. In this comparison group, responsiveness was assessed using the JFK Coma Recovery Scale Revised (CRS-R), a validated tool for assessing the minimally conscious state from which the RES was derived. We analyzed the score distributions for the CRS-R subscales used to derive most RES items, and compared these results to RES scores in partial seizures. Results: We found that RES scores tend to be bimodally distributed, such that scores of 0 (no response) and 4 (unimpaired response) occured most frequently for all RES items. Furthermore, 75 of 83 partial seizures tested received a score of 0 or 4 on the first RES question administered, and this initial performance predicted impairment on subsequent items. These distinct patterns of impairment correspond with those seen in simple partial and complex partial seizures. Additionally, we found that scores in brain-injured patients are not bimodal, and are more evenly distributed than in partial seizure patients, suggesting that the bimodal nature of RES scores is not a result of scale bias but may be a finding unique to partial seizures. Conclusions: Our results indicate that partial seizures can often be cleanly separated into those with vs. without overall impaired responsiveness. These findings suggest that impaired level of consciousness affecting overall behavioral is often the dominant feature of partial seizures. The bimodal distribution of deficits suggests a model in which seizures either do or do not propagate into key subcortical structures responsible for impaired level of consciousness and global cognitive performance in partial seizures. Further work is needed to investigate the fundamental network mechanisms of impaired consciousness, hopefully leading to improved cognitive function in people living with epilepsy.