Testing for minimal consciousness in complex partial and generalized tonic–clonic seizures

Abstract

Summary Impaired consciousness in epilepsy has a major negative impact on quality of life. Prior work suggests that complex partial seizures (CPS) and generalized tonic-clonic seizures (GTCS), which both cause loss of consciousness, affect similar fronto-parietal networks. Milder involvement in CPS than in GTCS may spare some simple behavioral responses, resembling the minimally conscious state. However, this difference in responses has not been rigorously tested previously. During video/EEG monitoring, we administered a standardized prospective testing battery including responses to questions and commands, as well as tests for reaching/grasping a ball and visual tracking in 27 CPS (14 patients) and 7 GTCS (6 patients). Behavioral results were analyzed in the ictal and post-ictal periods based on video review. During both CPS and GTCS, patients were unable to respond to questions or commands. However, during CPS patients often retain minimally conscious ball grasping and visual tracking responses. Patients were able to successfully grasp a ball in 60% or to visually track in 58% of CPS, and could carry out both activities in 52% of CPS. In contrast, during GTCS preserved ball grasp (10%), visual tracking (11%) or both (7%) were all significantly less than in CPS. Post-ictal ball grasping and visual tracking were also somewhat better following CPS than GTCS. These findings suggest that impaired consciousness in CPS is more similar to minimally conscious state than to coma. Further work may elucidate the specific brain networks underlying relatively spared functions in CPS, ultimately leading to improved treatments aimed at preventing impaired consciousness.

Transcranial magnetic stimulation combined with high-density EEG in altered states of consciousness

“…In NREM sleep, general anaesthesia and UWS, the loss of integration gives rise to the simple, local and short lasting response observed [35,36,40]. During general seizures, where the entire cortex is firing anarchically, there is no specialization and, hence, no information, leading to an alteration of consciousness [69].…”

Mechanisms of sudden unexpected death in epilepsy: the pathway to prevention

“…Patients with these seizures are unresponsive to commands and questions during the post-ictal state, however patients with CPS are able to grasp a ball and visually track 44 . These data suggest that although consciousness is reduced in CPS, they are closer to a minimally conscious state than a post-ictal coma as occurs following GTCS, which could increase risk of SUDEP.…”

Impaired consciousness in partial seizures is bimodally distributed

“…22,24,25 The cohort with brain injury serves as a reasonable comparison group, because prior studies suggest that complex partial seizures resemble the minimally conscious or vegetative states more closely than coma. 8,19,26,27 We expect a similar pattern of graded impairment scores in other populations, such as poststroke patients or patients with encephalitis who should be investigated in further studies. Our current results suggest that the bimodal nature of ictal impairment is not the result of scale bias, but rather may be a finding unique to partial seizures and distinct from other disorders of consciousness.…”

“…9 For example, visual tracking, blink to visual threat, or grasping movements are preserved in approximately half of complex partial seizures, but not in generalized tonic-clonic seizures. 9,19 We acknowledge that there are limitations to our study. It is important to note that the duration of seizures is brief compared with other disorders of consciousness, such that slower test administration in TBI might allow more gradations in impairment to be detected.…”

“…Of note, the current cohort included 60 seizures from 26 patients that were previously analyzed through similar but distinct methods. [17][18][19] Patients with structural brain abnormalities were included in the seizure cohort, including 8 patients with hippocampal atrophy or increased signal, 7 with cortical gliosis or poststroke encephalomalacia, 5 malformations of cortical development, 4 previous resections, and 1 brain tumor (table e-1).…”