Authors :
Presenting Author: Lisa Gillinder, MD – School of Medicine, University of Queensland, St Lucia, Queensland, Australia
Amy Halliday, MD – St Vincent's Hospital Melbourne, Melbourne, Victoria, Australia
holly Fontenot, MT, CCRA – Epiminder Ltd
Ramya Raghupathi, MD – Penn Neuroscience Center
Mark Cook, MBBS, MD – Univeersity of Melbourne
Rationale:
Seizure lateralisation is a critical factor in surgical planning for epilepsy. Poorer surgical outcomes have been reported when seizures are bilateral (Akhakhani et al., Epilepsia 2014). Inpatient video-EEG is often limited by under-sampling, leading to uncertainty in determining laterality, particularly in cases with high laterality ratios. Long-term EEG studies suggest that around 8 months of recording or approximately 50 seizures are required to accurately define seizure lateralisation (Chiang et al., Epilepsia 2014). This study aimed to determine seizure laterality using the Minder system, a bilateral implantable continuous EEG monitoring (iCEM™) system.
Methods:
Patients with focal epilepsy were implanted with the Minder iCEM system. Pre-implantation lateralisation (unilateral or bilateral) was determined from existing clinical data. Events were identified through two processes: (1) patient-reported events triggered targeted review of Minder EEG data, and (2) a systematic 6-month technician-led review of consecutive Minder data, with confirmation by two board-certified neurophysiologists. Signal quality and timing were assessed for each seizure. Lateralisation was defined by pre-ictal/ictal spiking and evolving rhythmic ictal activity maximal in one hemisphere. Minder-based lateralisation was compared with pre-implantation data for potential diagnostic reclassification.
Results:
Nineteen patients were evaluated. Minder provided sufficient signal quality to assess lateralisation in all cases. Five patients were previously classified as having bilateral onset. Among the 14 thought to be unilateral, 8 were reclassified as bilateral based on Minder recordings. Most bilateral activity was seen within 1–2 months, but in some, it took 4–5 months. The median time from the first seizure to first contralateral seizure was about 20 days, though in some cases this extended to several months. Four patients previously thought to have unilateral temporal lobe onset had significant contralateral seizure activity on Minder. In these cases, about 20% of seizures arose from the opposite hemisphere. Challenges to lateralisation included partial capture of events, seizure-related artefact, short duration, low-amplitude onset, rapid propagation, and evolving ictal morphology.
Conclusions:
Prolonged bilateral monitoring with the Minder iCEM system can overcome the sampling limitations of standard inpatient video-EEG. In potential surgical candidates, extended recordings can confirm or refute unilateral seizure onset, supporting earlier resection in suitable cases and avoiding inappropriate surgery in those with bilateral onset, especially where high laterality ratios exist.
Funding:
Funding was provided by Epiminder Pty. Ltd.