Authors :
Presenting Author: Wonhee Lee, MD – The University of Chicago
hiba Haider, MD – The University of Chicago; Sandra Rose, MD – The University of Chicago; James Tao, MD, PhD. – The University of Chicago; Shasha Wu, swu4@bsd.uchicago.edu – The University of Chciago; naoum Issa, MD, PhD. – The University of Chicago
Rationale:
The objective of this study was to assess the sensitivity of scalp EEG in detecting hippocampal seizures and identify scalp EEG correlates of hippocampal seizures in patients diagnosed with mesial temporal lobe epilepsy (mTLE).Methods:
We conducted simultaneous scalp and intracranial EEG recordings in 27 consecutive surgical candidates with mTLE. Hippocampal seizures, defined as lasting at least ten seconds and involving a minimum of three electrode contacts, were identified from depth electrodes during SEEG recording in our epilepsy monitoring unit. Scalp EEG correlates of these hippocampal seizures were also identified.
Results:
A total of 1709 hippocampal seizures were recorded, with a wide range of occurrences, ranging from 1 to 793 seizures (mean ± SD: 63.3 ± 164) among the subjects. Among these seizures, 4.4% (75) were clinical, while the remaining 95.6% were subclinical. Subclinical hippocampal seizures were predominantly associated with hippocampal sclerosis and had favorable surgical outcomes. Of all the seizures, 2.5% (43) showed scalp ictal EEG patterns. The scalp EEG correlates of hippocampal seizures included focal slowing, mid-temporal rhythmic discharges (RMTD), rhythmic theta ictal onset, and rhythmic delta ictal onset.
Conclusions:
The frequency of hippocampal seizures is greatly underestimated by scalp EEG, with the majority of seizures being subclinical. These findings underscore the challenges in early diagnosis of mTLE. Additionally, scalp EEG correlates of hippocampal seizures exhibit morphological heterogeneity. RMTD, traditionally considered benign EEG variants, showed correlation with hippocampal seizures and may potentially represent an ictal scalp EEG pattern.
Funding: none