Abstracts

Rationale: Psychomotor variant is a rare rhythmic EEG pattern in the theta frequency range during drowsiness. The location is maximal in midtemporal region, and can be unilateral, bilaterally independent, or bisynchronous. Most electroencephalographers considered this uncommon pattern to be a normal variant. However, psychomotor variant was often observed in patients with temporal lobe epilepsy. The objective of this study is to determine if there is a relationship between psychomotor variant and hippocampal ictal discharges associated with mesial temporal lobe epilepsy (mTLE). Methods: Retrospective review of simultaneous scalp and stereo EEG recordings from 28 patients with mTLE being evaluated for epilepsy surgery. Scalp EEG waveforms were assessed at the time of ictal hippocampal epileptiform discharges identified on intracranial hippocampal depth electrodes. Results: Psychomotor variant on scalp EEG was observed in 7 of 28 patients and were time locked to hippocampal ictal epileptiform discharges measured intracranially. These hippocampal seizures tended to be subclinical. Psychomotor variants were often correlated with the middle part of hippocampal seizures in which ictal discharges evolved into theta frequency range. The cycles of the scalp psychomotor variant EEG patterns were phase locked to the hippocampal epileptiform discharges. Conclusions: There is a tight coupling between a subset of pathological hippocampal ictal discharges and scalp psychomotor variant, suggesting that psychomotor variant might be an epileptiform EEG pattern and can be an ictal EEG marker for mTLE. Funding: None