Abstracts

Rationale: Small sharp spikes (SSS) are classically considered benign, normal variants on the scalp EEG (Gibbs & Gibbs, 1952; White et al., 1977; Westmoreland et al., 1979), despite the morphology of the waveform, which resembles pathological spikes except that SSS are smaller in amplitude and shorter in duration. The significance of SSS has been debated with some epidemiological studies showing a higher prevalence of SSS in patients with epilepsy than in those without (Hughes and Gruener, 1984; Saito et al. 1987). The goal of this study is to determine if SSS are associated with epileptiform discharges identified on intracranial electrodes. Methods: Simultaneous recordings of stereo-EEG from hippocampal and temporal neocortical regions and 26-channel scalp EEG were analyzed in patients with medically refractory mesial temporal lobe epilepsy being evaluated for surgery. Scalp EEG epochs with SSS were collected and their intracranial EEG correlates were assessed. Results: In four of 15 patients assessed, small sharp spikes observed on scalp EEG were consistently time-locked with hippocampal interictal spikes recorded on depth electrodes. The latencies and amplitudes of the SSS were consistent with volume conduction of hippocampal spike potentials to the scalp, rather than synaptic propagation of the spikes to lateral neocortex. Scalp SSS were not observed in EEG recordings after MR-guided laser amygdalohippocampectomy in one of the patients. Conclusions: These findings suggest that some SSS may be EEG markers of hippocampal epileptiform discharges, rather than normal EEG variants. Future studies will be needed to assess the predictive value of SSS in different clinical contexts. Funding: N/A