Focal cortical high-frequency oscillations trigger epileptic spasms: confirmation by digital video subdural EEG

To localize high-frequency oscillations (HFOs) on the cortex during epileptic spasms using video subdural EEG and Multiple Band Frequency Analysis (MBFA).

Using video subdural EEG sampled at 1 kHz, we studied a 14-year-old boy with asymmetric epileptic spasms of possible left frontal origin. We identified HFOs, then analyzed and localized their distributions by MBFA. We correlated HFO distribution to clinical spasm intensity.

Ictal subdural EEG recorded HFOs at 60-150 Hz lasting 0.3-4 s. MBFA showed extensive but noncontiguous distribution of HFOs predominantly over the left frontal and temporal regions. HFOs began and became quasiperiodic before manifestation of clinical spasms. As clinical spasms intensified, HFOs persisted in regions where they initiated subclinically but were of higher frequency and greater power than HFOs in other regions. We performed cortical resections over the left frontal and temporal regions with predominant HFOs. Six months after surgery, the patient remained seizure free.

HFOs were present over the ictal onset zone during epileptic spasms. Periodic spasms in this patient had the characteristics of partial seizures.

We show that HFOs occurred over the cerebral cortex during epileptic spasms, and we suggest that these focal cortical HFOs triggered the spasms.