Interictal Slow and High-Frequency Oscillations: Is it an Epileptic Slow or Red Slow?

Purpose: We reported the presence of interictal slow and high-frequency oscillations (HFOs) (IIS + HFO) and its temporal change so as to elucidate its clinical usefulness as a surrogate marker of epileptogenic zone in a patient with intractable focal epilepsy. Methods: We focused on one of the core electrodes of epileptogenicity, and investigated IIS + HFO in the pre-and post-segment of 30 minutes to all the 6 seizures. We adopted interictal slow in duration of 0.33 to 10 seconds, amplitude >= 50 mV and co-occurring with HFOs, and then divided into 5 groups depending on the amplitude of slow wave. Results: Before and after all the 6 seizures, the number of IIS + HFO was 2,890 at one electrode in the core epileptogenic zone. The number of IIS + HFO significantly decreased for 30 minutes after seizures. Furthermore, the number of IIS + HFO with the amplitude of 200 to 399 mu V significantly decreased after seizures. Conclusions: IIS + HFO with the amplitude of 200 to 399 mu V was influenced by and decreased after seizures. It may reflect the core part of epileptogenic area as similarly as ictal direct current shifts and ictal HFOs do. IIS + HFO could be called as the term "red slow," which may be useful to delineate at least a part of the epileptogenic zone.