High-Density EEG in Current Clinical Practice and Opportunities for the Future

High-density EEG (HD-EEG) recordings use a higher spatial sampling of scalp electrodes than a standard 10-20 lowdensity EEG montage. Although several studies have demonstrated improved localization of the epileptogenic cortex using HD-EEG, widespread implementation is impeded by cost, setup and interpretation time, and lack of specific or sufficient procedural billing codes. Despite these barriers, HD-EEG has been in use at several institutions for years. These centers have noted utility in a variety of clinical scenarios where increased spatial resolution from HD-EEG has been required, justifying the extra time and cost. We share select scenarios from several centers, using different recording techniques and software, where HD-EEG provided information above and beyond the standard low-density EEG. We include seven cases where HD-EEG contributed directly to current clinical care of epilepsy patients and highlight two novel techniques which suggest potential opportunities to improve future clinical care. Cases illustrate how HD-EEG allows clinicians to: case 1dlateralize falsely generalized interictal epileptiform discharges; case 2dimprove localization of falsely generalized epileptic spasms; cases 3 and 4dimprove localization of interictal epileptiform discharges in anatomic regions below the circumferential limit of standard lowdensity EEG coverage; case 5dimprove noninvasive localization of the seizure onset zone in lesional epilepsy; cases 6 and 7dimprove localization of the seizure onset zone to guide invasive investigation near eloquent cortex; case 8didentify epileptic fast oscillations; and case 9dmap language cortex. Together, these nine cases illustrate that using both visual analysis and advanced techniques, HD-EEG can play an important role in clinical management.