Long-Term Ambulatory Intracranial EEG.

Background: Long-term ambulatory intracranial EEG is beginning to transform epilepsy care by revealing new insights into seizure patterns and treatment responses over the course of months to years. The feasibility of such monitoring was initially demonstrated through a dedicated recording system. Subsequently brain-implanted neurostimulators became available with integrated recording functionality, revealing numerous clinically useful applications.

Summary: Chronic intracranial EEG allows long-term characterization of patient events, which can clarify which are epileptic, and also help identify unrecognized or subclinical seizures, which can vastly outnumber reported ones. Longitudinal recordings allow monitoring of epilepsy burden over the course of months to years, including responses to treatments such as neuromodulation and antiseizure medications. Medication efficacy can be assessed in a matter of weeks rather than months. In patients with more than one potential localization, the predominant seizure focus can be identified, enabling further surgical options such as resection. Temporal patterns including circadian and multi-day cycles may be revealed with the potential to enable temporal-specific treatments, seizure forecasts, and seizure warnings. Beyond direct clinical applications, ambulatory intracranial EEG has also opened up a new field of neuroscience in naturalistic environments.

Key messages: Long-term intracranial recordings have led to new discoveries about the individualized course of epilepsy and how it responds to treatment. They are clinically useful but are currently limited to patients with specific neurostimulators which are not available worldwide. Current systems allow long-term monitoring with intermittent EEG and/or hourly summary data but do not have continuous EEG availability. Expansion to patients without neurostimulators could provide broader clinical benefit. Scalp and implanted sub-scalp monitoring systems are now entering clinical care and may offer some of the same advantages as intracranial recording systems, although comparisons have not been made.