Unilateral ultra long-term subcutaneous EEG monitoring in drug-refractory idiopathic generalized epilepsy

Seizure self-reporting is known to be unreliable, particularly with non-convulsive seizures. There is increasing interest in long-term monitoring systems to detect and count seizures, including the use of the minimally-invasive CE-marked subcutaneous unilateral electroencephalography (EEG) recording system, which has been shown to accurately detect ipsilateral focal seizures.

We implanted the subcutaneous EEG system in nine patients with refractory idiopathic generalized epilepsy (IGE), following initial characterization of their inter-ictal and ictal EEG abnormalities, with in-patient video-EEG monitoring as gold standard comparison. We compared the in-patient video-EEG findings to the abnormalities detected on the long-term subcutaneous system in seven of the nine patients. We compared EEG signal characteristics for convulsive seizures, and for spike and wave discharges of duration of <3 s, between 3 to 10 s, and greater than 10 s.

Three generalized convulsive seizures were recorded in total during video-EEG monitoring, and all were easily detected by the long-term subcutaneous EEG system. Ninety percent of significant spike and wave discharges lasting >3 s were identified using the subcutaneous EEG device. There were minimal adverse effects from use of the device; the patients were satisfied that the device was easy to use and were likely to recommend the use of the device to other patients with epilepsy, as measured by Likert scales. The device implantation was judged to be easy by our epilepsy neurosurgeons.

This study demonstrates that ultra long-term monitoring with unilateral subcutaneous EEG can reliably detect all convulsive and most non-convulsive generalized seizures in patients with refractory IGE. The device is well tolerated and easy to insert, and it can be used as a useful adjunctive seizure monitoring system in select patients. Furthermore, it may guide therapy to optimize seizure control, and it may confer cost savings by avoiding the need for in-patient video monitoring in appropriate patients.