Expert Perspective: Who May Benefit Most From the New Ultra Long-Term Subcutaneous EEG Monitoring?

Abstract

Today's modalities for short-term monitoring of EEG are primarily meant for supporting clinical diagnosis of epilepsy or classifying seizures and interictal epileptiform discharges while long-term EEG adds the value of differential diagnosis investigation or pre-surgical evaluation. However, longitudinal epilepsy care relies on patient diaries, which is known to be unreliable for most patients and especially those with focal impaired awareness or nocturnal seizures. The subcutaneous ultra long-term EEG (ULT-EEG) systems alleviate those issue by enabling objective, continuous EEG monitoring for days, weeks, months, or years. Albeit a great advance in continuous EEG over extended periods, it comes with the caveat of limited spatial resolution of two channels. Therefore, the new subcutaneous EEG modality may be especially suited for a selected group of patients. We convened a panel of experienced epileptologists to consider the utility of a subcutaneous, two-channel ULT-EEG device with the goal of developing a consensus-based expert recommendation on selecting the optimal patient types for this investigative technique. The ideal patients to select for this type of monitoring would have focal impaired awareness seizures without predominant motor features and seizures with medium to high voltage patterns. As this technology matures and we learn more about its limitations and benefits we might find a wider array of use case scenarios as it is believed that the benefits for many patients are most likely to outweigh the risks and cost.

Keywords: chronotherapy; circadian rhythm; epilepsy monitoring and recording; seizure detection; sub-scalp; subcutaneous EEG.

Figure 1

The two physical parts of the discussed ultra long-term subcutaneous EEG recorder. The implantable part (A) is placed extracranially underneath the skin. It measures bipolar EEG from the contact points (B_D-B_REF and B_P-B_REF) with the center electrode as the reference and an interelectrode distance of 3.5 cm. The external part (C) is attached to the clothes of the person with epilepsy and the disk (D) is attached to the skin aligned with the housing of the implant (A). As soon as the external disk and the implant housing are aligned, EEG is recorded and stored.

Figure 2

Apart from the direct value of ictal electrographic seizure description, the subcutaneous EEG has the potential to add valuable knowledge in the interictal phase about IEDs and sleep as well as the postictal phase about suppression level and length. Inspired by Beniczky et al. (24).