Interictal spike quantification in continuous spike-wave of sleep (CSWS): Clinical usefulness of a wearable EEG device

Abstract

Introduction: Continuous spike-wave of sleep (CSWS) syndrome is one of the most common epileptic encephalopathies of childhood. Because the associated cognitive/behavioral disturbances relate more to the amount of spike activity than of seizures, methods of spike quantification gained relevance in diagnosis and monitoring treatment. The conventional methodology for quantification of spike index (SI) relies on repeated full 10-20 long-term ambulatory electroencephalography (aEEG), which is both expensive and poorly tolerated.

Objective: The objectives of this study were to demonstrate the clinical value of repeated SI assessments in CSWS and to build and validate a wearable device allowing inexpensive and well-tolerated, repeated quantifications.

Methods: A group of N = 38 patients with CSWS were submitted to repeated SI quantifications based on aEEG, as seen fit by the medical clinical assistant. Responses to therapy with corticosteroids (N = 10), sulthiame (N = 7), and the ketogenic diet (N = 3) were monitored. We used a conventional method based on a semiautomatic template match spike search. The individual variability in time spans of days (N = 4) or months (N = 10) was assessed and used to determine the meaningful neurophysiological responses to the diverse therapies. A wearable device capable of recording 2 bipolar EEG channels for 24 h was used to simplify SI quantification.

Results: Corticosteroids produced the most powerful SI reduction, but a large individual variability in both amount and time of onset of clinical response with some patients exhibiting recurrence shortly after therapy. A more frequent sampling of SI would provide a more accurate follow-up, with clinical benefit. The comparison of the SI obtained from standard 10-20 electrodes and 2 bipolar EEG channel subsets in aEEG or between the 10-20 and simultaneous wearable recordings, demonstrated that the new method provides an accurate SI quantification.

Conclusions: A wearable EEG device with 2 bipolar channels simplifies the process of obtaining repeated SI quantification allowing a more accurate follow-up of spike activity in the clinical setting.

Keywords: CSWS; EEG; Epilepsy; Epileptic encephalopathy; Wearable.