Authors :
First Author: Asbjoern Helge, MSc – UNEEG medical
Presenting Author: Troels Kjaer, MD, PhD – UNEEG medical, Denmark
Sirin Gangstad, PhD, MSc – T&W engineering; Troels Kjaer, PhD, MD – UNEEG medical; Jonas Duun-Henriksen, PhD, MSc – UNEEG medical
Rationale:
Low-frequency power has been proposed as a biomarker/precursor for interictal epileptiform discharges (IEDs). Studies show that low-frequency power increases immediately preceding an IED and that the delta power increases on scalp EEG simultaneous with IEDs that can only be observed on intracranial EEG. Both delta power and IEDs have also been coupled to sleep macrostructure, but the three-way interaction between these parameters has only been sparsely investigated, and without accounting for long-term effects.
Methods:
A woman with epilepsy was implanted and monitored with a two-channel subcutaneous EEG recording device from UNEEG medical for a duration of 145 days. The patient was on a 500 mg b.i.d. of levetiracetam at the beginning of the recordings, and the dose was increased to 750 mg b.i.d. after 52 days. Automatic algorithms were used to segment the data into sleep stages and to identify IEDs. IEDs presented during N3 sleep and therefore, the nightly IED rate was normalized according to amount of N3 sleep (N3-IED rate). Inspired by Zubler and colleagues
(Zubler et al., 2017) we computed the delta power during N3 and converted it into measures of delta power amplitude (DPA3) and delta power instability (DPI3). N3-IED rate, nightly DPA3 and nightly DPI3 were correlated over the entire period. DPA3 and DPI3 in the five minutes before and after an IED were also compared excluding ten seconds before and after the IED. Results:
Nightly DPA3 and DPI3 were positively correlated with time, increasing throughout the study, and negatively correlated with N3-IED rate (Figure 1). Similarly, it was shown that the relative amount N3 increased over time.
We also showed an increase in DPI3 from pre-IED to post-IED but no change in DPA3, supporting findings that nocturnal IEDs can disturb sleep homeostasis (Figure 2).
Conclusions:
Our results support the well-established link between delta power and IEDs from a continuous ultra long-term EEG perspective. They indicate that the individual correlation between delta power during sleep and IED rate is stable over time and that a reduction in IED rate might lead to longer and more stable bouts of N3. Thus, the results can be considered as a small push towards the argument of medicating based on nocturnal IEDs. However, these findings will have to be confirmed on a cohort level.
Funding: Lundbeck foundation. AWH, TWK and JDH are full-time employees of UNEEG medical