Interictal Epileptiform Activity in the Foramen Ovale Electrodes of a Frontotemporal Dementia Patient

Abstract

Frontotemporal dementia (FTD) is a frequent cause of cognitive decline. While epilepsy is an important comorbidity of Alzheimer's disease, we lack studies on its presence in FTD. We report on an FTD patient with transient, short-term changes of behavior and cognitive performance suggesting non-convulsive epilepsy. Video-EEG recording with foramen ovale (FO) electrodes revealed mesio-temporal epileptiform potentials, undetectable by scalp leads. We also found beta spindles in the FO electrodes, not described in the literature. We conclude that video-EEG monitoring with FO electrodes might usefully complement the assessment of dementia-associated epilepsy opening new perspectives in dementia-research.

Keywords: EEG; epilepsy; foramen ovale; frontotemporal dementia; neurocognitive disorders; spindles.

Fig.1

Preoperative brain MRIs (left: coronal view; right: sagittal view) of the patient. MRI brain scan revealed diffuse cortical atrophy; the frontal and temporal lobes were the most affected, predominantly on the left side.

Fig.2

Postoperative cranial CT of the patient. The postoperative CT demonstrated the position of foramen ovale electrodes inside the subarachnoidal space of the cisterna ambiens below the parahippocampal gyri (indicated by arrows).

Fig.3

Epileptiform discharges seen in FO leads. (High pass filter 0.5 Hz, low pass filter 70 Hz). Bilateral, independent spikes on the left side (circles) with amplitudes lower than l00 μV. In some cases, spikes were associated to beta runs with 11-12 Hz activity superimposed on 5 Hz theta elements (right side, marked with a rectangle). The spikes and beta-run-related spikes occurred predominantly in the right FO leads. None of them propagated to the scalp.

Fig.4

Spindle-like graphoelements in the FO leads during wakefulness. (High pass filter 0.5 Hz low pass filter 70 Hz). Runs of bi-, or unilateral, spindle-shape sharp elements with 11-12 Hz frequency appeared in the FO leads on both sides, predominantly during NREM sleep (left side, marked with rectangle). In wakefulness, variable length (1 s-15 s) beta spindles with 15-16 Hz frequency were often seen in the FO leads, preceding eye movements, blinking or other muscle activity (right side, marked by rectangle). The circle demonstrates the EEG artefact of blinking.