Cortical excitability changes associated with fixation-off sensitivity: A case report

Electroclinical Presentations of Fixation-off Sensitivity in Adults With Symptomatic Epilepsy

PURPOSE

Fixation-off sensitivity (FOS) is a discharge pattern on EEG that occurs owing to the loss of central vision or fixation. Knowledge regarding the relationship between FOS and symptomatic epilepsy is limited. Therefore, we aimed to evaluate the electroclinical features of FOS in adult patients with symptomatic epilepsy.

METHODS

Outpatient video-EEG records of the Hacettepe University Faculty of Medicine were reviewed from 2009 to 2019. Patients aged >18 years with symptomatic epilepsy with a FOS pattern were included. Demographic, clinical, EEG, and neuroimaging data were retrospectively evaluated from an electronic database and patient files.

RESULTS

Eight patients (50% female) were included in this study; seven (87%) had refractory epilepsy. Prominent risk factors were family history of epilepsy in five patients and prenatal/natal insult in four patients. Notable MRI signs included cortical developmental malformation, posterior gliosis, and frontoparietal porencephalic cyst. The FOS pattern was generalized with posterior emphasis in two patients and lateralized or localized in six patients: frontocentroparietal ( n = 1) and temporoparietooccipital ( n = 5). Fixation-off sensitivity discharges were found to be increased by hyperventilation and decreased by drowsiness and sleep in 50% of patients. Fixation-off sensitivity disappeared in one patient with good seizure control.

CONCLUSIONS

In this study, the disappearance of FOS in an epileptic patient with a structural lesion and detection of FOS activity related to a frontoparietal porencephalic cyst were remarkable. Family history of epilepsy was also substantially high. Our results indicate that the underlying mechanism of FOS is much more complicated than previously thought.

Altered brain rhythms and functional network disruptions involved in patients with generalized fixation-off epilepsy

Generalized Fixation-off Sensitivity (CGE-FoS) patients present abnormal EEG patterns when losing fixation. In the present work, we studied two CGE-FoS epileptic patients with simultaneous EEG-fMRI. We aim to identify brain areas that are specifically related to the pathology by identifying the brain networks that are related to the EEG brain altered rhythms. Three main analyses were performed: EEG standalone, where the voltage fluctuations in delta, alpha, and beta EEG bands were obtained; fMRI standalone, where resting-state fMRI ICA analyses for opened and closed eyes conditions were computed per subject; and, EEG-informed fMRI, where EEG delta, alpha and beta oscillations were used to analyze fMRI. Patient 1 showed EEG abnormalities for lower beta band EEG brain rhythm. Fluctuations of this rhythm were correlated with a brain network mainly composed by temporo-frontal areas only found in the closed eyes condition. Patient 2 presented alterations in all the EEG brain rhythms (delta, alpha, beta) under study when closing eyes. Several biologically relevant brain networks highly correlated (r > 0.7) to each other in the closed eyes condition were found. EEG-informed fMRI results in patient 2 showed hypersynchronized patterns in the fMRI correlation spatial maps. The obtained findings allow a differential diagnosis for each patient and different profiles with respect to healthy volunteers. The results suggest a different disruption in the functional brain networks of these patients that depends on their altered brain rhythms. This knowledge could be used to treat these patients by novel brain stimulation approaches targeting specific altered brain networks in each patient.

Reproducibility of EEG-fMRI results in a patient with fixation-off sensitivity

Blood oxygenation level-dependent (BOLD) activation associated with interictal epileptiform discharges in a patient with fixation-off sensitivity (FOS) was studied using a combined electroencephalography-functional magnetic resonance imaging (EEG-fMRI) technique. An automatic approach for combined EEG-fMRI analysis and a subject-specific hemodynamic response function was used to improve general linear model analysis of the fMRI data. The EEG showed the typical features of FOS, with continuous epileptiform discharges during elimination of central vision by eye opening and closing and fixation; modification of this pattern was clearly visible and recognizable. During all 3 recording sessions EEG-fMRI activations indicated a BOLD signal decrease related to epileptiform activity in the parietal areas. This study can further our understanding of this EEG phenomenon and can provide some insight into the reliability of the EEG-fMRI technique in localizing the irritative zone.