Functional neuroimaging in startle epilepsy: Involvement of a mesial frontoparietal network

Abstract

Purpose: Startle epilepsy is a rare form of epilepsy with seizures triggered by unexpected stimuli. Previous studies have suggested the participation of several brain regions, such as the supplementary motor area (SMA) or the mesial aspect of the frontal and parietal lobes in the generation of startle epilepsy. However, how these brain regions interact with each other during seizures remains largely unknown. The aim of this study was to get insight into brain structures involved in startle-induced seizures using an approach with functional neuroimaging. Methods: Four patients with startle epilepsy secondary to unexpected sounds were studied. All of them underwent a presurgical evaluation including ictal-single-emission computed tomography/subtraction ictal SPECT coregis-tered to MRI (magnetic resonance imaging) (SPECT/ SISCOM). We searched for areas with ictal changes of perfusion higher than two standard deviations (2 SD) above the reference. In one patient, a fluorodeoxyglu-cose-positron emission tomography (FDG-PET) and an ictal electroencephalography-functional MRI (EEG-fMRI) were also performed. In this patient, the results of FDG-PET and sequential analysis of EEG-fMRI were compared to SISCOM. Key Findings: All the patients had their typical startle-induced seizures, consistent with bilateral asymmetric tonic seizures. Ictal-EEG pattern was located over the mesial centroparietal region in all of them. In three of four patients, a significant hyperperfusion over the mesial frontocentral region was seen, involving the SMA, the perirolandic region, and the precuneus. In one patient, who had a congenital bilateral perisylvian polymicrogyria, it was located over the lateral perirolandic region. 18F-FDG-PET results in the patient in whom it was done, were concordant with SISCOM findings. Ictal EEG-fMRI showed an initial activation located over the precuneus, SMA, cingulate gyrus, and the precentral/perirolandic area. Significance: By using a functional neuroimaging approach we have found that startle-induced seizures could be generated by the interaction of a frontoparietal network located over the mesial surface of the brain.

Seizure-free after surgery in a patient with non-lesional startle epilepsy: A case report

“…For this patient, the startle stimuli may be amplified in the SSMAs to provoke a startle-induced seizure or disappeared in the SSMAs without abnormal reaction. We believed that other cortices which were not covered by the electrodes, such as the cingulate gyrus and precuneus, were involved in startle seizures [6,10,15]. Based on a study using ictal EEG-fMRI and SPECT coregistered to MRI (SPECT/SISCOM), it was proposed that startle seizures resulted from the interaction of all those regions-mainly from parietofrontal networks-that include the motor/premotor cortex, precuneus and SSMA [6].…”

“…Onset of the seizures is during childhood or adolescence [3]. The ictal onset zone in startle epilepsy has been attributed to the primary motor cortex, premotor cortex, parietal lobe, peri-insular auditory cortex and the SSMA [4][5][6]. It was reported that most cases of startle epilepsy were associated with structural lesions found on MRI [6][7][8].…”

Vagus nerve stimulation therapy is effective and safe for startle-induced seizures

“…Nevertheless, functional studies with MEG, ictal SPECT and PET support the hypothesis of a large network associated with SISs [6,7]. This epileptic network appears, based on functional neuroimaging studies, to extend beyond the frontal motor/premotor cortex, the primary sensory cortex, and the SMA, constituting to a frontoparietal epileptic network.…”

Adult onset startle epilepsy

“…Startle-provoked seizures typically arise between the ages of 10 months and 14 years and are seldom diagnosed in adults 1–3. The presumed insults resulting in startle epilepsy (including hypoxic-ischaemic injury, central nervous system infection and traumatic brain injury) often occur in the perinatal or postnatal period 1–4.…”

“…Startle-provoked seizures typically arise between the ages of 10 months and 14 years and are seldom diagnosed in adults 1–3. The presumed insults resulting in startle epilepsy (including hypoxic-ischaemic injury, central nervous system infection and traumatic brain injury) often occur in the perinatal or postnatal period 1–4. Although the exact cerebral structures responsible for the generation of startle-provoked seizures have not been fully elucidated, mesial structures, including the supplementary motor area (SMA), precuneus and primary motor/somatosensory areas, have been suggested by some 1.…”