EEG findings in frontal lobe epilepsies

Abstract

As a group, epilepsies of frontal lobe origin are thought to be poorly localized using surface EEG recordings. This finding may depend on the specific areas of frontal lobe from which the seizures originate or the pathologic substrate. We reviewed the presurgical surface EEGs of patients with frontal lobe epilepsy who underwent epilepsy surgery. The specific area of the frontal lobe where seizures originated was determined by 1) intracranial ictal EEG recordings, or 2) the presence of a structural lesion, identified by imaging studies in patients who achieved complete seizure control following surgery. We differentiated patients whose seizures began in the dorsolateral frontal convexity from those whose seizures began in the medial frontal region, and we correlated EEG findings in the interictal, postictal, and ictal states with seizure semiology, pathologic substrate, and surgical outcome. Four of nine patients had seizures originating in the dorsolateral frontal convexity and five had medial frontal onset seizures. Patients whose seizures originated from the dorsolateral convexity had focal interictal epileptiform abnormalities that localized to the region of seizure onset. Patients whose seizures began in the medial frontal region had either no interictal epileptiform abnormality or had multifocal epileptiform discharges. Patients whose seizures began in the dorsolateral convexity showed focal electrographic seizure activity that was localizing. This rhythmic fast activity did not appear to be substrate-specific. Patients whose seizure onset localized to the medial frontal region did not show focal electrographic seizure at clinical onset. We conclude that the scalp EEG recordings of frontal lobe epilepsies contain features that enable differentiation of seizures originating from two different regions of the frontal lobe.

Does the region of epileptogenicity influence the pattern of change in cortical excitability?

“…This is supported by evidence from EEG-fMRI studies (Yu et al, 2009;Kobayashi et al, 2006) (Tyvaert et al, 2008) as well as human and animal data (Keller and Roberts, 2008;Blumenfeld et al, 2007); (Holmes et al, 1999;Zilles et al, 1998;Silva-Barrat et al, 1986) which show regional as well as distant cortical and subcortical changes associated with focal interictal spikes, being more so in patients with extra-temporal foci. It also would correlate well with the described increased incidence of bilateral features in extra-temporal lobe seizure semiologies (Luders et al, 1998;Gastaut, 1970) and of bilateral interictal and ictal discharges seen in patients with extra-TLE (Bautista et al, 1998;Taylor et al, 2003;Gibbs and Gibbs, 1955) as opposed to TLE where most reports show that even if bilateral interictal discharges are recorded, they are predominant over the side with seizure onset in 60-70% of patients (Hirsch et al, 1991;Williamson et al, 1993). Extra-temporal lobe seizures also tend to spread more rapidly, and secondarily generalize more frequently, compared to temporal lobe seizures (Luders et al, 1998;Gastaut, 1970).…”

The Sleep Manifestations of Frontal Lobe Epilepsy

“…Often the interictal EEG is entirely normal, or shows only nonspecific bilateral or midline slowing [14]; when interictal epileptiform discharges are present, they are often of limited lateralizing or localizing value, being located in the midline or diffusely over both frontal regions [4,14,17].…”

“…Nonspecific electrographic changes such as attenuation of background rhythms or diffuse postictal slowing are common [14], and subtle changes are often obscured by muscle and movement artifact [7,17]. As a result, many subjects with FLE may be incorrectly diagnosed with pseudoseizures or other nonepileptic events [14].…”

Nonepileptic seizures

“…Clinical observation, lack of response to AEDs, and prolactin levels all have significant limitations in reliability [13,14,15]. Lack of correlation of EEG changes with seizures during VEEG observation of a patient's typical seizures is universally regarded as the most reliable diagnostic evidence of NES, but even VEEG misses deep or frontal lobe epileptic foci [16][17][18]. Negative EEG ictal and peri-ictal EEG findings must be combined with clinical observations to assure reasonable diagnostic reliability.…”