- Top of page
Summary: Purpose: The International League Against Epilepsy (ILAE) classification distinguishes medial and neocortical temporal lobe epilepsies. Among other criteria, this classification relies on the identification of two different electroclinical patterns, those of medial (limbic) and lateral (neocortical) temporal lobe seizures, depending on the structure initially involved in the seizure activity. Recent electrophysiologic studies have now identified seizures in which medial and neocortical structures are both involved at seizure onset. The purpose of the study was therefore to study the correlations of ictal semiology with the spatiotemporal pattern of discharge in temporal lobe seizures.
Methods: The 187 stereoelectroencephalography-recorded seizures from 55 patients were analyzed. Patients were classified into three groups according to electrophysiologic findings: medial (M; seizure onset limited to medial structures, n = 24), lateral (L; seizure onset limited to lateral structures, n = 13), and medial-lateral (ML; seizure onset involving both medial and lateral structures, n = 18). Clinical findings were compared between groups.
Results: Initial epigastric sensation, initial fear, delayed oroalimentary and elementary upper limb automatisms, delayed loss of contact, long seizure duration, and absent or rare secondary generalizations were associated with M seizures. Initial auditory illusion or hallucination, initial loss of contact, shorter duration of seizures, and more frequent generalizations were associated with L seizures. Initial epigastric sensation, initial loss of contact, early oroalimentary and verbal automatisms, and long duration of seizures were associated with ML seizures.
Conclusions: Although the syndrome of mesial temporal epilepsy is now relatively well defined, our findings support the idea that the organization of temporal lobe seizures may be complex and that different patterns exist. We demonstrate three distinct patterns, characterized by both semiologic and electrophysiologic features. This distinction may help to define better the epileptogenic zone and the subsequent surgical procedure.
Since the early work from the Montreal and Paris schools using a number of approaches, including depth electrodes and cortical stimulation studies (1,2), the introduction of video-EEG analysis has resulted in a better knowledge of the phenomenology of temporal lobe seizures (3) and its distinction from that of complex partial seizures of extratemporal origin (4,5). Some early works have attempted to correlate ictal symptoms with several anatomoelectroclinical seizure subtypes (1,6,7). Subsequently, the International Classification of Epileptic Syndromes (8) made a distinction between medial and lateral temporal lobe epilepsies. Among other criteria such as medical history and pathologic data, this classification relies on the identification of two electroclinical patterns, that of medial (limbic) and lateral (neocortical) temporal lobe seizures (TLS) depending on the structure initially involved in the seizure activity. This classification has prompted extensive studies of the two corresponding syndromes (9–17). Some clinical features have been shown to be characteristic when comparing patients with medial temporal lobe seizures (MTLS) and those with lateral temporal lobe seizures (LTLS). A history of febrile convulsions, an ictal epigastric sensation, and early oral automatisms were more frequently associated with MTLS, whereas sensory hallucinations were more often associated with LTLS (16).
However, from an anatomic point of view, dense interconnections exist between the limbic and neocortical regions (18). Moreover, TLS related to a widespread epileptogenic zone involving both the limbic and neocortical structures have long been described, as reflected in earlier classifications (1,7,19). Recently, by using depth-EEG recordings and signal processing, we showed that the epileptogenic zone in TLE better corresponded to a network organization (20,21) and that this neural network sometimes involved in both medial (limbic) and lateral (neocortical) structures, thus defining a third subtype of seizures. This third subtype has never been individually characterized in previous semiologic studies comparing medial and neocortical TLE.
The purpose of the present study was to determine how the anatomic localization of the initial discharge influences the ictal semiology, by studying the correlations between clinical characteristics and the three electrophysiologic subtypes of TLS: medial, lateral, and medial-lateral.