Mesial temporal lobe epilepsy: what have we learned?

Abstract

Mesial temporal lobe epilepsy is the most common form of human epilepsy, and its pathophysiological substrate is usually hippocampal sclerosis, the most common epileptogenic lesion encountered in patients with epilepsy. The disabling seizures associated with mesial temporal lobe epilepsy are typically resistant to antiepileptic drugs but can be abolished in most patients by surgical treatment. Anteromesial temporal resection, therefore, is the most common surgical procedure performed to treat epilepsy, and stereotactically implanted intracerebral electrodes are required in some patients to localize the epileptogenic region. This clinical setting provides a large number of patients for invasive in vivo research with microelectrode and microdialysis techniques and in vitro research following surgical resection on a single epileptic disorder. Consequently, much has now been learned about the fundamental neuronal mechanisms underlying the epileptogenic properties of the human hippocampus in mesial temporal lobe epilepsy. Parallel reiterative studies in patients and animal models of this disorder indicate that enhanced inhibition, in addition to enhanced excitation, underlies the appearance of hypersynchronous neuronal discharges responsible for generating spontaneous seizures. Recent studies have elucidated what may be unique electrophysiological markers of epileptogenicity, which could have valuable diagnostic utility. Although basic research on mesial temporal lobe epilepsy may ultimately suggest novel approaches to treatment and prevention, attention must also be given to maximizing the application of available effective treatments. In particular, the safety and efficacy of surgical therapy has greatly improved in recent years, yet this alternative treatment remains seriously underutilized worldwide. An appropriate increase in referral of patients with this surgically remediable syndrome to epilepsy centers will not only relieve a great many patients of their disabling seizures and reduce the burden of epilepsy but will also provide increased opportunities for invasive research that could ultimately result in even more effective therapies or cures.