The cortical excitability profile of temporal lobe epilepsy

Transcranial magnetic stimulation (TMS) was used to characterize measurable changes of cortical excitability in patients who were undergoing medical and surgical management of temporal lobe epilepsy (TLE) to investigate whether these alterations depended on timing of achieving seizure control throughout the course of illness and method of management.

Eighty-five patients with TLE divided into (1) drug naive-new onset, (2) early medically refractor, and (3) late medically refractory, (4) early seizure-free on antiepileptic drugs, and (5) late seizure-free on antiepileptic drugs, (6) postoperative refractory, and (7) postoperative seizure-free groups were studied. Motor threshold (MT) and paired-pulse TMS at short (2, 5, 10, and 15 msec) and long (100-300 msec) interstimulus intervals (ISIs) were measured. Results were compared to those of 20 controls.

A significant interhemispheric difference was observed early at onset prior to starting medication, with higher cortical excitability in the hemisphere ipsilateral to the seizure focus, whereas the unaffected hemisphere was normal. After that, cortical excitability was higher in both hemispheres in the refractory groups (medical and postoperative) compared to the seizure-free and drug-naive groups (p < 0.05). This effect was most prominent at the long ISIs.

Changes in cortical excitability seen in patients with TLE are influenced by the course of the disease. The alterations that occur due to epilepsy are closely related to course of illness and degree/timing of seizure control. Successful management leads to resolution of this cortical hyperexcitability in a similar fashion regardless of method: medication (intact generator, but modulated by drugs) or surgery (generator removed).