The peri-ictal state: cortical excitability changes within 24 h of a seizure

Abstract

In this study, transcranial magnetic stimulation was used to investigate motor cortical excitability changes in the peri-ictal period, in drug-naive new-onset epilepsy patients. Eighty-seven studies were performed on 58 patients (23 with idiopathic generalized epilepsy and 35 with focal epilepsy) within 72 h before or after a seizure. Fifty studies in 35 patients were within 24 h of a seizure. In all 58 patients, an interictal baseline study was performed, at least 14 days from a seizure. Motor threshold and paired pulse recovery curve results obtained at short (2-15 ms) and long (50-400 ms) interstimulus intervals in each hemisphere (at <24 h pre- or post-seizure and 24-72 h pre- and post-seizure) were compared against the interictal results and normal control values obtained from 32 subjects. The nature of the seizure (generalized, focal or focal with secondary generalization) was also recorded. Increased motor cortex excitability, measured by decreased motor threshold, increased intracortical facilitation and decreased intracortical inhibition at short and long interstimulus intervals was seen in the 24 h before a seizure. Conversely, decreased excitability occurred in the 24 h after a seizure. These effects were bilateral in tonic-clonic seizures in idiopathic generalized epilepsy and also in secondarily generalized seizures in patients with focal epilepsy. Similar changes were seen in the hemisphere ipsilateral to the seizure focus in focal seizures that did not secondarily generalize, accompanied by complex excitability changes in the contralateral hemisphere. These effects were not apparent in the 24-72 h window. These results show that there are major and prolonged changes in motor cortex excitability in the pre and the postictal 24 h. Increased excitation precedes the seizure by hours and there is a similar period of decreased excitability following a seizure.