The Role of Investigative Modalities in Epilepsy Work-up

"nEpilepsy is a common disorder, affecting 50 million people worldwide. The prevalence of epilepsy has significant medical, social, and economic implications both for the individual and for the society. "nIn evaluating the epilepsy patient, it is helpful to be familiar with the etiologies commonly associated with this disease. Identifiable causes of partial epilepsy have been divided into 5 categories, namely neoplasms, vascular abnormalities, mesial temporal sclerosis (MTS), non-vascular developmental disorders and indeterminate substrates (consisting mostly of non-specific gliosis, traumatic, atrophic or inflammatory abnormalities). In studies of surgical epilepsy patients, hippocampal sclerosis is the most common cause (50% to 70%). "nLocalization of the epileptogenic focus is the major task in preoperative evaluation of surgical candidates. Presently, no single technique can precisely identify the epileptogenic zone. In the past, EEG was essentially the only method of localizing the seizure focus. Accuracy of the noninvasive scalp EEG is limited and often inadequate for preoperative evaluation. "nComputed tomography is the appropriate modality to evaluate the underlying cause of new-onset seizures in the emergent setting. It has little or no role in the evaluation of patients with intractable seizures. In cases of refractory seizures, MR has significantly greater sensitivity for lesion detection than does CT. Because of its ability to depict neuroanatomy, MR is ideally suited for identifying focal brain abnormalities, and it can detect structural lesions with a high degree of sensitivity. The accuracy of MR in determining the substrate category in intractable epilepsy has been reported to be 88%. "nMR and video monitoring EEG are widely available and are the most critical noninvasive studies in the evaluation of the epileptogenic zone. There is an approximately 70% correlation of MRI findings with EEG abnormality for patients with temporal lobe epilepsy. In such patients, there is an approximately 97% satisfactory post-operative outcome. In cases with discordant EEG and MR findings or when confirmation of the epileptogenicity of the MR-identified lesion is lacking, intracranial EEG recording using subdural or parenchymal depth electrodes are warranted. Invasive electrophysiological studies are also indicated in cases with more than one MR abnormality, when MR shows a large atrophic region or developmental abnormality, and when functional mapping of the brain is indicated based on MR findings or other reasons. "nOther modalities for preoperative evalu