Abstracts

Rationale: Neuroimaging and electroencephalography (EEG) are the essential elements of the initial diagnostic workup for focal epilepsy. Prior work from the Human Epilepsy Project (HEP) demonstrated that approximately one in five adults and adolescents with newly diagnosed focal epilepsy have a potentially epileptogenic lesion on magnetic resonance imaging (MRI). The objective of this study was to determine the frequency of localizing EEG abnormalities in this cohort, as well as the correlation between structural lesions and EEG findings.

Methods: 409 patients between the ages of 11 and 65 with a new diagnosis of focal epilepsy were enrolled in the HEP, an observational cohort study. All patients underwent EEGs and 3 T brain MRIs using a standardized protocol. MRI findings were classified as normal, abnormal, or incidental, with the abnormal findings further categorized as likely epileptogenic lesions or unknown relation to the underlying epilepsy (primarily diffuse atrophy). EEG findings were classified as either localizing or non-localizing. Chi-squared tests were performed to assess the association between MRI and EEG findings.

Results: 244 patients (59.6%) had normal MRI findings, 145 patients (35.5 %) had abnormalities, and 20 patients (4.9 %) had incidental findings. Of the patients with abnormal MRI findings, 75 (18.3% of the total cohort) had likely epileptogenic abnormalities. 250 patients (61.1%) had normal or non-localizing EEGs, while 159 patients (38.9 %) had EEGs with localizing abnormalities. 206 patients (50.3 %) patients had either a likely epileptogenic lesion on MRI or a localizing abnormality on EEG, while only 28 patients (6.8%) had both findings. A likely epileptogenic lesion on MRI was not associated with the presence of localizing EEG abnormalities (p = 0.86).

Conclusions: In this cohort of adult and adolescent patients with newly diagnosed focal epilepsy, one in five patients had a likely epileptogenic lesion on MRI, while two in five patients had a localizing abnormality on EEG. Half of patients had at least one of these findings, while only a very small number had both. There was no association between epileptogenic findings on MRI and localizing abnormalities on EEG. These findings confirm that both MRI and EEG must be performed as part of the initial diagnostic work up. However, 50% of patients remain without laboratory confirmation and thus a careful clinical history remains paramount for a diagnosis.

Funding: No targeted funding reported. Creation of Human Epilepsy Project (HEP) was sponsored by the Epilepsy Study Consortium. Funding for HEP was provided by industry, philanthropy, and foundations (UCB Pharma, Eisai, Pfizer, Lundbeck, Sunovion, the Andrews Foundation, the Vogelstein Foundation, Finding a Cure for Epilepsy and Seizures [FACES], and Friends of Faces). The funders of HEP had no role in the design or conduct of this study; collection, management, analysis, or interpretation of the data; preparation, review, or approval of the manuscript; or decision to submit the manuscript for publication.