Electroencephalography features of primary epileptogenic regions in surgically treated MRI-negative infantile spasms

Objective: To evaluate the surgical outcome for intractable, MRI-negative infantile spasms (IS), and to identify diagnostic targets in the focal epileptogenic area by methods other than MRI. Methods: We retrospectively studied 9 patients who had had surgery for intractable IS, and whose lesions did not appear on MRI. We analyzed video/electroencephalography (EEG), single photon emission computed tomography (SPECT) and positron emission tomography (PET) findings and their surgical outcomes. In 7 patients who were seizure free after surgery, we analyzed the EEG parameters for characteristics expected in the primary epileptogenic region. Results: All patients underwent resective surgery including frontal lobectomy and multilobar resection. Seven patients showed an Engel class I outcome, and 2 patients showed a class III outcome. Interictal SPECT results showed 66.7% concordance for the hemisphere affected (lateralization), and 55.6% for lesion location (localization). Ictal SPECT showed 71.4% concordance for lateralization and localization. PET showed 66.7% concordance for lateralization, and 55.6% for localization. EEG parameters, including localized paroxysmal fast activities, spindle-shaped fast activities, repetitive or rhythmic sharp/spike wave discharges, and subclinical seizures showed highly localized specificity, and may serve to identify the epileptogenic lesion. Conclusion: Surgical treatment of MRI-negative IS should be justified using a combination of diagnostic methods.